Research On Preparation By Microwave Sintering And Properties Of Vitrified Bond CBN Grinding Tools

Vitrified bond cBN grinding tool has been widely used in aerospace,automotive parts and other fields because of its high temperature resistance,good self-sharpening,good thermal conductivity and other excellent performance.However,there are a lot of problems to be solved in the process of application.These problems are mainly caused by the temperature gradient and the brittleness of vitrified bond.In this paper,the methods of preparation and performance improvement of vitrified bond cBN grinding tools were mainly discussed from three aspects of sintering methods,nanometer additives?nanometer vanadium carbide,nanometer chromium carbide and their nanocomposites?and auxiliary abrasive?green silicon carbide?.Universal material testing machine,thermal expansion instrument,scanning electron microscope and X-ray diffraction instrument were used as the detection means.The Na₂O-CaO-B2O3-Al₂O₃-SiO₂ system was taken as the basic vitrified bond system.Firstly,the effect of microwave sintering method on the properties of vitrified bond and cBN abrasives of was systematic discussed.And the process parameters of microwave sintering of vitrified bond cBN abrasives were investigated.Then the effect of three kinds of nanometer transition metal carbide and their content on the properties of vitrified bond cBN abrasives was analyzed.Finally,the effect of green silicon carbide as auxiliary abrasive on the preparation of microwave sintering system was detected.The results showed that:?1?Vitrified bond can be fired at lower temperature?800?,200 ? lower than the traditional sintering temperature?by microwave sintering,and then the flexural strength of vitrified bond was 116.12 MPa,which was improved by 12.9% than that of traditional sintering method?102.89MPa?.Besides,the optimum sintering temperature of grinding tools by microwave was 850??150? lower than that of traditional sintering method?,and then the bending strength of the samples?69.53MPa?was increased by 21.5% than that of traditional sintering method?57.21MPa?.?2?In the condition of microwave sintering,when the adding content of nanometer vanadium carbide was 1.0wt.%,the comprehensive thermodynamic properties were the best.Then the average linear coefficient of expansion of vitrified bond was decreased from 6.63×10^-6?^-1 to 5.83×10^-6?^-1?decreased by 12.1%?,and the fluidity was increased from 108.8% to 144.0%?increased by 35.2%?.The porosity of grinding tools was increased from 25.53% to 26.80%?increased by 1.27%?,and the flexural strength improved from 69.53 MPa to 79.75MPa?improved by 14.7%?;?3?In the condition of microwave sintering,when being added 1.5wt.% nanometer chromium carbide powder,the comprehensive thermodynamic properties reached the optimization.The average linear coefficient of expansion of vitrified bond was decreased from 6.63×10^-6?^-1 to 5.83×10^-6?^-1?decreased by 16.0%?,and the fluidity increased from 108.8% to 165.2%?increased by 56.4%?.The porosity of grinding tools was increased from 25.53% to 28.21%?increased by 2.68%?,and the flexural strength was improved from 69.53 MPa to 96.27MPa?improved by 38.5%?;?4?In the condition of microwave sintering,when being added 4.0wt.% V8C7-Cr3C2 nanocomposites,the comprehensive performance of grinding tools was much better.The average linear coefficient of expansion of vitrified bond was decreased from 6.63×10^-6?^-1 to 4.56×10^-6?^-1?decreased by 31.2%?,and the fluidity was increased from 108.8% to 158.8%?increased by 50.0%?.The flexural strength of grinding tools changed a little?improved by 4.6%?.In addition,the grinding performance for die steel was improved,and the grinding ratio was increased by 26.0%,and the average friction coefficient was decreased by 38.4%.?5?Using green silicon carbide as white corundum to be auxiliary abrasive,the optimum sintering temperature of the grinding tools was decreased by 50?,and the flexural strength of samples was improved from 69.53 MPa to 80.30MPa?improved by 15.5%?.And the Rockwell Hardness was increased from 75.5HRB to 95HRB?increased by 25.8%?.But its grinding performance was reduced.