Microstructure and properties of a YG18/40Cr joint vacuum–brazed by Cu–Sn–Ti filler metal

Abstract

In this study, dissimilar YG18/40Cr joints were prepared using a Cu–Sn–Ti filled metal by a vacuum brazing process, and the microstructural evolution and bonding mechanism of the YG18/Cu–Sn–Ti/40Cr joints were studied. By adjusting the brazing parameters, the formation process of interface structure, the joint structure and matrix internal structure, and the changes in the joint microstructure and properties under different parameters were systematically analyzed. A TiC reaction layer was formed at the interface on both sides of the joint. The brazing performance can be improved by the formation of a reasonable size reaction layer. A TiC–WC cemented carbide was formed near the middle layer inside YG18, and this tenon–and–tenon structure improved the bonding between the YG18 side and the filler alloy. The connector structure was YG18/TiC/CoTi + Co2SnTi/Cu [s, s]/eutectic structure (Cu [s, s] + Cu Sn3Ti5)/CuSn3Ti5/TiC/40Cr, and its eutectic structure changed as the parameters changed. The maximum average shear strength of the YG18/40Cr joint brazed at 940 °C for 5 min reached 216 MPa, which was ≈25% higher than the joint shear strength of the pure copper used in a previous study. The fracture morphology of the joint showed a large number of fossae and tear edges, indicating ductile fracture.