Microstructure and resultant properties of ex-situ Alloy 625+TiB2 nanocomposites processed via suction casting as filler material for Ni-based superalloys repair applications

In this study, Alloy 625+xTiB 2 (x=1.25, 2.5, 3.75, 5.0 wt%) nanocomposites were successfully fabricated via suction casting. Their microstructure, thermal stability and selected properties were investigated using thermodynamic simulations, X-ray diffraction, light and scanning electron microscopy, scanning-transmission electron microscopy, energy-dispersive X-ray spectroscopy, dilatometry, differential scanning calorimetry, Vickers hardness testing, dry-sliding wear test, and oxidation resistance tests. The incorporation of TiB 2 nanoparticles significantly influenced the dendritic microstructure of Alloy 625. The Nb-rich carbides and Laves phase precipitates were primarily located in the interdendritic regions. Upon the addition of TiB 2 , the particles reacted with the molten matrix during suction casting, leading to the formation of new phases, such as (Mo, Cr, Nb) 3 B 2 and TiN. The TiB 2 additions markedly enhanced the mechanical properties, increasing the hardness from 201 HV10 to 470 HV10 (at 5.0% TiB 2 ) and improving wear resistance by a factor of 8, reducing mass loss to 0.0241%. Long-term annealing at 704 °C for up to 1000 h in an Ar+0.25% SO 2 atmosphere confirmed the excellent thermal stability of the composite containing 5.0% TiB 2 , with a mass gain of less than 0.4 mg/cm 2 , over three times lower than that of the reference Alloy 625. These results highlight the potential of TiB 2 reinforcement for enhancing both the mechanical and thermal performance of Alloy 625.