Study On Preparation And Properties Of TiC_0.7N_0.3-based Cermets Tool Materials Containing TaC And (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C

Ti(C,N)-based cermets have high red-hardness,oxidation resistance,wear resistance and chemical stability,and are used extensively as cutting tools in the field of machining.Ti(C,N)-based cermets mainly include Ti(C,N)matrix,metal bonding phase and reinforcing phase,where the reinforcing phase can form solid solution with Ti(C,N)matrix to improve the hardness,toughness and wear resistance of cermets.Ta C and(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C reinforced phases have excellent mechanical properties,and are expected to further improve the comprehensive properties of cermets as reinforcement phase.Therefore,in this thesis,Ta C and(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C were introduced to prepare Ti C_0.7N_0.3-based cermets by vacuum sintering technology,and the effects of Ta C and(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents on the phase,densification,microstructure,mechanical properties and thermal conductivity were systematically investigated.Then,the cermets with excellent comprehensive performance were preferably machined into round blocks and standard turning inserts,and their wear resistance and cutting performance of machining QT500-7 ductile iron were studied,and the cutting parameters were optimized with the goal of maximum material removal.The details and conclusions are as follows:Firstly,Ti(C_0.7N_0.3)-WC-Mo₂C-VC-Ta C-Al N-Ni/Co cermets with different Ta C contents(0 wt%,5 wt%,10 wt%,15 wt%)was prepared by vacuum sintering at 1500?,1600?and 1700?with Ta C as reinforced phase.The effects of Ta C contents and sintering temperature on phase,densification,microstructure,mechanical properties and thermal conductivity of cermets were studied.The results show that at the same temperature,Ta C content increased from 0 to 15 wt%,relative density of cermets decreases gradually,volume fraction of the rim phase increases gradually,Vickers hardness and fracture toughness increase first and then decrease,and thermal conductivity decreases gradually.With the same Ta C contents,as the sintering temperature increases in the range of 1500?1700?,relative density of cermets increases greatly at first and then decreases slightly,the thickness of the rim phase increases gradually,Vickers hardness increases first and then basically remains unchanged,fracture toughness increases first and then decreases,and thermal conductivity stays basically unchanged at first and then decreases significantly.Ti C_0.7N_0.3-based cermets containing 10 wt%Ta C sintered at 1600?have excellent comprehensive mechanical properties.Vickers hardness is 17.79±0.15 GPa,fracture toughness is 10.20±0.39 MPa·m^1/2,and the highest thermal conductivity of cermets without Ta C is 16.00 W·m^-1·K^-1.Then,using self-synthesized(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C high entropy carbide as reinforcement phase,different(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents(0 wt%,5 wt%,10 wt%,15 wt%)were prepared by vacuum sintering at 1500?,1600?and 1700?Ti(C_0.7N_0.3)-WC-Mo₂C-VC-(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C-Al N-Ni/Co cermets,The effects of(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents and sintering temperature on the phase,densification,microstructure,mechanical properties and thermal conductivity of cermet were studied.The results show that(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents increased in the range of 0?15 wt%at the same sintering temperature,relative density of cermets does not change significantly,the Vickers hardness increases gradually,and fracture toughness of cermets sintered at 1500?and 1600?increases first and then decreases,and the fracture toughness of cermets sintered at 1700?gradually decreases,the thermal conductivity of cermets sintered at1500?gradually decreases,and the thermal conductivity of cermets sintered at 1600?and 1700?firstly increases and then decreases.At the same(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents,as the sintering temperature increases in the range of 1500?1700?,relative density increases first and then remains unchanged,the volume fraction of rim phase increases continuously,the Vickers hardness increases first and then remains unchanged,and the fracture toughness increases first and then decreases.Ti C_0.7N_0.3-based cermets containing10 wt%(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C prepared at 1600?have excellent comprehensive mechanical properties.Vickers hardness is 18.42±0.33 GPa,fracture toughness is12.56±0.23 MPa·m^1/2,the highest thermal conductivity of cermets with(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents of 5 wt%is 16.25 W·m^-1·K^-1.Finally,Using cermets(sintering at 1600?)with better comprehensive properties,the friction and wear properties and dry turning QT500-7 ductile iron performance test to study the effects of Ta C and(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C on wear resistance and cutting performance of Ti C_0.7N_0.3-based cermets.The results show that among the cermets containing Ta C series,the cermets with Ta C contents of 5 wt%have the best wear resistance and cutting performance,and its tool life was 590 s.Among the cermets containing(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C,the cermets containing(Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C contents of 15wt%have the best wear resistance,and the cermets containing 5 wt%have the best cutting performance,with a tool life of 720 s.The tool wear forms are rear tool surface wear and crescent crater wear,and the main wear mechanisms are bond wear,oxidation wear,diffusion wear and abrasive wear.