•70Ti/α-TCP/Ti mesh was successfully prepared by SPS at low temperatures.•There is almost no phase reaction for the sintering of the composite at lower than 900 °C.•The composite exhibits high compressive strength, low modulus and good bioactivity.•The composite has high potential applications for orthopedic implants.A titanium mesh scaffold composite filled with Ti/α-TCP particles was prepared by spark plasma sintering (SPS). The microstructures and interfacial reactions of the composites were investigated by scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The compressive strength and elastic modulus were also measured. In vitro bioactivity and biocompatibility was evaluated by using simulated body fluid and cells culture, respectively. After high temperature sintering, Ti oxides, TixPy and CaTiO3 were formed. The formation of Ti oxides and TixPy were resulted from the diffusion of O and P elements from α-TCP to Ti. CaTiO3 was the reaction product of Ti and α-TCP. The composite of 70Ti/α-TCP incorporated with Ti mesh showed a high compressive strength of 589 MPa and a low compressive modulus of 30 GPa. The bioactivity test showed the formation of a thick apatite layer on the composite and well-spread cells attachment. A good combination of mechanical properties and bioactivity indicated a high potential application of Ti/α-TCP/Ti-mesh composite for orthopedic implants.

In this work, nanorod-assembled NiCo2O4 hollow microspheres have been successfully prepared by an ionic liquid-assisted hydrothermal method for the first time. The as-obtained nanorod-assembled NiCo2O4 hollow microspheres manifest a high specific capacitance (764 F g−1 at 2 A g−1), exceptional rate capability (53.5% of capacity retention at 30 A g−1) and good cycling stability (101.7% of initial capacity retention after 1500 cycles). The superior electrochemical performance can be attributed to the unique hollow micro-/nanostructure, which can provide more active sites for the faradic redox reaction, provide an easy electrolyte penetration path and alleviate the volume change during the charge–discharge process. These results suggest that the nanorod-assembled NiCo2O4 hollow microspheres could be promising electrode materials for supercapacitor applications. Additionally, this synthetic method can be extended to the fabrication of other hollow micro-/nanostructure materials for energy and other related applications.

•The main phase changes from α2 phase to γ phase after SPS.•Nucleation of γ phase during SPS is dependent on recrystallization.•Heterogeneous nucleation of γ and distribution of α2 lead to uneven γ grain size.•Fully dense alloy with fine and uniformly distributed γ and α2 grains is obtained.High Nb containing TiAl alloy powders with or without mechanical milling were consolidated by spark plasma sintering (SPS) technique. The effects of SPS temperature and mechanical-milling treatment on phase constitution and microstructure were studied, and the mechanical properties at room temperature were tested. The phases in the as-atomized powder are composed of major α2 phases, a few γ phases and a trace of β phases. After milling, the diffraction peaks for α2 phase are obviously broadened, and the intensities of diffraction peaks for both γ phase and β phase are decreased. Similar phase constitution including a large quantity of γ phases and a few α2 phases are exhibited in the alloys sintered by either as-atomized powder or as-milled powder. At a sintering temperature of 1200 °C, the microstructure of the alloy sintered by using as-atomized powder consists of inhomogeneous γ and α2 phases as well as a few α2/γ lamellar colonies. By contrast, the densities increase and the microstructures are apparently refined for the alloys sintered by using as-milled powder. Fully dense alloys with uniformly distributed γ and α2 grains can be obtained at extending milling time or increasing rotating speed. The nucleation of γ phase during SPS of the powders is dependent on recrystallization. The heterogeneity of deformation should be responsible for the formation of heterogeneous γ grains in the alloys sintered by using as-atomized powder. The heterogeneous grain size for the alloys sintered by using as-milled powders is mainly derived from the inhomogeneous nucleation of γ phase and the uneven distribution of α2 grains. Good mechanical property accompanied by a fine grain size and a dense microstructure can be achieved by optimizing the process parameters.

