CrN–Ag nanocomposite coatings: Effect of growth temperature on the microstructure

CrN–Ag composite layers, 5-µm-thick and containing 22 at.% Ag, were co-deposited by reactive magnetron sputtering on Si(001) substrates in a 0.4 Pa pure nitrogen atmosphere at growth temperatures Ts = 500, 600, and 700 °C. A combination of X-ray diffraction and cross-sectional microscopy analyses show that Ag segregates to form precipitates with an average size that increases from < 25 nm to ~ 300 × 300 × 100 nm3 to ~ 600 × 600 × 200 nm3 for Ts = 500, 600, and 700 °C, respectively. At high Ts, the precipitates extend along the surface plane to form horizontal lamellae that cause grain re-nucleation and, in turn, a disruption of the columnar microstructure and a transition from a strong 002 texture for pure CrN to a mixed preferred orientation for the composite coatings. In addition, Ag segregates to form mounds on the growing layer surface that result in the nucleation of nodules which exhibit an increased growth rate and extend up to 1 and 5 µm above the surface for Ts = 600 and 700 °C, respectively, but are absent for Ts = 500 °C. The cross-sectional microhardness increases with Ts from 17 to 20 to 24 GPa for Ts = 500, 600, and 700 °C, respectively, which is attributed to a decrease in the effective Ag concentration associated with temperature-activated segregation. The measured hardness for pure CrN is 28 GPa.