Investigation of Microstructural Evolution and Mechanical Properties of IN617 Superalloy During Long-Term Operating at High Temperature

In the present paper, microstructural evolutions and its effect on the mechanical properties of IN617 were investigated in as-received and worked conditions. Worked samples had been operated at 800 °C, under average working stress for operating times of 65,000 and 98,000 h. The different phases were extracted by phase extraction methods. The OM, SEM, TEM, XRD, hardness, impact, stress rupture and tensile tests are used to investigate the microstructure and mechanical properties of operated alloys. The main phases in the specimens are M₂₃C₆ and M₆C carbides and Ti(C,N) compounds. In addition to these three compounds, γ' phase was also observed in both samples, despite the long operating time; although its volume fraction in the second sample (98,000 h) was less than the first sample (65,000 h). A very small amount of δ phase, topologically closed packed phase, was also detected in the samples. With increasing operating time, the area fraction of carbides increased from 0.5% in the as-received plate to 5.5% in the 98,000 h specimen. Unlike M₂₃C₆ carbide, which has an increasing trend with operating time, M₆C carbide decreased from 25.7% in the 65,000 h sample to 18.7% in the 98,000 h sample. This decrease is attributed to the M₆C + M′ → M₂₃C₆ + M′′ reaction. The observed phases are in the form of plate shape, quasi-spherical and irregular and their dimensions increase with increasing operating time. The hardness and strength values are higher in the 65,000 h sample than both the 98,000 h sample and the as-received plate. However these values in the 98,000 h are higher than as-received plate.