Investigation of Conditions of Directed Thermal Influence on Changes of Physical and Mechanical Properties of Diamond Grains in a Grinding Wheels

The article presents information on the features and physical and mechanical characteristics of synthetic diamonds made in Ni–Mn–C and Fe–Si–C systems, their impurity composition. It is proved that in the Fe–Si–C and Ni–Mn–C systems different contents of inclusions and impurities in diamonds are formed, and therefore different ranges of the value of specific magnetic susceptibility, moreover, diamonds of the Ni–Mn–C system have a range of up to 100⋅10–8 m3/kg, but for diamonds of the Fe–Si–C system it is larger – from 100 to 1200⋅10–8 m3/kg, and, therefore, potentially have much greater opportunities in the directional change their properties. Using scanning electron microscopy, an elemental analysis of the faces of diamond crystal faces synthesized in both systems was performed after their heat treatment, which showed that the surfaces of diamond faces contain impurities and inclusions that are under the influence of high-temperature heating through cracks and pores came to the surface of the faces of the crystals. The analysis of the obtained data indicates that for synthetic diamond grains made in both systems, the effect of increasing the strength of grains under the action of thermal action is triggered only when there is a sufficient number of inclusions in diamonds, and therefore their increased magnetic susceptibility. That is why magnetic diamonds of the Fe – Si – C system give a noticeable effect in increasing the strength of grains during heat treatment. This is explained by the fact that such diamonds, having a significant (up to 7% wt.) number of inclusions have a significant mass base for moving impurities and inclusions during heat treatment to ensure the effect of “healing” defects of the diamond surface. This indicates that the thermal effect on diamonds of low strength depending on the number, type of impurities and inclusions allows to change the surface elemental composition of diamonds, the value of the specific magnetic susceptibility of grinding powders and the strength of diamonds to increase their value wear resistance of the grinding tool.