Dynamic recrystallization (DRX) refine grains of high entropy alloys (HEAs) and significant improve the mechanical property of HEAs, but the effect of high melting point element molybdenum (Mo) on high temperature deformation behavior has not been fully understood. In the present study, flow behavior and microstructures of powder metallurgical CrFeCoNiMo0.2 HEA were investigated by hot compression tests performed at temperatures ranging from 700 to 1100 °C with strain rates from 10−3 to 1 s−1. The Arrhenius constitutive equation with strain-dependent material constants was used for modeling and prediction of flow stress. It was found that at 700 °C, the dynamic recovery is the dominant softening mechanism, whilst with the increase in compression testing temperature, the DRX becomes the dominant mechanism of softening. In the present HEA, the addition of Mo results in the high activation energy (463 kJ mol−1) and the phase separation during hot deformation. The formation of Mo-rich σ phase particles pins grain boundary migration during DRX, and therefore refines the size of recrystallized grains.

•Mica glass ceramics were prepared at low temperatures by melting and powder metallurgy.•The relative sintered density of mica glass ceramics at 850 °C can be 90%.•The microstructures of sintered glass ceramics are well crystallized, with mica and nepheline as main phases.•The transverse rupture strength and the hardness of mica glass ceramics can be 97 MPa and 6 GPa, respectively.Mica glass-ceramics usually have high melting temperatures. In this work, mica glass-ceramics were prepared by the combination of melting and powder metallurgy at low temperatures. Firstly, a SiO2-CaO-B2O3-MgO-Na2O-ZnO glass powder with a melting temperature as low as 1000 °C was prepared. Subsequently, the glass powder mixed with different contents of fluorphlogopite was remelted at 1300 °C to synthesize the ultimate glass frit. After disintegration, the mica glass-ceramic powder can be sintered at low temperatures of 800–950 °C, and a relative density as high as 90% can be obtained. The phase constitutions and microstructures of the bulk glass-ceramics were characterized by X-ray diffraction and scanning electron microscopy. The results illustrated that the glass-ceramics were mainly made up of flake-like fluormica and columnar nepheline, accompanied by augite, forsterite and some other minor phases. The transverse rupture strength and the hardness of mica glass-ceramics were both low at 800 °C for the high porosity, and decreased with the increase of mica phase at 850 °C. Nevertheless, the highest strength of the glass-ceramic with 30% mica reached 97.42 ± 10.2 MPa, which can be potentially applied for engineering applications.Download high-res image (148KB)Download full-size image

•PREPed High-Nb TiAl powder feature two kinds of rapid solidification microstructures.•Molten droplets will form dendritic or smooth martensitic structure for different cooling rates.•Characteristic of powder has intrinsic effect on property of HIPed billets.In the present research, the microstructure and phase composition of high-Nb TiAl powder, produced by plasma rotating electrode process (PREP) have been investigated in details. PREPed powder with a mean particle size larger than 150 μm demonstrates a dendrite structure, and that smaller than 75 μm indicates a martensitic structure. PREPed powder is mainly composed of a hexagonal a2 phase, while in fine powder and coarse powders minor β phase and γ phase are detected, respectively, which is related to solidification path and cooling rate of molten droplets in PREP process. Phase composition and microstructure of the high-Nb TiAl powder have intrinsic effects on the resultant microstructure of hot isostatic pressed (HIPed) billets. After HIP processing, most martensitic and dendritic particles transformed into near γ structure, while few coarse dendritic powder was prone to introduce defects, such as residual primary particle boundaries (PPBs) or coarse lamellae structure, which were harmful to the mechanical properties of HIPed billets. The residual primary particle boundaries (PPBs) or coarse lamellae structure obviously decreased the ultimate tensile strength at room and elevated temperature.In order to produce high-quality high-Nb TiAl billet, the different rapid solidification microstructures and their forming reasons of high-Nb TiAl powder prepared by PREP were investigated, and the microstructure's hereditary effects on the HIPed billet were also studied.Download high-res image (297KB)Download full-size image

A TiC-based ceramic composite with refractory high-entropy-alloy (HEA) binders was developed through a novel reactive sintering method. In the process, refractory carbide powders were reacted with Ti powder at high temperature, and in situ formation of Ti carbides and refractory HEA phases occurred. The results indicate that only body-centered-cubic HEA phases and TiC phases are formed after the reactive sintering. The microstructure of the composite is homogeneous, consisting of ultra-fine TiC particles with an average size of 0.85 μm and HEA grains with an average grain size of 1.8 μm. The TiC/HEA composite shows an ultra-high room-temperature compressive strength (>3000 MPa), compared to 1790–2210 MPa for the conventional TiC cermets.

