1. CBN particles
The influence of CBN particles on the preparation of PCBN mainly includes three aspects: first, the influence of CBN particles on the surface cleanliness. Excessive impurities will affect the bond between CBN-CBN particles and CBN and binder, resulting in reduced PCBN strength and wear resistance. Second, the size of CBN particles. Generally speaking, the smaller the granularity of CBN, the better the impact resistance and wear resistance of PCBN. However, if the CBN particles are too small, the gap between the CBN particles will be reduced, thereby reducing the infiltration of binder elements. Therefore, mixed granularity should be selected when using. Third, the influence of CBN content. The higher the content of CBN, the higher the hardness and thermal conductivity of PCBN. However, if the content of CBN (ultra-hard world: chaoyingTD) is too high (generally higher than 95wt %), the performance of sintered body will become worse, CBN grains will fall off easily and wear resistance will be reduced. On the other hand, if the content of CBN is too low (generally less than 50wt %), the quality of sintered body will decline.
2. Binding agent
PCBN can be divided into pure PCBN and binding PCBN according to whether the system contains binding agent or not. Among them, pure PCBN has almost no non-cbn components, so its strength, hardness and thermal stability are much higher than ordinary PCBN. However, due to the high chemical inertia of CBN, good sintering between lattices is hindered. In other words, it is very difficult for CBN to bond directly with CBN grains. Therefore, the effect of binder on the synthesis of PCBN is particularly important.
In the process of CBN polymerization, a variety of binding materials are added to strengthen the connection between CBN grains, so as to improve the overall performance of PCBN. For example, high-melting metal components TiC, TiN, WC, especially ti-based compounds, have improved the wear resistance and damage resistance of PCBN. Some rare earth elements (such as oxides and nitride of Y and Dy, etc.), along with aluminum boride and titanium boride, infiltrate into CBN intergrain and ceramic binder, which can promote the compactness of polycrystals and improve the strength of PCBN.
When preparing PCBN, the selection of binder is very important. Due to the different application ranges of binder, the binder should meet the following conditions in general, no matter it is the preparation of cutting tool or grinding wheel:
First, the binder should have high thermal stability;
Secondly, the binder should have a strong chemical affinity with nitrogen or boron.
Third, at high temperature, the binder should not produce chemical affinity with the alloy elements in the workpiece.
Fourth, the binder should improve the strength or toughness of the sintered body.