Research On Diffusion Bonding Technology Of Electrodeposited Nano-nickel-cobalt Interlayer On Titanium Alloy

In this paper,based on the research project of TC4 titanium alloy sheet low-temperature diffusion connection technology,the parameters of titanium alloy low-temperature diffusion connection are studied.The preparation technology,parameter optimization,thermal stability of electrodeposited Ni-Co intermediate layer,low-temperature diffusion bonding joint morphology and mechanical properties were mainly studied.Nano-Ni-Co electrodeposition layers with different thicknesses and different compositions were prepared on TC4 titanium alloy by pulse electrodeposition method.The effects of Co element and current density on grain size,adhesion force,microhardness and surface roughness were studied.The structure of the electrodeposited layer was measured by X-ray diffractometer as a face-centered cubic structure.The crystallite size of the electrodeposited layer was observed to be about 20 nm through Sherrer formula and transmission electron microscope.The crystallite size decreased with the increase of current density and Co element content.The hardness of the electrodeposition layer is between 395.3?537.6HV,which increases with the current density increasing and the cobalt content of the electrodeposition solution increasing.The adhesion force is between 40-67.8N,with the current density decreases.The surface roughness of the substrate increases,regardless of the content of cobalt.The roughness decreases as the current density decreases and the cobalt element content increases,and increases as the titanium alloy matrix roughness increases.The element distribution of the electrodeposited layer conforms to the law of abnormal co-deposition.Finally,when the current density was 2A/dm2,the content of cobalt in the electrodeposition solution was20g/L,and the titanium alloy substrate was polished with 1500 mesh sandpaper,the grain size and surface quality of the electrodeposition layer were optimal.The elemental distribution of the electrodeposited layer conforms to the law of anomalous co-deposition.Finally,when the current density was 2A/dm2,the content of cobalt in the electrodeposition solution was 20g/L,and the titanium alloy substrate was polished with 1500 mesh sandpaper.The grain size and surface quality of the electrodeposition layer were optimal.The grains of the oxide layer and the electrodeposited layer are refined with the increase of the Co content of the electrodeposition solution and the heat treatment time growing up.Vacuum heat treatment results show that with the heat treatment,the grains grow abnormally,and the grain size increases with the Co content of the electrodeposited layer.Itdecreases first and then increases.The average grain size is about 100 nm.The Co element content of the electrodeposition solution is 20g/L,and the grains grow rapidly when heat treated for more than 1.5h,so the diffusion bonding time within1.5h is the best parameter.The diffusion bonding temperature is 800?.The Co content of electrodeposition liquid is 20g/L,the current density is 2A/dm2,the titanium alloy substrate is polished with 1500 mesh sandpaper,and the electrodeposition time is 7.5min;the diffusion bonding pressure is 3MPa The diffusion bonding time is 1h,the thickness of the intermediate layer is 2.5?m,and the shear strength of the diffusion connection joint is 664 MPa.