Microstructural aspects of the failure analysis of nickel base superalloys components

The main reason for the existence of superalloys is their outstanding strength at high temperatures, which make them suitable for the fabrication of gas turbine components. Contributing factors are the high modulus of their close packed FCC lattice and the presence of elements, like aluminum and titanium, which enable the formation of gamma' phase, Ni-3(Al,Ti), that dispersed in the gamma matrix has a hardening effect. The presence of chromium is essential to guarantee oxidation resistance and other alloying elements are important to impart high-temperature strength. Carbon content is usually sufficient to allow the formation of carbides which improve creep resistance. In this work, two failure cases of nickel base superalloy components were analyzed by scanning electron microscopy (SEM). The microstructural aspects provided sufficient evidences to conclude that, in the first case overheating led to failure and in the second case the significant microstructural degradation of the surface can lead to failure. (C) 2004 Elsevier Ltd. All rights reserved.