Co-reporter:Wenjie Ren, Fenggui Lu, Pulin Nie, Renjie Yang, Xia Liu, Kai Feng, Zhuguo Li
Journal of Materials Processing Technology 2017 Volume 247(Volume 247) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.jmatprotec.2017.05.003
During thermal exposure between 500 h and 7000 h at 850 °C and 950 °C, Ti(C,N), M6C-type (Ni,Co,Cr)3Mo3C, M23C6-type (Cr,Mo,Ni)23C6 carbides and non-topological close-packed phases (TCP) phases formed in the welds. M6C and M23C6 carbides formed due to both the reaction between C, Mo and Cr and the dissociation of M23C6, M6C and Ti(C,N). The coarsening (Ostwald ripening) rate of M6C carbides was greater than that of M23C6 carbides. The area fractions and average diameters of M23C6 carbides increased due to the long-range diffusion of Cr atoms at 950 °C. Hardness of weld metals decreased with increasing exposure time both at 850 °C and 950 °C due to a decrease of Mo and Cr in solution. From 500 h to 7000 h, the impact energy values of the weld metals exposed at 850 °C decreased due to an increment in area fractions and sizes of M6C carbides, while the impact energy values of weld metals exposed at 950 °C increased because of a decrease of Cr in solution and an increase in the sizes and spaces of GB M23C6 carbides.
Co-reporter:Junhao Sun, Pulin Nie, Kai Feng, Zhuguo Li, Baochao Guo, En Jiang
Journal of Materials Processing Technology 2017 Volume 248(Volume 248) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.jmatprotec.2017.05.011
A laser power of 10 kW was used to weld 304 stainless steel. Different shielding gases including Ar, N2 and no gas were used. The porosity in the laser welds was examined. The metallic plume, liquid melt pool and laser keyhole were observed by a high-speed video camera. Bubbles were produced in all the laser welds. Many pores were retained in the 304L stainless steel laser welds made in Ar. Almost no pores were found in the laser welds made in N2 or no shielding gas. The dissolution of N2 bubbles in the liquid melt pool led to the elimination of the pores in the 304L laser welds. The retention time of liquid melt pool was 1.1 s at a laser power of 10 kW and a welding speed of 0.8 m/min. It took 30 μs to absorb all the N2 bubbles in the liquid melt pool. The increase of the nitrogen content in weld metal was 3.4 × 10−5 wt.%.
Co-reporter:Junhao Sun, Kai Feng, Ke Zhang, Baochao Guo, En Jiang, Pulin Nie, Jian Huang, Zhuguo Li
Materials & Design 2017 Volume 118(Volume 118) pp:
Publication Date(Web):15 March 2017
DOI:10.1016/j.matdes.2017.01.015
•Thick plate was successfully welded by high-power laser welding in a horizontal (2G) butt joint configuration.•A U-shaped groove fabricated on the thick plate greatly increased the weld penetration and decrease the weld width.•The wire tip located in the center of the laser spot produced a smooth and continuous surface of the weld bead.•The columnar grains of the weld metal grown in different orientations contributed to a higher tensile strength.An innovative laser technique has been developed for welding 16 mm thick 304L stainless steel in the horizontal (2G) butt joint configuration. Autogenous laser welding (ALW) was applied to join the thick plate with a square groove and zero air gap, and laser welding assisted with a cold wire (LWACW) was used to fill the unfilled joint. The dimension of the square groove was optimized to achieve full penetration joint with smooth reinforcement at the back side. The wire feed process was also optimized to produce a sound weld appearance. The microstructure and mechanical properties were observed and evaluated by optical microscope, electron backscatter diffraction, microhardness measurement and tensile test. The results showed that the square groove contributed to produce a joint with deeper penetration and narrower width. The relative position of weld wire with respect to the laser spot had a great influence on the weld appearance. Sound appearance with defect-free joint was successfully produced for the 16 mm thick plate in the horizontal position. The microstructure and microhardness of the top and middle samples are different, resulting in the different tensile strength and fractured location.Download high-res image (323KB)Download full-size image
Co-reporter:Chendong Shao, Fenggui Lu, Xiongfei Wang, Yuming Ding, Zhuguo Li
Journal of Materials Science & Technology 2017 Volume 33, Issue 12(Volume 33, Issue 12) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.jmst.2016.12.001
The high cycle fatigue (HCF) tests of modified 9Cr-1Mo dissimilarly welded joint were carried out at different elevated temperatures and the fracture mechanism was systematically revealed. The fatigue strength at 108 cycles based on S–N curve can be estimated as a half of weld joint’s yield strength for all conducted temperatures, which can be a reliable criterion in predicting the fatigue life. The results show that the inter-critical heat affected zones (IC-HAZs) of both sides are the weak zones due to their low hardness and inferior fatigue resistance property. HAZ of COST-FB2 (BM2) is the weakest zone at room temperature due to the existence of numerously distributed defects and the initiation of cracks, either in the surface or interior zone, impacting a crucial effect on the fatigue life of the joint. While at elevated temperatures, fatigue life was controlled mostly by the intrusion–extrusion mechanism at the specimen surface under high stress level and subsurface non-defect fatigue crack origin (SNDFCO) from the interior material under low stress amplitude. With increasing temperature, more and more fatigue failures began to occur at the HAZ of COST-E (BM1) due to its higher susceptibility of temperature. Besides, it is found that the δ-ferrite in the BM1 has no harm to the HCF behavior of the joint at the conducted temperatures.
Co-reporter:Youlu Yuan, Zhuguo Li
Applied Surface Science 2017 Volume 423(Volume 423) pp:
Publication Date(Web):30 November 2017
DOI:10.1016/j.apsusc.2017.06.080
•In-situ WC/Fe carbide coatings were successfully synthesized by PTAMR.•The in-situ carbides gradiently distribute in the composite coating.•3D morphology and performance of in-situ WC crystal were analyzed.•Friction and wear properties of in-situ WC/Fe carbide coating were tested.•Wear mechanisms of in-situ WC/Fe carbide coating were studied.In order to improve the dry sliding tribology properties of mild steel compound, the in-situ WC carbide coatings with 18, 32, 54 vol% WC were successfully synthesized using plasma transferred arc metallurgic reaction (PTAMR) with alloy powders W, C and Fe-30Ni. The composition, microstructure and microhardness of the carbide coatings were characterized. It was found that the carbide coating consisted of WC, M6C and γ phases, carbides distribute gradually from the coating bottom to top, the in-situ WC crystal grows into triangle prism structure with high hardness and good toughness. Dry sliding tribology behaviors were studied on block-on-wheel dry sliding wear tester with load 300 N, sliding speed 0.836 m/s and distance 500 m. Results show that the friction coefficient diagrams contain three stages, variation of friction coefficient increase with the content of WC, friction temperature increase with the sliding distance, increasing the content of WC can directly increase the antiwear property of WC/Fe carbide coating. The main wear mechanisms of in-situ WC/Fe carbide coating are adhesive, oxidation, micro-cutting and ploughing wear.
Co-reporter:Junhao Sun;Pulin Nie;Fenggui Lu
The International Journal of Advanced Manufacturing Technology 2017 Volume 93( Issue 9-12) pp:3517-3530
Publication Date(Web):21 July 2017
DOI:10.1007/s00170-017-0734-y
The porosity produced in the 304 stainless steel laser welds was investigated. The laser welding process was conducted at a laser power of 10 kW. Different welding speeds and shielding gases were used. The porosity in the welds was characterized. The welding processes were observed using a high-speed video camera. The mechanism of the elimination of the porosity was revealed. The suppression of the porosity was made in N2 rather than Ar or He shielding gases. The porosity was mainly produced at the root and most of the porosity was less than 0.02 mm3. No significant differences of the metallic plume, liquid melt pool, and laser keyhole were found when Ar or N2 shielding gas was employed. The solubility of N2 in the liquid melt pool contributed to the reduction or elimination of the porosity in the 304-L laser welds.
