Mechanical properties of DCMS and HiPIMS deposited Ti1-xMoxB2±z coatings

Abstract

A promising strategy for enhancing the mechanical properties of sputtered transition metal diboride (TMB2) thin films, including hardness and fracture toughness, is the formation of ternary diborides. Theoretical calculations indicate that incorporating Mo on the metallic sublattice of TiB₂ enhances the overall mechanical properties; however, no experimental data are available. Accordingly, two series (DCMS & HiPIMS) of Ti1-xMoxB2±z coatings with varying Mo contents (x = 0 to 12 for DCMS and x = 0 to 9 for HiPIMS) were deposited using TiB2/MoB composite targets containing different MoB contents to investigate their structural and mechanical properties, focusing on fracture characteristics. HiPIMS growth processes have been proven to significantly enhance hard ness, fracture toughness, and fracture strength compared to DCMS. Specifically, a hardness increase from 38.8 ± 1.7 GPa to 43.7 ± 1.2 GPa (nanoindentation) with a simultaneous fracture toughness increase of 0.4 MPa√m (~17 %; using microcantilever bending tests) and an increase in fracture strength, Rp0.2 of approximately 2 GPa (micropillar compression) was observed for HiPIMS deposited coatings. Compared, our DCMS coatings showed a steady decrease in mechanical properties from H = 38.3 ± 1.5 GPa, KIC = 2.6 ± 0.15 MPa√m and Rp0.2 = 13.7 ± 1 GPa to H = 27.2 ± 0.4 GPa, KIC = 1.7 ± 0.06 MPa√m and Rp0.2 = 9.3 ± 0.3 GPa with increasing Mo content. Our research emphasizes the significance of energetics during film growth, particularly for new ternary diboride systems.