| Abstract Scope |
Over the past decade, efforts to develop multi-principal element alloys (MPEAs) as brazing filler metals have accelerated, largely because their broad single-phase fields offer exceptional flexibility for melting point control and ductile solid-solution matrices. However, MPEA brazing studies rarely address joint clearance, despite its critical influence on void formation, triaxial stress states, and secondary phase evolution. For traditional nickel-base fillers containing boron or silicon melting point depressants, wide joint clearances often limit solute diffusion, leading to continuous centerline eutectic constituents that are brittle and therefore severely degrade joint performance. This work systematically investigates the joint clearance sensitivity of a new face-centered cubic (FCC) MPEA filler—designed as a boron- and silicon-free alternative—and compares it to a commercial BNi-5 filler brazed under identical thermal cycles on 316L stainless steel. Microstructural characterization revealed that the MPEA filler exhibited an FCC matrix with minor secondary phases whose fraction remained constant regardless of joint clearance, but centerline voids were observed when the clearance exceeded 140 µm. Conversely, the BNi-5 joints exhibited centerline silicide phases that grew progressively extensive with increasing clearance. In single-lap-joint mechanical testing at a 50 μm clearance, the MPEA filler showed improvements of 65% in engineering shear stress, 82% in base material tensile stress, and 460% in elongation over BNi-5. At a wider 100 μm clearance, these relative advantages expanded significantly to 99%, 86%, and 620%, respectively. Crucially, the MPEA-brazed joints consistently shifted the failure location, always failing in the base material at 50 μm and occasionally at 100 μm, whereas all BNi-5 specimens suffered brittle failure at the braze interface. These findings demonstrate the exceptional wide-gap capability of the MPEA filler over traditional nickel-base alternatives. |