Technology And Mechanism Of Diffusion Bonding Hydrogenated TC4 Titanium Alloy And GH3128 Superalloy

Hydrogenated titanium alloy are widely used in heat process,on which many researches have been done. Recently years, researchers found that hydrogenated titanium alloy has unique advantages in joining. However few studies are focused on it. Therefore, technology and mechanism of diffusion bonding hydrogenated Ti6Al4V titanium alloy and GH3128 super alloy was carried out. In this paper, diffusion bonding with Ni foil, Nb foil and Nb+Ni foils and without interlayer were used, the effect of bonding parameters on microstructure and mechanical properties of joints was studied, the fracture of joints was analyzed, and the mechanism of diffusion promoted by hydrogen was discussed.The diffusion bonding without interlayer was carried out, the joint microstructure is hydrogenated titanium alloys/α+β/Ti2Ni/TiNi/Ni(s.s)+TiNi/Ni(s,s)/GH3128 super alloy. The thickness of diffusion reaction layers was affected by hydrogen, which increased with the increase of hydrogen content. When the bonding parameters increased, the shear strength of joints increased and then remained unchanged, which reached maximum 55MPa at 900℃/10min/5MPa. The cracks propagated in Ti2Ni reaction layer.When Ni foil used for bonding, new layer TiNi3 was formed, however Ti2Ni layer badly affected the joints mechanical property. So bonding with Nb foil was carried out, the joint microstructure is hydrogenated TC4 titanium alloy/(Ti,Nb)/Nb/(Nb,Ni)/ Ni3Nb /Ni(s,s)/GH3128 superalloy. Improving bonding parameters, the thickness of interface layers increased and the amount of Kirkendall holes decreased. When the holding time was too long, Ni6Nb7 was formed. At 860℃, 100min, 10MPa, the joint shear strength reached maxium 245MPa. To avoid the brittleness region near the basic materials, Ni+Nb foils were used. With the increase of bonding parameters, the thickness of Ni₃Nb increased. The max shear strength 271MPa obtained at 860℃, 80min, 10MPa.When the heating rate is 25℃/min, the dehydrogenation of hydrogenated TC4 titanium alloy occured between 25min³0min. The maximum rate of dehydrogenation reaction was found at 750℃. The hydride in original hydrogenated TC₄ did not exist after isothermy dehydrogenation.The reasons why hydrogen could improve the diffusion of alloy elements are that hydrogen dissolved in TC4 as a interstitial solid at lower temperature causes decohesion effect, which reduces the diffusion activation energy of Ni and Nb that relate to vacancy formation energy and migration energy; hydrogen but also diffused out of TC4 at higher temperature leads to lattice distortion which lower the vacancy migration energy.