Morphology Modification Of In-situ TiC_x Particles And The Effects On Microstructure And Mechanical Properties Of Cu Matrix Composites

The copper alloys are widely used in automotive,electronics,electrical,machinery manufacturing and other fields due to their good conductive and thermal conductivity,corrosion resistant and formability.With the rapid development of the automobile,electronics and machinery manufacturing industries,higher requirements are put forward.The good electrical conductive and thermal conductivity combined with high strength and wear resistance,especially good high-temperature mechanical properties and high-temperature corrosion resistance,were required.The mechanical and physical properties of the copper alloys can be improved by incorporating some alloying elements.For example,Cu-Zr,Cu-Cr,Cu-Cr-Zr and Cu-Co-Be alloys have been used as electrode materials for resistance welding for its good conductive and thermal conductivity.However,the copper alloys also show some disadvantages under friction and wear and high temperature working conditions.Therefore,a new kind of Cu material with good conductive and thermal conductivity as well as high strength and good wear resistance under high temperature was in urgent need.Particles reinforced copper matrix composites（PRMMCs）are new kinds of materials in which the Cu alloy is chosen as the matrix and the particles are chosen as the reinforcement particles.PRMMCs possess the excellent performance of the Cu matrix composites and the high temperature stability,low thermal expansion coefficient,high elastic modulus,etc.of ceramic.Titanium carbide（TiC_x）,a typical transition metal carbide,is the most widely-used phase of the particle-reinforced metal matrix composites owing to its high melting point,high Young’s modulus,low density and excellent conductive and thermal performances.However,the morphologies and sizes control of in situ TiC_x in particles reinforced Cu matrix composites are rarely reported.The TiC_x/Cu composites were fabricated by combustion synthesis combined with vacuum hot pressing in Cu-Ti-C sustem.It revealed the control mechanism of the morphologies and sizes and the action mechanism of reinforced phase with various morphologies,sizes and volume fractions on compression performance,electrical conductivity and wear properities at room and high temperature for the TiC_x/Cu composites.In this paper,the main innovation points are as follows:1.The effect law and action mechanism of in situ TiC_x with various types of source,reactants content,C/Ti molar ratio and ball milling process on particle sizes wererevealed:a)It revealed that the in situ TiC_x particles become smaller with the decreasing in the size of C-source.With the decreasing in the size of C-source,the reactivity improved and surface area become larger,the contact area between CNTs and Cu-Ti binary liquid phase is larger,leading to the quickening in speed of C atoms dissolve into the liquid during the reaction process.The nucleation core amounts of TiC_x particles increased,resulting in the decreasing of TiC_x size.b)The in situ TiC_x sizes decreased with the increasing of reaction content when it is less than 20 vol.%.The in situ TiC_x sizes increased with increasing of reaction content when it is more than 20 vol.%.c)It revealed that the in situ TiC_x become smaller with the increasing of C/Ti molar ratio in Cu-Ti-C system.With the increasing of C/Ti molar ratio,the content of C source increased,which was beneficial for C-source to dissolve C atom into Cu-Ti-C ternary liquid phase to form the nucleation core,the increasing of nucleation core amounts leading to the decreasing of in situ TiC_x size.d)The premilling process of Cu and milled CNTs powders is conducive to increase the contact area between CNTs and Cu-Ti binary liquid phase.The amounts of dissolved C atoms increased in the unit time leading to the increase of nucleation core amounts.The in situ TiC_x size becomes smaller.2.The effect law and action mechanism of in situ TiC_x with various C/Ti molar ratio and reactants content on particle morphologies were revealed:a)When C/Ti molar ratio is low,the system can not provide enough C atoms during the reaction process.The TiC_x particles tend to grow into the two-dimensional nuclei on the{100}surface,so the{100}plane gradually shrinks and stabilizes,finally forming octahedrons surrounded by{111}surfaces.C atoms amount increased with the increasing of C/Ti molar ratio,the growth rate of{111}surfaces is close to{100}surfaces’,forming sphere and close-to-sphere particles.With the continuous increasing of C/Ti molar ratio,The Ti C_x particles tend to grow into the two-dimensional nuclei on the{111}surface,so the{111}plane gradually shrinks and stabilizes,finally forming cubes surrounded by{100}surfaces.b)With the decreasing of reactants content and the increasing of Cu content,The amounts of dissolved C atoms increased in the unit time,the growth rate in{100}surface of TiC_x particles become slow and the growth rate of{111}surface become fast.The morphology of in situ TiC_x changed in the order of octahedron?close-to-sphere,sphere?cube with the increasing of C/Ti molar ratio in Cu-Ti-C system.3.The effect law and action mechanism of in situ TiC_x with various morphologies and sizes on the compression performance and electrical conductivity of TiC_x/Cu composites were revealed:a)It revealed the effect law and action mechanism of in situ TiC_x with various morphologies and sizes on the compression performance of TiC_x/Cu composites.When the particle sizes are the same,the pinning effect of cubic-shaped TiC_x is stronger than that of spherical ones,leading to the higher ultimate compression strength(s_UCS)and yield strength(σ_0.2);When the particle morphologies are sphere,The performance reduction of the TiC_x/Cu composite with decreasing particle size was attributed to the agglomeration of TiC_x particles,which played a role as the source of crack,contributing to the reduction of performance.TiC_x can play a role in pinning the movement of the dislocation and grain boundary;the pinning effect was enhangced with the increasing of TiC_x content,leading to the increasing of ultimate compression strength(s_UCS)and yield strength(σ_0.2).b)It revealed the effect law and action mechanism of in situ TiC_x with various morphologies and sizes on the electrical conductivity of TiC_x/Cu composites.When the particle sizes are the same,the solution of more Ti atoms in Cu matrix for spherical-TiC_x/Cu composite resulted in the enhancement of electron scattering and the decrease in electrical conductivity,compared with the cubic one.When the particle morphologies are sphere,the increase in the interface between particles and matrix enhanced the scattering of the electron and reduced the electrical conductivity of the composite,leading to the decrease of the electrical conductivity.4.The effect law and action mechanism of in situ TiC_x with various morphologies and sizes on the wear behavior at room and high temperature of TiC_x/Cu composites were revealed:a)The effect law of in situ TiC_x with various morphologies and sizes on the wear behavior at room and high temperature of TiC_x/Cu composites were revealed.When the particle sizes are nearly the same,the enhancing effect of spherical particles is better than that of cibic ones.The wear resistance of TiC_x/Cu composites increased with the increasing of TiC_x content.The volume wear rate of the TiC_x/Cu composites increased with the increasing of temperature and load.b)TiC_x can play a role in pinning the movement of the dislocation and grain boundary; the resistance of room temperature plastic deformation and high temperature softening behavior of the composites were enhanced.TiC_x can transmit load and enchanced the strength of the composites.The increasing strength and hardness improved the wear resistance.The increasing hardness leading to the decreasing of depth penetrated into the matrix and improved the wear resistance.At the meanwhile,a layer of mechanical mixing layer was formed during the wear process,containing CuO,Fe₂O₃ and nano-sized TiC_x,which enchanced the wear resistance of the composites.