| In recent years, the producers and users of diamond pay more and more attention on its thermal stability (TS). Both British Element Six (former De Beers) and American GE make great effort on test and study of the thermal stability of diamond products. The TS of diamond is made as an important evidence for ascertaining the application field of diamond abroad. Now, the property assessment of diamond products has not been limited on test of strength, hardness, wear resistance, etc. but is a comprehensive estimation including the TS. In this paper, considering the practical applications, the author quantitively analyzed the internal factors influencing the TS of synthetic single crystal diamond, and combining the fabrication of polycrystalline diamond (PCD) compacts tools, analyzed the TS of PCD compacts and thermal damage on PCD layer induced by induction heating.There are many factors influencing the TS of diamond, and these factors influence each other. So, based on the Grey System Theory, a method that can make the best of original information of products is provided, that is, the grey relationship analysis. Using this method, quantitively analyzed influencing ability of 4 kinds of internal factors for the TS of diamond, and obtained the grey relationship sequence. Furthermore, the grey forecasting model for the TS prediction of Ib-type synthetic single crystal diamond is established. The results show that the model is appropriate. At the same time, it is proposed that the extrapolated onset temperature is taken as the characteristic temperature for the TS of single crystal diamond.The brazing of PCD tools requires exact heating temperature and soaking time. Hence, the fuzzy control ℃ sync data collecting system was developed for hi-frequency induction heating of PCD tools. The system, which is based on the fuzzy control theory and SCM technology, and combine the principle and characteristic of hi-frequency equipment using the Silicon Controlled to control the heating, realized the parameter controlling for induction heating. The results show that the controlling effect of the system is good. It is the basic device for further studying the technics of PCD tool brazing and the thermal damages on PCD layer induced by induction heating.Utilizing the above device, the several questions related to the procedure of PCD tool brazing were deeply studied. They are the following facets: a) wettability of filler metal to brazing materials; b) the influence of heating temperature on joint strength; c) the influence of soaking time on joint strength; d) the influence of surface roughness of brazing materials onjoint strength.Using the modern analysis methods including DTA, TGA, XRD, and SEM, the oxidation behavior of PCD heated in Air was deeply studied, 4 kinds of thermal damage forms were analyzed, and the mechanism of thermal damage for PCD compacts heated by induction heating in Air was profoundly probed.The influence of induction heating for PCD compacts determines the quality of the welded tools. Hence, the thermal damage layers on the rake face and the major flank of tool induced by induction heating were studied by SEM. The analysis of thermal damage layer for the rake face can provide theoretical guidances for confirming the machining allowance of surface grinding. The study of thermal damage layer for the major flank can provide theoretical guidances for determining the minimum machining allowance of edge grinding.For the TS of PCD compacts, the DTA & TG curves of PCD layer heated in Air were deeply analyzed, the SEM micrographs of PCD compacts heated by induction heating were observed, and the starting oxidation temperature on the DTA curve of PCD compacts was put forward as the characteristic temperature for the TS of PCD compacts. According to the results, using the grey relationship analysis, the influence ability of 2 kinds of internal factors for the TS of PCD compacts was quantitively estimated. Furthermore, the problem, that is, if the oxidation and graphitization of PCD compacts occur simulta...
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