Quench Cracking Characterization of Superalloys Using Fracture Mechanics Approach

Abstract

In the expectation of developing a new quench cracking criterion, an approach based on fracture mechanics has been investigated in order to improve computer modeling of quenching process. A fully automatic computer controlled data acquisition and processing system was set up to simulate the quenching process. Based on the study of the quench cracking resistance of several gamma prime strengthened superalloys, including U72OLi, Rene’95, Rene88DT and HW model alloys, the mechanism of quench cracking was studied. Effects of the grain size, solution temperature, the composition of alloy as well as specimen size on quench cracking resistance have been investigated. Results show that quench cracking is featured with intergranular failure. The quench cracking toughness and the failing temperature is related to the quench fracture mode. There is a transition in fracture modes with the decrease of temperature. Grain size, composition and solution temperature were found to be the three major factors influencing quench cracking resistance. Fine grain structure can sustain more temperature drop and requires higher thermal stress to initiate the cracking. Intermediate grain structure, which was heated at either supersolvus or subsolvus temperatures, failed at higher temperature and hence developed lower quench toughness. y’ content in alloys only influences the cracking resistance of subsolvus quenched specimen, but does not show significant influence on that of supersolvus quenched one.