Preparation and characterization of (Ti, Al, Si)N coatings developed by d.c. reactive magnetron sputtering

Several nanostructured (Ti, Al, Si)N coatings were deposited by DC reactive unbalanced magnetron sputtering. The target was Ti-Al-Si (40 at.% Al, 40 at.% Ti, 20 at.% Si). The reactive sputtering process was performed in a mixture of Ar and N-2 atmosphere. A constant sputtering power of 400 W was selected during all depositions. The nitrogen flow was in 0 ... 2 sccm range and the argon gas flow was 6.0 sccm. The effect of nitrogen flow rate on morphology and microstructure of thin films was investigated. TEM microscopy (BF and DF) and SAED revealed distinct evolution for different samples. In the absence of nitrogen the microstructure of the coating is a polycrystalline one with 10 ... 20 nm grains. By introducing N2 at a low flow rate the coating microstructure changes to a globular one. Increasing the nitrogen flow leads to a change in the coating microstructure, an amorphous SixNy phase appears embedding 2 ... 3 nm nanograins of hard (Ti,AI)N phase. The ratio between crystalline phase and amorphous phase is very important in order to develop hard and ultrahard coatings. Present research work allows us to conclude about the optimum preparation parameters in the case of our DC reactive UM sputtering system.