| High-speed cutting tools are one of the critical tools to improve production efficiency and processing quality,reduce energy consumption and processing costs as well as promote the upgrading of machinery manufacturing.As a cutting tool material,Ti(C,N)-based cermets has a well red hardness,thermal stability,and wear resistance.At the same time,it has excellent adhesion resistance and low friction coefficient to steel.The various indexable inserts made are suitable for high-speed finishing and semi-finishing of carbon steel,alloy steel,and other materials.However,it is challenging to consider both the strength-toughness and the high hardness of Ti(C,N)-based cermets at the same time,and the machining requirements are often met at the expense of strength-toughness.Given the above problems,this paper proposes the new idea of using hot-pressing sintering technology to prepare whiskers and high-entropy alloys to synergistic reinforced and toughen Ti(C,N)-based cermets.The preparation of ZrO2 whiskers and HEA,as well as the microstructure,mechanical properties,and high-temperature performance of Ti(C,N)-based cermets were investigated.The research results in this work may provide actual theory and application basis for the development of Ti(C,N)-based cermets tools with good strength-toughness as well as hardness.The Ti(C,N)-WC-Mo2C-TaC-Ni/Co cermets materials were prepared through optimizing the sintering process and binder content.Among them,when the content of Ti(C,N)was 70 wt.%and Ni/Co was 10 wt.%,the density,hardness,flexural strength,and fracture toughness of cermets reached 99.1%,19.39 GPa,1488 MPa,and 7.84 MPa·m1/2,respectively.When the content of Ti(C,N)was 55 wt.%and Ni/Co was 25 wt.%,the density,hardness,flexural strength,and fracture toughness of cermets separately reached 99.39%,12.71 GPa,and 1674 MPa,and 8.99 MPa·m1/2.The monoclinic rod-shaped ZrO2 whisker was developed by perfecting the flux types,powder molar ratio,and sintering process.The whiskers have a length of about 600～1000 nm and a diameter of 50～100 nm,which exhibited a smooth surface and high crystallinity and integrity.The growth mechanism of the ZrO2 whiskers prepared by the flux method was revealed,including three processes of dissolution-nucleation-growth:The flux first formed a supersaturated solution,and then the ZrO2 particles were dissolved to form ZrO2 nuclei.Recrystallization occurs at the liquid-solid interface,and the cores extend along the[011]direction to form ZrO2 whiskers,finally.To improve the toughness,ZrO2 whisker modified Ti(C,N)based cermet was developed.When the whisker content was 7.5 wt.%,its relative density,bending strength,hardness,and fracture toughness reached 98.1%,1623 MPa,18.57 GPa,and 9.54 MPa·m1/2,respectively.It was revealed that the strengthening and toughening mechanism of ZrO2 whiskers at room temperature were bridging and pulling of whiskers,crack deflection,bridging and branching,and phase transformation and toughening.The weakening mechanism of high-temperature strength and toughness was attributed to the softening of grain boundaries,the decrease in elastic modulus,the oxidation of materials,the grain boundary slip,and the formation of voids of Ti(C,N)-based cermets with Ni/Co as bonding phase.The enhancement mechanism of high-temperature strength and toughness was attributed to bridging,deflection and pulling out of whisker,the grain boundary phase,and improved oxidation resistance.The high-temperature wear mechanism was adhesive wear.To enhance the high-temperature hardness,Ti(C,N)-based cermets with whiskers and HEA synergistically strengthening and toughening were developed.When the temperature was 1000℃,the hardness,flexural strength,fracture toughness,and elastic modulus reached 10.78 GPa,913 MPa,6.57 MPa·m1/2,and 196.7 GPa,respectively.The high-temperature overall performance was the best.The weakening mechanism was attributed to the grain boundary softening,elastic modulus decreases,material oxidation,and grain boundary slip of Ti(C,N)-based cermets with HEA as the bonding phase.The enhancement mechanism was attributed to the high grain boundary strength of cermets,the high-temperature oxidation resistance and obstruction of the dislocation slip of HEA,and the high-temperature enhancement of whiskers.It revealed that the high-temperature wear mechanism was bond wear. |
