New Thermally Controlled Solidification Optimization of IN718 Superalloy

A new thermally controlled solidification characterized by “low-temperature pouring, high-temperature filling, and sequential solidification” had been developed to address the problems of misrun, coarse grain and microporosity in complex thin-walled castings of superalloys. The influence of mold temperature (1 260–1 350 ℃) and withdrawal rate (6–48 mm · min⁻¹) on the microstructure of IN718 superalloy cylindrical samples was studied at a pouring temperature of 1 380 ℃, and the forming test of complex thin-walled characteristic structural parts was carried out under the optimized process. The results show that with the increase of mold temperature, the grain size increased from 2.33 mm to 7.46 mm, the uniformity of the microstructure was deteriorated, the proportion of equiaxed grains in the cross-section decreased from 98% to 41%, and the quanity and size of microporosity decreased. With the increase of the withdrawal rate, the grain size decreased from 3.66 mm to 2.69 mm , and the quanity and size of microporosity in creased. When the withdrawal rate was not less than 24 mm · min⁻¹, the microstructure uniformity was good. The optimized process was the mold temperature of 1 290 °C and the withdrawal rate of 24 mm · min⁻¹. A large area thin-walled structural part of IN718 superalloy with a minimum wall thickness of 1.8 mm, grain size of 0.81 mm and microporosity area fraction of only 0.2% was prepared by this process.