High-strength GH4169D joint brazed with medium temperature Cu-30Ag-32Zn-1Sn filler metal

Abstract

The η-Ni₆AlNb in GH4169D could pin grain boundaries, and hinder crack propagation. However, the dissolution of the η phase at 1020 °C causes the notch sensitivity in GH4169D. So low-melting-point alloys, Cu-30Ag-32Zn-1Sn (wt%) (CuAgZnSn), were employed to achieve high-strength brazing of GH4169D at different brazing temperatures (850, 870, 890, 910, and 930 °C) for 30 min and 890 °C for different holding time (10, 60, and 120 min). The influence of the brazing process on the interface microstructure, mechanical properties, and fracture behavior of GH4169D/CuAgZnSn/GH4169D joints was investigated. The brazed seam (BS) was mainly composed of (Cu, Zn)_ss and (Ag, Zn)_ss. The BS achieved isothermal solidification at 890 °C for 30 min and an ordered solid solution Cu₂NiZn formed at 890 °C for 60 min. Meanwhile, the content of (Ag, Cu, Zn)_ss decreased. However, as the holding time increased from 60 min to 120 min, the content of (Ag, Cu, Zn)_ss increased from 0.7 % to 40.3 %. This was mainly because of the reduced solid solubility of Ag in the (Cu, Zn, Ni)_ss as the Ni increased. The interface structure of the brazed joint at 890 °C for 60 min was GH4169D/Cu₂NiZn + Cr-rich (Cr, Ni, Cu)_ss/Cu₂NiZn + Ag-rich (Ag, Cu, Zn)_ss + Cu-rich (Cu, Zn, Ni, Cr)_ss/Cu₂NiZn + Cr-rich (Cr, Ni, Cu)_ss/GH4169D. The shear strength of the joints reached 708 MPa. As the holding times increased, the crack initiated from the BS/substrates interface with drastic changes in hardness to the BS. The fracture morphology changed from typical brittle cleavage fracture characteristics to dimples and cleavage steps.