Research On High Performance Ti(C,N)-based Cermets Material Used As Cutting Tools

In this thesis,the relationship among raw powders properties,chemical composition,microstructure,mechanical properties and high-temperature performance of Ti?C,N?-based cermets have been systematically investigated by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and energy dispersive X-ray analysis?EDX?.The essence was obtained.Ti?C,N?-based cermets with good room temperature mechanical properties and high temperature mechanical properties have been prepared,which was used to cutting tools.That laid the foundation for the application of the cermets materials in the field of cutting.Firstly,the effects of N/C ratio and particle size of Ti(C_1-x,N_x)solid solution on microstructure and room-temperature mechanical properties of the cermets with low Ni content were studied.The results showed that with the increase of N/C ratio,the dissolution and reprecipitation process was inhibited,the ceramic particles of the cermets became finer gradually.However,when the N/C ratio exceeded 5:5,the porosity increased and the bright white grains appeared.Meanwhile,with the decrease of size of the solid solution powders,the grain size of the ceramic particles decreased.When the size of the Ti(C_0.5,N_0.5)powders was 1.71?m,the cermets showed the better mechanical properties with the transverse rupture strength of 2387 MPa,hardness of 92.1 HRA,and K_Ic of 8.88MPa·m^1/2.The effects of chemical component,such as binder phase Ni,additives NbC and TaC on the microstructure and room-temperature mechanical properties of the cermets were investigated.The main conclusions were as follows:with the decrease of Ni content,the ceramic particle became finer and the volume fraction of hard phase increased gradually,which were owned to the agglomeration of the ceramic particles,which made the TRS of the cermets increase first and then decrease,the hardness gradually increase,and the fracture toughness gradually decrease.Adding NbC and TaC made the rim phase preferentially precipitate on the surface of the white core rather than the black core.When the contents of NbC and TaC were 3 wt.%and 4 wt.%respectively,the cermets showed the transverse rupture strength of 2440 MPa,hardness of 92.2 HRA and K_Ic of 8.71 MPa·m^1/2,which were all attributed to the fine and uniform grains as well as the moderate thickness of rim phases.The thermal shock resistance of Ti?C,N?-based cermets with different NbC and TaC contents was studied.It was found that increase of NbC and TaC contents improved the thermal expansion coefficient,Young's modulus and transverse rupture strength of the cermets.However,when NbC and TaC were added excessively,the TRS of the cermets reduced rapidly.Therefore,with the increase of contents of NbC and TaC,the thermal shock resistance of Ti?C,N?-based cermets increased first and then decreased.When the contents of NbC and TaC were 3 wt.%and 4 wt.%respectively,the thermal shock resistance of the cermets was the best.When the thermal shock temperature difference was constant,the retained TRS of the cermets decreased with the number of thermal shock cycles increase.The number of thermal shock cycles was less than 5 times,the retained TRS of the cermets was slightly reduced.When the number of thermal shock cycles exceeded 10 times,the retained TRS of the cermets was decreased rapidly,due to the decrease of the plastic deformation of the edge of the pit and appearance of the microcracks in the fracture microstructures.Finally,the effects of the additions of NbC and TaC and test temperature on the high-temperature transverse rupture strength of Ti?C,N?-based cermets were studied.The results showed that when the additions of NbC and TaC was suitable,the oxidation resistance of the cermets,the interface bonding strength at high temperatures and the high temperature strength of the binder phase were improved.When the contents of NbC and TaC were 3 wt.%and 4 wt.%respectively,the TRS of the cermets was1515 MPa at 800°C.However,when NbC and TaC were added excessively,the high-temperature transverse rupture strength decreased,resulting in the increase of the porosity,and the decreases of the oxidation resistance of the cermets and the interface bonding strength.With the increase of test temperature,the oxidation corrosion of the cermets was aggravated,the crack propagation path shortened in the fracture microstructures and the bonding strength between hard phase and binder phase decreased,which made the high-temperature TRS of the cermets decrease.