Research On Process And Mechanism Of Low Temperature Diffusion Bonding Hydrogenated TC4and GH3128

At present, the researches of the hydrogenated titanium is mainly focused on theplastic processing, and with few research on the joining of hydrogenated titanium,especially on low temperature joining. Low temperature diffusion bonding ofhydrogenated TC4and GH3128with direct joining and different interlayers was carriedout, The effect of Hydrogenated content and process parameters on the microstructureand properties of joints was studied, and optimized the low temperature joining processparameters; The fracture location of joints was analyzed; Mechanism of hydrogen in thejoining process of low temperature diffusion bonding was discussed.Through low temperature direct diffusion bonding formed interface: TC4（α+β）/Ti₂Ni/TiNi/TiNi+（Ni,Cr）_ss/（Ni,Cr）_ss/GH3128. Hydrogenated content and the processparameters just affected the thickness of reaction layers in joints and strength ofjoints.Under the same process parameter, the thickness of TiNi layer increased while thatof Ti₂Ni decreased with the increasing of hydrogend content of joints. The thickness ofthe reaction layers in joints increased with the process specifications raising. With thehydrogenated content and process specifications improving, the shear strength of jointsincreased to a maximum and then decreased. the shear strength maximum was80.16MPa,which obtained with hydrogenated0.3wt.%at the process of T=680℃/t=60min/P=15MPa. Connector fractured in the Ti₂Ni and TiNi layer, mainly in Ti₂Ni layer.In order to avoid the brittle layer and relieve stress, then improve joint strength,adopted interlayers to joining. It didn’t obtain a good joining with V or Cu interlayer bylow temperature diffusion bonding for the extremely inadequate diffusion at lowtemperature or the interface brittle reaction layer. Using Nb interlayer to connect formedthe interface: TC4（α+β）/Ti（s,s）/Nb interlayer/Ni₃Nb/（Ni,Nb）_ss/GH3128. The strength ofjoints was low, and fractured in Ni₃Nb and （Ni,Nb）_sslayer. Using ladder process of twiceconnecting with Nb/Ni composite interlayers to resolve the problem that the GH3128side took a large amount of unhealing holes and Ni₃Nb layer was thin and evenuncontinuous, achieved joints with high strength finally. The typical interface was:TC4（α+β）/Ti（s,s）/Nb interlayer/Ni₃Nb/Ni interlayer/GH3128. The thickness of Ti（s,s）layer increased with the improving of hydrogenated content and process parameters, thepores between Ni₃Nb layer and Ni interlayer lefted by first connection completelydisappeared thougth secondary joining; The joint strength increased with the increasingof hydrogenated content, which firstly increased to a point and then retained with theimproving of joining process parameters, the maximum was299MPa which obtained atprocess of750℃/150min/15MPa（0.3wt.%）; With the joining parameters to improve, thefracture location of the connector changed apparently: Fully fracture in Ti（s,s） layer; Partly fracture in Ti（s, s） layer, Partly fracture in Ni₃Nb layer and Ni foil; All fracture inNi₃Nb layer and the Ni interlayer.Combinaned interface elements dynamics calculations and hydrogen TC4differential thermal analysis results. Mechanism of hydrogen in the three joining processof low temperature diffusion bonding are：Change the organization and improve theplastic deformation and reduce oxidation, promote surface purification; Occurrence ofhydrogen reaction prompt the surface activation, produce the effect of the weak bond;Reduce the vacancy formation energy, increase the number of vacancies in the material,lowered diffusion activation energy of the atoms in the material, thereby increase thediffusion coefficient. Phase transitions in hydrogenated TC4base metal enhance theplastic deformation of the joining interface, The hydrogenhydrogen releaseing reactionweakens the the oxide of joining interface, and promotes the surface purification;continuous hydrogenhydrogen releaseing reaction prompts the connection surfaceactivation, take a good ready for the next atomthe proliferation; the weak bond effectcaused by the solution of H reduces the vacancy formation energy, lowers diffusionactivation energy of the atoms in the material, thereby increases the diffusion coefficient,obtain a reliable joints.