Multi-Principal Element Alloy Fillers for Brazing Gas Turbine Engine Components at Two Distinct Temperature Ranges

Brazing is widely employed in the assembly and repair of gas turbine engine components, but 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 can provide excellent ductility at a fraction of the noble metal filler cost. For brazing of FCC base materials such as stainless steels and solid solution nickel alloys, MPEA fillers capable of producing a compatible single-phase FCC microstructure in the resultant joint metal after incorporating material from each substrate are identified. Additionally, in the design of these MPEA fillers, intentional melting temperature selection is critical to maximize compatibility with existing industrial brazing procedures and the thermal exposure limits of base materials.

This work investigates two distinct MPEA filler compositions selected for brazing in disparate temperature ranges: (1) approximately 990 – 1050°C, and (2) approximately 1170 – 1200°C. Brazing experiments employed composition (1) on 304 stainless steel and composition (2) on Haynes 214 and 233 alloys. For both compositions, the MPEAs demonstrated complete metallurgical compatibility with their substrate material(s), with accommodation of base material elements and no terminal intermetallic phases in the resultant joint metal regardless of the initial joint clearance. Consistent with this result, lap-shear testing of MPEA-brazed specimens demonstrated no increase in interfacial failure rates with increasing joint clearance up to at least 250 µm (0.010 in). For the Haynes alloy brazes, the influence of the MPEA filler and commercially available AMS 4782 on the distribution of byproduct gamma-prime formation during cooling at two different rates, and its implications on mechanical behavior, were also critically evaluated.