Effect of η Phase on Mechanical Properties of the Iron-based Superalloy Using Shear Punch Testing

In this paper, the shear deformation behavior of A286 Iron-based superalloy was studied with an emphasis on the influence of eta phase on shear strength. The eta (Ni3Ti) phase precipitates at high temperature heat treatment or during services at the expense of gamma prime phase. According to the microstructural features, no evidences of eta phase were found at 650 and 720 degrees C. eta phase precipitated at 780 and 840 degrees C and the amount of it increased with an increase the time and temperature. Because of using the alloy as fasteners, investigation of shear properties and the influence of eta phase on it are indispensable. The shear strength of the alloy with different volume fractions of eta was examined. It was found that, with an increase of eta volume fraction, the ultimate shear strength decreases. The shear punch fracture surfaces were also examined by the scanning electron microscopy. The fracture surfaces of sheared samples indicated that low and high volume fraction of eta phase result in interior cracks and grain boundary decohesion, respectively. In fact, the fracture of weak grain boundary films (eta phase) produces this kind of decohesive cracking.