Correlation between the mechanical properties and the microstructural behaviour of Al2O3–(Ag–Cu–Ti) brazed joints

A micro-indentation technique was used to determine the strength of Al2O3–(Ag–Cu–Ti) brazed joints. Different Ag–Cu–Ti alloy compositions were used for brazing Al2O3 at temperatures of 800, 900, 1000, 1100 and 1200 °C under vacuum with a constant load. EPMA, SEM–EDX and XRD analyses of the brazed samples reveal that adjacent to the Al2O3, the amount of diffused Ti is much higher than Cu and the reaction layer is identified as TiO, whereas, between TiO and the filler metal, the phase Ti3Cu3O was confirmed. An attempt was made to correlate the bond strength and the microstructure of the brazed samples. It has been observed that higher amounts of Ag present in the filler metal increases the activity of Ti, which improves the bond strength. The filler metals having higher amounts of Cu form different Cu–Ti intermetallics, but these intermetallics do not directly react with the ceramics. The alloys 97(Ag28Cu)3Ti and 97(Ag40Cu)3Ti exhibited good performance to join Al2O3 ceramics.