Improving Tensile Properties of Inconel 718 Alloy by Ultra-Short Annealing

Abstract

In order to uniformly refine the grains to obtain an excellent combination of strength and ductility, a novel heat treatment method combining high temperature ultra-short annealing with double aging was propose in this work. The effect of annealing treatment between cold rolling and double aging on the microstructure evolution and tensile properties of Inconel 718 alloy was studied. The results showed that the sample ultra-short annealed at 980 °C for 1 min was partially recrystallized and consisted of refined recrystallized grains and elongated deformed grains. The KAM map and hardness evolution confirmed that dislocation recovery and recrystallization nucleation formed even in deformed grains, suggesting that ultra-short annealing at high temperature can overcome the recrystallization barrier. Therefore, subsequent recrystallization process can be completed at a lower temperature. In consequence, completely recrystallized microstructure obtained in the ultra-short annealed sample after double aging treatment (980-1min-aged sample), and the average grain size was uniformly refined to 3.59 µm. The 980-1min-aged sample exhibited outstanding tensile properties. When deformed at room temperature, the ultimate strength and total elongation were about 1600 MPa and 19%. For the high temperature (650 °C) tensile properties, the ultimate strength was ~ 1350 MPa and the total elongation was ~ 26%. In comparison, due to the coarse grain size and grain inhomogeneity, the hot tensile strength and elongation of the sample subjected to fully recrystallization annealing at 980 °C for 30 min and double aging treatment were about 1180 MPa and 22%, which were inferior to that of 980-1min-aged sample. Consequently, high temperature ultra-short annealing coupled with double aging treatment can be a promising and cost-effective processing route for the improvement of tensile properties of Inconel 718 alloy.

Keywords: Ultra-short annealing, Aging treatment, Recrystallization behavior, Tensile properties, Inconel 718 alloy