Grain growth and pore elimination in Inconel 625 deposited by APS

• Application of air plasma spraying of superalloy materials
• Investigation on grain growth and pore elimination during heat treatment of coating materials
• Microstructural study during heat treatment process

Due to the nature of the thermally sprayed structures, the mechanical and physical properties of such structures are completely different from commercially produced alloys such as cast and forged structures. The existence of lamellae, splat boundaries, micro cracks and pores and a high level of residual stresses due to the rapid solidification process could affect the properties of the thermally sprayed alloys. In order to improve the properties of the as-sprayed structure, post-deposition heat treatment is necessary. In the current study, Inconel 625 was deposited by atmospheric plasma spraying. Then, the microstructural evolution during the post-deposition heat treatment was investigated. Splat boundaries and micro crack elimination, pore morphology conversion, and grain growth mechanisms were comprehensively elucidated. Results showed that the splat boundaries disappeared partially after heat treatment. The pore morphology converted from irregular to spherical shape. Initially, the grain growth rate accelerated after 200 min. The mean grain size increased from less than 1 μm to 3.5 μm after 300 min isothermal treatment time. The rate of pore growth was fast at first 200 min heat treatment time and reduced slightly after around 200 min heat treatment time.