Study on thermal stability and mechanical properties of nanocomposite Zr-W-B-N thin films

The effect of microstructure on thermal stability and mechanical properties of co-sputtered deposited Zr-W-B-N thin films on Si (100) substrates have been studied in detail. The power density of boron target has been varied from 0.1 to 7.5 W/cm2 to obtained films of varying microstructure. Electron microscopy, X-ray diffraction analysis, atomic force microscopy, Raman scattering spectra, nano and micro indentations were used to investigate the interrelations between the microstructure and the variations in strength properties of nanocomposite Zr-W-B-N thin films. It has been observed that films with boron content < 2.3 at.% exhibited (200) preferred crystallographic orientation of grains and columnar structure. While the films of boron content ≥ 7.5 at.% are columnarless with crystal phase grain size less than 7 nm and of amorphous-crystalline structure. The film with boron concentration ~ 7.5 at.% exhibits maximum hardness (~ 37 GPa), wear resistance (H/Er ~ 0.24) and fracture toughness (2.9 MPa·m1/2). Post annealing of the film with ~ 7.5 at.% boron concentration has been carried out in vacuum (Tv) and air (Tn) up to 900 °C. Zr-W-B(7.5 at.%)-N film retains its fcc structure during vacuum annealing up to 900 °C. Oxygen starts to incorporate at Tn = 500 °C and its percentage goes up with increasing Tn up to 900 °C.