Study On The Mechanical Properties Of CBN-based Composites Sintered At High Pressure And High Temperature

Cubic boron nitride?cBN?has high hardness,high wear resistance,high thermal stability and chemical inertness.It is widely used in the field of mechanical processing.However,because of certain synthesis limitations,it was still not easy to synthesize pure cBN bulk.Often,cBN-based composites were fabricated using binders at high pressure and high temperature.In this work,effects of binder systems,binder contents and temperature on phase compositions,microstructure and mechanical properties of cBN-based composites were investigated.The results are as follows:When sintered with AlN-Al-Ni binders,the main phases of cBN-based composites were cBN,AlN,AlB₂ and AlNi;The best sintering temperature was1500°C,and the relative density was up to 99.6%sintered at this condition;The best binder content was 17wt.%.Excellent flexural strength and fracture toughness of cBN-based composites,sintered with 17wt.%binder,were 661MPa and 7.19MPa·m^1/2,respectively.The optimum value of hardness and abrasive ratio of composites at binder content of 13wt.%were 47.92GPa and 2.99,respectively.Raw cBN materials were replaced with some diamond powder in the case that binder content was 17wt.%.Flexural strength and hardness of cBN-based composites with addition of 7.5wt.%diamond,were 771MPa and 48.26GPa,respectively.Raw metallic binders were replaced with glass in the case that content was 17wt.%.Crystalline SiO₂ was precipitated at high temperature;Excellent flexural strength,abrasive ratio and hardness of cBN-based composites were 671MPa,1.97 and 42.31GPa,respectively.The method could reduce the cost of binder and the performances could meet the requirements of practical applications.When sintered with TiC-Al-Ti binders,the major phases of cBN-based composites were cBN,AlN,AlB₂ and Al₃Ti.The product Al₃Ti would reduce the mechanical properties of the composites.The optimum sintering temperature was1500°C,and the relative density reached 99.4%sintered in this case;The most suitable binder content was 16wt.%.Flexural strength and fracture toughness of cBN-based composites were 627MPa and 6.60MPa·m^1/2,respectively.The maximum value of hardness and abrasive ratio of composites at binder content of 14wt.%were45.64GPa and 3.2,respectively.Carbon fiber/CNTs were added based on original binder content of 16wt.%.The phase composition of cBN-based composites did not change significantly,and the carbon fiber/CNTs existed in the form of reinforcement;Excellent flexural strength,abrasive ratio and fracture toughness of cBN-based composites with addition of 1.0wt.%CNTs,were 610MPa,1.38 and 7.12MPa·m^1/2,respectively.The toughness value increased by 7.88%.The mechanical properties of the carbon fiber sintered cBN-based composites were not significantly improved,but still meet the practical requirements.