A novel H2S gas sensing composite based on tubular hydroxyapatite (HAp) and Acidithiobacillus ferrooxidans (At.f) was prepared, and the gas sensing properties of pure HAp and the composite to H2S were studied. The microstructures, crystalline phases and chemical groups of the composites were characterized by SEM, TEM, XRD, and FTIR. Results show that jarosite was formed during the cultivation of At.f. Compared to pure HAp, the composite exhibited a more excellent response to H2S. With the increase of the amount of Acidithiobacillus ferrooxidans added, the sensitivity of the composite to H2S increased. The composite showed a highest sensitivity of 76% to H2S at 2000 ppm, which is 2.5 times that of pure HAp. The probable sensing mechanisms of the composite to H2S were proposed. Other than the At.f, the structure and the chemical groups of jarosite are also beneficial for H2S gas sensing.

•Alloying Sn and laser rapid melting were applied to slow down the degradation rate of Mg.•With Sn content increasing, the grain sizes decreased, while the new Mg2Sn phase increased.•The effects of grain sizes and Mg2Sn phase volume fraction on the degradation rate were studied.•The hardening mechanisms were investigated.Mg is a potentially biomaterial for bone implant due to its biodegradability and biomechanical compatibility. However, the too fast degradation rate limits its clinical application. In the study, both alloying treatment and laser rapid melting were applied to slow down its degradation rate. The microstructure, mechanical properties and degradation behavior of the MgxSn (x = 0–7 wt %) alloys were investigated. With Sn content increasing, the grain sizes decreased, while the new Mg2Sn phase increased. The refined grain slowed the degradation rate due to the reduced segregation. While the Mg2Sn phase accelerated the degradation rate owing to the couple galvanic corrosion. Thus, the optimal degradation behavior was obtained with a balanced grain size and Mg2Sn phase volume fraction. Besides, the compression strength increased firstly (up to 5 wt %) and then decreased with Sn increasing.

•Surface mechanical grinding treatment was conducted on a Ti–45Al–7Nb–0.3W alloy.•The γ→α2 phase transformation is observed.•Nanocrystallized α2 grains (20 nm) are found in the treated surface.•The micro-hardness of the top surface increases significantly, which is 50% higher than that of the substrate.•The mechanisms of γ→α2 phase transformation and nanocrystallization are proposed.Surface mechanical grinding treatment was conducted on a Ti–45Al–7Nb–0.3W intermetallics. The results show that the penetration depth plays an important role in the microstructural evolution. The γ→α2 phase transformation is observed at a penetration depth of 100 μm. Nanocrystallized α2 grains (20 nm) are found in the treated surface at a penetration depth of 200 μm. After the surface mechanical grinding treatment, the micro-hardness of the top surface increases significantly, which is 50% higher than that of the substrate. It is also found that the γ→α2 phase transformation is induced by the localized strain in the surface, while the mechanism for the nanocrystallization is proposed to be the twin–twin intersection.

•Nanoindentation was used to investigate room temperature creep behavior of gum metal.•The creep stress exponent of gum metal is sensitive to the cold deformation history.•The creep stress exponent of cold worked gum metal is approximately equal to 1.•The creep of the cold-worked gum metal is governed by the shear deformation of giant faults.The room temperature creep behavior and deformation mechanisms of a Ti–Nb–Ta–Zr–O alloy, which is also called “gum metal”, were investigated with the nanoindentation creep and conventional creep tests. The microstructure was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the creep stress exponent of the alloy is sensitive to cold deformation history of the alloy. The alloy which was cold swaged by 85% shows high creep resistance and the stress exponent is approximately equal to 1. Microstructural observation shows that creep process of the alloy without cold deformation is controlled by dislocation mechanism. The stress-induced α" martensitic phase transformation also occurs. The EBSD results show that the grain orientation changes after the creep tests, and thus, the creep of the cold-worked alloy is dominated by the shear deformation of giant faults without direct assistance from dislocations.

