Effects of forming temperature, soaking time and dwell time on the microstructure and mechanical properties of thixoformed nickel-based superalloy parts

Abstract

Thixoforming has unique characteristics over the traditional casting and forging processes, but there is few research focusing on thixoforming of nickel-based superalloys. In this paper, nickel-based superalloy GH4037 parts were successfully formed by thixoforming with different parameters. The effects of forming temperature, soaking time and dwell time on the microstructure and mechanical properties of the formed parts were investigated. The results indicated that forming temperature and soaking time exerted a crucial role in microstructure evolution. With the increase of temperature and soaking time, the proportion of liquid phases in the microstructure increased. During thixoforming, liquid phases were squeezed from the middle region to the peripheral region, resulting in more liquid phases at the edge of the parts. MC-type carbides rich in Ti, V, W and Mo were observed in the liquid phases. When semi-solid billet was heated at 1380 °C for 30 min, the best mechanical properties including an ultimate tensile strength of 973 MPa, a yield strength of 634 MPa and an elongation of 45.6% were achieved. The dwell time had a slight effect on the microstructure and mechanical properties of the parts. The fracture surfaces of the tensile specimens exhibited mostly dimple surfaces and presented a transgranular ductile fracture mode.