EFFECT OF IRON ON THE MICROSTRUCTURE, PROPERTIES AND PRECIPITATE KINETIC OF SIGMS PHASE IN A CAST NICKEL-BASE SUPERALLOY

The effect of iron（0-25%）on the sigma phase preciptate kinetic and properties of a Ni-Cr-Mo-Al-Ti alloy by different heat treatment has been investigated. It was shown that sigma phase formation is related to iron content. Iron as alloying element could change the partitioning ratios of alloying elememts between γ-γ’ phases and increase average electron vacancy number Nv, and thus promote sigma phase to precipitate. Stress rupture strength of alloy is decreased in increase of iron content, but its effect on tensile properties is little.