A metallic glass coating with the composition of Fe51.33Cr14.9Mo25.67Y3.4C3.44B1.26 (mole fraction, %) on the Q235 stainless steel was developed by the detonation gun (D-gun) spraying process. The microstructure and the phase aggregate were analyzed by scanning electron microscopy and X-ray diffractometry, respectively. Microhardness, wear resistance and corrosion behavior were assessed using a Vickers microhardness tester, a ball-on-disk wear testing machine and the electrochemical measurement method, respectively. Microstructural studies show that the coatings possess a densely layered structure with the porosity less than 2.1%. The tribological behavior of the coatings examined under dry conditions shows that their relative wear resistance is five times higher than that of the substrate material. Both adhesive wear and abrasive wear contribute to the friction, but the former is the dominant wear mechanism of the metallic glass coatings. The coatings exhibit low passive current density and extremely wide passive region in 3.5% NaCl solution, thus indicating excellent corrosion resistance.

The Ti–36Nb–2Ta–3Zr–0.35O (mass fraction, %) (TNTZO) alloy was produced by cold isostatic pressing and sintering from elemental powders, followed by hot and cold deformation. The effects of deformation process on microstructures and mechanical properties were investigated using the SEM, TEM, OM and the universal material testing machine. Results show that the alloy can be easily hot forged and cold swaged due to the fine-grained microstructure. Only after cold swaging by 85%, the alloy shows the typical “marble-like” structure. And the cold deformation is accompanied by stress-induced α” phase transformations. Moreover, both the strength and the ductility of the alloy are significantly improved by hot and cold working.

•High entropy alloy (HEA) prepared via powder extrusion exhibits high tensile strength and ductility.•The high strength results from solid solution strengthening, grain boundary strengthening and homogenous microstructure.•Powder extrusion can be considered as a promising way for preparing large-sized HEAs with high mechanical properties.An equiatomic FeCoCrNi high alloy (HEA) with both high tensile strength and ductility was produced by a powder metallurgy (P/M) method. The P/M process includes a gas atomization and a hot extrusion of pre-alloyed HEA powder. Microstructures and mechanical properties were characterized using optical microscopy (OP), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and tensile tests. The results show that the P/M FeCoCrNi HEA has a single face centered cubic (fcc) structure and an equiaxed microstructure. No obvious porosity and brittle intermetallic phase was found. The as-extruded alloy exhibits a very high tensile strength of 712.5 MPa, and still maintains an elongation as high as 56%. The improvement of the tensile properties is caused by the solid solution strengthening, grain boundary strengthening and homogenous microstructure. Therefore, the powder hot extrusion can be considered as a promising way for preparing large-sized HEAs with high mechanical properties.

•Polymers/hydroxyapatite composites were firstly fabricated for the enhancement of the sensing properties to ammonia.•The composites containing 5% PPy and 20% PAni exhibited the best sensing properties to ammonia.•The enhanced sensing mechanisms of the composites to ammonia were firstly proposed.In order to improve the gas sensing properties, hydroxyapatite (HAp)-based composites were prepared by mixing with different contents of conductive polymers: polypyrrole (PPy) and polyaniline (PAni). The compositions, microstructures and phase constitutions of polymer/HAp composites were characterized, and the sensing properties were studied using a chemical gas sensing (CGS-8) system. The results showed that, compared to pure HAp, the sensitivities of the composites to ammonia were improved significantly. 5%PPy/HAp and 20%PAni/HAp composites exhibited the best sensitivities to ammonia, and the sensitivities at 500 ppm were 86.72% and 86.18%, respectively. Besides, the sensitivity of 5%PPy/HAp at 1000 ppm was up to 90.7%. Compared to pure PPy and PAni, the response and the recovery time of 5%PPy/HAp and 20%PAni/HAp at 200 ppm were shortened several times, and they were 24 s/245 s and 15 s/54 s, respectively. In addition, the composites showed a very high selectivity to ammonia. The mechanism for the enhancement of the sensitivity to ammonia was also discussed. The polymer/HAp composites are very promising in applications of ammonia sensors.

•Nanocrystalline CrMnFeCoNi HEAs can be prepared by powder metallurgy (PM) method.•The PM HEAs have a high tensile strength and a suitable ductility.•The original morphology and defects in the powders can be inherited to the bulk materials.In this work, nanocrystalline CrMnFeCoNi HEAs were prepared by powder metallurgy. It was found mechanical milling can further refine the microstructures and morphologies of the gas-atomized powder, and increase the sintering ability. The HEAs sintered from the mechanically milled powder have much finer microstructures than that from the gas-atomized powder. The original morphology and defects in both the gas-atomized and the mechanically milled powders can be inherited to the bulk forms after the SPS. The SPSed HEAs have a tensile strength as high as 1000 MPa at room temperature and reasonable ductility. The strengthening mechanism can be attributed to the nanocrystalline microstructures, in which grain boundaries block the movement of dislocations. Powder metallurgy can be taken as a promising way for preparing HEAs with high mechanical properties.

