Interrelationship between atomic species, bias voltage, texture and microstructure of nano-scale multilayers

A matrix of binary and ternary nitrides containing lighter elements (Al, Ti, V and Cr) with atomic mass <52 and heavier elements (Nb and W) with atomic mass >89 has been formulated. These have been grown as nano-scale multilayer coatings (bi-layer thickness approx. 3.0 nm) on stainless steel substrates using an industrial size multiple-target ABS coater. When lighter elements are incorporated into the multilayer at a lower bias voltage (UB=−75 V) pronounced {111} or {110}, textures develop which are determined by the dominating species present. A {111} or {110} texture develops when TiAlN or VN and or CrN dominates the matrix, respectively. In contrast when a heavier element is incorporated a {100} texture is observed. Additionally, there is a strong indication that in the case when heavy elements (>89) are involved in the growth process, which evolves by continuous re-nucleation. Conversely, when only light elements (<52) are involved then the coating evolves by competitive growth. This observation is limited only for the lower bias voltage range of UB −75 to −120 V. However, as the bias voltage is increased (up to UB=−150 V) the texture becomes increasingly sharp and in all cases a {111} texture develops. A lower residual compressive stress (typically −1.8 GPa) is observed when one of the bi-layers is dominated by a heavier element. The stress increases (up to −6.8 GPa) in these coatings when the bias voltage is increased to UB=−150 V which is always systematically lower than in coatings containing only lighter elements which are typically up to −11.7 GPa at the same bias voltage. In parallel this results in an increase in plastic hardness (80 GPa) and in the sliding wear coefficient by an order of magnitude regardless of the type of lattice growth observed.