Influence of bias variation on residual stress and texture in TiAIN PVD coatings

it is recognized that the quality and performance of PVD coatings on tungsten carbide based cutting tools are strongly affected by the level of residual stress as it may cause the coatings to delaminate from the substrate and affect the tool life. Here we report on the substrate bias as an important parameter to affect the compressive stress and the texture in TiA1N PVD coatings on WC/Co cutting inserts as analyzed by X-14 ray diffraction. Approximately 3 mu m TiA1N coatings were deposited by arc evaporation with constant process parameters except for the negative substrate bias, which was varied between 40, 70, 100, 140 and 200 V. The residual stress was analyzed using X-ray diffraction and the sin(2)psi method was used to evaluate the data. The compressive stress increased with increasing bias from -1.7 GPa for the coating deposited at 40 V to about -5 GPa for the 70-200 V coatings. As seen in SEM-images, the coatings prepared at higher bias (140 and 200 V) showed a glassy-like type of structure, with {111} texture and with a lattice parameter close to TiN. For the 40 V coating, a columnar type of structure with pronounced {200} texture was observed. Nano-indentation measurements show an increase in hardness by 15% in the bias range studied. Cutting tests show a correlation between the increase of the substrate bias and the edge line coating delamination, and also give an indication of a critical residual stress level for these coatings. (c) 2005 Elsevier B.V. All rights reserved.