Influence of the Vacuum Treatment on Wearing Capacity of Sintered Polycrystalline Diamond (PCD)

The surface state of the diamond grains greatly affects the working capability of the PCD sintered under super pressure and high temperature. Usually the diamond grains are treated by vacuum or cation bombardment so that its surfaces are in a purer state than those sintered only under super pressure and high temperature, such diamond grains are more intense. This paper discusses the effects of the vacuum treatment method with different binders and grain sizes. First the raw material are treated for an hour in the condition of 10-3 Pa and 600 ℃, next sintered them by high temperature in a type DS-029B 5.884106 N/35.304106 N (600/3 600 T) super pressure apparatus, lastly we test their wearing capacity. We choose three kinds of binders: TiSi-B, CrSi-B and NiSi-B, in which the weight percentages of Si, B and metals all keep the same. The weight proportions of all the binder to diamond are 1∶9. When the raw material were not treated by vacuum, the wearing capacity sequence of the binding PCD was: TiSi-BCrSi-BNiSi-B. After treatment in vacuum, their wearing capacity are all increased and their sequence is changed to TiSi-BCrSi-BNiSi-B. Obviously, the wearing capacity of TiSi-B increased greatly. Using TiSi-B type binder and choosing two diamond grain sizes, one was coarse and another was fine, the weight proportions of binder to diamond were the same as above. We compared the effects of vacuum treatment and grain sizes. When it was not treated by vacuum, the wearing capacity of the coarse grain was higher than that for fine grain. After treatment, the wearing capacities of both cases are increased, but that of the fine grain increases 4.8 times and the coarse one only 2.2 times, the sequence order is reversed. So the authors suggest that if using diamond of fine grain size and binders of transition element with loss in more d-electrons, treated in vacuum, it is possible to get high wearing capacity PCD.