Argon-arc Clad Injection Diamond Surface Composite Coating

To solve the problems of low bonding strength and thermal damage of diamond in the diamond wear resistance coatings making processes, argon-arc clad injection(ACI) process was investigated in this thesis. The substrate is a Q235 low carbon steel plate. The injected particles are nickel-coated diamond particles of 420~500μm. A new way to make diamond wear resistant coating was proposed.Process experiments were carried on with adjustable parameters, which are operating current, powder flow rate and scanning velocity to determine the optimal parameters. The microstructures and bonding strength of the diamond and matrix were analyzed by means of SEM, XRD and EDS. Microhardness and wear resistance of the coatings were tested.The results show that the Ni-coated diamond particles can enter the molten pool smoothly and distribute in the certain depth uniformly. In the coating, the microstructure is compact, and the diamond particle is complete with edges and corners distinct. The coating consists of (Fe,Ni)solid solution, Fe23B6, Ni and C(diamond). There is an obvious un-melted Ni layer around the diamond with metallurgical bonding to the matrix, The diamond is not thermally damaged. The nickel layer around the diamond particle dissolves less upside than in the middle. The microstructures in non-overlapped area of multi-passes and the single pass coatings are the same. The Ni layer is preserved completely, the diamond particles are not thermally damaged. But in the overlapped area, because of the reheating, the Ni layer around the diamond particle which is injected firstly dissolve completely, and the diamond particle is thermally damaged and becomes round.The microhardness of the composite coating is about HV0.2360, higher than that of coating produced by argon-arc cladding with nickel-based self-fluxing alloy. The microhardness of overlapped area of multi-passes coating fluctuates evenly. The wear resistance of the composite coating produced by ACI is enhanced greatly. Wear resistance of the single pass coating is ahout 56 times higher than that of the Q235 substrate, and that of the multi-passes coating is about 46 times higher than that of Q235 substrate. The composite coating is of adhesion wear primarily and a little abrasion wear at the same time. After the wear test, the diamond particles are of three kinds of appearance, full, worn, and broken. The diamond particles are bonded to the matrix well. No cracks or spallation of diamond are found.