1999 Volume 17 Issue 1 Pages 35-40
In brazement with nickel filler metal, the formation of brittle phase degrades the reliability and the strength of the joint. This phase is composed of melting temperature depressants in the filler metal, such as silicon, boron or phosphorus. In particular, this phase tends to form in brazed joint with a wide clearance. In order to avoid the formation of the brittle phase, a strict control of brazing clearance is required, which is kept as narrow as possible during the brazing process. In some cases, however, such a strict control may be difficult.
The purpose of this study is to develop the filler metals free of or less in silicon, boron and phosphorus, thereby suppressing the formation of the brittle phase. The nickel-copper alloy was chosen as the bass alloy of the filler metal, and two kinds of Ni-Cu-Sn-Si and Ni-Cu-Mn-Si filler metals were developed. The experiments were carried out to investigate the mechanical properties of the joints brazed with these filler metals.
The tensile test of butt joints of SUS316 stainless steel brazed with developed filler metals was conducted, whose clearance were in the range of 10 to 100 micrometers. Hardness distributions of the brazed joints were also measured. Same experiments were carried out on the brazed joints with BNi-2 and BNi-5.
The tensile strength of the Ni-Cu-Sn-Si filler brazed joints was about 500 MPa for the clearance of 10μm and was about 300 MPa for 100μm. In the joins with the Ni-Cu-Mn-Si filler metal, the tensile strength was about 600 MPa for 10μm and 350 MPa for 100 μm. In the joints of clearance more than 50 μm, tensile strength of the developed filler metals were superior to those of BNi-2 and BNi-5, in which the hardness of the joints increased obviously.