Co-reporter:Youlu Yuan, Zhuguo Li
Surface and Coatings Technology 2017 Volume 328(Volume 328) pp:
Publication Date(Web):15 November 2017
DOI:10.1016/j.surfcoat.2017.08.050
•In-situ WC/Fe-30Ni ceramic-metal composite coatings were successfully synthesized.•The content, grain number, and grain size of in-situ WC were measured.•The metallurgical reaction mechanism of in-situ WC grain was studied.•The growth characteristic and mechanism of in-situ WC grain was analyzed.•The hardness, toughness, and wear properties of in-situ WC grains were examined.In-situ synthesis of WC/Fe-30Ni ceramic metal coating (CMC) by plasma transferred arc metallurgical reaction (PTAMR) with raw materials W, C and Fe-30 wt% Ni were investigated. The in-situ metallurgical reaction was investigated by thermodynamic calculation and X-ray diffractometry (XRD). The in-situ WC grain size, grain growth characteristic and microstructures were analyzed by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). The mechanical properties such as hardness, toughness and wear resistance were tested. Results show that the morphology of in-situ WC grain is triangular prism which is a multi-layered crystal structure with high hardness, good toughness and high wear resistance. The excellent mechanical behaviors of in-situ WC are decided by its growth mechanism. Increasing the contents of in-situ WC will directly increase the wear resistance of WC/Fe-30Ni coating.
Co-reporter:Chao Zhang, Kai Feng, Zhuguo Li, Fenggui Lu, ... Paul K. Chu
Acta Materialia 2017 Volume 133(Volume 133) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.actamat.2017.05.037
Nanocrystalline Ni thin film exhibits poor thermo-mechanical properties due to its unstable microstructure at elevated temperature. Here, the paper endows a new approach to solve above issue via addition of nano-multilayers and incorporation of W for nanocrystalline Ni-based films, to provide novel Ni/Ni3Al-W nano-composite multilayered structure with high hardness and good thermal stability. The thermal evolution of microstructure and mechanical properties was investigated to reveal nanocrystalline stability and strengthening mechanisms for co-sputtered Ni/Ni3Al-W multilayers with varied W concentrations and annealing temperature. The lamellar structure and nonequilibrium phases are well maintained in 600 °C annealed multilayers, while nano-grains are further refined with increasing W addition. Annealing at 800 °C results in the appearance of elemental redistribution and phase separation in multilayers, leading to the layered structure dissolved and globular W-related particles precipitated. Annealing hardening is founded in most of annealed Ni/Ni3Al-W multilayers. Based upon microstructure observation, grain boundary relaxation and W-related phase precipitation are mainly responsible for the hardness enhancement of multilayers at 600 °C and 800 °C, respectively. Notably, the best hardness is achieved at the value of 15.6 GPa for 800 °C annealed 12.5 at% W doped Ni/Ni3Al-W multilayer, which shows the residual layer interfaces with larger precipitations in microstructure. This hardness increment for annealed Ni-based multilayers can be attributed that the high degree of strengthening is provided by a combination of hardening precipitation and survived lamellar structure via the Orowan mechanisms, offering a feasible insight to develop nano-metallic coatings for further increasing thermo-mechanical properties.Download high-res image (225KB)Download full-size image
Co-reporter:Yuan Chen, Fenggui Lu, Ke Zhang, Pulin Nie, Seyed Reza Elmi Hosseini, Kai Feng, Zhuguo Li
Carbon 2016 Volume 107() pp:361-370
Publication Date(Web):October 2016
DOI:10.1016/j.carbon.2016.06.014
Electroless Ni-P coating was plated on the surface of multi-walled carbon nanotubes (MWCNTs). The Ni-P coated carbon nanotubes (NiPCNTs) were dispersed into Inconel 718 (IN718) powder by ball milling. Then the powder mixtures were deposited into the IN718/NiPCNTs composite coatings by laser powder deposition process. The survivability of MWCNTs, susceptibility to heat affected zone (HAZ) liquation cracking and tensile mechanical properties of the coatings were studied. The results showed that the MWCNTs were successfully incorporated into the IN718 coatings but most of them were transformed into the porous carbon nano ribbons (CNRs), graphene nano sheets (GNSs) and diamond-like nano particles (DNPs). The CNRs were resulted by the inter-welding of the MWCNTs and GNSs. Large thin CNRs bridging with the Laves particles and interdendritically bonded regions improved the stress transfer across the interdendritic regions. The stress localized on the last remaining liquation film could be depressed and the susceptibility to HAZ liquation cracking was suppressed. Furthermore, the tensile strength of the IN718/NiPCNTs coatings was increased significantly whereas the ductility of the coatings was somewhat reduced, which was attributed not only to the addition of the carbon nano allotropes but also the increased formation of the hard but brittle Laves phase.
Co-reporter:Kai Feng, Xingwu Guo, Zhuguo Li, Chengwu Yao, Yixiong Wu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 14) pp:6020-6028
Publication Date(Web):20 April 2016
DOI:10.1016/j.ijhydene.2016.02.147
•Magnesium alloy is coated by electroless Ni coating and PVD carbon film.•Ni + C coating exhibits the best corrosion resistance among these coatings.•Ni + C coating has the lowest ICR of 2.97 mΩ-cm2 at compaction force of 150 N cm−2.•Further improvement in corrosion resistance is required for magnesium alloy.Magnesium alloy bipolar plates offer great advantage in weight reduction of polymer electrolyte membrane fuel cell. An attempt to improve the corrosion resistance and surface conductivity of magnesium alloy has been made by a medium electroless plating Ni coating prior to PVD deposition of carbon film, envisaging the application of these coating/substrate systems as bipolar plate in PEMFC. The results show that Ni + C coated magnesium alloy GW83 has the best corrosion resistance of 8.65 μA cm−2 and 0.80 μA cm−2 in the simulated cathodic and anodic environments. The release of metallic ions is also greatly inhibited by Ni + C coating. The interfacial contact resistance (ICR) of the magnesium alloy GW83 is decreased from 196.5 mΩ-cm2 to 2.97 mΩ-cm2 by Ni + C coating at the compaction force of 150 N-cm−2. After potentiostatic tests, Ni + C coated sample has the lowest ICR of 15.6 mΩ-cm2 and 52.6 mΩ-cm2 in the anode and cathode environment, respectively.
Co-reporter:Chao Zhang, Kai Feng, Zhuguo Li, Fenggui Lu, Jian Huang, Yixiong Wu
Applied Surface Science 2016 Volume 378() pp:408-417
Publication Date(Web):15 August 2016
DOI:10.1016/j.apsusc.2016.04.027
Highlights
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Ni/Ni3Al multilayers are prepared by magnetron sputtering.
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Both grain size and phase constitution of annealed Ni/Ni3Al multilayers are dependent on individual layer thickness.
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The hardness of annealed Ni/Ni3Al multilayers varies with individual layer thickness and annealing temperature.
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40 nm Ni/Ni3Al multilayer exhibits excellent hardness at elevated temperature.
