Effects of Y2O3 on the microstructures and wear resistance of Si–Al–Y co-deposition coatings prepared on Ti–Al alloy by pack cementation technique

Abstract

Si–Al–Y co-deposition coatings were prepared on a Ti–Al alloy by pack cementation process at 1050 for 4h. The effects of pack Y2O3 content (from 0 to 5wt%) on the microstructure and constituent phases of the co-deposition coatings were studied, the wear resistance of the substrate and the coated specimens were also compared at 600°C in air. The results showed that the pack Y2O3 content imposed strong influences on both coating structures and phase constituents. The coatings prepared with the pack mixtures containing 1 and 2wt% Y2O3 were composed of an TiSi2 out layer, an (Ti, X)5Si4 and (Ti, X)5Si3(X represents Nb and Cr)middle layer, an TiAl2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi2,(Ti, X)5Si4 and (Ti, X)5Si3 in the out layer of the coating prepared with the pack mixture containing 3wt% Y2O3. Moreover, (Ti, X)5Si4 and (Ti, X)5Si3 phases were observed in the outer layers of the coatings prepared with the pack mixtures containing 0 and 5wt% Y2O3. The coating growth could be catalyzed obviously when the content of Y2O3 in the pack mixtures increased from 1 to 2wt%, but this phenomenon was not observed when further increased the pack Y2O3 content to 3 or 5wt%. Si–Al–Y co-deposition treatment improved the surface hardness and wears resistance of the Ti–Al alloy significantly. The wear resistance of the tested samples could be sorted in the following sequence: 1% Y2O3-coating>no RE-coating>bare Ti–Al alloy.