Diffusion Bonding Between Steel/titanium With Copper Interlayer

Diffusion bonded trimetallic tube was carried out by a drawn and internal pressure diffused method, with pure titanium and carbon steel as base metals and pure copper as a interlayer. The microstructures near the interfaces were observed using optical and scanning electron microscopes (SEM) and the elemental distribution was determined across the interfaces by energy dispersive spectroscopy. Shear strength and microhardness were obtained using shearing and hardness tests.The results show that: the organizations and fracture morphology of the sample interface were observed by SEM. After diffusion annealing, the interface combined closely, no significant gap. Between copper and titanium on the complex interface occurred the atomic inter-diffusion, with the result that the matrix organization and hardness changed, and the compound layer of TiCu was formed on the copper/titanium interface. With the diffusion temperature and time increasing, the thickness of compound layer was increasing. Above 900℃, the columnate crystals area was formed on the steel side of copper/steel interface; the big area feather organization was formed on the titanium side of copper/titanium interface, the non-crystal boundary region was formed between the feather organization and the contact surface. At 950℃, the thickness of copper reduced, diffusing to the titanium and steel completely.The hardness experiment indicated that the hardness of titanium side increased as the temperature increasing, nearer the interface, the degree of hardness was higher, it is indicated that the compound phase increased.The experiment of specimen shearing strength indicated that at low temperature, the diffusion speed was slow, the diffusion was not adequate, the shearing strength is low, with the diffusion time extending, the interface shearing strength was higher; at high temperature, the diffusion speed was quick, the shearing strength wais high, but with the diffusion time extending, the thickness of compound layer increased, the shearing strength droped. Obviously, the shearing strength has the best diffusion time and temperature.The fracture pattern of shearing specimen was observed by scanning electron microscopes, and its interface ingredient was analysed by energy dispersive spectroscopy. The fracture of titanium side of titanium and copper was smooth, mainly including two elements of titanium and copper, which explained that the copper/titanium compound formed. Tt was because the solubility was not mutually big between titanium and copper, and the solubility changed when the temperature changed, it had a the very big tendency to form intermetallic compound and eutectic. The fracture of steel side of steel and copper interface had formed two cracks, which explained that the interface was crisp, including two elements of titanium and copper, it indicated that the titanium and copper had transfered to the steel side. The diffusion process was full, and the bonding was good.