•Functionally graded cemented carbides (FGCCs) were prepared by pre-sintering and subsequent carburizing.•The addition of submicron WC increases the thickness of the gradient layer and refines the average grain size in FGCCs.•The addition of submicron WC efficiently improves the hardness and the transverse rupture strength of FGCCs.•A simplified equation for estimating the average grain size in FGCCs is provided.Functionally graded cemented carbides (FGCCs) were prepared by pre-sintering and carburizing of carbon-deficient WC–Co cemented carbides. Submicron WC powder with different contents was added in FGCCs with coarse grains to study the influences of microstructures, kinetics and mechanical properties. The results show that the addition of submicron WC can increase the thickness of the gradient layer, and improve the carburizing rate in FGCCs. The average grain size becomes finer with the content of submicron WC increasing. The FGCCs with the addition of submicron WC has a higher grain growth rate, and the grain growth kinetics is proposed to be diffusion-controlled. Meanwhile, a simplified equation for estimating the final average grain size of FGCCs is provided. The hardness and the transverse rupture strength of FGCCs can be efficiently improved by the addition of submicron WC due to the fine microstructures and thick gradient layer.

The fatigue characteristics of powder metallurgy (P/M) Ti6Al4V (wt%) alloys prepared by powder sintering and hot rolling were studied under tension–tension loading conditions at R=0.1 and 25 Hz in air, where R=σmin/σmax (σmin and σmax are the applied minimum and maximum stresses, respectively). The results show that for the as-sintered Ti6Al4V alloy the fatigue limit is about 325 MPa, and the fatigue cracks initiate from the residual pores open to the surface of the gauge area and propagate along the α/β interfaces. Hot rolling markedly enhances the fatigue properties, and the fatigue limit increases to about 430 MPa. The reducing of porosity and refining of grain size through hot rolling are the dominant mechanisms for the improvement of fatigue properties. In addition, the microstructure of α/β interfaces//RD and the texture of <0001>α//RD formed during hot rolling act as barriers for the fatigue crack propagation, which partly attributes to the improvement of the fatigue properties.

•Acetylene black decorated NiCo2S4 hollow microsphere is prepared via soft template method.•The composite shows high specific capacitance and ultrahigh rate capability.•Unique hollow structure and high conductivity give the excellent electrochemical performance.•The asymmetric supercapacitor exhibits high energy or power density.High-rate acetylene black (AB) decorated NiCo2S4 hollow microsphere is prepared via a gas bubble soft template and hydrothermal methodology. Benefiting from the combined advantages of the AB with high conductivity and the nanopetals assembled NiCo2S4 with unique hollow micro-/nano- structures, abundant porosity and high conductivity, the as-obtained composites are found to exhibit high specific capacitances (768 F g−1 at 2 A g−1) and remarkable rate capabilities (92.2, 80.1 and 70.3% of capacity retention rate at 20, 50 and 100 A g−1). The fabrication mechanism of the AB-NiCo2S4 composite is also proposed. Furthermore, an asymmetric supercapacitor is fabricated by using the AB-NiCo2S4 composite as a positive electrode and activated carbon as a negative electrode. Owing to the excellent electrochemical properties of the AB-NiCo2S4 electrode, the asymmetric device delivers high energy density (24.7 Wh kg−1) at a power density of 428 W kg−1 or high power density (17.12 kW kg−1) at a reasonable energy density of 7.1 Wh kg−1, and exceptional cycling stability (105.6% of the initial capacity retention at 5 A g−1 over 5000 cycles). These results above demonstrate the significance and great potential of mesoporous NiCo2S4 hollow microsphere-based composites in the development of high-performance energy-storage systems.

