Effects of Ti Activity on Mechanical Properties and Microstructures of Al 2 O 3 /Ag-Cu-Ti/Fe-Ni-Co Brazed Joints

Abstract

Abstract Al2O3 ceramic/Fe-Ni-Co joints were achieved using Ag-Cu-Ti filler alloy to investigate the dependence of the joint microstructure and mechanical properties on the Ti content. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and electronic universal testing machine were used to characterize the microstructure and mechanical properties of the joints. The results show that the increase of Ti content can obviously intensify the interaction between Al2O3 and Ag-Cu-Ti. A layer of Ti-Al and Ti-O products is observed at the interface of Al2O3/Ag-Cu-Ti. The tensile strength of Al2O3/Ag-Cu-Ti/Fe-Ni-Co joint increases as the Ti content increases from 2 wt% to 8 wt%, and the tensile strength of the brazing joint reaches the maximum value of 78 MPa. Good reaction layer is formed by metallurgical reaction at the interface of Al2O3/Ag-Cu-4Ti, and the typical microstructure is Al2O3/TiAl+Ti3O5/NiTi+Cu3Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co when brazed at 890 oC for 5 min. Compared with AgCu4Ti filler, the microstructure of the joints changes slightly when addition of the active element Ti to 8 wt% except for the increase of the thickness of reaction layer adjacent to Al2O3 ceramic, which is accompanied by the formation of TiO and Ti3Al in the Al2O3/Ag-Cu-Ti interface.