Effects of heat treatments on the microstructure and the adhesion of Cr, Ti, Al, Zr HiPIMS films deposited on APS Al2O3 and ZrO2-8Y2O3 coatings

Abstract

While several studies deal with thin film depositions on bulk ceramics, little is known about film applications on thermally sprayed ceramics. Hence, atmospheric plasma sprayed Al2O3 and ZrO2-8Y2O3 coatings served as substrates for the deposition of metallic films (Cr, Ti, Al, and Zr) by means of high power impulse magnetron sputtering (HiPIMS). Subsequently, these duplex coatings were heat treated in a vacuum furnace at 300 °C and 600 °C to investigate influences on the phase formation, residual stress state, mechanical properties, and film adhesion. The Cr and Al films crystallized in a cubic lattice and the Zr films exhibited a hexagonal lattice. The crystallization of the Ti film was substrate dependent, i.e. on alumina substrate the Ti film was cubic, while it was hexagonal on zirconia. Furthermore, heat treating the Ti and Zr films at 600 °C in vacuum led to an oxygen exchange generating c-TiO and m-ZrO. Heat treating the Cr film on Al2O3 substrate provoked a significant stress relaxation leading to an increased adhesion. However, depositing Al films on alumina and zirconia substrates resulted in the highest adhesion in the as-deposited state due to the low Young's modulus. In general, it was shown that phase transformations, increased lattice mismatches as well as differences in the thermal expansion behavior of the substrate and the film had a negative influence on the film adhesion.