Co-reporter:Zhiyuan Wang, Kai Feng, Zhuguo Li, Fenggui Lu, Jian Huang, Yixiong Wu, Paul K. Chu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 13) pp:5783-5792
Publication Date(Web):13 April 2016
DOI:10.1016/j.ijhydene.2016.02.076
•W-doped carbon films exhibit low ICR value ranging from 6.25 to 7.21 mΩ-cm2.•Electrochemical results show carbon film with metallic W has better corrosion resistance.•Corrosion resistance during pulse polarization is greatly improved by proper W concentration.•Metallic W on surface is oxidized after polarization enabling self-passivating ability.•A proper W concentration is preferred while formation of WC by overdoping should be avoided.The effects of W doping on the microstructure, ICR, and corrosion resistance of carbon films are systematically investigated. The W-doped carbon film has a compact structure and the surface topography changes slightly with W concentration. W exists in mainly the metallic state when the concentration is small, but amorphous WC is formed in the CW2(A) and CW3(A) samples. The ICR at a typical compaction force of 150 N cm−2 increases marginally in the range of 6.25–7.21 mΩ-cm2 as the W concentration is varied. The carbon films with smaller W concentrations have better corrosion resistance and even the self-passivating ability. During pulse polarization, the bare SS316L shows a very large current density of 150 μA cm−2 due to breakdown of the passive film, but CW1(A) shows a stable and low current density of about 0.6 μA cm−2 due to the good self-passivating ability. The self-passivating ability originates from oxidation of metallic state W in the carbon film and so a proper W concentration can yield the desirable self-passivating effect.
Co-reporter:Kai Feng, Zhuguo Li, Chengwu Yao, Yixiong Wu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 32) pp:14191-14206
Publication Date(Web):24 August 2016
DOI:10.1016/j.ijhydene.2016.05.179
•Mg–Nd–Zn–Zr exhibits different corrosion behavior in anodic and cathodic environments.•The corrosion rate decreases logarithmically with the immersion time.•Amorphous MgCO3 and Mg(OH)2 corrosion products layer is formed in cathodic environment.•Mg(OH)2 corrosion products layer formed in anodic environment is porous.•ICR after immersed in cathode is higher than that in anode due to accumulation of Mg(OH)2 and MgCO3.The corrosion behavior and interfacial contact resistance (ICR) of Mg–Nd–Zn–Zr magnesium alloy in simulated PEMFC environments are investigated systematically. The corrosion rate decreases logarithmically with the immersion time due to accumulation of corrosion products. At first, Mg–Nd–Zn–Zr magnesium alloy exhibits lower corrosion rate in anodic environment because the reactions involving formation of hydrogen gas and dissolution of magnesium are inhibited. After long time immersion, it presents higher corrosion rate because of pitting corrosion and cracked corrosion products layer. In the cathodic environment, a compact corrosion products layer composed of amorphous MgCO3 and Mg(OH)2 is formed as a result of precipitation of carbonate-containing corrosion products. The ICR of Mg–Nd–Zn–Zr magnesium alloy immersed in cathodic environment is higher than that in anodic one due to the accumulation of amorphous Mg(OH)2 and MgCO3 corrosion products layer.
Co-reporter:Jingzhen Zong, Kai Feng, Zhuguo Li, Abdul Mateen Qasim, Paul K Chu
Materials Letters 2016 Volume 183() pp:244-247
Publication Date(Web):15 November 2016
DOI:10.1016/j.matlet.2016.07.008
•Studied difference between post and in situ annealing on roughness of NiTi film.•Hydrophobic property of sputtered NiTi thin films was discussed.Surface morphology and hydrophobic property of NiTi thin films are investigated under various in situ and post annealing temperatures. The XRD and AFM results reveal that in situ annealed NiTi thin films crystallize at lower temperature and have larger surface roughness than post annealed samples. Heating during sputtering provides energy for atoms to move to position of equilibrium, thus more regular crystal structure is observed in in situ annealed NiTi thin films. Another reason for the smoother surface observed in post annealed thin films is that large amount of Ni4Ti3 precipitation in hinders the formation of B19′ phase. The contact angle becomes larger with the increase of surface roughness and the maximum contact angle of 123.5° is achieved in 600 °C in situ annealed thin film with 41.7 nm surface roughness.
Co-reporter:Yanbing Guo, Kai Feng, Fenggui Lu, Ke Zhang, Zhuguo Li, Seyed Reza Elmi Hosseini, Min Wang
Applied Surface Science 2015 Volume 357(Part A) pp:309-316
Publication Date(Web):1 December 2015
DOI:10.1016/j.apsusc.2015.08.132
Highlights
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Nanobainitic coatings under 200, 250 and 300 °C heat treatments are fabricated.
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The size of bainite sheaves increased with the isothermal temperature increasing.
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Textured and chaotic distributions are observed in 200 and 300 °C microstructures.
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The evolution model of nanobainite morphology is established and analyzed.
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The bainitic ferrite of 200 °C heat treatment has a true thickness of 45 nm.
Co-reporter:Yan Mao, Zhuguo Li, Kai Feng, Xingwu Guo, Zhifeng Zhou, Jie Dong, Yixiong Wu
Applied Surface Science 2015 Volume 327() pp:100-106
Publication Date(Web):1 February 2015
DOI:10.1016/j.apsusc.2014.11.151
Highlights
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The carbon film with nickel interlayer (Ni + C coating) is deposited on GW83.
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In Ni + C composite coating the carbon coating has good adhesion with the nickel interlayer.
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The wear track of Ni + C coating is narrower compared to the bare one.
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The wear resistance of GW83 is greatly improved by the Ni + C coating.
Co-reporter:Wenjie Ren, Fenggui Lu, Renjie Yang, Xia Liu, Zhuguo Li
Journal of Materials Processing Technology 2015 Volume 226() pp:214-220
Publication Date(Web):December 2015
DOI:10.1016/j.jmatprotec.2015.07.004
•Most liquation crackings are prevalent in the neck zone region of welded fusion zone.•The mechanism of grain boundary liquation is analyzed.•The formation of the continuous (Cr, Mo)-rich resolidified phase is investigated.•HAZ liquation cracking is decreased by increasing heat input.•Liquation cracking is decreased by preheating base material in the laser welding.Liquation cracking in the fiber laser welding Inconel 617 joint under different heat input and preheating conditions was systemically investigated. Liquation cracking is prevalent in the necking region of the welded fusion zone. The liquation of the grain boundaries (GBs) is mainly caused by the constitutional liquation of M23(C,B)6 carbides. The continuous (Cr, Mo)-rich phase is re-solidified due to the continuous liquid film along GBs during the solidification. The continuous (Cr, Mo)-rich phase decreases as the heat input and preheating temperature increases. The presence of the GB resolidified phase around liquation cracking is one of the features in the formation of liquation cracking. As well as, liquation cracking in heat affected zone (HAZ) would also decrease with increasing heat input and preheating temperature in the fiber laser welding of Inconel 617.
