Effect of phosphorus on the stress rupture properties of IN706 superalloy

Abstract

The effect of phosphorus (P) and the form it exists on the stress rupture properties of IN706 superalloy has been investigated by testing alloys with four different P contents and heat treated under two schemes. The results showed that a maximum stress rupture life was obtained when 0.008 wt% P was added for the alloy subjected to the phosphide precipitation promotion heat treatment; whilst the stress rupture life of the alloy was continuously increased when the P content was ranged from 0.002 wt% to 0.017 wt% for the alloy subjected to the phosphide precipitation suppression heat treatment. The beneficial effect of P when the phosphide precipitation was suppressed was attributed to its segregation at the grain boundaries, leading to grain boundary strengthening and improvement in intergranular oxidation resistance. However, this beneficial effect was weakened when needle-shaped η phase precipitated at the grain boundaries combined with the decreased P grain boundary segregation. Additionally, no obvious effect of P on the stress rupture ductility of IN706 alloy was identified.