Microstructure Characteristics and Mechanical Properties of High-Strength Invar Alloy by Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) is a viable technology for manufacturing complex and medium-to-large-sized invar alloy components. However, the cyclic thermal input during the WAAM process may cause the austenite grains in the component to grow abnormally, adversely impacting the material's mechanical properties. The addition of alloying elements such as Cr, Mo, and V can refine the microstructure of invar alloy to solve these problems. This study examines the influence of Cr, Mo, V, and N on the microstructure and mechanical properties of invar alloy produced through wire arc additive manufacturing. The elements Cr, Mo, and V can form various carbides and nitrides in invar alloys. These precipitation phases are distributed in various forms at grain boundaries and inside the grain, which can refine both the grain and the cellular substructure inside the grain. Moreover, these precipitation phases are distributed in different forms, impeding dislocation movement, thereby enhancing the strength of the invar alloy. The mean tensile strength of WAAM-fabricated high-strength invar alloy in this study attained 793 MPa, approximately 99% higher than that of ordinary invar alloy. The mechanical anisotropy of WAAM-fabricated invar alloy can be ascribed to the thermal interactions between adjacent deposition units.