Influence Of Pre-Solid Solution Powders On The Microstructure And Properties Of Ti(C,N)-Based Cermets

Ti（C,N）-based cermet tools still have the advantages of high hardness,corrosion resistance and adhesion resistance in high-speed cutting,and are ideal candidates for making high-precision cutting tools.However,due to its insufficient strength and toughness,the wide application of Ti（C,N）-based cermet materials is restricted.Quantitative regulation of the typical"core-rim"structure of Ti（C,N）-based cermets is one of the most effective means to achieve its toughness,and thus has attracted much attention.In this thesis,pre-solid solution powders of secondary carbides and carbonitrides with different thermodynamic stabilities were designed and prepared based on thermodynamic calculation simulation.Influence rules of structure and mechanical properties.（Ti,W,Ta）C and（Ti,W,Ta,Mo）C pre-solid solution powders synthesized by carbothermic reduction technique to replace part of carbides,namely Ta C,Mo₂C and（Ti,W）C.On this basis,two Ti（C,N）-based cermets were prepared.The phase evolution of these two Ti（C,N）-based cermets was analyzed when the temperature was increased from1250°C to 1400°C.With the help of thermal stability analysis of pre-solution powders,the effects of pre-solution treatment on the cermet core-rim structure and mechanical properties were investigated.Compared with the traditional preparation process,the size of the"white core-grey ring"in the cermets with（Ti,W,Ta）C and（Ti,W,Ta,Mo）C pre-solid solution powders increased significantly,and the With the increase in the number of elements in the pre-solid solution powder,the ring thickness increases significantly.The thermal stability of solid solution carbides increases gradually compared with Ti（C,N）,and thicker rim structures are formed with increasing element content in the solid solution powders.The comprehensive mechanical properties were better when（Ti,W,Ta）C pre-solid solution was added,which indicated that proper pre-solution treatment of secondary carbides under the same composition conditions could further strengthen Ti（C,N）-based cermets.The prepared pre-solid solution powders（Ti,61.3W,8.6Ta）（C,N）,（Ti,53.3W,7.5Ta）（C,N）and（Ti,47.1W,6.6Ta）（C,N）prepared three cermets with the same nominal composition.The effects of the composition of（Ti,W,Ta）（C,N）pre-solid solution on the structure and mechanical properties of cermet multi-core rims were investigated.The results show that the reduction of W and Ta content in the pre-solid solution leads to an increase in white cores with thinner rims and a decrease in black cores with thicker rims.Thermodynamic calculations show that the reduction of W and Ta content enhances the thermal stability of the pre-solid solution.As the thermal stability difference between black-core Ti（C,N）and white-core（Ti,W,Ta）（C,N）decreases,more acyclic black particles remain.Statistical analysis of rim thickness and grain size shows that the cermet containing solid solution（Ti,53.3W,7.5Ta）（C,N）has the smallest grains and the thinnest rim.The best comprehensive mechanical properties were obtained when the three cermets were added（Ti,53.3W,7.5Ta）（C,N）.This means that proper pre-solution of W and Ta in（Ti,W,Ta）（C,N）can ensure a good multi-core rim structure.