Study On Diffusion Bonding Of Zr-based Bulk Metallic Glasses

The superplastic and diffusion bonding of 2mm thick Zr44Ti11Ni10Cu10Be25 (vit1b)bulk metallic glass(BMG) plate with an excellent thermally supercooled liquid state to itself and Al metal foil were investigated.The BMG was welded to itself and Al with the temperature of 648-733K, bonding time of 30-60min and welding pressure of 20-75MPa.By employing the X-ray diffraction (XRD), differential scanning calorimetry(DSC),scanning electron microcopy(SEM) and Energy disperse spectroscopy(EDS),the effects of bonding temperature,bonding time,bonding pressure and deformation ratio on the quality of the welded joint and the diffusivity of the elements in interface were examined.The effect of diffusion bonding on the amorphous structure was also examined.Besides,the mechanism of superplastic and diffusion bonding for amorphous alloys was studied.The quality of the welded joint increases with the bonding temperature,bonding time and bonding pressure when the BMG was welded to itself, and the deformation ratio had a direct and obvious relationship with the quality of the welded joint, that was a BMG plate can be welded to itself successfully when the deformation ratio was large enough.The BMG was welded to Al metal foil successfully at experimental conditions and diffusion of Al was higher than that of the elements of the BMG, and the level of diffusion increases with the bonding temperature when the deformation ratio was large enough.According to the results,the welding parameters can be optimized to achieve the no defect or crack joint with small deformation ratio as follows:by increasing the bonding time (between 45min and 60min) or increasing the bonding pressure appropriately(greater than 75MPa) when the parameters were 688K-45min-75MPa, and by decreasing the bonding pressure(between 50MPa and 25MPa)or decreasing the bonding time(between 60min and 30min)when the parameters were 713K-60min-50MPa. The appropriate parameters were 713K-60min-35MPa when the BMG was welded to Al metal,and the level of diffusion was large in interface with a relative small deformation ratio of 26%.The deformation ratio had a strong influence on the joint quality. When the deformation ratio was too small,no joining was achieved, and when the deformation ratio was large enough it can make a joint,considering that the large deformation ratio of amorphous alloys can cause the high quality joining by breaking the stable real-surface sufficiently. The diffusion of elements had also a relationship with the deformation ratio which was the precondition of the diffusion,and the plastic deformation can promote the diffusion by breaking the oxide film.A BMG plate was successfully welded to itself and Al metal with keeping the amorphous structure and no reaction with Al in interface.The structural relaxation caused by superplastic diffusion bonding in supercooled liquid region diminished the thermal stability.