Co-reporter:Yan Mao, Zhuguo Li, Kai Feng, Xingwu Guo, Zhifeng Zhou, Yixiong Wu
Journal of Materials Processing Technology 2015 Volume 219() pp:42-47
Publication Date(Web):May 2015
DOI:10.1016/j.jmatprotec.2014.12.003
•Ni + C composite coating was deposited on GW83.•Ni + C coating was dense with large number of disordered band in the carbon layer.•In Ni + C coating the carbon coating had good adhesion with nickel interlayer.•The corrosion resistance was improved by Ni + C coating.The carbon film with electroless nickel interlayer (Ni + C) was fabricated to improve the corrosion resistance of the magnesium alloy GW83. Compared to other coatings used in this study, the dense Ni + C coating improved adhesion with the substrate. The corrosion potential (Ecorr) of the Ni + C coated magnesium alloy was about −1.37 V vs saturated calomel electrode (SCE) in contrast to about −1.67 V vs SCE of the bare one in 3.5 wt% NaCl solution. The corrosion current density was reduced from 186 μA cm−2 to 11 μA cm−2. The 5 h immersion test revealed that the Ni + C coated magnesium alloy GW83 showed much less corrosion compared to the bare alloy. These evidences indicated that applying Ni + C coating could effectively improve the corrosion resistance of the magnesium alloy GW83.
Co-reporter:Hong Chen, Ke Zhang, Chengwu Yao, Jie Dong, Zhuguo Li, Claus Emmelmann
Applied Surface Science 2015 330() pp: 393-404
Publication Date(Web):1 March 2015
DOI:10.1016/j.apsusc.2014.11.132
•Mg–Al–Gd coatings with different Gd contents were fabricated by fiber laser cladding.•Chemical compositions and crystal structures of the second phases were characterized.•Dispersion of Al2Gd led to further grain refining and elevated mechanical properties.•Al2Gd improved high-temperature performances by preventing tiny liquation.In order to investigate the effects of Gd addition on the microstructures and properties of magnesium coatings, the Mg–7.5Al–xGd (x = 0, 2.5, 5.0 and 7.5 wt.%) coatings on cast magnesium alloy were fabricated by laser cladding with wire feeding. The results indicated that the gadolinium (Gd) addition led to the formation of a cubic Al2Gd phase as well as suppressed the precipitation of eutectic Mg17Al12 phase. The laser clad coating containing nominally 7.5 wt.% Gd presented the highest microhardness, ultimate tensile strength and yield strength at both room temperature and high temperatures. The enhancement of heat resistant capacities was chiefly attributed to the existence of thermally stable Al2Gd particles, which prevented tiny liquation of eutectic phases along the grain boundaries and made great contributions on maintaining high yield ratio during high-temperature deformation.
Co-reporter:Wenjie Ren, Fenggui Lu, Renjie Yang, Xia Liu, Zhuguo Li, Seyed Reza Elmi Hosseini
Materials & Design (1980-2015) 2015 76() pp: 207-214
Publication Date(Web):5 July 2015
DOI:10.1016/j.matdes.2015.03.033
Co-reporter:Kai Feng, Zhuguo Li, Fenggui Lu, Jian Huang, Xun Cai, Yixiong Wu
Journal of Power Sources 2014 Volume 249() pp:299-305
Publication Date(Web):1 March 2014
DOI:10.1016/j.jpowsour.2013.10.103
•C/Cr–Ti–N multilayer coatings with varying Cr:Ti target current is deposited on SS316L.•Metal ion corroded during 10 h potentiostatic test is reduced by more than 30 times by multilayer.•Superior conductivity of around 2 and 3 mΩ cm2 before and after 10 h polarization is achieved.High electrical conductivity and corrosion resistance are central to advances in wider application of metallic bipolar plates in polymer electrolyte membrane fuel cell (PEMFC). In this study, C/Cr–Ti–N multilayer coatings are deposited by physical vapor deposition and the effect of Cr:Ti ratio on the corrosion resistance and interfacial contact resistance (ICR) are systematically investigated. Scanning electron microscopy (SEM) result shows that the carbon layer is compact and uniform. Excellent corrosion resistance of 0.127 μA cm−2 current density at operating voltage in PEMFC cathode environment and low ICR of 2.03 mΩ-cm2 at compaction force of 150 N cm−2 are achieved when Cr:Ti ratio is 2:4 and 3:3, respectively. The significant enhancement in surface conductivity is probably because that the current comes from carbon paper is homogenized by two electrically conductive layers and flows to the passive film with much more contact area. After polarization, ICR increase to 3.07 mΩ-cm2 and 3.02 mΩ-cm2 in the simulated PEMFC cathode and anode environment, respectively. However, the Raman spectroscopy results disclose that the bonding type of top carbon film before and after polarization shows little difference. The results indicate that C/Cr–Ti–N multilayer coating with Cr:Ti ratio of 2:4 achieves the optimal composition.
Co-reporter:Wei Meng, Zhuguo Li, Fenggui Lu, Yixiong Wu, Jianhong Chen, Seiji Katayama
Journal of Materials Processing Technology 2014 Volume 214(Issue 8) pp:1658-1664
Publication Date(Web):August 2014
DOI:10.1016/j.jmatprotec.2014.03.011
A high-speed camera and X-ray transmission observation system were used to observe the keyhole and molten pool dynamic behavior in laser lap welding T-joints. The oscillation frequency of the molten pool and the keyhole increases with increasing gap. The lower keyhole becomes slant with the large gap and large quantities of bubbles are formed at the bottom tip of the keyhole. The molten pool is divided into three different zones by the large gap and a small eddy is formed at the lower molten pool. The bubbles are difficult to escape from the lower molten pool and the gap when the gap is large, resulting in the formation of porosity at the gap and root of weld seam. The distribution characteristics of porosity in different gap have an excellent agreement with the keyhole and the molten pool dynamic behavior. Porosity can be suppressed by maintaining a small gap or adopting high welding speed. The paper provides fundamental insights into the mechanism of porosity formation during laser lap welding T-joints and guidance to aid in its elimination.
Co-reporter:Yanbing Guo, Zhuguo Li, Chengwu Yao, Ke Zhang, Fenggui Lu, Kai Feng, Jian Huang, Min Wang, Yixiong Wu
Materials & Design 2014 63() pp: 100-108
Publication Date(Web):
DOI:10.1016/j.matdes.2014.05.041
Co-reporter:Youlu Yuan, Zhuguo Li
Surface and Coatings Technology 2014 Volume 248() pp:9-22
Publication Date(Web):15 June 2014
DOI:10.1016/j.surfcoat.2014.03.029
•Fe-based coatings reinforced by different sizes and contents of M7C3 were fabricated.•Friction and wear behaviors at variable loads and sliding distance were tested.•Wear mechanisms vary with normal loads and contents of M7C3.•Cracks on the worn surface of M7C3 rod increase with the normal loads.•Crack mechanisms under different loads were analyzed.In this paper, three distinct sizes of rod carbide (Cr,Fe)7C3 (20.9, 35.2 and 66.3 μm) were in-situ synthesized in the composite coatings using three mass ratios of Cr3C2/Fe–CrNiBSi (1:5, 3:5 and 5:5) powder blends via plasma transferred arc (PTA) welding. The present investigations evaluate the effects of rod carbide sizes, contents, loading and sliding distance on the friction and wear behaviors of (Cr,Fe)7C3-reinforced α-Fe composite coating as sliding against hard alloy AISI W1-1.0C on a block-on-wheel dry sliding wear tester. The focuses are given on the friction coefficient (FC) and wear rate (WR) as function of parameters such as sliding distances (210–1260 m) and normal loads (100–300 N). It was found that the size and content of rod carbide (Cr,Fe)7C3 increase with the mass ratio of Cr3C2, by which the hardness and wear resistance of the coatings were improved. The stability of FC increases with the content of rod carbide (Cr,Fe)7C3 as the load increased from 100 to 300 N. The coatings' worn surfaces were examined and analyzed by using SEM and EDS. It was found that the main wear mechanisms of the coatings vary with the applied normal loads. Cracks nucleated and propagated on the worn surfaces of (Cr,Fe)7C3 rods as the loads increased from 100 to 300 N. The micro-mechanisms of crack formation were analyzed.
