Mechanism for oxygen enhanced crack growth in inconel 718

Abstract

Department of Mechanical Engineering and Mechanics, Zettlemoyer Center forSurface Studies, Lehigh University, Bethlehem, PA 18015, USA(Received September 25, 2000)(Accepted in revised form January 11, 2001)Keywords: Oxygen enhanced crack growth; X-ray photoelectron spectroscopy (XPS); Niobium;Crack growth mechanism; Ni base alloyIntroductionNickel based superalloys are used extensively in high temperature applications, for example, turbinedisks in jet engines. Since turbine discs operate in air at 700 to 973 K, these alloys have receivedconsiderable attention with respect to their sensitivity to environmentally enhanced crack growth(EECG). Previous studies have shown that oxygen increased the rates of crack growth in niobiumcontaining alloys (such as Inconel 718, Rene-95 and3750) at high temperatures (.800K) by up to 4.5orders of magnitude over those observed in an inert environment (1–7). Several mechanisms have beensuggested for this crack growth enhancement which include: (a) the oxidation of metallic carbides orcarbon at the grain boundaries to form high pressures of CO and CO