•Ti–Ta alloys with low modulus and high strength were fabricated by powder metallurgy.•The incomplete diffusion between elemental powders leads to the formation of Ti-rich and Ta-rich zones.•The existence of pores helps to reduce the elastic modulus as well as facilitates the attachment of osteoblast-like cells.•Fine grain size, solid solution, and fine α phase account for the high tensile strength of the alloys.In this work, powder metallurgical (PM) Ti–Ta alloys were sintered using blended elemental powders. A dual structure, consisting of Ti-rich and Ta-rich zones, was formed due to the insufficient diffusion between Ti and Ta powders. The microstructure, mechanical properties and in vitro biological properties of the alloys were studied. Results indicated that the alloys have inhomogenous microstructures and compositions, but the grain structures were continuous from the Ti-rich zone to the Ta-rich zone. The Ta-rich zone exhibited a much finer grain size than the Ti-rich zone. The alloys had a high relative density in the range of 95–98%, with the porosity increasing with the content of Ta due to the increased difficulty in sintering and the formation of Kirkendall pores. The alloys had a good combination of low elastic modulus and high tensile strength. The strength of alloys was almost doubled compared to that of the ingot metallurgy alloys with the same compositions. The low elastic modulus was due to the residual pores and the alloying effect of Ta, while the high tensile strength resulted from the strengthening effects of solid solution, fine grain size and α phase. The alloys had a high biocompatibility due to the addition of Ta, and were suitable for the attachment of cells due to the surface porosity. It was also indicated that PM Ti–(20–30)Ta alloys are promising for biomedical applications after the evaluations of both the mechanical and the biological properties.

Tubular hydroxyapatite (HAp) was prepared by a combined method of cation exchange membrane-assisted and electrochemical deposition. For comparison, rod-like HAp was also fabricated by the hydrothermal method. The products were characterized by scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and Brunauer–Emmett–Teller (BET) analysis. The gas sensing properties toward ammonia were studied particularly. The selectivity to various volatile organic compounds was also investigated, then, the response and the recovery time were determined. Results showed that the hollow mesoporous and nanocrystalline nature are the key factors that increases the sensing properties of HAp. Tubular HAp based sensors exhibit 1.35–1.65 times of response value to ammonia than the rod-like based one. At the concentration of ammonia of 2000 ppm, the response value of HAp tubes was up to 84.58%, and the response time was as short as 10 s. Even at a low concentration of 50 ppm, the response was still detectable. Furthermore, tubular HAp shows great stability and reproducibility for gas sensing. Results also indicated that tubular HAp has obvious response to various gases, but has the highest response to ammonia. The growth mechanisms of tubular HAp and the gas sensing mechanisms were proposed.

•Dynamically recrystallized γ grains were found in the deformed regions after SPS.•Formation and growth of sintering necks occurred at 1000 and 1200 °C, respectively.•Plastic deformation was a preferred mechanism for densification of SPS at 1200 °C.•Local melting and surface bulging contributed to densification of SPS at 1200 °C.•Closure of pores plays a role in the later densification of SPS at 1200 °C.Gas-atomized Ti–45Al–7Nb–0.3W alloy powders were consolidated by the spark plasma sintering (SPS) process. The densification course and the microstructural evolution of the as-atomized powders during SPS were systematically investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) techniques. As a result of SPS densification, special (α + γ) precipitation zones are formed in the initial stage of sintering, and the residual β phases in the microstructure of the powders are fragmentated. During the following SPS course, α2/γ lamellar colonies at the edge of the precipitation zone, α2 and B2 phase as well as dynamic recrystallized γ grains are found to form. For the as-atomized powders sintered at 1000 °C, the densification is preceded by the early rearrangement of the powder particles and the following formation of sintering necks. For the powders sintered at 1200 °C, plastic deformation plays an important role in densification. Local melting and surface bulging between two adjacent particles can also serve as one of the densification mechanisms. In the later stage of sintering, the growth of sintering necks controlled by diffusion and the pore closure would make important contributions to the densification.

