Removal of casting porosity in superalloy IN738 using hydrostatic pressure sintering

Abstract

The cast nickel-base superalloy IN738 is used as a blading material in the HP stage of various Avon and Olympus gas turbines within the Central Electricity Generating Board. Porosity arises in this alloy during casting, and has a detrimental effect on such properties as creep life and high cycle fatigue strength. Heat treatments have been performed under a superimposed hydrostatic pressure of argon gas and these have been successful in removing the majority of casting porosity. High sensitivity density measurements are used to monitor the progressive sintering of pores, the kinetics of which are discussed in terms of vacancy diffusion in the combined stress field of the hydrostatic pressure and the pore surface tension.

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