Stress state or TiN/TiAlN PVD multilayers

A multilayer system consisting of TiN and TiAlN layers is deposited by mean s of a PVD process onto stainless and tool steel substrates. The study is a imed at determining the microstructure and the macrostresses in these layer s with X-ray diffraction. The multilayer system is composed of a relative t hick TiAlN layer (similar to 150 nm) and a set of smaller alternating TiN/T iAlN layers of approximately 15-20 nm each with a total thickness of 150 nm . This basic building block of the structure is repeated throughout the coa ting and is sandwiched between two thicker layers: a TiN layer (400 nm) to achieve good adhesion with the substrate, and a top layer of TiAlN (400 nm) . The total thickness of the coating is approximately 4.4 mum. From X-ray d iffraction it is concluded that the layers are only slightly textured and t here is a weak (311) texture. The strain measurements show a difference in strain for the layers on stainless and toll steels, which is owing to a dif ference in the linear expansion coefficient for the two substrates. It is p ossible to determine the unstrained lattice spacing of the TiN and TiAlN su blayers and to calculate Poisson's ratio for both materials. Furthermore, t he residual stresses in the different sublayers could be derived and it was found that they were much higher in the TiN than in the TiAlN. This may be explained by the thermal origin of the residual stress in the TiAlN sublay ers, whereas in the TiN sublayers the atomic peening process during deposit ion introduces an additional residual stress. (C) 2001 IoM Communications L td.