•We prepare novel Ti–Mg alloys by powder metallurgy.•The alloys have low elastic modulus and high strength.•The release of Mg ions induces the formation of calcium phosphate during the immersion in simulated body fluids.•The alloys show good bioactivity and biocompatibility.In this work, powder metallurgical (PM) Ti–Mg alloys were prepared using combined techniques of mechanical alloying and spark plasma sintering. The alloys mainly consist of super saturations of Mg in Ti matrix, and some laminar structured Ti- and Mg-rich phases. The PM Ti–Mg alloys contain a homogeneous mixtures of nanocrystalline Mg and Ti phases. The novel microstructures result in unconventional mechanical and biological properties. It has been shown that the PM Ti–Mg alloys have a much lower compression modulus (36–50 GPa) compared to other Ti alloys, but still remain a very high compressive strength (1500–1800 MPa). In addition, the PM Ti–Mg alloys show good biocompatibility and bioactivity. Mg can dissolve in the simulated body fluids, and induce the formation of the calcium phosphate layer. The compression modulus of PM Ti–Mg alloys decreases with the amount of Mg, while the bioactivity increases. Although the corrosion resistance of Ti–Mg alloys decreases with the content of Mg, the alloys still show good stability in simulated body fluid under electrochemical conditions. The indirect and direct cytotoxicity results show that PM Ti–Mg alloys have a good biocompatibility to NIH-3T3 cells. Therefore, the PM Ti–Mg alloys are promising candidates in biomedical applications.

•Function graded cemented carbides (FGCCs) show satisfactory bonding with diamond coatings.•Crystal growth and bonding strength of diamond coatings depend on different regions in FGCC.•η-Phase is beneficial for the growth of diamonds.Cemented carbides with diamond coatings have been widely used for cutting tools. However, the reaction of Co with the diamond coating during the deposition leads to the deterioration of the coating structure and the bonding strength. In this work, functionally graded cemented carbides (FGCCs), with a WC-rich surface, Co-rich intermediate layer and η phase-containing central part, were prepared. Diamond coatings were prepared on the FGCC by the hot filament chemical vapor deposition (HFCVD), a method of catalytic decomposition of methane and hydrogen mixtures at a heated filament. The crystal growth and the bonding behavior of diamonds to different layers in FGCCs were investigated. Results indicated that the different regions of FGCCs show apparently different grain sizes and morphologies of diamond coatings. The Co-poor layer has a high crystallinity and purity of diamond, and the η phase-containing region is beneficial for the formation of fine diamond grains. The Co-rich layer has a diamond coating of low bonding strength due to the formation of graphite and porosity, while the η phase-containing region has a high bonding strength. By the combined effects of the three different layers, FGCC shows generally a high bonding strength, and is promising for using as a substrate for the diamond coating.

Isothermal sintering experiments were performed on the 316L stainless steel fiber felts with fiber diameters of 8 μm and 20 μm. Surface morphologies of the sintered specimens were investigated by using scanning electron microscopy (SEM) and optical microscopy. The results show that the amount of the sintering necks and the relative densities of the fiber felt increase with the increasing of both the sintering temperature and the sintering time. And the activation energies estimated present a decline at high relative densities for both 8 μm and 20 μm fiber felts. Moreover, the sintering densification of the fiber felts is dominated by volume diffusion mechanism at low temperature and relative densities. As more grain boundaries are formed at higher temperature and relative density, grain boundary diffusion will also contribute to the densification of the specimen.

Fine-grained titanium 6Al–4V alloy, which typically has a grain size of about 1–2 μm, can be made to superplastic form at around 800 °C with special processing. The normal temperature for superplastic forming (SPF) with conventional titanium 6Al–4V sheet material is 900 °C. The lower temperature performance is of interest to the Boeing Company because it can be exploited to achieve significant cost savings in processing by reducing the high-temperature oxidation of the SPF dies, improving the heater rod life for the hot presses, increasing operator safety and replacing the chemical milling operation to remove alpha case contamination with a less intensive nitric hydrofluoric acid etchant (pickle). In this report, room temperature tensile tests and elevated temperature constant strain rate tensile tests of fine-grained Ti–6Al–4V sheets provided by the Baoti Company of Xi׳an, China, were conducted according to the test method standards of ASTM-E8 and ASTM-E2448. The relationships among the processing parameters, microstructure and superplastic behavior have been analyzed. The results show that two of the samples produced met the Boeing minimum requirements for low-temperature superplasticity. The successful material was heat-treated at 800 °C subsequent to hot rolling above the beta transus temperature, Tβ-(150–250 °C). It was found that the sheet metal microstructure has a significant influence on superplastic formability of the Ti–6Al–4V alloy. Specifically, fine grains, a narrow grain size distribution, low grain aspect ratio and moderate β phase volume fraction can contribute to higher superplastic elongations.

