NiTi形状记忆合金电弧熔融涂覆及微连接机理

NiTi Shape memory alloys (SMAs) is one of the most promising coating materials to improve the wear and oxidation resistance of the base components. In the study, the conventional direct current and ultra high-frequency pulsed (UHFP) current were respectively utilized to deposit 3-layer NiTi-coating on TA1 pure titanium substrates with tungsten inert gas welding (TIG)arc-fused coating technology. Using FLUENT software, a computational fluid dynamics (CFD) simulation model was established to analyze the coating process and micro-joining mechanism. The multiphysics, NiTi droplet transfer, Ni element transport and distribution in the micro interlayers were numerical analyzed under UHFP current compared with the direct current case. The numerical and experimental results agree well. It can be concluded that the 3-layer coatings are mainly composed of B19' NiTi martensites and NiTi₂ phases, in which NiTi with nearly equal atomic ratio is dominant. The coating of the direct current case is mainly composed of coarse globular grains, while refined into smaller dendrites once UHFP current is used. In addition, the UHFP current is beneficial to the vibration of the molten pool, which promotes the uniform distribution of Ni element and effectively improves the forming quality of the coatings.