Investigation On The Brazing Of Alumina To Ti6Al4V Alloy And The Joining Mechanism

In this thesis,two kinds of brazing alloy:Ag-Cu-Ti and Ag-Cu were utilised to braze alumina and Ti6Al4V alloy.The residual stress in the joint was moderated by applying an interlayer in the joint and using composite brazing filler.The typical microstructure of the joint was systemically characterised,the effect of the brazing parameters on the microstructure and the strength of the joint was investigated and the optimised joining parameters were achieved.It was found that the joining between alumina and Ti6Al4V alloy can be successfully achieved by using both of the brazing alloys.The joint by Ag-Cu-Ti brazing alloy,which was brazed at a higher temperature,showed better strength.The microstructure was studied by SEM,XRD and TEM and was determined to be alumina/TiAl+Cu₃Ti₃O/Ag?s.s?+TiCu₄+Ti₃Cu₄/TiCu₄/Ti₃Cu₄/TiCu/Ti₂Cu/?-Ti/Ti6Al4V alloy.The joining could also be achieved by Ag-Cu at a lower temperature and similar microstructure to that of the joint by Ag-Cu-Ti brazing alloy,despite that the Cu?s,s?could be found in the joint.The strength of the joint was measured by the shear test.The results showed that when using Ag-Cu-Ti as the brazing filler,the highest strength of 142MPa was achieved when the joining temperature was 850?,the holding time was 10min and the inserting Cu interlayer was 180?m thick.When using Ag-Cu as the brazing filler,the highest shear strength was achieved at 820?for 10min and the 180?m Cu interlayer was applied.To moderate the residual stress in the joint,Ag-Cu+SiC composite brazing filler was applied.The effect of the SiC content,joining temperature and the holding time on the joining strength was investigated.The highest strength of 110MPa was achieved when the Ag-Cu+3wt%SiC was used as the brazing filler,the joining temperature was870?and the holding time was 3min.