The effect of the Ta content on the structure, mechanical properties and adhesion of magnetron-sputtered Ti1-x-y-zAlxTaySizN coatings was studied. According to the energy-dispersive X-ray spectroscopy analysis, the coatings studied had the following chemical compositions: Ti0.41Al0.49Si0.10N, Ti0.38Al0.47Ta0.05Si0.10N, Ti0.36Al0.44Ta0.10Si0.10N and Ti0.35Al0.40Ta0.15Si0.10N. The X-ray diffraction experiments revealed the B1-type fcc crystal structure of the coatings. The increasing Ta content was found to induce the texture evolution from (200) to (111), which was attributed to a significant increase in the residual compressive stress in the coatings. The hardness monotonically increased from 32.7 to 42.2 GPa with increasing the Ta content, while the reduced Young’s modulus decreased from 369 to 353 GPa. The adhesion of the coatings to the Ti substrate was evaluated by scratch testing. It was found that the Ti0.36Al0.44Ta0.10Si0.10N coating was characterized by maximum adhesion strength, while incorporation of a larger amount of Ta resulted in earlier coating spallation due to the high residual compressive stress.
Ti-Al-Ta-N coatings are characterized by attractive mechanical properties, thermal stability and oxidation resistance, which are superior to ternary compositions, such as Ti-Al-N. However, because of their open columnar microstructure, the Ti-Al-Ta-N coatings deposited by conventional direct current magnetron sputtering (DCMS) exhibit insufficient wear resistance. This work is focused on obtaining the Ti-Al-Ta-N coatings with improved microstructure and mechanical and tribological properties by middle-frequency magnetron sputtering (MFMS). The coatings are deposited by the co-sputtering of two separate targets (Ti-Al and Ta) using pure DCMS and MFMS modes as well as hybrid modes. It is found that the MFMS coating has a denser microstructure consisting of fragmented columnar grains interspersed with equiaxed grains and a smaller grain size than the DCMS coating, which is characterized by a fully columnar microstructure. The modification of the microstructure of the MFMS coating results in the simultaneous enhancement of its hardness, toughness and adhesion. As a result, the wear rate of the MFMS coating is less than half of that of the DCMS coating.
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