To protect aluminum parts in vehicle engines, metal-based thermal barrier coatings in the form of Fe₅₉Cr₁₂Nb₅B₂₀Si₄ amorphous coatings were prepared by high velocity oxygen fuel (HVOF) spraying under two different conditions. The microstructure, thermal transport behavior, and wear behavior of the coatings were characterized simultaneously. As a result, this alloy shows high process robustness during spraying. Both Fe-based coatings present dense, layered structure with porosities below 0.9%. Due to higher amorphous phase content, the coating H-1 exhibits a relatively low thermal conductivity, reaching 2.66 W/(m·K), two times lower than the reference stainless steel coating (5.85 W/(m·K)), indicating a good thermal barrier property. Meanwhile, the thermal diffusivity of amorphous coatings display a limited increase with temperature up to 500 °C, which guarantees a steady and wide usage on aluminum alloy. Furthermore, the amorphous coating shows better wear resistance compared to high carbon martensitic GCr15 steel at different temperatures. The increased temperature accelerating the tribological reaction, leads to the friction coefficient and wear rate of coating increasing at 200 °C and decreasing at 400 °C.

Titanium-tantalum (Ti-Ta) alloy has excellent biomechanical properties with high strength and low Young’s modulus, showing great application potential in the biomedical industry. In this study, Ti-Ta alloy samples were prepared by laser powder bed fusion (LPBF) technology with mixed pure 75 wt.% Ti and 25 wt.% Ta powders as the feedstock. The maximum relative density of Ti-Ta samples prepared by LPBF reached 99.9%. It is well-accepted that four nonequilibrium phases, namely, α′, α″ and metastable β phase exist in Ti-Ta alloys. The structure of α′, α″ and β are hexagonal close-packed (HCP), base-centered orthorhombic (BCO) and body-centered cubic (BCC), respectively. X-ray Diffraction (XRD) analysis showed that the α′ phase transformed to the α″ phase with the increase of energy density. The lamellar α′/α″ phases and the α″ twins were generated in the prior β phase. The microstructure and mechanical properties of the Ti-Ta alloy were optimized with different LPBF processing parameters. The samples prepared by LPBF energy density of 381 J/mm³ had a favorable ultimate strength (UTS) of 1076 ± 2 MPa and yield strength of 795 ± 16 MPa. The samples prepared by LPBF energy density of 76 had excellent ductility, with an elongation of 31% at fracture.

Hydroxyapatite (HA) coatings with strong (002) preferred orientation were successfully prepared on Ti-6Al-4V substrates with conventional atmospheric plasma spraying (APS). The intensity changes of (002) preferred orientation along the coating depth were investigated and the mechanical properties of these coatings were analyzed. Results indicated that the intensity of (002) preferred orientation at a distance of longer than ~90 mm from the interface showed a high value, where uniformly distributed columnar grains in a direction perpendicular to the coating surface were observed. The results obtained from experiments on the mechanical properties revealed that the (002) oriented coatings prepared by conventional APS technique exhibited excellent mechanical properties. Meanwhile, this study provided a simple and rapid method for the preparation of HA coatings with (002) preferred orientation.

High-entropy alloys exhibit some interesting mechanical properties including an excellent resistance against softening at elevated temperatures. This gives high-entropy alloys (HEAs) great potential as new structural materials for high-temperature applications. In a previous study of the authors, oxidation behavior of Al_0.6CrFeCoNi and Al_0.6CrFeCoNiSi_0.3 high-entropy alloys at T = 800 °C, 900 °C and 1000 °C was investigated. Si-alloying was found to increase the oxidation resistance by promoting the formation of a continuous Al₂O₃ layer, avoiding the formation of AlN at T = 800 °C. Obvious phase changes were identified in the surface areas of both alloys after the oxidation experiments. However, the effects of heat treatment and Si-alloying on the phase transition in the bulk were not investigated yet. In this study, Al_0.6CrFeCoNi and Al_0.6CrFeCoNiSi_0.3 high-entropy alloys were heat-treated at T = 800 °C and T = 1000 °C to investigate the effect of heat treatment on microstructure, phase composition and mechanical properties of both alloys. The results show that alloying Al_0.6CrFeCoNi with Si caused a phase transition from dual phases consisting of BCC and FCC to a single BCC phase in an as-cast condition. Furthermore, increased hardness for as-cast and heat-treated samples compared with the Al_0.6CrFeCoNi alloy was observed. In addition, the heat treatment facilitated the phase transition and the precipitation of the intermetallic phase, which resulted in the change of the mechanical properties of the alloys.