Study Of Influence Of Different Binders On Properties Of CBN Composites

Cubic boron nitride(cBN)is a kind of superhard material second only to diamond.It possesses excellent mechanical,electronic,optical and thermal properties and has important research and application value in many high-tech areas.Polycrystalline cubic boron nitride(PcBN)mainly composed of cBN grains is sintered under high pressure and high temperature(HPHT).It is widely used as a cutting tool material.During the sintering process,binder material is an important factor and will influence the properties of prepared PcBN to a great extent.Therefore,the research of binder materials of PcBN is worth studying.There are a lot of binder materials used in PcBN sintering,including metallic,ceramic and other binder materials.In this paper,the commonly used metal Al,ceramic TiC and the novel ternary compound Ti3SiC2 and Ti3AlC2 were used as binder materials to sinter PcBN composites.Compositions,bending strength,compressive strength,hardness,microstructures and thermal stabilities were studied.It was found that when A1 was used as binder material,it would react with cBN under high pressure and high temperature in the sintering process and formed AIN and AlB2.With the content of Al increasing from 5 wt.%to 10 wt.%and 20 wt.%,the bending strength and compressive strength of PcBN first decreased,then increased.AIN and AlB2 formed in the sintering process could bond the PcBN composites as a whole body to a certain extent,but also the place where crack took place.With respect to TiC.because of the great inertness and high melting point of TiC,there was no new phase formed in cBN-TiC mixtures after HPHT and the sintered composites still consist of cBN and TiC.When TiC addition was 10 wt.%,the PcBN composites could be sintered with the densest structure and good mechanical properties.When Ti3AIC2 and Ti3SiC2 were used to fabricate PcBN,during sintering,Ti3AIC2 and Ti3SiC2 will decompose and react with cBN.TiC,TiC0.7N0.3,TiB2,SiC and AIN were formed.With regard to PcBN sintered with Ti3AlC2 as binder,when Ti3AlC2 addition was 20 wt.%,the sintered PcBN was with the densest microstructure,highest bending strength,compressive strength and micro hardness.For PcBN sintered from cBN-Ti3SiC2,when Ti3SiC2 content was 10 wt.%,the prepared PcBN had the highest bending strength.When Ti3SiC2 content was 20 wt.%,the prepared PcBN had the highest compressive strength.When Ti3SiC2 content was 40 wt.%,the prepared PcBN had the highest hardness the denest structure.In the prepared PcBN with different kinds of additives,we select one specimen to test their thermal behaviors and analyze their surfaces' compositions.It was found that after oxidation,titanium and aluminum oxides formed on the surface with cracks.The formed oxide layers were not dense enough,but could protect the interior materials from further oxidation to a certain extent.