Size and Shape Effects for Gamma Prime in Alloy 738

Abstract

Cast IN-738 and wrought Inconel 738 are generic applications for most metallurgical designers of gas turbine blades in the Power Generation Industry on a worldwide basis... Particularly, where first stage buckets are concerned. This is the case because both alloy types exhibit outstanding creep and stress rupture properties to provide an extended service period in a harsh environment. Typically, Alloy 738 is fired in the turbine at 1970 °F (1074 °C) which is about 0.9T _m where T _m represents the melting temperature... A very demanding service temperature, indeed. Furthermore, Alloy 738 is expected to endure this high temperature for a duration of 26,000 h at base load before being retired (R) or replaced (R′) or reused (R′′) issues are ever considered. When these three (3) problems (R-R′-R′′) are brought before a given Materials Review Board for appropriate debate, many pro and con arguments are always evident because (1) Gas turbine blades are not inexpensive and (2) The threat of field failures with possible product liability litigation is of maximum interest to all gas turbine repair shop personnel. The intent of this paper is show how gamma prime precipitate particles can be better examined and more efficiently evaluated using a new characterization method. This research is offered as a contribution to the sum of total knowledge.