Abstract
Brazeability of high purity alumina (99.9 wt% Al2O3) to commercially pure titanium (CP Ti) and Ti-6A1-4V alloy with Ti-Zr base filler metals has been investigated by microscopy, EDX microanalysis, X-ray diffraction, and shear test of the joints. Filler metals used were two types of amorphous foils, developed for trial, of 25Ti-25Zr-5OCu (Type 5000) and 37.5Ti-37.5Zr-l5Cu-lONi (Type 1510), whose melting points were about 815°C and were apploximately 100°C lower than those of conventional Ti-base fillers.
Shear strength of joints brazed with Type 5000 filler metal had a tendency to decrease with increase in both brazing temperature and time. However, in case of brazing at comparatively low temperature for a short time using Type 5000 filler metal, it was possible to get sufficient joints having shear strength of above 150 MPa. Metallurgical test results showed that in the joint of alumina to CP Ti with Type 5000 filler metal, (Ti, Zr)2Cu was formed at joint region nearby CP Ti base metal at the beginning of brazing, and that the composition of the region varied with increase in brazing time. A thin titanium and/or zirconium oxide layer was also detected at the interface between alumina and the joint region, and the growth of this oxide layer was related to the decrease in joint strength and to the occurrence of cracking at the joint.
As for using Type 1510 filler metal, the joints were flaked during cooling after brazing, because of rapid formation of brittle Ti and Zr rich layer at the joint interface, which indicates that the brazeability of Type 1510 filler metal is fairly inferior to that of Type 5000 filler metal.
