Vacuum Diffusion Bonding Of SiC Particulate Reinforced LD2 Matrix Composite

SiCp/LD2 Metal Matrix Composite(MMC)has been applied in aerospace,traffic and transportation,sport and electronic industries,due to its high specific strength,high specific modulus,low thermal expansion coefficient,good wear resistance and isotropic properties,With further decreasing in its products cost,its application fields will expand. However,the problems in the main second fabrication process,e.g.welding,have been a main obstacle to its further application.So it is necessary to study joining technology of SiCp/LD2 MMC.In this paper,the diffusion bonding of SiCp/LD2 MMC was first investigated,and the problems in diffusion bonding of SiCp/LD2 MMC were discussed.Then the SiCp/LD2 MMC was joined by transient liquid phase bonding(TLP).The formation process of TLP bonded joint was investigated systemically before the experiment.The mathematic models of each stage of TLP process are established and the analytical solutions of them were also obtained.The calculated holding time of SiCp/LD2 MMC TLP with Cu foil as interlay was 77 minutes.The shear strength of diffusion bonding joints of SiCp/LD2 MMC was extremely low, which was only 26%of composite.With Cu,Ni,Al-Li alloy,Al-Cu-Mg alloy as interlayers,the shear strength of the joint of SiCp/LD2 MMC increased slightly.The joint bonded with Al-Li interlayer exhibited the highest strength among them,which is approximately 50%of composite.The main joint problems are:①the defects such as oxide film and reinforcement segregation exist in the welded joint,which block the well bond between matrix and reinforcement.②it is difficult to remove alumina film. Al-Li alloy foils breaks up the alumina barrier by chemical mechanism.However,the shear strength of the joint obtained by diffusion bonding was still low.The TLP bonding of SiCp/LD2 MMC was investigated by using interlayers in order to increase the strength.With 10μm-thick Cu foil used as interlayer,transient liquid phase formed at a temperature of 560℃,because of eutectic reaction between copper and aluminum, wetting the reinforcement particle,eliminating the reinforcement-reinforment contacts, and filling in micro-cavities existing in the joint area and accelerants velocity of atom's diffusion.The results show that SiCp/LD2 MMC was joined successfully by the following bond parameter at the bonding temperature of 560℃,bonding pressure of 1MPa,holding time of 75 min.The joint shearing strength is 206.5MPa,nearly 85%of composite.At the meantime,SiCp/LD2 MMC was also joined using 30μm thickness Ni foil as interlayer.The results show that the joint strength decreased sharply because of the intermetallic Al_0.9Ni_1.1formed in the joint.The SiC particulates were segregated in the interface of bond when SiCp/LD2 MMC was joined by TLP using Cu foil.The segregation of SiC particles may cause some weak connection like P-P bond,there may be another weak connection P-M bond in some particle segregation,this usually lead to the test specimens break apart.In order to reduce the segregation tendency of SiC particulates in the bond zone,the TLP of SiCp/LD2 MMC using multi-interlayer was investigated in this paper.With the Cu/Al/Cu compound interlay,the segregation of SiC particles in the bond interface was successfully avoided,and the formation mechanism of joint improved. With the same bond parameters as TLP with Cu foil used:T_b=560℃.bonding pressure 1 MPa,holding time 75min,the isothermal solidification and homogenization of the bond region were fully completed.Element Cu distributed uniform in the bond region.The shear strength was up to 228.8MPa,which was as high as 94.3%of the base composite. The Cu/Ni/Cu compound interlayer was also investigated,however,the joint strength increased slightly because of the formed intermetallic Al-Ni-Cu in the joint even the segregation of SiC particulates was avoided.