Microstructure and mechanical properties of cold spray additive manufactured and post heat treated high-entropy alloys with mixed CoCrFeNi and Ti powders

Abstract

Solid-state cold spray additive manufacturing has the potential to fabricate high-strength bulk high-entropy alloys (HEAs). Through systematic experiments, this study examined the microstructure and mechanical properties of cold spray fabricated bulk HEAs with mixed CoCrFeNi and Ti powders and explored the effects of Ti content in 4 and 7 at% and post-heat treatment at 800 °C/6 h and 1000 °C/6 h. It is found that the bulk HEAs are highly densified and remain nearly defect-free after the post-heat treatment. The addition of Ti serves as an mixing powder effect to further densify the alloys. Moreover, the addition of Ti and post-heat treatment promote the formation of fine precipitates, including Fe2Ti, Co2Ti, CrFe, CoTi2, and Ni3Ti, which contributes to the strengthening of the alloys. Furthermore, post-heat treatment improves the cohesion of the alloys and yields fine and relatively uniform grains by stimulating static recovery and recrystallization. These synergistic effects improve the hardness, elastic modulus, strength, and ductility properties. The average hardness and elastic modulus of the bulk alloys are as high as 377.6 HV and 94.8 GPa, respectively; the best ultimate tensile strength and elongation to failure are 626.7 MPa and 22.1 %, respectively. Synchrotron X-ray diffraction validates the complex precipitates formed and confirms that there is no phase change during tension. The study offers insights into the microstructure and mechanical properties of cold spray additive manufactured HEAs and the effects of mixed powders and post-heat treatment on tuning microstructure and properties.

Keywords

• Cold spray
• High-entropy alloy
• CoCrFeNi
• Microstructure
• Mechanical properties