| Abstract: |
Nickel-based brazing filler metals combine excellent mechanical properties and corrosion resistance with high melting temperatures, and so they commonly see application in the manufacture and repair of nickel superalloy components. In such brazing alloys, melting point depressants (MPDs) such as boron and silicon are often added, reducing the liquidus temperature to a suitable level. However, the addition of these elements can result in the formation of undesirable brittle intermetallic phases, which can be detrimental to the mechanical properties of the joint. The present work forms part of an ongoing alloy design project, with two broad aims: the development of novel reduced-boron nickel-based brazing alloys, and evaluation of the ability to accurately predict thermodynamic properties of such alloys. Thermo-Calc, which uses the semi-empirical CALPHAD (CALculation of PHAse Diagrams) method, was employed to identify and explore potential novel compositions; utilising alternative MPDs, and concepts such as High Entropy Alloys (HEAs), a new class of multi-principal component materials. Promising alloy compositions, both nickel-based and high entropy alloy-like, were fabricated via arc-melting and used to braze nickel superalloy Inconel-718, with microstructural and mechanical characterisation presented. Comparisons between the Thermo-Calc predictions of the phases formed in such systems and the experimental observations are discussed.
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