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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 1 7 2 7 though Stankowski and Beckel [14] pro- posed the use of Ni- and Ni-Co-base nanosized brazing powder to repair SC superalloys. LASER BRAZING Laser brazing is favorable be- cause it enables local heating of high melting-temperature brazing materi- als without melting the base materi- al. Bridges et al. [15] took advantage of the small heating area when laser braz- ing Inconel 718 with a Ni-Co-Cu-Fe- Mn brazing material despite reaching temperatures above the melting point of Inconel 718. With nanobrazing, la- ser-brazed joints exhibit a significant- ly higher density compared with most pressureless brazing techniques (Fig. 4). Bridges et al. evaluated Ag and Cu-Ag nanopastes as filler metals for brazing Inconel 718 against a commer- cially available eutectic Cu-Ag brazing alloy (BAg-8). Their lap-joint brazing procedure was slightly unconvention- al in that the top plate in the lap joint configuration was heated directly by the laser. The nanobrazed joints pos- sessed higher shear strength than joints brazed using BAg-8, which was attributed to Hall-Petch strengthen- ing [15] . The study also showed that the particle shape effect on joining is not limited to low-temperature sintering [16] ; Fig. 3 — Possible melting and solidification mechanisms of nanobrazing for fast and slow heating rates. T melting is the melting point of the particle and T surface is the surface melting point of the particle. Fig. 4 — Laser-brazed Inconel 718 using (a) Ag nanowire and (b) Cu-Ag core-shell nanowire paste [15] . Ag nanowire (NW) and Ag nanoparti- cle pastes exhibited different bond- ing strength and different behavior as part of a composite paste with Cu-Ag core-shell nanowires (CSNWs). Ag NWs have a stronger bonding strength than Ag NPs. A composite paste consist- ing of Ag NW + Cu-Ag CSNW has a low- er threshold bonding temperature, but also lower strength compared with an Ag NP + Cu-Ag CSNW. Nanobrazing of SC superalloys us- ing laser brazing has high application potential. Vilar and Almeida [17] demon- strated the potential of laser powder deposition as a manufacturing and repair technique for SC superalloys (Fig. 5). Theoretically, laser powder deposition can be applied to nano- powder if issues of agglomeration and nanopowder manufacturing costs can be lowered. POTENTIAL TECHNOLOGIES High-entropy alloys (HEAs) con- tain five or more elements in equi- molar or near equimolar quantities and are of great interest for use in cryogen- ic and high-temperature applications. A combination of the four core HEA ef- fects (cocktail effect, sluggish diffusion kinetics, severe lattice distortion, and high entropy effect) produce highly fa- vorable mechanical properties such as good creep resistance, high hard- ness, and high fracture toughness. Gao et al. [18] show that an HEA brazing ma- terial used as a filler metal for nickel superalloys has good fracture tough- ness, and interdiffusion between the HEA and Inconel 718 profoundly affects bonding strength and hardness via the cocktail effect and lattice distortion. The cocktail effect states that material