Structure and Mechanical Properties of TiAlSiY Vacuum-Arc Coatings Deposited in Nitrogen Atmosphere

The effect of a negative bias potential applied to the substrate on elemental composition, structure, and mechanical properties of vacuum-arc TiAlSiY nitride coatings is investigated by different methods. It is ascertained that applying a high (up to –500 V) bias voltage leads to a selective sputtering of target as well as significant microdeformation of the coating, small-sized growth of crystallites, and their preferred orientation along the [110] direction. In this case, the coating deposited has a low hardness H = 6.95 GPa and propensity to intense wear under scratch and tribological tests. Crystallites with stoichiometric composition ~140 nm in size and [111] preferred orientation perpendicular to the surface of growth are formed at the bias potential about –200 V, and superhard (H = 49.5 GPa) and wear-resistant coatings are grown under such conditions. The mechanisms of formation of the structure of multielement coatings are discussed. It is shown that for- mation of an amorphous phase and nanocrystal [110] texture takes place at a high bias potential owing to the process of radiation-stimulated selective spraying of the target. Formation of microstrained crystallites 10 nm in size caused by the weakening of interatomic bonds is observed in the coating under such deposition condi- tions, and it leads to the decrease in coating hardness and fast destruction during tribological testing. Sub- stantial bias voltage dependence of deposited coating properties is established in our investigations