Metallographic characterization of metallic heat shields, accidentally precipitation-hardened with tripled soaking time

Abstract

Heat treatment (HT) problems, or the lack of necessary HT, are a regular topic of discussion in the papers published in this section Failure Analysis of Practical Metallography. In this present contribution, a case study is presented that shows how an erroneous furnace run almost caused the scrapping of an entire engine set of Metallic Heat Shields (MHS) of a heavy-duty gas turbine engine. The authors readily admit that the subject components did not fail. They were not even put in engine service yet. That means that this case study does not describe a failure in the original sense of the word. However, from a metallurgical point of view, it is still an interesting case that shows that without proper scrutiny during metallurgical investigation in the laboratory, considerable economic loss could have resulted from a simple fabrication problem, that involved a malfunctioning control system of a heat treatment furnace. It was concluded from the metallurgical investigation that is the subject of this contribution that an almost tripled soaking time during aging, i. e., precipitation hardening, of an entire engine set of MHS did not cause any microstructural alterations that could have detrimentally affected mechanical properties of the subject components.