THERMO-MECHANICAL AND MICROSTRUCTURAL EVALUATION OF POST-ANNEALED WIRE ARC ADDITIVE MANUFCATURED(WAAM) NITI ALLOYS

Abstract

Nickel-Titanium (NiTi) alloys are well-known for their remarkable shape memory effect and superelasticity, making them highly desirable in various industrial applications such as smart actuators, adaptive valves, and precision fasteners. This study focuses on the thermo-mechanical and microstructural evolution of NiTi alloys produced using Wire Arc Additive Manufacturing (WAAM), a technology known for its ability to create complex geometries efficiently. The research examines the impact of annealing followed by furnace cooling on the mechanical behavior and structural integrity of WAAM-deposited NiTi alloys. Tensile testing was conducted to assess the static mechanical properties, including strength and ductility, crucial for industrial applications. Following a detailed analysis, the findings reveal that the heat treatment significantly enhances the properties of WAAM-produced NiTi parts. The transformation peaks associated with the Ti2Ni phase reduced significantly, indicating a higher formation of the desired NiTi phase. Mechanical properties improved notably, with the ultimate tensile strength (UTS) increasing from 199.13 MPa to 286.53 MPa in the austenite phase and from 237.53 MPa to 404.8 MPa in the martensite phase. Microstructural analysis revealed an increase in grain size from 9.04 µm in the as-deposited condition to 12.81 µm after annealing, while hardness decreased from 337.3 Hv to 302.54 Hv, suggesting improved ductility and strength. These findings highlight the effectiveness of heat treatment in controlling the mechanical, thermal and microstructural characteristics of NiTi components, making them more suitable for challenging industrial settings. © © 2025 by ASME.