Effect of deformation and annealing process on microstructure and properties of Inconel 718 foil

Abstract

In this study, the Inconel 718 foil with a thickness of 0.05 mm and an average grain size of 1.78 ⁓ 2.68 μm was prepared by multi-pass rolling and annealing. In the annealing process after rolling, two kinds of multistage heat treatments were designed to improve the plasticity and strength of the foil respectively by regulating precipitation phase. The RT process for plasticity enhancement (900 °C × 4 h + 960 °C × 1 h) provides a better elongation of 12.8% and a tensile strength of 1305 MPa. The sufficient pre-precipitation of the fine δ phase promotes nucleation and growth of recrystallized grain to refine the equiaxed grains and improve the strength of the alloy. Fine grains inhibit crack initiation and delay crack propagation to improve the toughness of the foil. Furthermore, the dispersed δ phase balances the stress at the grain boundaries and within the grain, resulting in uniform deformation of the grains to enhance the plasticity of the foil. Based on RT process, strength enhancement process (RT + DA process, RT process +720 °C × 8 h + 620 °C × 8 h) increases the tensile strength of the foil to 1480 MPa and reaches a suitable elongation of 8.52%. The improved tensile strength indicates a significant contribution of intensive γ” precipitation to impede the movement of dislocations. This paper is anticipated to provide as a reference for foil preparation regarding microstructure and property adjustment.