Microstructural Modification by Redesigning the Chemical Composition of Ni 620 Filler Metal

Abstract

Ni 620 is a widely used brazing alloy, especially in cases where high‐temperature strength and corrosion resistance are required. The formation of undesirable intermetallic phases in the brazing joint due to the addition of boron and silicon as melting point depressants affects the mechanical properties of the joint. Reducing the formation of intermetallic phases during brazing is an important issue in the application of Ni 620. In this study, two approaches, inoculation with Nb and variation of the B and Si content in Ni 620, are pursued to selectively influence the microstructure of the brazed joint. Therefore, the solidus and liquidus temperatures of the new brazing alloys are investigated by means of differential scanning calorimetry measurements. Also, the microstructure of brazed joints is analyzed and evaluated by scanning electron microscope/electron‐dispersive spectroscopy as well as the hardness properties using nanoindentaion. It is observed that the addition of Nb, as well as the variation of the B and Si content, leads to a change in the brittle phase band. Especially brittle borides can be reduced in this way. The results contribute to produce brazing joints with more adapted properties, despite low brazing temperatures and short holding times.