Study On TiB₂-TaC Ceramic Tool Material And Its Oxidation Resistance

The aim of this study is to obtain the favorable comprehensive properties of TiB₂-TaC ceramic tool material.According to the designing principles of ceramic tool material,TiB₂ was chosen to be the based material,TaC be the second phase and Ni as the metallic additive.The wettability between Ni and TiB₂ and TaC was studied.And the physicochemical compatibility among these raw materials was also studied.In addition,the preparation technology,sintering process,and the test method of microstructure and mechanical properties were also introduced in detail.Firstly,we have prepaired the TiB₂-TaC ceramics with the vacuum hot-presing method,and studied and analyzed their microstructure and mechanical properties.The results showed that when the sintering temperature was 1600℃,Ni content was 8wt.%and TaC content was 5wt.%,TiB₂-TaC ceramic tool material obtained well microstructure and mechanical properties,the grains were fine and distributed uniform,and its Vickers hardness was23.5GPa,flexural strength was 911.4MPa and fracture toughness was7.2MPa·m^1/2.The toughening mechanisms of TiB₂-TaC ceramic tool material were mainly crack deflection.Then,to further improve the comprehensive mechanical properties of TiB₂-TaC ceramic tool material,this study optimized the sintering temperature,TaC content and Ni content by orthogonal experiments.The experimental data from orthogonal experiments were analyzed,and determined the optimal system was that of 1575℃sintering temperature,5wt.%TaC content and 8wt.%Ni content,which was not exists in the previous orthogonal experiments.So,the optimal system needs to be verified by experiment.We have studied the microstructure by SEM and mechanical properties of TiB₂-TaC ceramics prepared with the optimal system,and the results showed that the hardness was21.61GPa,flexural strength was 1140.13MPa and fracture toughness was7.8MPa·m^1/2 of TiB₂-TaC ceramic tool material prepared with the optimal system,which were accords with the theoretical result when the optimal combination scheme of orthogonal experiment is determined and its mechanical properties were improved indeed.The toughening mechanisms of TiB₂-TaC ceramic tool material prepared with the optimal system were mainly crack deflection.Finally,this study research the oxidation resistance of TiB₂-TaC ceramic tool materials prepared with the optimal system.The results showed that the mainly oxidation products were TiO₂ and B₂O₃;The surface morphologies of TiB₂-TaC ceramic tool material were mainly affected by oxidation temperature.The higher the temperature,the more obvious the grain growth and the more severe the oxidation;After oxidation for 10h at different temperature,with the oxidation temperature increased,oxidation became severe of TiB₂-TaC ceramic tool material,and the flexural strength decreased obviously.when the oxidation temperature was 1000℃,the material oxidation severe and fracture surface was appeared between the different oxide layers,which was mainly because the inner stress difference between different oxide layer exceeded the yield limit of the material.Meanwhile,the appeared fracture surface resulted the flexural strength decreased dramatically to 276.42MPa when the oxidation temperature was 1000℃.Therefore,when the cutting temperature was not exceed 1000℃,TiB₂-TaC ceramic tool material could continuous cutting for a long time;After oxidation at 1100℃for different time,with the oxidation time prolonged,the oxidation became severe.When the oxidation time was 7h,TiB₂-TaC ceramic tool material oxidation severe and appeared the fracture surface between different oxidation layers.At the same time,the appeared fracture surface resulted in the flexural strength decreased dramatically to 324.95MPa,which was not satisfied the conventional cutting behavior of ceramic tool material.Therefore,when the cutting temperature was about1100℃,the cutting time of TiB₂-TaC ceramic tool material should not exceed 4h.