The Effect of Niobium Addition on the Microstructure and Tensile Properties of Iron-Nickel Base A286 Superalloy

Abstract

Niobium addition is an appropriate approach for improvement of superalloy’s operation. The purpose of this study is twofold: (1) to investigate on the η and γ/ phase precipitations along with (2) to identify the high-temperature tensile properties in A286 and Nb-A286, as a modified type. The heat treatment of both alloys was carried out in a two-stage aging procedure at 760°C for 16 h and 820°C for 2 to 30 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 10.7% to 12%, decreased its size, from 94 to 71 nm, and rising the γ/-dissolution temperature from 987°C to 1007°C. Moreover, the γ/ to η phase transformation was sluggishly occurred in Nb-A286 due to more stable of γ/ precipitations. Furthermore, the Nb-A286 alloy demonstrates higher mechanical properties than A286 one, approximately 100MPa improvement, which it was contributed to the much large volume fraction and finer size of more stabilized γ/ phase.

Keywords

• a286 superalloy
• niobium addition
• η and γ/ phases
• microstructure evaluation
• hot-tensile properties