Investigation On Diffusion Bonding Of Nanocrystallized Cu

As one of pressure welding, diffusion bonding technology is of many merits, such as good quality of welded joints, lower welding temperature, small extent of microcructure and performance deterioration and so on, compared with traditional welding methods. And diffusion bonding could weld the materials with great difference between physical and chemical properties, even some different materials that are undisso lved mutually or would generate intermetallic compounds at fusion welding. Therefore diffusion bonding has a good application prospect.Surface nanocrystallization technology is relatively new as one of surface modification technologies, and it also has ma ny unparalleled advantages compared with traditional modification technologies, such as simple technology, nano- layer that is not easy to peel off, maintaining the base status and so on. Especially after the surface of metallic materials exhibit many excellent performances, such as higher surface strength and hardness, stronger corrosion and wear resistance, improving the fatigue performance, enhancing surface atom diffusion capacity. Due to the higher diffusion performance of nano- materials, it would increase the quality of diffusion welding joints significantly, through combining surface nanocrystallization technology with diffusion bonding.To study the impact of surface nanocrystallization technology on microstructure and properties at diffusion welded joints, pure copper after surface nanocrystalization using surface mechanical rolling(SMR) technology was produced firstly in this paper. Through some testing methods like OM, SEM, microhardness tester and universal testing machine, the influence of surface nanocrystallization technology on properties at surface layer of copper was analyzed. And this paper also researched impacts of surface nanocrystallization technology on diffusion welded joints from microstructural characterization, microhardness and shear strength etc.. And by adding nickel intermediate layer, the diffusion behavior of nickel atoms was discussed in the copper samples.Using surface mechanical rolling(SMR) technology, surface nanocrystallization treatment was conducted on Cu. The results showed that the surface grains were refined gradually with the increase rolling times, and the deformation region also deeper. Copper surface grains reached the nanoscale after 20 rolling times, and the grain size presented gradient distribution from surface layer to the interior. Compared with the matrix, the microhardness of copper specimen was improved extraordinarily, nearly half.The diffusion bonding tests were conducted on pure copper base samples without surface nanocrystallization and pure copper samples with surface nanocrystallization at 300 ℃, 400 ℃ and 500 ℃ respectively. The results showed that, at the same temperature, the welded joints of those specimens with surface nanocrystallization combined well, with smaller grains, higher microhardnes s and shear strength. With the increase of temperature, from 300 ℃to 400 ℃, the shear strength was improved. But at 500 ℃, due to tissue deterioration, the shear strength did not increase, even declined. After adding nickel intermediate layer, the mutual d iffusion of copper-nickel atoms in the intermediate was rarely at 300 ℃. And as the temperature rised, the nickel intermediate layer gradually disappeared. At 500 ℃, the mutual diffusion of copper-nickel atoms was more ful y.