From grain to chip: Influence of manufacturing route on micro-turning behaviour of Inconel 718

The influence of manufacturing route on the microstructure and machinability of Inconel 718 (IN-718) remains an important consideration for precision micromachining applications. In this study, IN-718 produced by conventional forging and laser powder bed fusion (L-PBF) was subjected to identical standard heat treatments to establish comparable metallurgical conditions and enable meaningful comparison. Microstructural characterization was performed to examine grain morphology, phase evolution, and hardness response, followed by micro-turning experiments conducted at three cutting speeds (30-60 m/min) and feed rates (10-30 μm/rev) using uncoated tungsten carbide tools. Cutting force, surface roughness, and flank wear were evaluated to assess the combined effects of microstructure and machining parameters. The results show that L-PBF IN-718 exhibits finer grains and a larger relative increase in hardness after heat treatment, whereas forged IN-718 retains a coarser, equiaxed grain structure with higher absolute hardness. During micro-turning, forged IN-718 generated higher cutting forces, while L-PBF IN-718 achieved superior surface finish, particularly at lower cutting speeds and feeds. Although both materials exhibited similar dominant wear mechanisms, including abrasion, adhesion, and micro-chipping, their severity and morphology varied significantly with manufacturing route and cutting conditions. Overall, the findings demonstrate that manufacturing-induced microstructural characteristics strongly govern machinability and tool wear behaviour in micro-turning of IN-718. • Forged and L-PBF Inconel 718 were subjected to identical standard heat treatment to enable direct machinability comparison. • Forged IN-718 exhibited higher post-treatment hardness, while L-PBF IN-718 showed greater relative hardness improvement due to precipitation strengthening. • L-PBF IN-718 achieved superior surface finish at lower cutting speeds and feeds, whereas forged IN-718 generated higher cutting forces. • Distinct wear mechanisms were observed, with adhesion and micro-chipping dominating in L-PBF IN-718 and plowing and abrasion prevailing in forged IN-718.