•Two typical morphologies of PREPed TiAl powders were characterized.•The two PREPed powders lead to the formation of different microstructures in HIPing.•The deformation behavior of PM high-Nb TiAl alloys largely depends on γ phase.•Microstructural evolution and mechanical behaviors of as-rolled sheets were studied.In this work, high Nb-containing TiAl alloy sheets were hot rolled starting from powder metallurgical billets. The prealloyed powder prepared by the plasma rotation electrode process (PREP) was characterized. Results show that there are two typical morphologies of powders: martensitic (M) and dendritic (D) powders, which are formed due to different local cooling conditions. The two PREPed powders lead to the formation of different microstructures in HIPing. The coarse D powder will introduce defects, such as residual primary particle boundaries and interfacial porosity in the as-HIPed microstructures. The deformation behavior of PM high-Nb TiAl alloys largely depends on γ phase. Besides the dynamic recrystallization and the superplastic deformation, due to the large amount of the γ phase in PM high-Nb TiAl alloy and the high rolling rate, the mechanical twinning in γ phase plays a critical role in the hot rolling process. The mechanical properties of high-Nb TiAl alloys can be significantly improved by the hot rolling, through the refinement of microstructures and the elimination of primary particle boundaries. However, a large deformation may introduce defects and coarsened microstructures, and thus 60% deformation may be suitable for the purpose of improving mechanical properties.

•Present dislocation climbing model for creep deformation to estimate theoretically.•Threshold stress improves as temperature drops.•Threshold stress rises with increasing average nanoprecipitate radius.•The smaller precipitate size causes the more significant effect of interface stress.•The positive (negative) interface stress relaxes (rises) creep activation energy.Based on creep mechanism of lattice self-diffusion controlled dislocation climb process in the high temperatures range (873–923 K), dislocation climb model for creep deformation is presented with elastic interaction of climbing lattice dislocation with coherent nanoprecipitate to estimate theoretically the temperature and size dependence of creep behavior in NiAl nanoscale precipitation-strengthened ferritic alloy. The significant factors governing creep threshold stress and activation energy are evaluated quantitatively, such as temperature, nanoprecipitate size and interface effect as well as the mismatch between nanoprecipitate and matrix. The results show that creep rate data obey a good power-law dependence on applied stress with stress exponent of 4. In the temperature region investigated threshold stresses ranging from 0.4 to 0.5 σO and creep activation energies from 260 to 300 kJ/mol are evaluated, which are reasonable for characterizing the power-law dislocation creep mechanism. Model predictions presented in this work show good agreement with experiments for this ferritic Fe–Cr–Ni–Al alloy.

•We study the transverse propagation of the deformation twinning in a phase field model.•A new surface energy form is introduced to describe the twin boundary anisotropy.•The prismatic/basal planes on the twin front are well reproduced in the simulation.•The twin boundary anisotropy is not responsible for the large aspect ratio nature of twins.•The kinetics of twin boundaries is discussed in configurational forces theory.The thickening mechanism of the deformation twinning (DT) has been frequently studied in numerous researches and the transverse propagation of that is beginning to trigger the attention of scholars. Recently, some researchers report that the twin front of {101¯2} mode of Magnesium is composed of a conjugate twin plane and prismatic/basal (PB) planes, and the combined mobility of these planes rule the overall kinetics of twin propagation. Focusing on that, a continuum phase field model is proposed to investigate the equilibrium shape of tensile twins and the kinetics of the twin front. A new form of surface free energy is introduced in this model for the purpose of describing the orientation-dependent properties of twin boundaries. The simulations well reproduce the PB interfaces and the results indicate that the anisotropic surface energy plays a dominant role in forming the irregular facets on the twin front. A generalized energy-momentum tensor is derived and analyzed for shear loading in order to investigate the equilibrium and mobility of twin boundaries, and the simulations show that the configurational forces distributed on the PB interfaces are smaller than that on the other twin planes, which implies that the growth of twin is beneficial for the formation of PB interfaces. The simulations also indicate that the anisotropic twin boundary energy is not responsible for the large aspect ratio nature of twins, which may be governed by the competition between thickening mechanism and transverse propagation mechanism of the DT.