Development and Characterization of a Damage Tolerant Microstructure for a Nickel Base Turbine Disc Alloy

A modified heat treatment has been developed for the nickel-base superalloy, PWA 1113, to create a damage tolerant microstructure @TM) using mechanistic microstructural design concepts. The DTM was designed with the aim of imparting improved fatigue crack growth resistance without forfeiture of other vital properties such as tensile strength, stress rupture life, and low cycle fatigue lifetimes. This was achieved by optimizing the material’s grain size, grain boundary morphology, and the intragranular precipitate size and distribution. Mechanical testing demonstrated that when compared to the conventional microstructure (CM), the short crack growth rate for the DTM was slower by a factor of 3 at room temperature, and 2.2 times slower at 482 “C. Creep test results showed that at 690 MPa (100 ksi) and 705 “C, the creep-rupture life was extended by a factor of almost 4 for the new DTM. Tensile test results indicated minimal strength losses for the DTM with respective YS and UTS values of 80% and 90% of the CM baseline values at both test temperatures. Introduction Emerging safety standards for rotating engine components are now starting to demand properties in engineering materials, that may not meet the required specifications’. 2. In particular, the damage tolerance specifications imposed upon turbine disc materials have prompted researchers to investigate ways to improve crack growth properties of presently used alloys without compromising the traditional safe life limits. As a result, a microstructural design philosophy has been successfully developed that is aimed at improving the damage tolerance of conventional disc materials.3 Damage tolerance, by definition, is the ability of the disc material to exhibit greater resistance to the growth of inherent or service induced flaws under creep and/or fatigue loading conditions, while still maintaming adequate low cycle fatigue pro erties, tensile strength, as well as stress rupture strength. ! Consequently, improving the damage tolerance of conventional Ni-base disc alloys has become an area of substantial interest amongst disc material manufacturers and engine designers alike. Superalloys 2000 Edited by T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. McL.eaa, S. Olson, aad J.J. Schina TMS (The Minerals, Metals &Materials Society), 21X0