An investigation of the failure mechanisms in high temperature materials subjected to isothermal and anisothermal fatigue and creep conditions

Many engineering components are subjected to conditions which have a detrimental effect on the materials from which they are made. Such components are used, for example, within high temperature regions of aeroengines (e.g. turbine discs) and power plant (e.g. steam pipes) and such conditions can include periods of isothermal and/or thermo-mechanical cyclic loading which may cause fatigue, excessive plasticity and creep. The combination of conditions to which the materials are subjected can have a strong influence on the failure mechanisms induced within the material.This study is concerned with the identification of the failure mechanisms which occur in RR1000 (a Nickel-based superalloy used in aeroengine turbine discs) tested under both isothermal and anisothermal cyclic conditions. The various types of test conditions applied to the specimens (e.g. waveforms which contain high temperature tensile conditions or alternatively low temperature tensile conditions) and the related failure mechanisms (e.g. intergranular, transgranular or mixed cracking), have been identified. Comparisons of the predictions of failure lives with experimental data from tested specimens, subjected to various test conditions, are also presented