Performance evaluation of laser surface alloyed hard nanostructured Al2O3–TiB2–TiN composite coatings with in-situ and ex-situ reinforcements

Hard and wear resistant Al2O3–TiB2–TiN composite coatings have been developed on low carbon steel (AISI 1025) substrate by following two different routes involving laser surface treatment. In the first (termed ‘in-situ’ process), reinforcing phases TiB2 and TiN, as well as the matrix Al2O3 of the composite are synthesized in-situ by laser-triggered self-propagating high temperature synthesis (SHS) from a mixture of Al, TiO2 and h-BN and coated onto the substrate surface by laser surface alloying (LSA). In the second (termed ‘ex-situ’ process), the constituents Al2O3, TiB2 and TiN of the coating are provided directly as a pre-placed precursor powder mix and laser surface alloyed onto the substrate. Of these two laser assisted manufacturing procedures, it is of interest to determine the one that is more appropriate for the development of a hard, wear resistant coating. In the present work, investigation of the comparative merits and demerits of Al2O3–TiB2–TiN coatings produced by in-situ and ex-situ processes is attempted through analysis of microstructure and evaluation of mechanical and tribological properties.