Co-reporter:Kai Feng, Zhuguo Li, Hailin Sun, Lei Yu, Xun Cai, Yixiong Wu, Paul K. Chu
Journal of Power Sources 2013 Volume 222() pp:351-358
Publication Date(Web):15 January 2013
DOI:10.1016/j.jpowsour.2012.08.087
The two most important issues that plague wider use of stainless steel bipolar plates in polymer electrolyte membrane fuel cells (PEMFCs) are insufficient corrosion resistance and surface conductivity. In this study, C/CrN multilayer coatings are deposited on 316L stainless steel samples by close-field unbalanced magnetron sputtering ion plating. SEM shows that the C/CrN coatings are dense, continuous, and composing of carbon granules on the surface. Raman spectroscopy reveals an amorphous structure with a large sp2 constituent. The corrosion resistance and interfacial contact resistance (ICR) are investigated systematically. A superior ICR in the range of 2.6–2.9 mΩ-cm2 at a compaction force of 150 N/cm2 is achieved and it is even better than that of graphite. The deposited film possesses high chemical inertness thereby significantly enhancing the corrosion resistance of the coated SS316L. A thickness of 800 nm is sufficient to protect against corrosion. C/CrN multilayer coatings are beneficial in that it can lead to a faster PVD deposition process and lower material cost, while permitting a superior performance in terms of surface conductivity and corrosion resistance.Highlights► C/CrN multilayer coatings with dense structure and high percentage of sp2 bond are deposited on SS316L. ► C/CrN multilayer coatings exhibit superior surface conductivity that is even better than that of graphite. ► Electrochemical results disclose that the C/CrN multilayer coatings have excellent corrosion resistance.
Co-reporter:Yaocheng Zhang, Zhuguo Li, Pulin Nie, Yixiong Wu
Journal of Materials Science & Technology 2013 Volume 29(Issue 4) pp:349-352
Publication Date(Web):April 2013
DOI:10.1016/j.jmst.2013.01.002
The microhardness distribution of the diode laser epitaxially deposited IN718 alloy coating was investigated. The Laves concentration in different regions of the coating was measured by binarization processing. The strengthening phase of the coating was characterized by transmission electron microscopy (TEM). The results showed that the microhardness increased along the depth of the coating. Part of Laves dissolved into austenitic matrix during the successive laser deposition. A little amount of strengthening phase was precipitated in the bottom region of the coating. It was attributed to the heat effect from the thermal cycle of successive deposition on the microstructure in the bottom region of the epitaxially deposited coating.
Co-reporter:Weihong Jin, Kai Feng, Zhuguo Li, Xun Cai, Lei Yu, Danhua Zhou, Paul K. Chu
Thin Solid Films 2013 Volume 531() pp:320-327
Publication Date(Web):15 March 2013
DOI:10.1016/j.tsf.2013.01.036
Carbon films are deposited on 304 stainless steel (SS304) by close field unbalanced magnetron sputter ion plating using different substrate bias voltages and target currents to improve the corrosion resistance and electrical conductivity of bipolar plates made of SS304 in proton exchange membrane fuel cells (PEMFCs). The surface morphology, Raman scattering spectra, corrosion resistance, interfacial contact resistance (ICR), and contact angle with water of the carbon films are determined. A dense carbon film is produced on the SS304 by this technique and the corrosion resistance is improved significantly. The ICR value diminishes drastically and water contact angle increases after deposition. In addition, the passive current density in the simulated PEMFC environment decreases initially, increases as the substrate bias voltage is increased, and drops with decreasing target current. As the substrate bias is increased, the ICR between the carbon film and carbon paper exhibits an initial diminishing trend and then increases, but the effect of the target current on the ICR is not as substantial as that of the bias voltage.Highlights► Carbon films are deposited on SS304 by unbalanced magnetron sputter ion plating. ► The corrosion resistance of SS304 is greatly improved. ► The interfacial contact resistance value of SS304 drastically decreases. ► Bias voltage and target current effect on the carbon film properties are clarified.
Co-reporter:Kai Feng, Zhuguo Li
Thin Solid Films 2013 Volume 544() pp:224-229
Publication Date(Web):1 October 2013
DOI:10.1016/j.tsf.2013.03.115
•Dense TiN and Ti0.9Si0.1N films are deposited by magnetron sputtering.•Preferred growth orientation of TiN depends on the bias voltage and Si doping.•TiN and Ti0.9Si0.1N films have excellent corrosion resistance.•Surface conductivity of TiN and Ti0.9Si0.1N films evolves with bias voltage.As potential application in bipolar plate of polymer electrolyte membrane fuel cell, the microstructure, corrosion resistance and the electrical conductivity of titanium nitride (TiN) and Si doped titanium nitride (Ti0.9Si0.1N) films deposited by magnetron sputtering with different bias voltages are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), electrochemical test and four-point probe method, respectively. XRD, SEM and AFM results reveal that the texture and topography of TiN film depend on the bias voltage and incorporation of Si. When the bias voltage is − 20 V and − 30 V, the TiN and Ti0.9Si0.1N films exhibit a dense (111) plane preferred growth, denser structure and smoother surface topography. The potentiodynamic test results indicate that the TiN and Ti0.9Si0.1N films have higher chemical inertness and better corrosion resistance. The films can satisfy the requirement of current density for bipolar plate materials. Incorporation of Si element into TiN film makes the passive current density more stable. Four-point probe measurement results show that the resistivity of both TiN and Ti0.9Si0.1N films reaches minimum when the deposition bias voltage is − 20 V.
Co-reporter:Youlu Yuan, Zhuguo Li
Surface and Coatings Technology 2013 Volume 228() pp:41-47
Publication Date(Web):15 August 2013
DOI:10.1016/j.surfcoat.2013.04.002
•Structure of (Cr,Fe)7C3 nucleated on Cr3C2 particles was viewed in 3-D space.•Plenty of (Cr,Fe)7C3 grow radialy around Cr3C2 from buds to long hexagonal rods.•Cr3C2 can act as substrate for the nucleation of carbide (Cr, Fe)7C3.•Cr3C2 surface craters can promote forming (Cr,Fe)7C3 in the coating.•The size of (Cr,Fe)7C3 embryo is related to the contact angle and shape factor.The nucleation of carbide (Cr, Fe)7C3 on the Cr3C2 particle in the Cr3C2/Fe-CrNiBSi composite coating was studied. It was found that there were a great deal of craters on the surface of half-dissolved Cr3C2 particle, and plenty of carbide (Cr, Fe)7C3 buds nucleated and grown out there. The analysis of crystallographic relationship shows that the lattice misfit between (013)Cr3C2013Cr3C2 and 101−0CrFe7C3 is 8.66%, indicating Cr3C2 can efficiently act as the heterogeneous nuclei of (Cr, Fe)7C3. The thermodynamic analysis indicates that the Cr3C2 surface craters can promote forming (Cr, Fe)7C3 nucleus, and the size of (Cr, Fe)7C3 buds grow on the craters was influenced by the shape factor x = R/rc (R: crater concave radius and rc: critical (Cr, Fe)7C3 nucleus radius) and the contact angle θ between (Cr, Fe)7C3 embryo and Cr3C2 crater surface.
