Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs). As a promising series of TBC candidates, rare-earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO4 (Ln = Nd, Sm, Gd) compounds to CMAS attack at 1250 °C. Due to the chemical reaction between molten CMAS and LnPO4, a dense, crack-free reaction layer, mainly composed of Ca3Ln7(PO4)(SiO4)5O2 apatite, CaAl2Si2O8 and MgAl2O4, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO4 (Ln = Nd, Sm, Gd) decreased in the sequence of NdPO4, SmPO4 and GdPO4. GdPO4 had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO4.

•The bimodal WC-Co coating presented denser structure and higher average hardness and fracture toughness than that of conventional coating.•The bimodal coating presented lower friction coefficient and wear rate compared to the conventional coating at the test temperature of 450 °C.•The tribofilm, composed of WO3 and CoWO4, could be formed on the worn surface of bimodal WC-Co coating. The formation of tribofilm could reduce friction and wear.In this work, the bimodal WC-Co coatings were sprayed by high-velocity oxygen-fuel (HVOF), and the conventional WC-Co coatings were also fabricated for comparison. The microstructure, mechanical properties and high temperature wear performance were investigated. The bimodal WC-Co coating presented denser structure (porosity lower than 1.0%), higher average hardness (1164 HV0.1) and fracture toughness (11.5 ± 1.4 MPa·m1/2) than that of conventional coating. The Weibull analysis of microhardness data of the bimodal coating presents a mono-modal distribution. The friction coefficient and wear rate of the bimodal coating were 0.61 and 2.96 × 10− 6 mm3·N− 1·m− 1, respectively, which is lower than that of conventional coating at the test temperature of 450 °C. The tribofilm could be formed on the worn surface of bimodal WC-Co coating, which is composed of WO3 and CoWO4. The formation of tribofilm could reduce friction and wear.

•USWed Al/Al joints with and without interlayer has been successfully fabricated.•Effect of interlayer on the temperature of weld interface was illustrated.•The weldability and mechanical properties for the joint with interlayer were improved.Ultrasonic spot welded Al/Al joints with Al2219 particle interlayer for enhancing the temperature of the weld interface were successfully conducted. The results indicate that Al2219 particle interlayer is beneficial to the increase of temperature at the weld interface, and the increased temperature further facilitates the weldability of Al/Al joints. Meanwhile, no unbonded regions are discovered, and the combination of Al/interlayer interface is high close. The peak tensile shear load of ∼5.47 kN is achieved for the joint with Al2219 particle interlayer, which is 35.7% higher than that (∼4.03 kN) for the joint without Al2219 particle interlayer.

•WCN coatings were deposited by reactive magnetron sputtering.•The best wear resistance was found for the coating which has the highest hardness (H), H/E and H3/E2 ratios.•The corrosion resistance of the substrate which coated with W2N or WCN coatings was superior to the bare substrate.•The corrosion resistance of the W2N coatings was improved by doping some carbon content.WCN coatings with carbon content ranging from 0 to 19.2 at.% were deposited by reactive magnetron sputtering technique. The structure, mechanical, tribological properties and corrosion performance were investigated by XPS, XRD, SEM, HRTEM, nano-indentation CSM, ball-on-disk tribo-meter, AFM, Bruker 3D Profiler and corrosion testers. The results show that the incorporation of carbon does not affect the cubic structure. WCN coatings consist of WCN and amorphous C and CNx phases. The incorporation of carbon results in the crystallite size refinement and the decrease of the average roughness. The H, H/E and H3/E2 ratios of WCN coatings first increase and then decrease and the maximum values are 36.7 GPa, 0.110 and 0.30 GPa, respectively, at 14.8 at.% C. All the H, H/E and H3/E2 ratios of WCN coatings are higher than that of W2N coating. The friction coefficient and wear rate of WCN coatings first decrease and then increase with increasing the carbon content. The friction coefficient and wear rate are mainly related to the lubricant wear debris. Moreover, the hardness and the ratios of H/E and H3/E2 also have a certain influence on the wear rate of the coatings. The corrosion resistance of the substrate which coated with W2N or WCN coatings is superior to the bare substrate. The corrosion resistance of the W2N coating is improved by doping some carbon content.

Gd2Zr2O7 has been considered as a promising thermal barrier coating candidate for operating above 1300 °C, but the relatively poor fracture toughness limits its application. In this study, effort was made to toughen Gd2Zr2O7 with the addition of metastable tetragonal (t′) phase. For 3.5 mol% RE2O3 (RE=Dy, Y, Er, Yb) stabilized ZrO2 (RESZ) ceramics, the t′ phase stability increased with the decrease of RE3+ ionic radius. Among these compounds, YbSZ exhibited the best phase stability and had excellent toughness, thus it was selected as the toughening agent for Gd2Zr2O7. The phase structure and mechanical properties of YbSZ doped Gd2Zr2O7 were investigated. YbSZ first dissolved in Gd2Zr2O7 lattice, then it presented as a second phase when its content reached to 15 mol%. With YbSZ content increasing, the fracture toughness of the compounds increased, and the related mechanisms were discussed.

