On cold dwell facet fatigue in titanium alloy aero-engine components

Abstract

This paper investigates the mechanisms of facet nucleation through combining aero-engine manufacturer disc component test data with microstructure-sensitive crystal plasticity finite element (CPFE) models. Full-scale component testing has been carried out in a manner representative of in-service conditions. Elastic FE analyses of discs under these conditions and fully accounting for thermal and residual processing strains have also been carried out. Disc facet nucleation sites have been identified and the local stress states evaluated in order to establish crystal plasticity oligocrystal sub-models. The oligocrystal RVE models provide knowledge of hard-soft grain stresses under dwell loading, and the consequent load shedding in order to provide stresses required for the facet nucleation. The disc component facet observations together with the crystal plasticity sub-model oligocrystal approach provide persuasive evidence that a hard-soft grain combination is required for facet formation, that the remote stress state influences the resolved shear stress on the soft grain initiating slip (with tensile uniaxial stress state more damaging than a tension-tension biaxial stress state), and that the load shedding which results is essential in pushing up the hard-grain basal stress to nucleate facets

An analysis of macro- and micro-scale residual stresses of Type I, II and III using FIB-DIC micro-ring-core milling and crystal plasticity FE modelling

“…A relevant example can be the dwell fatigue failure which is a well-known failure mechanism experienced in aero-engine discs. This type of failure manner is thought to be highly influenced by the presence of very localised residual stress arising by the interaction between hard and soft grains during cycling [18], giving rise eventually to facet formations followed by crack nucleation.…”

Micromechanical approaches to understand dwell fatigue: from titanium a-b microstructures to disc thermal alleviation

“…Superimposed on the map are the thermo-mechanical loadings associated with the first cycle only of each of four loading scenarios considered: the three rig tests (A, B and C) and the inservice (labelled Redline) conditions. The criteria defining the regions are that a basal (hard grain) stress greater than 1200MPa is taken to be a necessary condition for facet nucleation (determined from rig spin tests [3]), that a temperature in excess of 200°C inhibits facet nucleation [20,22], and that soft grain slip is also a prerequisite for facet nucleation (which defines the elastic region shown). However, the diagram…”

“…Cold dwell fatigue was first recognised through an air accident in the 1970s due to the failure of two titanium fan disks in Rolls-Royce RB211 engines [1,2]. A significant lifetime reduction, known as dwell debit, occurs when titanium alloys are subjected to cyclic loading with stress hold at maximum magnitude (dwell period) in each cycle at low temperatures [3][4][5][6]. Dwell sensitivity of titanium alloys has been an important research interest since then.…”

Electrospark deposition of tungsten carbide powder on titanium alloy Ti6Al4V

“…Титановые сплавы широко применяются в авиастроении, авиакосмической технике, химической промышленности, морской, судостроительной, оружейной и биомедицинской областях, благодаря их коррозионной стойкости, низкой плотности, высокой прочности, низкому модулю упругости и отсутствию цитотоксичности [1][2]. Однако слабая жаростойкость при температуре выше 500°C, сравнительно низкая твердость и высокая вязкость, обуславливающие плохие трибологические свойства, являются характерными недостатками этих материалов [3].…”