Co-reporter:Yaocheng Zhang;Pulin Nie
Metallurgical and Materials Transactions A 2013 Volume 44( Issue 2) pp:708-716
Publication Date(Web):2013 February
DOI:10.1007/s11661-012-1459-z
An IN718 alloy coating was prepared by high-power diode laser cladding. 980STA standard heat treatment and direct aging (DA) were employed to improve the properties of this coating. The niobium segregation in the as-deposited coating and the heat-treated coating had been investigated using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDAX). The results showed that 980STA standard heat treatment improved the microhardness of the coating significantly, and Laves concentration was reduced from 30.6 vol pct to about 11.4 vol pct after 980STA. The niobium concentration in Laves of the 980STA-treated coating was higher than that of DA-treated coating and as-deposited coating. Only a small portion of niobium in the coating was precipitated in the form of γ″ during the 980STA heat treatment. The rest of niobium was the alloying element for solid-solution strengthening and the constituent element of Laves. The niobium segregation facilitated the formation of Laves.
Co-reporter:Wei Meng;Jian Huang;Yixiong Wu
The International Journal of Advanced Manufacturing Technology 2013 Volume 69( Issue 5-8) pp:1105-1112
Publication Date(Web):2013 November
DOI:10.1007/s00170-013-5095-6
The aim of the present research is to discuss the effect of gap on plasma plume, keyhole, and molten pool dynamics during laser lap welding for T-joints. The authors observe plasma plume, keyhole opening, and molten pool images by high-speed camera in different gaps during CO2 laser overlap welding of T-joints. The results show that gap causes beam energy fluctuations in the keyhole and leads to the instability of welding process. In laser spot welding, zero-gap and small gap greatly affect the stability of plasma and keyhole, which causes the formation of cavities in the weld metal, while a proper gap can help prevent porosity formation. In laser continuous welding, the disruption and closure of front keyhole wall at the gap periodically changes with the gap, which causes the formation of plenty of porosities at the gap. The instability of keyhole is closely related to dynamics of plume and molten pool, which gives an insight into the mechanism of porosity formation during laser overlap welding.
Co-reporter:Y.Y. Zhu, Z.G. Li, R.F. Li, M. Li, K. Feng, Y.X. Wu, T. Wada, H. Kato
Surface and Coatings Technology 2013 Volume 235() pp:699-705
Publication Date(Web):25 November 2013
DOI:10.1016/j.surfcoat.2013.08.050
•Fabricated amorphous composited coating successfully by one step laser cladding method.•The microstructure and properties of the coating showed layered distributions.•NbC phase embedded in the amorphous matrix improved the properties of the coating.Fe–Co–B–Si–C–Nb amorphous composite coating about 0.6 mm in thickness was fabricated by using a one-step laser cladding method. Microstructures and phases were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electron probe microanalysis. Microhardness and wear resistance tests were conducted to evaluate the mechanical properties of this coating. Near the interface of coating/substrate, the region showed a layered microstructure, which could be generally categorized into three layers: layer I (columnar dendrites phase), layer II (equiaxed dendrites phase) and layer III (amorphous-particle composite phase). The main reason for this layered structure was due to the difference in chemical compositions of the three layers. With regard to mechanical properties, the microhardness and wear resistance of the Fe–Co–B–Si–C–Nb amorphous composite coating also exhibited layered characteristics. The mean value of the microhardness for layer I, layer II and layer III was 729, 680 and 1245 HV, respectively. The friction coefficient of the transitional layer III was 0.28 times lower than that of the substrate under the same sliding friction condition.
Co-reporter:Kai Feng, Tao Hu, Xun Cai, Zhuguo Li, Paul K. Chu
Journal of Power Sources 2012 Volume 199() pp:207-213
Publication Date(Web):1 February 2012
DOI:10.1016/j.jpowsour.2011.09.095
The desirable properties of metallic bipolar plates in polymer electrolyte membrane fuel cells are good corrosion resistance and high electrical conductance. In this study, carbon-implanted SS316L stainless steel bipolar plates are evaluated by various ex situ and in situ methods. X-ray photoelectron spectroscopy and transmission electron microscopy reveal a carbon-enriched layer with a thickness of about 240 nm thick. The structure depends on the ion implantation fluence. The interfacial contact resistance and electrochemical behavior are determined using ex situ techniques. The interfacial contact resistance decreases with increasing ion implantation fluence. The results obtained by potentiodynamic tests, potentiostatic tests, and inductively coupled plasma optical emission spectrometry measurements are consistent with each other confirming that the corrosion resistance is significantly improved after carbon ion implantation. The carbon-implanted stainless steel bipolar plates are assembled into single cells to undergo in situ evaluation. The peak power density of the carbon-implanted bipolar plate increases from 566.5 mW cm−2 to 840.0 mW cm−2 and the power density at 0.6 V increases by a factor of two compared to those measured from a single cell made of unimplanted stainless steel bipolar plates.Highlights► Ex situ and in situ tests are performed to study the effect of carbon implantation on performance of SS bipolar plates. ► XPS and TEM results disclose different surface composition and microstructure after carbon implantation. ► Carbon implanted SS316L exhibits superior performance in terms of surface conductivity and corrosion resistance. ► The single cell test shows great improvement in peak power density and output voltage after carbon implantation.
Co-reporter:Ruifeng Li, Zhuguo Li, Jian Huang, Yanyan Zhu
Applied Surface Science 2012 Volume 258(Issue 20) pp:7956-7961
Publication Date(Web):1 August 2012
DOI:10.1016/j.apsusc.2012.04.144
Abstract
Ni–Fe–B–Si–Nb coatings have been deposited on mild steel substrates using high power diode laser cladding. Scanning laser beam at high speeds was followed to remelt the surface of the coatings. Different laser cladding powers in the range of 700–1000 W were used to obtain various dilution ratios in the coating. The dilution effect on the chemical characterization, phase composition and microstructure is analyzed by energy dispersive spectroscopy, X-ray diffraction and scanning-electron microscopy. The microhardness distribution of the coatings after laser processing is also measured. The results reveal that Ni-based amorphous composite coatings have successfully been fabricated on mild steel substrate at low dilution ratio when the cladding power was 700 W, 800 W and 900 W. While at high laser power of 1000 W, no amorphous phase was found. The coatings with low dilution ratio exhibit the highest microhardness of 1200 HV0.5 due to their largest volume fraction of amorphous phase.
Co-reporter:Kai Feng, Guosong Wu, Tao Hu, Zhuguo Li, Xun Cai, Paul K. Chu
Surface and Coatings Technology 2012 206(11–12) pp: 2914-2921
Publication Date(Web):
DOI:10.1016/j.surfcoat.2011.12.021
Co-reporter:Weihong Jin, Kai Feng, Zhuguo Li, Xun Cai, Lei Yu, Danhua Zhou
Journal of Power Sources 2011 Volume 196(Issue 23) pp:10032-10037
Publication Date(Web):1 December 2011
DOI:10.1016/j.jpowsour.2011.08.050
Carbon film has been deposited on 304 stainless steel (SS304) using close field unbalanced magnetron sputter ion plating (CFUBMSIP) to improve the corrosion resistance and electrical conductivity of SS304 acting as bipolar plates for proton exchange membrane fuel cells (PEMFCs). The corrosion resistance, interfacial contact resistance (ICR), surface morphology and contact angle with water of the bare and carbon-coated SS304 are investigated. The carbon-coated SS304 shows good corrosion resistance in the simulated cathode and anode PEMFC environment. The ICR between the carbon-coated SS304 and the carbon paper is 8.28–2.59 mΩ cm2 under compaction forces between 75 and 360 N cm−2. The contact angle of the carbon-coated SS304 with water is 88.6°, which is beneficial to water management in the fuel cell stack. These results indicate that the carbon-coated SS304 exhibits high corrosion resistance, low ICR and hydrophobicity and is a promising candidate for bipolar plates.Highlights► Carbon film is deposited on SS304 by unbalanced magnetron sputter ion plating. ► Carbon film exhibits high corrosion resistance in the simulated PEMFC environment. ► Interfacial contact resistance of carbon film satisfies the DOE goal. ► Carbon coated SS304 proves a promising material for bipolar plate.
