Study on Ultrasonic Image Evalution of Braze Bonded Joints between Cemented Carbide Alloy and Cu-W

This report discussed the new method to evaluate the brazed joint strength between cemented carbide alloy and sintered Cu-W joint by using the ultrasonic image. The brazing was performed in a vacum at 1213 K to 1333 K for 60 s to 1.2 ks to vary the joint strength. Although the joint strength made by filler metal containing Pd closed to that of the base metal, Cu-W, at 1213 K, it decresed at higher temperature heating and after prolonged holding time. The ultrasonic image of the brazed joint was measured through the cemented carbide alloy of 4 mm in thickness. In order to correlate a brightness of the ultrasonic image with the joint strength, the relative echo intensity, R, was defined by equation (1) R=1/16n nΣl=1 I/di/Iri (1) where Iri is reference data, Idi is sampling data and n is sampling number. R calculated from these data correlated to the shear strength. Good correlation with r=-0.86 was achieved between R and the joint strength. A microstructure in the joint cross section was investigated comparing with the ultrasonic image.