Effect of bias induced microstructure on the mechanical properties of nanocrystalline zirconium tungsten nitride coatings

Abstract

The utilization of substrate bias voltage to accelerate the sputtered ions in sputtering plasmas is an effective way to alter the properties of coating. In this work, hard nanocrystalline ZrWN coatings were sputter-deposited at relatively low deposition temperature (200°C) by varying the substrate bias voltage from −20V to −120V. The effect of negative substrate bias on the microstructure and mechanical properties of nanocrystalline ZrWN coatings has been studied in detail employing X-ray diffraction, field emission scanning electron microscopy, energy dispersive x-ray spectroscopy, atomic force microscopy, transmission electron microscopy, nano-indentation and micro-indentation. The results indicate that the microstructure and morphology were significantly altered as a function of the increasing bias voltage. The bias voltage of −20V to −60V lead to enhanced ion current density and deposition rate while the resputtering effect was induced as the bias voltage increased beyond – 60V. A dense glassy structure along with a maximum compressive stress (8GPa) and hence optimum mechanical properties (hardness~34GPa, reduced elastic modulus Er~145GPa, wear resistance~0.23 and fracture toughness~2.25MPa√m) were obtained in the ZrWN nanocrystalline coatings at a bias voltage of −100V. The results demonstrate that the enhancement of mechanical properties in ZrWN coatings can be achieved by carefully controlling the processing conditions, which in turn facilitate controlling the microstructure evolution, stress and mechanical properties.