Co-reporter:L.H. Hu, J. Huang, Z.G. Li, Y.X. Wu
Materials & Design (1980-2015) 2011 Volume 32(Issue 4) pp:1931-1939
Publication Date(Web):April 2011
DOI:10.1016/j.matdes.2010.12.007
Laser hybrid welding has become one of the most promising welding methods for high strength low alloy steels due to combining the advantage of the laser and arc. A novel Y-groove cold cracking test adapted to laser hybrid welding is designed to assess the weldability of 10Ni3CrMoV steels at room temperature and different preheating temperatures. The experimental results show that the orientation of the predominant root cracks generally follows the contour of the fusion line. As the temperature increases from 25 °C to 150 °C, at first the root crack rate decreases and then slightly increases at 150 °C. The root crack rate obtained at 120 °C is the lowest. The fracture model changes from a brittle cleavage fracture to a mixture fracture with quasi-cleavage facets and dimples. The thermal cycle curves of laser hybrid welding obtained by temperature measurement systems are used to evaluate the crack resistance and microstructure transformation. The microstructures of welded joints obtained at different temperatures are analyzed by optical microscope (OM). The results reveal that the microstructures of the coarse grained region and the fusion zone at 120 °C have higher cold crack resistance and good impact toughness. Mechanical properties of the welded joint obtained at 120 °C and 150 °C are comprehensively evaluated by microhardness test, uniaxial tensile test and charpy V-notch impact test with side notches. Fractographs of the impact specimens are studied by scanning electron microscopy (SEM). The test results show that the welded joints obtained at 120 °C have satisfactory mechanical properties that can meet the technical requirements for shipbuilding industry.Research highlights► A Y-groove cold cracking test is designed to assess the laser hybrid welded joints. ► As preheating temperature increases, the crack rate decreases and then increases. ► Thermal cycles of different preheating temperatures illustrate crack resistance. ► The preheating temperature changes the microstructures of laser welded joints.
Co-reporter:Chengwu Yao, Jian Huang, Peilei Zhang, Zhuguo Li, Yixiong Wu
Applied Surface Science 2011 Volume 257(Issue 6) pp:2184-2192
Publication Date(Web):1 January 2011
DOI:10.1016/j.apsusc.2010.09.070
Abstract
An investigation is reported on crack-free laser clad Fe-based alloy by use of biaxial powder feeding shielded with argon gas. The microstructure and phase structure of the coating were studied, and mechanical properties were analyzed through hardness, tension strength and wear resistance of the coating. Microstructure analysis showed that there was retained austenite with spherical particles distributed therein in the interdendritic and nearby grain boundary regions. The mechanical test results showed that net-like distributed retained austenite in the interdendritic region had certain toughening effect through blunting crack-tip. Under wear condition of high sliding speed and high loading, the wear resistance of the coating with net-like retained austenite was much higher than that of the coating with some discontinuous carbide network or carbide blocks. The results showed that toughening of laser clad Fe-based alloy with high hardness over 850 HV could be achieved by modifying interdendritic phases from net-like carbide to net-like austenite with spherical particles.
Co-reporter:Ruifeng Li, Zhuguo Li, Jian Huang, Peilei Zhang, Yanyan Zhu
Applied Surface Science 2011 Volume 257(Issue 8) pp:3554-3557
Publication Date(Web):1 February 2011
DOI:10.1016/j.apsusc.2010.11.073
Abstract
Ni–Fe–B–Si–Nb coatings have been deposited on mild steel substrates using high power laser cladding process followed by laser remelting. The influence of Ni-to-Fe concentration ratio in (Ni100−xFex)62B18Si18Nb2 (x = 55, 50, 45 and 40) powders on the phase composition and microstructure is analyzed by X-ray diffraction, scanning- and transmission-electron microscopies. The microhardness and corrosion resistance properties of the coatings are also measured. The results reveal that amorphous matrix layers are obtained for all coatings. The increase of the Ni-to-Fe ratio can promote the formation of γ(Fe–Ni) phase and decrease the formation of Fe2B phase and α-Fe phase. The coating with 1:1 ratio of Ni-to-Fe exhibits the highest microhardness of 1200 HV0.5 and superior corrosion resistance property due to its largest volume fraction of amorphous phase in the coating. Higher or lower than 1:1 ratio of Ni-to-Fe may result in lower amorphous forming ability. However, even that the coating with ratio of 3:2, shows a minimum of microhardness, it shows a better corrosion resistance than other two coatings.
Co-reporter:Kai Feng, Guosong Wu, Zhuguo Li, Xun Cai, Paul K. Chu
International Journal of Hydrogen Energy 2011 Volume 36(Issue 20) pp:13032-13042
Publication Date(Web):October 2011
DOI:10.1016/j.ijhydene.2011.07.058
The electrochemical behavior and change in the passive film formation of SS316L are investigated under polymer electrolyte membrane fuel cell (PEMFC) simulated (pH from 3 to 6 containing F−, SO42− and Cl− anions) and accelerated conditions (0.5 M and 1 M H2SO4 + 2 ppm HF). Potentiodynamic, potentiostatic, and EIS measurements are performed to investigate the electrochemical behavior of the SS316L specimens in both the anode and cathode PEMFC environments. The chemical composition of the passive film, surface topography of the specimens, and degree of metal ion release is characterized by XPS, SEM, and ICP-OES, respectively. The results reveal that the nature of the passive film depends on the pH value, external medium/environment, as well as applied potential during polarization. The corrosion behavior of SS316L is closely related to the chemical composition and structure of the passive film.Highlights► The electrochemical behavior of SS316L in the simulated and accelerated solutions is determined simultaneously investigated by potentiodynamic, potentiostatic, and EIS measurements. ► The chemical composition, surface topography, and metal ion release are investigated by XPS, SEM, and ICP measurements, respectively. ► The relationship between passive film composition in different environments and corrosion resistance are determined and discussed.
Co-reporter:Kai Feng, Zhuguo Li, Xun Cai, Paul K. Chu
Materials Chemistry and Physics 2011 Volume 126(1–2) pp:6-11
Publication Date(Web):15 March 2011
DOI:10.1016/j.matchemphys.2010.11.029
The major concerns of bipolar plates in polymer electrolyte membrane fuel cells (PEMFCs) are their corrosion resistance and interfacial contact resistance (ICR). Silver is well known for its excellent conductivity and good corrosion resistance. In this study, the performance of austenitic stainless steel 316L (SS316L) implanted with Ag is evaluated in the simulated polymer electrolyte membrane fuel cell (PEMFC) environment. The potentiodynamic test reveals that Ag implant improves the corrosion resistance of SS316L. The corrosion potential of SS316L shifts towards the positive direction from −0.30 V vs SCE to −0.04 V vs SCE in the anode environment and the passivation current density at 0.6 V is reduced from 11.26 μA cm−2 to 8.25 μA cm−2 in the cathode environment. The potentiostatic tests reveal a significant decrease from 10 μA cm−2 to 0.7 μA cm−2 after Ag implantation. Furthermore, the chemical stability in the simulated cathode environment and conductivity are improved after Ag implantation. The beneficial effects can be attributed to the addition of silver to the surface and reduction in the passive layer thickness caused by the ion implantation.Research highlights▶ Ion implantation decreases the thickness of the passive layer and the silver-rich layer is about 45 nm thick. ▶ The corrosion resistance and polarization resistance are improved by the silver-rich surface layer which is chemically stable in the simulated PEMFC cathode environment. ▶ Silver ion implantation decreases the ICR of SS316L substantially due to reduction in the passive layer thickness and increased amounts of silver and nickel. ▶ Introduction of silver by ion implantation can improve the performance of stainless steel bipolar plates while needing a small dose of silver compared to other coating methods.
