Effect of Ti on T15M composite coating fabricated by laser cladding technology

In this article, the T15M (belonging to a kind of high speed steel powder) composite coating with different Ti content was prepared by laser cladding technology (LCT). The microstructure and properties of the samples were investigated by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), automatic micro hardness tester and multifunctional friction and wear testing machine. The results show that the microstructure of the T15M composite coating is mainly composed of martensite, austenite and carbides which mainly distribute on the original austenite grain boundaries. With the increase of titanium element, the shape of carbides become more spherical and the carbides on the grain boundaries change from continuous to discontinuous which attributes to the destruction of carbon concentration balance at the interface. In contrast to the T15M composite coating without adding titanium, the carbides distribution in the coating are more uniform relying on preferential homogeneous nucleation of titanium compounds in solidification. By hardness test, it can be discovered that the addition of titanium to T15M composite coating has no significant effect on the average hardness, but the fluctuation range of the microhardness value decreases. After the sliding wear test, both the coefficient of friction and the mass loss after wear are reduced with the addition of titanium.