Synergistic effect of cold rolling and heat treatment on tribological performance of Inconel-718 at room and high temperature

This study explores how a combined thermomechanical processing route, including homogenisation, cold rolling with thickness reductions of 15%, 30%, and 60%, and subsequent double-aging heat treatment, influences the tribological performance of Inconel-718 superalloy, both at room and elevated temperature. Microstructural characterization using X-ray diffraction confirmed the presence of ${\gamma }^{\prime }$ and ${\gamma }^{\prime \prime }$ precipitate phases after aging, while electron backscatter diffraction revealed progressive grain refinement, increased kernel average misorientation, dominance of low-angle grain boundaries, and higher local lattice distortions with increasing rolling reductions. These microstructural changes collectively increased the alloy’s maximum hardness by $\sim 3.4\times$ compared to the homogenised state. Dry reciprocating tests, conducted against Si₃N₄ balls, at room temperature, demonstrated a reduction in the friction coefficient by up to 33% and in the specific wear rate by up to 65% compared to the homogenised state. At 450 °C, the friction coefficient dropped by up to 23% and the specific wear rate by up to 56% relative to the 15% cold-rolled and homogenised samples, respectively. Analysis of relative friction energy dissipation suggested that reduction in average friction coefficient did not fully translate to energy efficiency gains. Cold-rolled and heat-treated Inconel-718 demonstrated more energy-efficient performance than the homogenised. Worn surface examinations through scanning electron microscopy and energy-dispersive X-ray spectroscopy demonstrated the formation of protective Cr-Fe-Ni-rich composite tribo-oxide layers, with minor sacrificial wear observed from Si₃N₄ counterface. In summary, the combination of strain hardening from cold rolling and precipitation hardening from double-aging offers a simple, scalable, and industrially viable approach to enhance the wear resistance and friction behavior of Inconel-718.