Co-reporter:Ruifeng Li, Zhuguo Li, Yanyan Zhu, Lei Rong
Materials Science and Engineering: A 2011 528(3) pp: 1138-1142
Publication Date(Web):
DOI:10.1016/j.msea.2010.09.084
Co-reporter:Kai Feng, Xun Cai, Hailin Sun, Zhuguo Li, Paul K. Chu
Diamond and Related Materials 2010 Volume 19(Issue 11) pp:1354-1361
Publication Date(Web):November 2010
DOI:10.1016/j.diamond.2010.07.003
The desirable properties of the metallic bipolar plates in polymer electrolyte membrane fuel cells (PEMFC) are good corrosion resistance, high electrical conductance, hydrophobicity, and low cost. In this study, carbon films are deposited on stainless steel 316L (SS316L) samples by close field unbalanced magnetron sputtering. The AFM, SEM, and Raman results show that the carbon film is dense, continuous, and amorphous. The corrosion resistance, hydrophobicity, and interfacial contact resistance (ICR) of the carbon coated steel are investigated and compared to those of uncoated SS316L. The deposited carbon film has high chemical inertness thereby significantly enhancing the corrosion resistance of the coated SS316L. Furthermore, the carbon coated SS316L is more hydrophobic and the resulting ICR is elevated to that of graphite. Our results indicate that the properties of the carbon coated SS316L are better than those of conventional graphite bipolar plates.
Co-reporter:Jiaming Ni, Zhuguo Li, Jian Huang, Yixiong Wu
Materials & Design 2010 31(10) pp: 4876-4880
Publication Date(Web):
DOI:10.1016/j.matdes.2010.05.034
Co-reporter:Kai Feng, Zhuguo Li, Xun Cai, Paul K. Chu
Surface and Coatings Technology 2010 205(1) pp: 85-91
Publication Date(Web):
DOI:10.1016/j.surfcoat.2010.06.009
Co-reporter:Z.G. Li, S. Miyake
Applied Surface Science 2009 Volume 255(Issue 22) pp:9149-9153
Publication Date(Web):30 August 2009
DOI:10.1016/j.apsusc.2009.06.126
Abstract
N-doped TiO2 thin films have been deposited on unheated glass substrates by an inductively coupled plasma (ICP) assisted direct current (dc) reactive magnetron sputtering. All films were produced in the metallic mode of sputtering in order to achieve a high deposition rate. The structures and properties of the N-doped TiO2 films were studied by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and UV–Vis spectrophotometer. Experimental results show that we can obtain well crystallized N-doped anatase phase TiO2 thin films at low deposition temperature and at high deposition rate by using the ICP assisted dc reactive magnetron sputtering process. The doping of nitrogen into TiO2 lattices leads to a smooth shift of the absorption band toward visible light regions.
Co-reporter:Z.G. Li, Y.X. Wu, S. Miyake
Surface and Coatings Technology 2009 203(23) pp: 3661-3668
Publication Date(Web):
DOI:10.1016/j.surfcoat.2009.06.001
Co-reporter:Z.G. Li, S. Miyake, M. Makino, Y.X. Wu
Thin Solid Films 2008 Volume 516(Issue 19) pp:6548-6552
Publication Date(Web):1 August 2008
DOI:10.1016/j.tsf.2007.11.026
Ti–Si–N films with about 10 at.% Si were deposited onto silicon (100) substrates using inductively coupled plasma-assisted dc magnetron sputtering of Ti80Si20 target in a mixture of argon and nitrogen. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and nanoindentation analysis were employed to investigate the effects of ion flux and ion energy on the structure and hardness of as-deposited films. It was found that (i) high-flux ion irradiation with energy of 20 eV caused microstructure to change from non-assisted amorphous columnar form to one where there are globular nanocrystallites of TiN (nc-TiN) embedded in amorphous Si3N4 (a-Si3N4) network; (ii) the hardness of this nc-TiN/a-Si3N4 nanocomposite film was approximately 35 GPa, significantly higher than that of monolithic TiN film of approximately 20 GPa; (iii) upon increasing ion energy the structure of Ti–Si–N film became columnar again and the hardness of film decreased markedly.
Co-reporter:Z.G. Li, M. Mori, S. Miyake, M. Kumagai, H. Saito, Y. Muramatsu
Surface and Coatings Technology 2005 Volume 193(1–3) pp:345-349
Publication Date(Web):1 April 2005
DOI:10.1016/j.surfcoat.2004.08.148
Inductively coupled plasmas (ICPs) were generated to assist magnetron sputtering. By bombarding the growing film with a high-density (∼2.0 mA/cm2) low-energy (∼22 eV) ion flux, Ti–Si–N films containing 0–12 at.% Si were deposited on Si(100) substrates at low deposition temperature (<150 °C). The residual compressive stresses of these films were measured to be lower than 1.5 GPa. Film hardness was significantly enhanced by the addition of a small amount of Si and attained a maximum value of 48 GPa at approximately 5.8 at.% Si. From X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results, the superhard Ti–Si–N films were characterized as having a nanocomposite structure, consisting of nanocolumns of TiN crystallites with amorphous Si3N4 inside the column boundaries. The hardest Ti–Si–N film exhibited a pronounced TiN(200) texture. No refinement of crystallite size by the addition of Si was observed in the present series of Ti–Si–N films. Thus, the hardness enhancement was attributed to nanocomposite effect.
Co-reporter:Kai Feng, Yuan Chen, Pingshun Deng, Yuyan Li, Haixing Zhao, Fenggui Lu, Ruifeng Li, Jian Huang, Zhuguo Li
Journal of Materials Processing Technology (May 2017) Volume 243() pp:82-91
Publication Date(Web):May 2017
DOI:10.1016/j.jmatprotec.2016.12.001
Co-reporter:Da Shu, Zhuguo Li, Ke Zhang, Chengwu Yao, Dayong Li, Zhenbang Dai
Materials Letters (15 May 2017) Volume 195() pp:
Publication Date(Web):15 May 2017
DOI:10.1016/j.matlet.2017.02.076
•High volume fraction WC reinforced Ni-based coating is in situ synthesized.•The prepared coating is free of pores and cracks.•The solidification process and the mechanism of formation are investigated.An in situ synthesized high volume fraction WC reinforced Ni-based composite coating was fabricated on a mild steel substrate by using a high power diode laser. Three kinds of single-layer coatings of different amounts of W+C powder and Ni60 powder and a five-layer coating with different amounts of W+C and Ni60 powders in each layer were prepared. This work showed that the multilayer coating possesses the highest hardness among all coatings, and the maximum hardness of the coatings was about 3.7 times more than that of the substrate. The gradient coating technology combined with the feature that WC particles were liable to sink in the bottom of coating were employed as a new idea for preparing the composite coating free of pores and cracks.
