Influence of target phase-structure on microstructures and properties of sputtered TiAl coatings

The TiAl thin films were synthesized by magnetron sputtering on substrates of cemented carbide. The impact of the phase-structures of the Ti₃₃Al₆₇ targets (alloyed and unalloyed) on the growth mode, microstructures, contents, interface adhesion and properties of the coating was investigated. The TiAl coatings were characterized with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, and conventional mechanical probes. The results show that the alloying of Ti₃₃Al₆₇ target significantly affected the phase-structures, microstructures, interfacial adhesion, and growth mode of the TiAl coatings. For instance, grown with unalloyed target, HCP Ti and Al₂Ti were the dominant phases, whereas with the alloyed target, Al₂Ti phase was the main phase, accompanied with a small amount of HCP-Ti phase. Besides, the unalloyed target resulted in bigger grains, smoother surfaces, and stronger interfacial adhesion than the alloyed target, possibly because of the different growth modes, Frank-van der Merwe, and Volmer-Weber modes.