Pressureless sintering of cold sprayed Inconel 718 deposit

The deposition of Inconel 718 powders, by cold spray, was performed on a mild steel substrate. The deposits showed a porosity level lower than 3%, but lacked interparticle bonding, hence strength. To circumvent the problem, the deposits were used as green compacts for pressureless sintering at temperatures of 1200, 1225, and 1250 °C for 10, 60, and 180 min. The grain size, second-phase distribution, micro-hardness, and flexural strength were measured. Upon sintering, the flexural strength and strain increased from 187±41 to 1225±122 MPa, and 0.026±0.022 to 0.183±0.037, respectively. After a conventional aging treatment, a maximal strength of 2303 MPa was obtained. During the sintering treatment, minimal grain growth occurred in the 1200 and 1225 °C trials where the calculated grain growth exponent was n=1/8. However for the sintering trials at 1250 °C, the grain growth exponent was found to be n=1/2. The grain growth was found to be influenced by secondary MC carbides that precipitated during the sintering treatment but dissolved at 1250 °C. The carbides acted as a pinning phase during the sintering treatment, explaining the reduced grain growth for the 1200 °C and 1225 °C conditions.