Residual stress characterization of particulate-reinforced composite coating using x-ray diffraction technique

Laser processed composite coatings have been finding a wide range of applications because of their useful properties such as wear and erosion resistance and oxidation and corrosion resistance. However, due to the rapid solidification and cooling involved during laser processing, residual stresses are induced within the composite coating. The magnitude of the residual stress has a very important effect on the mechanical behavior of the composite. Particularly, the magnitude of the residual stress in the composite coating can affect its adhesion with the substrate. Therefore understanding the residual stress in the composite coating is important in order to provide good bonding and to obtain the desired surface properties. In this present study, the effect of processing parameters has been investigated in order to provide a better co-relation between the residual stresses and the laser input parameters. Al alloy 2024 and 6061 substrates were coated with ceramic-metal matrix (TiC/Al) composites using laser traverse speeds of 150, 175 and 200 cm/min and 100, 125 and 150 cm/min respectively. A reduction in the magnitude of the macro-residual stresses with increasing traverse speed was observed in the coatings for both 2024 and 6061 Al substrates. On the other hand, the micro-residual stresses were less affected by the changing processing conditions. Microstructural characterization of these coatings demonstrated delamination of the coating at high traverse speeds whereas strong bonding occurred at lower traverse speeds.