| Be/Cu-alloy compound structure is used as plasma facing material for the International thermonuclear Experimental Reactor (ITER).Bonding of Be to Cu-alloy was completed by diffusion bonding or brazing. Hot Isostatic pressing (HIP) diffusion bonding of Be to Cu-alloy was carried out in this paper. Scanning Electron Microscope (SEM), Energy Dispersive Spectrum (EDS), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectrumscopy (XPS) analysis were employed to investigate the interface structure of joint, fracture mechanism and phases of shear fracture surface were also studied. The formational free energy of the possible intermetallic compounds was calculated by Castep module of Material Studio, according to"flux-energy principal"to confirm the formation of interface reaction. The atomic population and overlap population of intermetallic compounds were analyzed. The formational energy of vacancy and diffusion migratory energy of Be, Cu,α-Ti andβ-Ti were calculated by Castep, the atomic population of simple-vacancy to Be, Cu,α-Ti,β-Ti were analyzed. Be to Cu-alloy were Bonded used Ti as interlayer under bonding temperature 850℃. It was found that TiBe2,α-Ti(there was some Ti2Cu phase segrated),Ti2Cu,Ti3Cu4,Ti2Cu3 and TiCu4 layered structure were formed on the joint interface. The shear strength of joints were lower. The fracture was cleavage-intergranular crack. The XRD analysis showed that the joints ruptured around the interface between Ti2Cu layer and Ti3Cu4 layer.Physical Vapor Deposite (PVD) Al on Be, Ti on CuCrZr, after this, used AlSiMg,Al and Ti foil as interlayers, Bonding Be to CuCrZr were tested under bonding temperature 555℃.The interface of the interface combined compactly, the intermetallic compounds Ti3Cu4 was formed in the interface between Ti and Cu. The shear strength of the joint was lower; the fracture was chiefly cleavage-dimple crack.After PVDing Cu on CuCrZr, Bond Be to CuCrZr under 580℃.Be2Cu phase on the Be side and Cu+BeCu phase on the CuCrZr side were observered. The interface between copperizing layer and original CuCrZr matrix were obvious. The shear strength was lower, quasi-cleavage crack occurred and ruptured around the interface between the copper layer and CuCrZr matrix.The interface layer of joint which gained by bonding Be to CuCrZr by direct HIP diffusion bonding under 580℃consisted of Be2Cu phase on the Be side and Cu+BeCu phase on the CuCrZr side. The joint strength was well , fracture occurred dimple-intergranular crack and ruptured around the interface between Be2Cu and BeCu phase. In contrast, the joints bonded Be(PVD 5μm Ti on it) and CuCrZr( PVD Cu with different thickness on it),Ti tended to diffuse in Cu rather than in Be, and unsymmetrical diffusion occurred. There were Ti3Cu4 and TiCu4 intermetallic compounds formed on the interface. All of fractures were quasi-cleavage crack.The diffusion between Be and Ti was incomplete for the joints which the thickness of Cu was respectively 10μm and 50μm, and fracture occurred around the interface between Be and Ti,the joints'strength were lower. However ,for the sample which the thickness of copperizing layer was 30μm, the joint ruptured around the interface betweenα-Ti and Ti3Cu4,and the shear strength was upper.The formational free energy of the possible intermetallic compounds was calculated by Castep module. According to the result, the formational mechanism of interface phase on the joints was studied. The atomic population and overlap population of intermetallic compounds were calculated, and the combined states of the intermetallic compounds were discussed. The diffusion migratory energies when Be ,Cu,α-Ti andβ-Ti diffuse in each other were calculated, from the result, it would be explained why that unsymmetrical diffusion occurred for Ti in Be and Cu. |
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