Diamonds brazing with a novel Cu35Ni35Cr10Fe10Sn10 high-entropy alloy filler

A novel Cu₃₅Ni₃₅Cr₁₀Fe₁₀Sn₁₀ high-entropy alloy (HEA) filler with a relatively low melting point (935°C) was designed for brazing diamonds, and its technical advantages over conventional NiCr-based fillers, that is, favorable wettability, high bonding strength, low thermal damage, and high mechanical performance, were convincingly demonstrated. The newly developed HEA filler had a contact angle of only 11° on the graphite (energetically close to diamond) surface and it could braze diamonds at 1000°C, much lower than the brazing temperature of conventional NiCr-based fillers. Consequently, the brazed diamond exhibited greatly decreased surface thermal damage, higher fracture strength, and better wear performance. The solidified microstructure of the HEA filler contained three solid solution phases, that is, FeCrNi-rich, CuNi-rich, and CuSnNi-rich phases that were formed through the liquid phase separation process, plus a minor phase of nanosized FeCr-rich precipitates. The reaction products at the HEA filler/diamond interface were simply an inner Cr₃C₂ layer and an outer Cr₇C₃ layer, without other complex brittle compounds that are commonly seen in NiCr-based fillers after diamond brazing. Apparently, the HEA filler reacted more sufficiently with diamonds, which contributed to improve the bonding strength and wear resistance of the brazed diamond. This work provided a new application scenario for HEAs as promising filler materials for brazing diamonds.