The Bonding Mechanism And The Thermal Stress Simulation Of High Temperature Brazed Diamond

Comparing with the multilayer impregnated brazed diamond tools, diamonds in traditional diamond tools often dropped off. And one of these brazed diamond tools’ key superiorities was improving the wettability and bonding of diamond grits to achieve better quality diamond tools. Also, the exposure level of diamond from the bond level was high and the space for accommodating cuttings was large. And its bonding mechanism aroused the interest of people. Actually, after the vacuum heat treatment, the pure diamond had no obvious changes and no cracks, while some of brazing diamond grits had some cracks or be broken. Thus, the research of the bonding mechanism and thermal stresses of brazing diamond grits will be important to improve the quality of the tools.In the paper, by means of the micro analysis methods of materials, analyzed the bonding mechanism of brazing diamond grits. Then, by the means of numerical analysis and finite element analysis (FEA), simulated thermal stresses which were produced in the cooling process of diamond grits. The main creative contents in the paper are as follows:First, the samples which included little spots brazing and entirety brazing diamond grits were prepared to be deep corrosive. By means of Phase shift microxam-3d, Scanning Electron Microscope (SEM, LEO-1450) and X-ray Diffraction (XRD, DMAX-RBX), studied the microstructure of the interface between diamond grits and Ni-Cr alloy for analyzing the bonding mechanism of brazing diamond grits. The result indicated that the chemical reaction happened in the interface and a reaction layer formed among diamonds and brazing alloy. The reason of the high bonding strength between diamond and Ni-Cr brazing alloy was the carbide which mainly contained needle-like Cr7C3, formed in the brazing process.Two, for the existence of transition layer, thermal stress appeared in the brazed diamond grits. The paper analyzed the cause of cracks of diamond. For there is no lattice distortion happening. It’s very useful for studying the reasons of the cracks of diamond grits. Then, by the means of numerical analysis method, studied the elastic thermal stresses of diamond. Analyzed thermal stresses of the brazing alloy to find out whether the cracks happen and when it happens. The result indicated that while the diamond radius and the cooling temperature range were defined, brazing alloy layer would be cracked. When the ultimate tensile strength of the brazing alloy was defined, the elastic model was built for numeric calculation. Finally, we got the criteria of the alloy layer cracking.Three, regarding for many factors, simulated the thermal stresses of brazing diamond grits by ANSYS. The paper selectively analyzed the effect of carbide layer in brazed diamond grits. The result indicated that the maximum residual tensile stress appeared in the middle of the carbide layer. While the maximum residual tensile stress was over the limit, the crack would appear in the carbide layer. The result was the same as the observed result by the SEM.The research of the bonding mechanism of brazing diamonds and simulation of thermal stresses had a wider significance for improving the brazing technique.