Investigation of compatibility between M-Cr-Al-X thermal spray coatings and 3rd generation γ-TiAl alloys

Third generation γ-TiAl alloys are known to possess low density, high strength, high oxidation resistance and reasonable room temperature plasticity. They are intended to use as advanced aero engine material for low pressure turbine blades, casings and other components.

In this work two alloy compositions (Ti-Al-Nb-Cr and Ti-Al-Nb-Cr-Zr-B-La) with homogeneous structure with fine-sized grains were chosen for investigation of physical and chemical compatibility with oxidation resistant M-Cr-Al-X thermal spray coatings. Ti and Al are main alloy elements to form γ-TiAl and α₂-Ti₃Al mixture. Alloy samples were produced by casting.

A number of standard M-Cr-Al-X powders were used as starting materials. To obtain coatings we used air plasma spray (APS) and high velocity oxygen fuel (HVOF) equipment. Optionally some samples were coated with APS ZrO₂-Y₂O₃ thermal barrier layer.

Our investigation of compatibility between M-Cr-Al-X thermal spray coatings and γ-TiAl alloys consists of three stages: thermal expansion compliance test, interdiffusion test and thermal cycling test. Substrate samples and freestanding coating samples used for thermal expansion measurement. Interdiffusion studied by SEM cross-sections investigation after isothermal heat treatment in air muffle furnace during 100 hours at 920°C. Finally, samples with M-Cr-Al-X coatings were subjected to the burner rig tests with surface temperature of 920…950°C.