Effect of phosphorus distribution on stress rupture properties of a low thermal expansion superalloy

The behavior of phosphorus in the Thermo-Span alloy in which the addition of Al and Cr was modified was studied. The phosphorus bearing phase was observed both in the grain interior and at the grain boundaries when the alloy was solutioned at 1093C. The phosphorus bearing phase was largely dissolved when the alloy was solutioned at 1160C, leaving only a small amount in the grain interior. The influence of phosphorus on the stress rupture properties was determined by the existing state of phosphorus in the alloy. Phosphorus largely reduced the stress rupture life when it caused the precipitation of the phosphorus-bearing phase, while it increased the stress rupture life of the alloys when it was concentrated at the defects such as grain boundaries or dislocations.