In recent years, the producers and users of diamond products pay more and more attention to the thermal stability of the products. At present, the evaluation of the properties of diamond products is no longer limited to strength, hardness, wear resistance, etc., but the comprehensive evaluation of thermal stability index is added.
There are many factors affecting the thermal stability of single crystal diamond, and each of them also affects each other. The parameters of heating temperature and time are strictly required for cutting tool welding of polycrystalline diamond composite sheet. Therefore, a fuzzy control and synchronous data acquisition system for high frequency induction brazing of polycrystalline diamond was established. Based on the principle of fuzzy control, using single-chip microcomputer technology, combined with the principle and characteristics of high frequency induction heating equipment using silicon controlled, the system realizes parametric control of the brazing tool of polycrystalline diamond composite sheet, and the control effect is remarkable. It is a basic test equipment for further study of tool welding process and thermal damage of polycrystalline diamond surface by induction heating.
Using the above equipment, the problems related to the process of tool brazing of polycrystalline diamond composite sheet, such as the moistening ability of the solder to the brazing metal, the influence of brazing temperature on the strength of brazing joint and so on, have been deeply studied.The oxidation behavior of polycrystalline diamond heated in air was studied by means of thermal differential analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and electron scanning electron microscopy (SEM). Four types of thermal damage of polycrystalline diamond in air were analyzed, and the mechanism of thermal damage of polycrystalline diamond under heating condition was discussed.
In view of the thermal stability of polycrystalline diamond, the differential thermal analysis curve and electron scanning electron microscope (SEM) photos were analyzed in depth, and the initial oxidation temperature on the differential thermal curve of polycrystalline diamond was proposed as the marking temperature of its thermal stability. Based on this, the influence of two internal factors on thermal stability of polycrystalline diamond composite was quantitatively evaluated by grey correlation analysis. It is concluded that the graphitization temperature of polycrystalline diamond is about 90 ℃. With the increase of heating temperature, the composite sheet tends to graphitization. Combined with the results of thermal damage study, it is considered that oxidation and graphitization of polycrystalline diamond composites may occur simultaneously during heating.