Abstract
The aim of this study is to prepare the Al-Cr-Ta-Ti-Zr-N multi-element coatings onto Si or WC-Co substrates in Ar+N2 mixed atmosphere by RF magnetron sputtering using a single euqimolar AlCrTaTiZr alloy target. The deposition parameters and post-deposition annealing temperatures were varied to investigate the change of structural and mechanical properties of these nitride coatings. The research is mainly divided into four sections. In the first section, Al-Cr-Ta-Ti-Zr-N films were deposited under various nitrogen flow ratios at room temperature without applying substrate bias. The AlCrTaTiZr alloy film exhibited an amorphous structure with smooth surface, while a face-center-cubic (FCC) solid-solution structure with strong (111) orientation, columnar structure and different surface features was observed in the nitride films prepared under different nitrogen flow ratios. The Al-Cr-Ta-Ti-Zr-N films exhibited high hardness as compared with conventional nitride and a nanocomposite structure was obtained for coatings deposited at nitrogen flow ratio of 9%. In the second section, the influence of the substrate temperature (100 to 500°C) on the properties of these Al-Cr-Ta-Ti-Zr-N coatings was investigated. A slight reduction of the N concentration is observed with increasing the substrate temperature. The Al-Cr-Ta-Ti-Zr-N coating of an FCC structure showed an increase in (200) peak intensity and a decrease in crystallite size and lattice parameter, for increasing substrate temperature. The coefficient of thermal expansion of coatings was determined from the rule of mixtures and the stress-temperature plot to see the contribution of thermal and intrinsic macrostress. An increase in substrate temperature results in a monotonic decrease of compressive residual macrostress from -3.2 to -2.0 GPa while the hardness and elastic modulus around 35 and 350 GPa, respectively, were obtained nearly independent of the substrate temperature. In the third section, Al-Cr-Ta-Ti-Zr-N coatings were deposited onto Si and WC-Co substrates to see the influence of substrate bias (0 to -200 V) on properties of these coatings. A reduction in the deposition rate and the concentration of N and Al was observed with increasing substrate bias. The application of substrate bias changed the coating from a voided to a dense columnar structure. The FCC-structured Al-Cr-Ta-Ti-Zr-N coatings showed an increase in both (111) peak intensity and grain size, for increasing substrate bias. The compressive residual macrostress, hardness and adhesion were enhanced with an increase of substrate bias. The lowest wear rate against 100Cr6 steel balls was obtained for the coating biased at -150 to -200 V. In the final section, the influence of post-deposition annealing (500 to 1100°C for 2 h) on the microstructure and mechanical properties for Al-Cr-Ta-Ti-Zr-N coatings was investigated. The coatings were found to retain their as-deposited single-phased FCC structure after all annealing temperatures. The columnar microstructure with a high defect density and the measured high hardness (~36 GPa) were observed to be unchanged after annealing up to 1000°C. The high thermal stability in structural and mechanical properties for this multi-element Al-Cr-Ta-Ti-Zr-N coating was considered as a promising candidate for application of cutting tools.