Wear behaviour of Al_2O3 dispersion strengthened MCrAlY coating

This work deals with the HVOF thermal spraying of an Al₂ O₃ dispersion strengthened NiCoCrAlY spray powder and its high temperature wear behaviour in comparison to the unstrengthened matrix. Due to low particle heating in the HVOF process, the fine microstructure of the strengthened powder remains almost unchanged after spraying. The Al₂O₃ dispersion strengthened NiCoCrAlY spray powder was produced using the high-energy ball milling process. Both the coatings from the milled powder and from the unstrengthened matrix material were characterised in terms of their microstructure by metallography and scanning electron microscopy in the as-sprayed state as well as after heat-treatment. The sliding wear resistance of the coatings was evaluated by ball-on-disc tests. It was found that under selected test conditions, the two coating systems presented almost the same wear rates, but the coefficient of friction for the disperse strengthened matrix attained a steady value of 0.75, while for the unstrengthened coating it increased steadily from 0.52 to 0.67. The HVOF gun was also employed as test facility to compare the wear resistance of both coating systems under a high temperature erosive environment. While the erosion behaviour of the NiCoCrAlY coating was evidently ductile, the dispersion strengthened coating showed mixed erosion behaviour and a higher erosion rate.