The Effect of Niobium Addition on the Microstructure and Tensile Properties of Iron-Nickel Base A۲۸۶ Superalloy

Niobium addition is an appropriate approach for improvement of superalloy’s operation. The purpose of this study is twofold: (۱) to investigate on the η and γ/ phase precipitations along with (۲) to identify the high-temperature tensile properties in A۲۸۶ and Nb-A۲۸۶, as a modified type. The heat treatment of both alloys was carried out in a two-stage aging procedure at ۷۶۰°C for ۱۶ h and ۸۲۰°C for ۲ to ۳۰ hours, following characterized by optical and Scanning electron (SEM-EDS) microscopies, differential thermal analysis (DTA) and high temperature tensile tests. The results showed that niobium addition was increased the volume fraction of γ/ phase, from ۱۰.۷% to ۱۲%, decreased its size, from ۹۴ to ۷۱ nm, and rising the γ/-dissolution temperature from ۹۸۷°C to ۱۰۰۷°C. Moreover, the γ/ to η phase transformation was sluggishly occurred in Nb-A۲۸۶ due to more stable of γ/ precipitations. Furthermore, the Nb-A۲۸۶ alloy demonstrates higher mechanical properties than A۲۸۶ one, approximately ۱۰۰MPa improvement, which it was contributed to the much large volume fraction and finer size of more stabilized γ/ phase.

Keywords:

A۲۸۶ superalloy , Niobium addition , η and γ/ phases , microstructure evaluation , hot-tensile properties