Effect of Hot Working on Creep Rupture Properties of PM Ni-base Alloy Consolidated by Hot Extrusion.

Abstract

Effects of hot working on elevated temperature tensile and creep rupture properties at 1000°C were investigated in powder metallurgy(PM) Ni-base alloy, Alloy X, with 50 ppm oxygen content consolidated by hot extrusion process in comparison with cast and wrought materials. It was found that the ductility of PM material at temperatures above 850°C was improved by the application of hot forging while the tensile strength was relatively unchanged. Furthermore, it was found that creep rupture properties of PM materials were not significantly affected by extrusion ratio ranging from 6 to 25, but improved by hot forging. Although aluminum oxides originating from powder surface oxidation during atomization aligned along grain boundaries in the extruded material, these oxides were redistributed within grains by nonuniform deformation of hot forging. It was considered that the improvement of creep rupture properties was realized by a decrease in cavity formation initiated at oxides at grain boundaries.