Multi-Principal Element Alloys Developed for Brazing of Ni-base Superalloys

Since the early 2000s, the vast composition space of multi-principal element alloys (MPEAs) has been increasingly studied, giving rise to a diverse spectrum of novel materials targeting an equally diverse set of engineering applications. Recently, part of this growing trend has been the development of MPEAs as brazing filler metals. Brazing is widely employed in assembly and repair applications across an array of industries, such as gas turbines. Existing brazing filler metals with boron and silicon as melting point depressants often fall short in providing adequate ductility, especially at wide gap widths, requiring expensive noble metal fillers based in gold and palladium to be used instead. Emerging multi-principal element alloy (MPEA) brazing fillers without embrittling melting point depressants, which exhibit single-phase solidification behavior, can provide excellent ductility at a fraction of the noble metal filler cost.

This work highlights three MPEA brazing filler alloy systems developed by the authors’ group. With the first system, the benefits of single-phase solidification behavior were demonstrated by comparing the mechanical performance of MPEA-brazed joints to those brazed with boron- and silicon-containing fillers on several Ni-alloy substrates. Depending on testing configurations, the MPEA-brazed joints exhibited up to ten times greater ductility than those brazed with conventional fillers. The second system was developed with a lower brazing temperature, approximately 200°C lower than the first, for brazing substrate materials with more limited tolerance to thermal exposure. This composition exemplifies that the vast MPEA composition space offers the ability to tailor melting temperature without including traditional melting point depressants. Finally, the third composition was developed as an alternative to the first with improved oxidation resistance, which was demonstrated by static oxidation testing comparing these two filler materials