High-Temperature Low-Cycle Fatigue Behaviour of MAR-M247 Coated with Newly Developed Thermal and Environmental Barrier Coating

Abstract

This study investigates the strain-controlled low-cycle fatigue (LCF) behaviour of an untreated and surface-treated MAR-M247 superalloy in a symmetrical push-pull cycle with a constant strain rate at 900°C in laboratory air. A newly developed experimental thermal and environmental barrier coating (TEBC) system, consisting of a 170 m thick CoNiCrAlY bond coat (BC) and a bilayer ceramic top coat (TC), with an interlayer and an upper layer, was deposited using air plasma spray techniques. The ceramic interlayer with an average thickness of 77 m was formed from agglomerated and sintered yttria-stabilized zirconia. An experimental mixture of mullite (Al6Si2O13) and hexacelsian (BaAl2Si2O8) at a ratio of 70/30 vol.% was sprayed as the upper layer. The average thickness of the TC was 244 m. The specimen sections were investigated using a TESCAN Lyra3 XMU scanning electron microscope (SEM) to characterise the microstructure of both the TEBC and the substrate material. The fatigue damage mechanisms in the TEBC-coated superalloy were studied. The fatigue life curves in the representation of the total strain amplitude versus the number of cycles to failure of the TEBC-coated and uncoated superalloy were assessed. TEBC was found to have a slight, positive effect on the fatigue life of MAR-M247.This study investigates the strain-controlled low-cycle fatigue (LCF) behaviour of an untreated and surface-treated MAR-M247 superalloy in a symmetrical push-pull cycle with a constant strain rate at 900°C in laboratory air. A newly developed experimental thermal and environmental barrier coating (TEBC) system, consisting of a 170 m thick CoNiCrAlY bond coat (BC) and a bilayer ceramic top coat (TC), with an interlayer and an upper layer, was deposited using air plasma spray techniques. The ceramic interlayer with an average thickness of 77 m was formed from agglomerated and sintered yttria-stabilized zirconia. An experimental mixture of mullite (Al6Si2O13) and hexacelsian (BaAl2Si2O8) at a ratio of 70/30 vol.% was sprayed as the upper layer. The average thickness of the TC was 244 m. The specimen sections were investigated using a TESCAN Lyra3 XMU scanning electron microscope (SEM) to characterise the microstructure of both the TEBC and the substrate material. The fatigue damage mechanisms in the TEBC-coated superalloy were studied. The fatigue life curves in the representation of the total strain amplitude versus the number of cycles to failure of the TEBC-coated and uncoated superalloy were assessed. TEBC was found to have a slight, positive effect on the fatigue life of MAR-M247.