Analysis On Mechanism Of Brazing Diamond With Active Alloy Containing Cr

Brazed monolayer diamond tools have characteristics: high grain protrusion, large swarf clearance space, machining efficiency, high bonding strength and long using life and so on, and they are applied extensively in optical glass, geological survey and stone grinding processing industries. The paper used Ni-Cr-B-Si alloy add Cu-P-Sn powder, CuSnCr, CuSnNiCr powder brazing diamond in vacuum, and research on mechanism of brazing diamond with active alloy containing Cr, and discusses to reduce the thermal damage of diamond.The research work in the paper are as follows:1. Considering the great heat damage to the diamond in brazing process when using Ni-Cr-B-Si as filler, A series of new composite fillers were got by adding 10%, 15% or 20% Cu-P-Sn in the primary filler Ni-Cr-B-Si respectively, then they were used to braze diamond particles. The interface morphology of diamond carbide and the microstructure of filler alloy were tested by SEM, EDS and XRD. The results show that: when the composite brazing filler metal containing 15% Cu-P-Sn alloy, the carbide on the surface of the diamond is more regular and less with brazing temperature decreases, which decreases the thermal damage to the diamond. In the brazed filler alloy, the microstructures such as dentrite included solid solution of Ni with some carbides like Ni31Si12, and Cr7C3 are formed. As the added component, Cu-P-Sn at different proportions can dissolved into the primary filler Ni-Cr-B-Si in large degree, which can adjust the properties of the filler and reduce the heat damage to the diamond.2. In order to reduce the thermal damage in brazing diamond and the cost of manufacture, Cu-Sn-Cr, a mixed metal powder suitable for brazing diamond was prepared, and was used to braze the diamond grits. The interfacial microstructures of the joints between diamond and Q235 steel brazed with Cu76Sn19Cr5 were analysis by SEM, EDS and XRD. The results show that the active ingredient for the brazing of diamond is Cu76Sn19Cr5, and higher strength bonding of the brazing diamond can be realized. There are carbides formed in the front of the interface between brazing alloy and diamond, and the microstructure is mainly composed of a-Cu solid solution, and Cu40.5Sn11. The morphologies of diamond after brazing are intact, and the surface is smooth. Continuous sheet Cr7C3 is formed in the surface.3. Considering the Cu alloy has easily abrasion, poor mechanical properties and the diamond is easy to fall off in the grinding process. So Ni power was added to Cu-Sn-Cr metal powder, and the experiment of brazing diamond abrasive grain was carried out with Cu-Sn-Ni-Cr metal powder as filler. SEM, EDS and XRD were used to analyze the microstructure of diamond and brazing filler. The results show that the active component of the brazing diamond is Cu75Sn15Ni5Cr5, the melting point of the brazing filler is suitable for brazing diamond, and it can realize the chemical metallurgical bonding with diamond. The morphology of diamond is complete, the surface is smooth, and the surface of the diamond is(Cr,Fe)7C3. The brazing filler solidification process of precipitated α-Cu dendrite, peritectic transformation and eutectoid transformation, the formation of dendrite, Cu5.6Sn, α-Cu and eutectoid α-Cu.