Wear behavior of graphite self-lubricating Babbitt alloy composite coating on 20 steel prepared by laser cladding

A tin-based Babbitt self-lubricating composite coating was fabricated on 20 steels substrate by laser cladding through the mixed powders of nickel-plated graphite (Ni-Gr) composite powders and Babbitt alloy powders, aiming at improving wear resistance of Babbitt alloy coating. The results showed that the self-lubricating phase (graphite) coated by the nickel still remained elemental in the composite coating after laser cladding. Both Babbitt coating and Ni-Gr/Babbitt composite coating were uniform and density, without pore, cracks or any other defects, and were mainly composed of alpha-Sn solid solution phase, Cu6Sn5 and SnSb precipitated phases. The grains were obviously refined for the composite coating due to the heterogeneous nucleation. The nano-hardness (H), nano-hardness/elastic modulus (H/E) and (H-3/E-2) for the Ni-Gr/Babbitt composite coating were 1.15 GPa, 0.0137 and 1.9 x 10(-4), which was much higher than that of the Babbitt coating with the value of 0.57 GPa, 0.0068 and 2.3 x 10(-5). With respect to the increase in the nano-hardness, Ni-Gr/Babbitt composite coating also exhibited a low friction coefficient and wear rate with the value of 0.301 and 6.31 x 10(-6) mm(3)/N.;m. The addition of Ni-Gr can effectively improve the self-lubricating and wear behavior of Babbitt alloys.