Of Tc4 Alloy Laser Cladding Wear-resistant Coating

In order to obtain wear-resistant coatings with good properties, the laser cladding of TC4 alloy substrate with Ti+TiC, Ti+ TiB₂, Ti+Cr₃C₂ and NiCrBSi, NiCrBSi+TiC, NiCrBSi+TiB₂, NiCrBSi+Cr₃C₂ was performed. Through the comparison analyses of macro-and microscopic quality for the above laser clad layers, the NiCrBSi and NiCrBSi+TiC powders were chosen as clad materials, and their laser cladding parameters were optimized. The microstructure of the clad layers was characterized using XRD, SEM. The wear properties of the two types of clad layers were examined using a pin-on-disk friction/wear tester under different pressures of atmosphere and various friction parameters.Experimental results show that the clad layers of Ti+TiC and Ti+Ci₃C₂ coatings consist of dendrite and near-spherical TiC phases in the top and bottom respectively. And the clad layer of Ti+TiB₂ coating consists of club-shaped TiB phases and undissolved TiB₂ particles. The Ti-based clad layers are concave-shaped with large pores.The microstructure analyses showed that three regions with different microstructure existed in the surface of layer of NiCrBSi clad samples: the clad layer, the binding zone of the clad layer with the substrate, and the heat-affected zone in the substrate. The microstructure of the clad layer consists of the primary γ-Ni, and the dispersed phases of CrB and M₂₃(C,B)₆. The microstructure of the binding zone shows the dendritic crystals. The heat-affected zone in the titanium alloy substrate has an acicular martensitic structure.The microstructure of NiCrBSi+TiC laser clad layers on TC4 alloy substrate consists of γ-Ni, M₇C₃, M₂₃C₆, TiC and CrB phases. The microstructure of NiCrBSi+ TiB₂ laser clad layers on TC4 alloy substrate consists of γ-Ni, TiB, TiB₂, TiC and CrB phases. The microstructure of NiCrBSi+Gr₃C₂ laser clad layers on TC4 alloy substrate consists of γ-Ni, Gr₇C₃, M₂₃(C,B)₆, TiC and CrB phases. During laser irradiation heating, the Cr₃C₂ particles can be dissolved into the Ni-based alloy melt to large extent in high laser energy. In the process of cooling, the Ti and C atoms in the melt can be precipitated in the form of TiC. In low laser energy, the Cr₃C₂ particles occur mutual striking and combination, with epitaxially growth in edge.The friction coefficient of NiCrBSi clad layer in the atmosphere is in the range of 0.2-0.3. The friction coefficient of NiCrBSi+TiC clad layer is in the range of 0.3-0.4 The wear mechanism of the NiCrBSi clad layer is a mixture of oxidation wear andabrasion. In the atmosphere, the wear of NiCrBSi+TiC clad layer is the abrasion, which is caused by the peeling-off TiC particles from the clad layer. The NiCrBSi and NiCrBSi+TiC clad layers could be strengthened by several mechanisms, including the hard particle strengthening, fine-grain strengthening and solid solution strengthening. Due to the multi-strengthening mechanism, the hardness and strengths of the laser clad layers are increased remarkably, and thus leading to an extremely high wear resistance.