•The TGO growth rate and Al depletion with heat-resisting iron substrate is faster.•Cr3+ and Al3+ ions may influence the mechanisms of phase transformation in TGO.•The TGO with heat-resisting iron substrate have a shorter stage of θ-Al2O3 → α-Al2O3.•The area of spinel oxide formed relies on the value of b/a geometric parameter.•Slow θ → α-Al2O3 stage retards to form spinel around the convex of undulated TGO.The objective of this work is to understand the influences of different chemical compositions of iron-based and nickel-based substrates on the TGO growth rate, the distribution of residual stress in TGO, the Quantity of the Spinel Cap Presence (QSCP) at the convex of undulated TGO, as well as the θ-Al2O3 to α-Al2O3 phase transformation. A thermal barrier coatings (TBCs) system consisting of the NiCrAlY bond coat and the 8YSZ topcoat (500 μm thickness) were successfully produced onto the substrates of nickel-based superalloy and iron-based alloy by atmospheric plasma spraying (APS), respectively. The results suggest that, compared with the iron-based substrate, both the TGO growth rate and the aluminum depletion in the bond coat with the nickel-based substrate develop significantly slower as the thermal exposure proceeds. It is proposed that the Cr3+ and Al3+ with small radii may considerably influence the mechanisms of phase transformation in the TGO, and these small ions can promote the θ-Al2O3 to α-Al2O3 phase transformation. Furthermore, the TBCs system with iron-based substrate was prone to have much shorter stage of θ-Al2O3 to α-Al2O3 phase transformation and a dramatic reduction of θ-Al2O3 content in the TGO, which had indirect effect on the thermo-dynamic behavior of TGO during the subsequent stage of isothermal oxidation. Furthermore, the apex of the convex of undulated TGO usually has the largest compressive residual stress. The spinel oxides can be inclined to form at the apex region of the convex of the undulated TGO with a lower value of b/a geometric parameter. However, only few spinel oxides appeared at the flank region of the convex. Nevertheless, the ‘spinel cap’ feature usually formed at the area of the apex and the flank of the convex of undulated TGO with a higher value of b/a geometric parameter. Compared with the nickel-based substrate, the more presence of ‘spinel cap’ at the area of the convex of undulated TGO with a iron-based substrate can be found at the convex of undulated TGO, and its earlier end of the θ-Al2O3 to α-Al2O3 phase transformation may result in the lower value of compressive residual stress in average.

Owing to the much concern with global environmental issues, Fe3O4 added photocatalytic TiO2 coatings were deposited using plasma spray for environmental depollution. The influence of the content of Fe3O4 additive to the TiO2 powder on the phase composition, microstructure and photo-absorption of plasma-sprayed TiO2 coatings was systematically studied. The results showed that the TiO2–Fe3O4 coatings consisted of anatase TiO2, rutile TiO2 and Fe2TiO5 pseudobrookite phase which appeared when the content of Fe3O4 additive was equal to or over 10%. The content of FeTiO3 was highest in the sprayed TiO2–10%Fe3O4 coatings. The addition of Fe3O4 improved the anatase–rutile transformation of TiO2–Fe3O4 powders. Furthermore, it was found that TiO2 coatings can decompose acetaldehyde under the illumination of ultraviolet rays, and the degrading efficiency was improved with an increase of FeTiO3 content in the coatings. A two-step electron transfer model was proposed to explain the good photocatalytic activity of the sprayed coating with high content of FeTiO3. However, presence of large amount of Fe2TiO5 compound substantially reduced the photocatalytic efficiency of the sprayed TiO2–Fe3O4 coatings for its unfavorable photo-excited electron–hole transfer process.

Nd2Zr2O7 is being explored as an alternate thermal barrier coating (TBC) material for operating above 1300 °C, and great effort has been made to enlarge its thermal expansion coefficient (TEC) and improve its toughness. In this study, Sc2O3 was doped to Nd2Zr2O7. The phase structure, TECs and toughness of (Nd1-xScx)2Zr2O7 (x = 0, 0.025, 0.05, 0.075, 0.1) compounds were investigated. (Nd1-xScx)2Zr2O7 (x = 0, 0.025, 0.05, 0.075) exhibited pyrochlore structure, while (Nd0.9Sc0.1)2Zr2O7 consisted of pyrochlore and fluorite phases. With the increase of the Sc2O3 content, the ordering degree of the pyrochlore in the compounds decreased. In (Nd1-xScx)2Zr2O7 series, (Nd0.925Sc0.075)2Zr2O7 exhibited the largest TEC, while the toughness of the compounds increased with increasing the Sc2O3 content. The related mechanisms were discussed based on the crystal structure analysis. Considering the TEC and toughness, 10 mol% Sc2O3 was suggested as the optimal doping content for Nd2Zr2O7 ceramic.