Effects of bias voltage on the microstructure and properties of AlCrN/AlTiN nanoscale multilayer coatings

Bias voltage has great influence on the microstructure and properties of multilayer coatings, but it is endowed less attentions compared with modulation periods. In this work, effects of bias voltage ranging from -120 V to -210 V on the microstructure and properties of the AlCrN/AlTiN multilayer coatings are investigated. Results show that the multilayer coatings possess fcc-(Al,Cr,Ti)N singular phase, and grow preferentially along the (111) plane, but the texture coefficient of the (111) plane drops greatly at -210 V. Surface roughness decreases firstly and then increases with the bias voltage. Conversely, the hardness increases gradually to the maximum value 33.0 GPa at -180 V, and then decreases to 26.4 GPa at -210 V caused by the texture variation and coarse structure. The adhesion strength decreases gradually with the bias voltage due to augmented residual stress. The friction coefficient and wear rate drop firstly and then increase at -210 V. Abrasion, oxidation and adhesion wear are primarily responsible for the failure of the coatings at mediate bias voltage, while spallation accelerates the failure of the coatings at -120 V and -210 V caused by their poor microstructure and mechanical property.