Elucidating friction properties and strengthening mechanisms of Ni-based surfacing layer containing 9R phase

This study analyzed the strengthening mechanisms and friction properties of Inconel 625 surfacing layers fabricated by plasma transfer arc surfacing (PTA-surfacing) in ball-on-disc friction tests at room temperature and 650 °C. Results showed that Inconel 625 exhibited poor tribological performance at room temperature, but excellent at 650 °C. The average Vickers hardness of the high-temperature wear area (1.6826 ± 0.4059 GPa) was higher than that of the room temperature wear area (1.3900 ± 0.1875 GPa). The coefficient of friction for Inconel 625 decreased from 0.5362 at room temperature to 0.2846 at 650 °C. The wear rates of Inconel 625 at 650 °C and room temperature were 1.2063 × 10−5 mm3/N·m and 20.9740 × 10−5 mm3/N·m, respectively. The wear mechanisms at 650 °C were mainly abrasive, adhesion, oxidation wear, and some degree of delamination wear. The microstructural characterizations revealed that the wear subsurface at 650 °C comprised polycrystalline-mixed oxide layers (Ni(Cr,Fe)2O4, (Cr,Fe)2O3, and NiO), gradient grain refinement, nanoscale precipitations (M23C6, M6C, and laves), 9R structural phases, I-type twinning, and high-density dislocations, which synergistically enhance the outstanding high-temperature friction properties and strength.