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

CrN-Ag composite layers, 5-mu m-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 T-s=500, 600, and 700 degrees 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 similar to 300x300x 100 nm(3) to similar to 600x600x200 nm(3) for T-s = 500, 600, and 700 degrees C respectively. At high T-s 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 I and 5 mu m above the surface for T-s=600 and 700 degrees C, respectively, but are absent for T-s=500 degrees C. The cross-sectional microhardness increases with T-s from 17 to 20 to 24 GPa for T-s=500, 600, and 700 degrees 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. (c) 2008 Elsevier B.V. All rights reserved.