Abstract
Robust Si3N4/Ti joints with Nb interlayer brazed using 68.8Ag26.7Cu4.5Ti (mass%) filler alloy (TICUSIL®) were developed. Interfacial microstructural evolution and mechanical behavior with respect to various brazing temperatures (1093–1153 K) and holding times (5–120 min) were mainly governed by reaction kinetics of dissolved Ti. Depending on the relative distribution of Ti atoms, types of Cu–Ti intermetallics formed differ across the interfaces. At Ti/Nb interface, multi–layered compounds consisted of Ag–solid solution sandwiched between Cu–Ti intermetallics were formed for all brazing conditions. At Nb/Si3N4 interface, competing Ti reactions occurred when brazed at 1093 K for 5 min. With rising brazing temperature, increasing preferential reactivity of Ti for Si3N4 instead of Cu minimized the formation of Cu–Ti intermetallics. Besides functioning as a residual stress reliever, Nb inhibited migration of ejected Ti from the substrate toward Si3N4, minimizing intermetallics formation at Nb/Si3N4 interface. All joints fractured at Nb/Si3N4 interface due to residual stress when tested at room temperature. Brazing at 1153 K for 10 min produced the highest average bending strength of 181 MPa. Quantitative analysis of relative residual stress caused by intermetallics is presented based on the fracture heights of Si3N4.
Published Version
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