Effect of deformation parameter on solution heat-treated microstructure of extruded Ni-based powder metallurgy superalloy

Abstract

The effect of forging temperature, strain rate and strain state on grain microstructure during solid solution heat treatment of extruded Ni-based Powder Metallurgy Superalloy was studied based on the heat-compression experiment of double cone (DC) specimens. The corresponding relationship between forging temperature, strain rate and grain microstructure in the range of forging temperature from 1060~1120 ℃ and strain rate from 0.003 s–1 to 0.3 s–1 was obtained. The results show that in the Double Cone compression experiment, at the same strain and temperature, the flow stress increases with the strain rate. And at the same strain rate, the higher the temperature, the lower the flow stress is. After supersolvus heat-treatment, at the same strain rate, the grain microstructure is inhomogeneous. And at the same forging temperature, the average grain size of the specimens under the three strain rates of three strain rate is 18~20 μm, but the specimens with higher strain rate clearly show inhomogeneous grain microstructures. In order to obtain the homogeneous grain structure, the more appropriate forging parameter is: the temperature of 1120 ℃, and the strain rate of 0.003 s–1. At the same forging temperature and strain rate, with the decrease of local strain, the average grain size is increased gradually.

Keywords

• Nickel-based P/M superalloy
• double-cone compression
• forging temperature
• strain rate
• grain microstructure