In-situ laser-fabrication and characterization of TiC-containing Ti–Co composite on pure Ti substrate

This work presents the in-situ fabrication of a layered metal-matrix composite coating on a pure Ti substrate. The coating consists of a matrix of cobalt-titanium intermetallics and the reinforcement phase of titanium carbide. The fabrication process is laser cladding, conducted using a pre-placed powder mixture of elemental titanium, cobalt, and graphite. Several materials characterization methods including microscopy, microhardness and nano-indentation are used to study the coating and coating–substrate interface. The intermetallic phases in the matrix vary from Co-rich phases at the coating surface to Ti-rich compounds near the substrate. The interface is revealed to have a smooth profile, free of any porosity or cracks, with good metallurgical bonding to the substrate. A relatively uniform hardness in the range of 1200–1300 HVN is achieved through a depth of 200 μm into the coating. The hardness then gradually decreases to 480 HVN at the substrate interface, approximately 300 μm from the surface. The hardness evolution, which is predictable using the Rule of Mixtures, is explained by the fraction of the carbide particles and the type of intermetallic compounds in the matrix.