| The overlarge residual stress caused by the great performance difference between two base materials is one of the key factors to ceramic and metal joining.It has two major solutions, using interlayer or reinforcement. In numerous interlayer materials, foam metal has been a hotspot in brazing field for its favourable deformability and porosity characteristic. However, it is worth noting that the fusion brazing filler would invade into the holes of foam metal interlayer, as well as mutual diffusion and dissolve could take place with the three-dimensional skeleton. This action could induce the collapse of interlayer and reduce the effect of remisson residual stress.As grapheme is a new-type nanometer material, it has been far-ranging researched and used in the composite material/brazing filler field. Graphene not only possesses excellent mechanical property but also has special sheet structure. It can suppose that if we could combine the advantages of both foam metal interlayer and graphene reinforcement, the ability of remisson residual stress would be greatly increased.In this task chemical vapor deposition method(CVD) was used in the in-situ synthesize graphene-copper foam interlayer. Firstly, copper foil was applied as a reference object for researching the technological parameters which impact on graphene growth quality. As follow are the optimal parameters, deposition temperature: 960℃; deposition time: 10min; ratio of CH4 and H2/Ar(H2=17%, Ar=83%): 10:90. Secondly, copper foam was utilized as base material for preparing the graphene reinforced interlayer. By calculated and measured, the addition of graphene in this reinforeced interlayer could up to 1.8vol.%. DSC test showed that graphene could not re-solution with copper basement before the molten temperature.Copper foam interlayer with graphene added or not was used respectively in a usual ceramic and metal joining system,namely Al2O3 and Nb.Under 880℃/10 min, the typical interfacial structure obtained by raw copper foam interlayer was: Al2O3/ Ti-O+Ti-Cu+Ti-Al+Cu3Ti3O/Ag(s,s)+Cu(s,s)/Ti-Cu+(Ti,Nb)/Nb. When graphene added, Extensive continuous Ag(s,s) and Cu(s,s) would transfer into Ag-Cu eutectic and dispersive Cu(s,s), meanwhile the latter joint would be broader. With temperature growth and time extension, the interfacial continuity got better and its distance became narrow, as well as the sheer strength presented a inflex tendency with the peak valued 104.2MPa. Compared with the raw copper foam interlayer, the application of reinforeced interlayer would improve the joint strength by 35% on the whole.The mechanism of soften collapse copper foam interlayer, as well as the action of graphene has been researched.Result showed that the interlayer soften in brazing caused by two factors, self collapse and mutual diffusion with melten filler. The addition of graphene could impede the diffusion on account of its special film structure. Thus the copper foam interlayer could give a full play to remisson residual stress.Finally strengthening mechanism of copper foam interlayer and graphene reinforcement was analyzed respectively. Relative to the commom copper foil interlayer, interlocking-type joint which has a higher CTE regulation ability could be obtained by copper foam interlayer. According to another quanlitative calculation to strain energy, the application of foam copper interlayer could make a further step to remisson residual stress. With regard to graphene reinforcement, its addition could not only retain the skeleton strcture as above mentioned, but also play a strengthening effect on joint due to its outstanding mechanical property on the basis of traditional composite material theoretical. |
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