Stellite alloys are widely used in the aerospace field owing to their excellent high-temperature strength and thermal fatigue resistance. However, with the rapid development of the aerospace industry, there is an urgent demand to further enhance the mechanical properties and thermal fatigue resistance of Stellite alloys. In the present study, we prepared a conventional CoCrW alloy (classified as a Stellite alloy) and a novel CoCrWAlNi alloy, which was formulated by introducing aluminum and nickel into the CoCrW matrix, using the direct laser deposition technique. Their microstructural characteristics, mechanical properties, and thermal fatigue performance were systematically investigated. The results indicated that the additions of aluminum and nickel contribute to stabilizing the γ-Co phase. Compared with the CoCrW alloy, the CoCrWAlNi alloy exhibited higher elongation at fracture. In situ observation was employed to study the initiation and propagation of thermal fatigue cracks. Meanwhile, the effects of oxidation on thermal fatigue resistance were analyzed through experimental tests and theoretical calculations based on the Huntz model. Finally, an optimized thermal fatigue mechanism tailored for cobalt-based alloys was established, which yields deeper insights into the failure mechanisms of these alloys under complex thermal-cycling fatigue conditions.

Additive manufacturing is becoming a popular and effective process for lightweight high-temperature TiAl alloys, but there is a lack of understanding regarding the corresponding microstructural formation mechanisms. In this study, various Ti-47Al-2Cr-2Nb alloys were additively manufactured with different laser power values, and the related microstructures were carefully characterized. The results show that a convoluted microstructure, a nearly full α₂/γ lamellar structure, and an α₂/β Widmanstatten structure were obtained as the laser power was increased. Moreover, the Al content of the as-deposited specimen decreased from 47 at.% to 40 at.%, which is considered to have strongly affected microstructural formation. As the Al content decreased, the solidified microstructure transformed from hexagonal dendritic α₂ to orthogonal dendritic β and cellular β, successively. Moreover, massive α → γ transformation is more likely when the Al content is high, and α → α₂ transformation tends to occur when the Al content decreases. The microstructure evolution processes are evaluated in the present paper by synthesizing the experimental results with a thermodynamics analysis.