The Study Of Preparation And Microstructure Characteristics Of TiN Reinforced Copper Matrix Composites Based On Ti-Si₃N₄ Reaction

With the continuous improvement of the process of industrial modernization,the traditional materials with single performance can not meet people’s needs.In recent years,the preparation of Cu alloys with high strength and wear resistance by transition metal nitrides and silicides has attracted people’s wide attention.Among them,TiN and Ti₅Si₃have become important reinforcement phases of Cu matrix composites due to their excellent mechanical properties.In Cu matrix,TiN is mostly granular,while Ti₅Si₃ often grows into a rod shape with a certain aspect ratio.When both of them are used as reinforcements,they can play a good synergistic effect and fully show the properties of composites.However,there are few pieces of research on TiN-Ti₅Si₃ hybrid reinforced Cu matrix composites,and there are many basic problems in the preparation process.In order to introduce TiN into Cu melts effectively,this paper prepared TiN-Ti₅Si₃ hybrid reinforced Cu matrix composites based on Cu-Ti-Si-N system through the in-situ reaction of Ti-Si₃N₄in Cu melts.The law of microstructure evolution of composites under different conditions was explored and the preparation process was optimized.To a certain extent,the structure of composite can be controlled,and a new idea for the application and development of Cu alloy was provided.In order to explore the influence of the size of Si₃N₄ on composite materials,the Si₃N₄with different sizes was selected as N source and reacted with Ti to introduce into Cu melt.When Si₃N₄ is small in size,such as 2μm,it can easily react completely with Ti to form TiN and Ti₅Si₃.Among them,the formed TiN are particle-like and their size ranges from0.5μm to 3μm,while eutectic and primary Ti₅Si₃ are rod-like with a certain length to diameter ratio.In addition,many Ti₅Si₃ rods are combined with Cu cores to form core-shell structure.When is large in size,such as 20μm and 50μm,the Si3N4 is difficult to completely react.As a result,besides TiN and Ti₅Si₃,several kinds of core-shell particles,including Si₃N₄@TiN,Cu@TiN,and Si₃N₄@TiN@Cu@TiN,will be formed.In order to investigate the phase evolution of Ti-Si₃N₄ in Cu melt,the compact which consists of 2μm Si₃N₄ and Ti was added into Cu melt,and the microstructures of the compacts under different holding times were analyzed.It is indicated that after adding Ti-Si₃N₄ compacts into Cu melts,Ti will react with Si₃N₄ immediately to form TiN and Ti-Si phases.However,different proportions of Ti and Si₃N₄ have different reaction paths in Cu melt.It is found that when the mass ratio of Ti:Si₃N₄ is higher,such as 3.09:1,TiN and Ti₅Si₃ are formed.The formed TiN are spherical and will cooperate with Ti₅Si₃ and depend on each other to nucleate and grow to form TiN/Ti₅Si₃ composites,and will uniformly disperse in Cu melts after being wetted by Ti₅Si₃.As the conditions of the mass ratio of Ti:Si₃N₄ is lower,such as 1.37:1,Ti and Si₃N₄ will firstly react to form TiN and Ti-Si liquid.The formed TiN are irregularly polygonal and connect with each other.The Ti-Si liquid phase will combine with Cu melt to form Cu-Ti-Si liquid phase,and finally,δCu₄Si,ηCu₃Si,andτ₁-Cu Si Ti phases will be crystallized during cooling.In this case,TiN are difficult to be wetted,and the Ti-Si₃N₄ compact will keep its original shape and not spread in Cu melts.By controlling the reaction materials,it is analyzed that when the mass ratio of Ti:Si₃N₄ is between 1.37:1 to 3.09:1,the formed Ti₅Si₃ will increase with the increase of the relative content of Ti.Thus,the dispersion of the compacts and the uniformity of TiN will be promoted.In addition,because 2μm Si₃N₄ is easy to aggregate with each other,the TiN will grow and connect with each other to form aggregates.And ball milling Si₃N₄ alone can increase the aggregation of formed TiN.While ball milling Ti-Si₃N₄ mixed powder for6h in a vacuum environment at a speed of 300rpm can significantly improve the microstructure uniformity of the prepared Cu-based composites.When the optimum milling time is exceeded,the uniformity of the composites will decrease.