Influence of iron on the structure and strength of the Kovar to stainless steel joints by using Cu-Mn-Co-Fe brazing filler metal

The paper presents the results of X-ray spectral microanalysis of dissimilar brazed joints between Kovar and stainless steel, produced by vacuum brazing with the application of Cu-Mn-Co-Fe brazing filler metals. X-ray microspectral analysis established that a two-phase structure is formed in brazed joints, which consist of two solid solutions: the primary phase is the alpha-Cu solid solution (based on the Cu-Mn system), which takes up the main zone of the seam. The gamma-phase (Fe-Mn) crystallizes in the form of isolated discrete grains. It also contains other components of the brazing filler metal. The influence of iron on the structure and mechanical properties of the brazed joints was investigated. It was found that an increase in iron concentration leads to an increase in the quantity of the gamma-phase. It was determined that increasing the iron concentration in the initial brazing filler metal from 1 to 2.5% results in the attainment of maximum strength (600 MPa) in the brazed joints, and the samples fail through the stainless steel.