Effect of nitrogen concentration on microstructure and microhardness of nanostructured (Ti, Al, Si)N coatings developed by d.c. reactive magnetron sputtering

Nanostructured (Ti, Al, Si)N thin film coatings were synthesized by d.c. reactive magnetron sputtering, performed in an Ar/N(2) gas mixture from a planar rectangular Al:Ti:Si=50:25:25 alloyed target. The mass flow of N(2) reactive gas was strictly controlled in sputtering process. Cross-sectional transmission electron microscopy (XTEM) investigation performed through the deposited films revealed distinct microstructure evolution for different samples. It was found that the variation of the reactive gas amount induced changes in film microstructure. The metallic AlTiSi coating, developed in the absence of the reactive gas, exhibited strong columnar growth with a polycrystalline structure. The addition of a small amount of nitrogen to the process gas leads to a crystallite refinement. Further increase in nitrogen amount leads to a nanocomposite structure consisting of crystalline Ti(3)AlN nanograins in 2 ... 3 nm size surrounded by an amorphous Si(x)N(y) and/or AlN matrix phase The microhardness of as-deposited (Ti, Al, Si)N coatings was measured using a CV-400 AAT microhardness tester and was found in 4 ... 24 GPa range.