In Situ Synthesized Graded TiC Particulate Reinforced Ni-based Composite Coating Prepared by Laser Cladding

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Abstract
Pure titanium (Ti) which had been processed by high energy ball milling, graphite and Ni60A self-melting alloy composite powder were used as the cladding materials. A test on the in situ synthesized graded TiC particulate reinforced Ni-based composite coating was carried out after presetting of the composite powder on the 42CrMo alloy structured steel base surface. Morphologies, tissue structures and microhardness values of samples were investigated by an optical microscope (OM), scanning electron microscope (SEM) and microhardness tester. Results show that in situ synthesis of TiC reinforced particulates is realized with pure Ti and graphite powder under laser cladding. TiC particulates which have a small density presents a graded distribution of less at lower and more at upper of the coating due to the floating effect in a melting pool. Therefore, in situ synthesized graded TiC particulate reinforced Ni-based composite coating was gained. Moreover, TiC particulates cluster and grow in the melting pool due to collision and bonding of TiC particulates in the floating process. Compared to TiC particulates at lower part of the coating, the TiC particulates at upper part of the coating possess a higher proportion of clusters and growth phenomena. The volume percentage of TiC particulates at middle and bottom of the composite coating is lower than 5%, while volume percentage of TiC particulates on the coating surface is no higher than 25%. Similar with distribution pattern of TiC particulates, microhardness of the composite coating is also high on surface and low deep layer of the coating.

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