ENVIRONMENTAL DAMAGE OF CAST Ni-BASE SUPERALLOY K17

Rupture and tensile properties of K17 before and after thermal exposure in vacuum,air and hot corrosion environments have been investigated.The results show that vacuum exposure es- sentially does not affect the rupture lives but it results in the decrease of high temperature ten- sile strength and increases of rupture and high temperature tensile ductilities;air or hot corro- sion environmental exposure results in the degradation of alloy:severely reduce the rupture and high temperature tensile properties,hot corrosion environmental exposure being more harmful.The former causes grain boundary oxidation and depletion of Cr,and the later makes the sulphurization at grain boundaries.This results in the concentration of S and de- pletion of Cr at grain boundaries and,consequently,weakens the grain boundaries.