Failure analysis of a gas turbine blade made of Inconel 738LC alloy Z. Mazur a, * , A. Luna-Ramı ´rez a , J.A. Jua ´rez-Islas b , A. Campos-Amezcua a a Instituto de Investigaciones Ele ´ctricas, Av. Reforma 113, Col. Palmira, 62490 Cuernavaca, Morelos, Me ´xico b Instituto de Investigacio ´ n en Materiales, Universidad Nacional Auto ´noma de Me ´xico, Circuito Exterior, Ciudad, Universitaria, 04510 Me ´xico, DF Available online 23 November 2004 Abstract The failure analysis of the 70 MW gas turbine first stage blade made of nickel-base alloy Inconel 738LC is presented. The blades experience internal cooling hole cracks in different airfoil sections assisted by a coating and base alloy deg- radation due to operation at high temperature. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely: loss of aluminium from coating due to oxidation and coating phases changing; decreasing of alloy ductility and toughness due to carbides precipitation in grain boundaries; degradation of the alloy gamma prime (c 0 ) phase (aging and coarsening); blade airfoil stress level; evidence of intergranular creep crack prop- agation. It was found that the coating/substrate crack initiation and propagation was driven by a mixed fatigue/creep mechanism. The coating degradation facilitates the crack initiation due to thermal fatigue. The substrate intergranular crack initiation and propagation were due to a creep mechanism which was facilitated by grain boundary brittleness caused by formation of a continuous film of carbides on grain boundaries, the degradation of c 0 due to elongation (rafting) and coalescence, and high thermomechanical stress level. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Failure analysis; Creep–fatigue interaction; Gas turbine failures; Turbine blade failure; Metallurgical examination 1. Introduction Gas turbine blades are made of nickel-base and cobalt-base superalloys principally. During the opera- tion of power generation gas turbines, the blades and other elements of hot gas path suffer service induced degradation which may be natural or accelerated due to different causes. The degradation or damage may 1350-6307/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2004.10.002 * Corresponding author. Tel.: +52 777 3623811; fax: +52 777 3623834. E-mail address: mazur@iie.org.mx (Z. Mazur). Engineering Failure Analysis 12 (2005) 474–486 www.elsevier.com/locate/engfailanal