Effects of Boron and Nitrogen Contents on the Microstructures and Mechanical Properties of Cr-B-N Nanocomposite Thin Films

Two series of Cr–B–N nanocomposite thin films with various nitrogen and boron contents were deposited by a co-sputtering process using a bipolar asymmetric pulsed DC reactive magnetron sputtering system, respectively. The crystalline structures and BN bonding nature of thin films were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanoindentation technique was used to evaluate the hardness and elastic modulus of thin films. The hardness, elastic modulus and H/E ratio increased with increasing nitrogen content, and decreased with increasing boron content. The optimal mechanical properties were achieved on the Cr-3.7 at.% B-54.6 at.% N thin film with a very fine and dense columnar structure.