Microstructure, stability and oxidation resistance of ex-situ Alloy 625 + TiC nanocomposites processed by suction casting intended for repair of aerospace components

• Analysis of the Alloy 625 + TiC primary microstructure produced by suction casting. • Thermodynamical prediction of the Alloy 625 + TiC microstructure stability. • High-temperature stability of the Alloy 625 + TiC composites. • Corrosion resistance of the Alloy 625 + TiC composites in steam and Ar + 0.25 % SO 2. In this work, nanocomposites based on the Alloy 625 superalloy with varying additions of xTiC particles (x = 1.25; 2.5; 3.75; 5.0, wt%) were prepared by suction casting. The microstructure and selected properties were analyzed using thermodynamic simulations, X-ray diffraction, light microscopy, scanning electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, dilatometry, differential scanning calorimetry, Vickers hardness and wear resistance tests, and oxidation tests. It was observed that the ex situ introduction of TiC particles into Alloy 625 strongly influenced its dendritic as-cast microstructure. In the reference alloy without TiC, Nb-rich carbides and Laves phase precipitates were found in the interdendritic spaces. During suction casting, TiC interacted with the melted Alloy 625, resulting in an increase in the amount of precipitates in the interdendritic spaces, including MC carbides and Laves phase. The phase transformation temperatures (solidus and liquidus) registered by differential scanning calorimetry shifted to lower values with increasing TiC content. The hardness increased by more than 50 % from 201 HV10 to 309 HV10 (5.0 wt% TiC), which was reflected in the improved wear resistance. Exposure tests to O-rich (steam) and O-reduced (Ar + 0.25 wt% SO 2 ) atmospheres at 704 °C for 1000 h showed that composites with 3.75 wt% and 5.0 wt% TiC were characterized by excellent stability and exhibited lower mass gain compared to the reference Alloy 625