Inconel 718 treated with two-stage solution and aging processes: microstructure evolution and enhanced properties

The effects of two-stage solution treatment (namely 900 °C for 60 min and 950 °C for 10 min) and subsequent aging at temperature between 600 °C and 750 °C for 1 to 10 h on the corrosion behavior and mechanical properties of the Inconel 718 are studied systematically. After the two-stage solution treatment, the matrix has no undergo grain overgrowth indicating inhibition of grain growth and with increasing aging temperature, the strengthening precipitates separate and coarsen gradually along the grain boundaries, but the grain size is almost unchanged. The superalloy aged at 700 °C for 10 h has the maximum ultimate tensile strength of 1,303 MPa and yield strength of 1,049 MPa. The corrosion current density I_corr of the alloys treated at 650 for 2 h is 1.392 μA•cm^-2. The MC-style carbides and needle-like δ phase precipitates in the grain boundaries play a crucial role in the changes in the mechanical properties and corrosion behavior. The results provide insights into optimization of the microstructure and properties of the superalloy by economical heat treatment.