High Cycle Fatigue and Cyclic Plastic Deformation Behav-iour of High Temperature Oxidation Resistant Titanium Aluminide Coated IMI834 Alloy at 873K

Abstract

High cycle and force-controlled (HCF) as well as low cycle fatigue (LCF) behaviour of titanium alloy IMI 834 was comparatively studied in bare condition and with titani-umaluminide (Al2Ti) coating, at 873K in air, for compressor disc of aero engines. HCF testing of bare and Al2Ti coated IMI 834 alloy at 873 K in air revealed t hat the coated materials has higher lifetime than the bare alloy.However, for low cycle, high stress lifetimes, the unprotected bare alloy is stronger, possibly due to early crack formation and growth in coated layer. In the case of LCF tests at higher values of total strain amplitudes Al2Ti coated IMI 834 alloy has longer fatigue life (Nf ) as compared to the bare IMI 834 alloy which appears to be due to load shift-ing to the coat, but at lower values of total strain amplitude, Al2Ti coating on IMI 834 alloy seems to have no effect on Nf . Higher values of cyclic strength coeffici-ent (K0) and cyclic hardening exponent (n0) for coated IMI 834 alloy indicate that coating offers resistance to cyclic plastic deformation at 873 K in air, and hence is beneficial. The coating adheres well to the substrate and is also fairly resistant to high temperature corrosion in sea water atmosphere at 873 K.