Research On Properties And Influencing Factors Of Diamond/aluminum Composites

In this paper,high volume fraction diamond/aluminum composites were successfully prepared by pressureless infiltration process using diamond particles with different diameters.The thermal conductivity,bending strength and elastic modulus of the composites were tested.The effects of particle quality,particle size and volume fraction on the properties of diamond/Al composites were studied by means of scanning electron microscopy(SEM)and X-ray diffraction(XRD),in order to improve the suitability of diamond/Al composites.SEM results show the uniform distribution of the diamond particles and the compact microstructure of the diamond/Al composite.During the pressureless infiltration process,most of the interfaces between the diamond and aluminum alloy matrix are clean and the molten alloy can infiltrate well into the gap between the diamond particles.However,the intrinsic defects such as pores and cracks on the surface of the diamond particles can hinder the infiltration of the molten aluminum alloy to a certain extent,resulting in a small amount of porosity in the interface region of the composite.The fracture mechanism of the composite is mainly of the fracture of aluminum matrix,as well as a low fraction of interfacial debonding behavior and a small amount of cleavage fracture of diamond particles.The interface reaction product Al4C3 is failed to be detected in the composite by XRD analysis.The thermal conductivity of the diamond/aluminum composites is affected by the size and volume fraction of diamond particle.Small diamond particle can reduce the bulk density and volume fraction of the composite.The infiltrating process of the molten aluminum alloy can be influenced negatively due to the narrowed gap between the small particles in the preforms.When the average diameter of the diamond particle is about 120?m,the particle volume fraction of the composite is the lowest,being about 53%,and the thermal conductivity of the corresponding composite is only 370 W/(m·K).The volume fractions are about 60%for both of the composites prepared by using diamond particles with average diameters being about 158.136?m and 234.984?m.Correspondingly,the thermal conductivity of the composite remains the same,being about 435 W/(m·K).The influences of the particle size and volume fraction are analyzed based on the experimental results and the H-J theoretical model,indicating that the effect of particle volume fraction on the thermal conductivity of composites is more significant than that of the particle size according to the results derived from the present experiments.The elastic modulus of the diamond/aluminum composites increase with the increasing particle volume fraction,which is directly affected by the size of diamond particle.As the particle volume fraction is increased frorm 53%to 63%,the elastic modulus of the composites increases from 342.83 GPa to 416.13 GPa,with an increment of 21%.The bending strength of the composite decreases slightly as the particle size is increased.This is due to the increasing probability of direct contact between large particles with increasing diameter of diamond particles,resulting in difficulty in local impregnation,which reduces the overall strength of the composite.In this paper,magnetron sputtering was used to deposit W coating on the surface of diamond particles to improve the interface bonding performance between aluminum matrix and diamond particles.However,the results show that the interfacial bonding strength is weak,with the thermal conductivity decreasing from 432.32 W/(m·K)to 305.87 W/(m K).Corresponding,the bending strength and elastic modulus are reduced from 325.58 MPa to 275.68 MPa and 359.83 GPa to 214.85 GPa,respectively.