| The poor surface properties of Titanium alloy such as lower hardness and easier to adhesive wear, restrict its applied fields. Laser cladding as one of excellent surface engineering technologies is widely used to improve its surface properties. In this paper, the composite coatings with better wear resistance were fabricated on the Ti6Al4 V substrate by laser cladding 4 groups of WC-Ni-Ni Cr BSi using a HL-5000 continuous wave CO2 laser. Then, 2 laser cladded coatings with the compositions of 30%WC-70%pure Ni and 30%WC-21% pure Ni-49% Ni Cr BSi were dealt with laser remelting under same process parameters. Effects of composition changes and laser remelting on microstructure of the alloyed coatings were investigated by X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM) coupled with energy dispersive spectrometry(EDS). In addition, mechanical properties were also evaluated by using a microhardness tester, a vickers hardness tester, a comprehensive friction and wear machine coupled with profiler and a electronic balance.The experiment about laser cladding 4 groups of WC-pure Ni-Ni Cr BSi composite coatings indicated that the coating(70 wt.% Ni) was mainly composed of WC and Ti C as reinforcements, a(Ti), Ti Ni and Ti2 Ni as the matrix. Two new phases(W, Ti)C and Ni3 B were formed in the coating(21 wt.% Ni-49 wt.% Ni Cr BSi). When the content of Ni Cr BSi was further increased to 63 wt.% and 70 wt.%, the matrix was transformed into Ti Ni and Ti Ni3, and microstructural uniformity was also improved. As the contents of Ni Cr BSi were varied(0 wt.%, 49 wt.%, 63 wt.%, 70 wt.%), the average microhardness of the coatings was increased gradually(745 HV0.1, 976 HV0.1, 1046 HV0.1 and 1107 HV0.1), however fracture toughness presents the opposite change trend(4.20 MPa·m1/2, 3.57 MPa·m1/2, 3.02 MPa·m1/2 and 2.92 MPa·m1/2). Wear mechanism was also changed from the micro-cutting into the mixture of the micro-cutting and the brittle debonding, into the brittle debonding. The appropriate addition of Ni(21 wt.%) into the Ni Cr BSi-WC cladding material(coating 2) was favorable to the improvement in wear resistance of the coating.The experiment about laser remelting 30%WC-21%pure Ni-49% Ni Cr BSi cladded coatings indicated that both coatings are composed of(W, Ti)C, Ti C, Ni3 B, Ni4B3, a(Ti), Ti Ni and Ti2 Ni. More a(Ti) and Ti2 Ni compounds rich in titanium were synthetized in the coating after laser remelting. After laser remelting, the average microhardness of the coating was decreased from 1021.7 HV0.1 to 923.7 HV0.1 while the fracture toughness was significantly increased from 3.57 MPa·m1/2 to 4.81 Mpa·m1/2.The experiment about laser remelting 30%WC-70%pure Ni cladded coatings indicated that the remelted coating became denser with the reduction in defects compared with the alloyed coating. The average microhardness of the coating had few changes after remelting(726.9 HV0.1 and 746.0 HV0.1), which is two times of the Ti6Al4 V substrate(386.0 HV0.1). However, fracture toughness of the coating was increased significantly by 20% from 2.63 MPa·m1/2 to 3.15 MPa·m1/2. Moreover, wear volume and mass loss of the coating before and after laser remelting also showed that laser remelting contributed to the improvement in wear performance. |
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