The curve of the friction coefficient of the composite coating of laser cladding with different components with friction time is shown infigure 1. It is clearly obvious that the friction coefficient of composite coating K1 without the BN lubricating phase has an obviously increases compared with the matrix, which is mainly related to the content of TiN reinforcing phases and NiTi intermetallic compound in the composite coating. During the dry sliding friction process, the friction pair and the reinforcing phase in the composite coating cause frictional wear of the double abrasive. As the friction process progresses, part of the reinforcing phase of embedded in the coating is peeled off. The friction process is changed from catamaran friction wear to trisomic friction wear, which leads to the increase of friction coefficient of composite coating. h-BN is similar to graphite and has good lubricity during dry sliding friction. With the increase of mass fraction of BN lubricating phase, friction coefficient of composite coating decreases. The decrease in friction coefficient is mainly due to the uniform distribution of BN on the surface of the coating, and the hexagonal structure is prone to shear during the friction process. When the BN mass fraction is 15%, the friction coefficient of the composite coating is significantly reduced and stabilized at about 0.35. Combined with the XRD and microhardness analysis of the coating, as the BN mass fraction increases, the content of the lubricating phase BN and NiTi intermetallic compound in the coating is higher, which leads to the greatly improves the toughness and self-lubricating property of the composite coating. However, the hardness of the coating is reduced due to the high content of lubricating phase.
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