Understandings the tribological mechanism of Inconel 718 alloy machined under different cooling/lubrication conditions

Machining of Ni-based superalloys is a challenging issue, and it may lead to tool deterioration, poor surface quality, and other structural defects. Therefore, the main theme of this study is to examine the effect of different sustainable cooling/lubrication conditions on the machining performance, surface integrity, and accompanying tribological aspects of Inconel 718 superalloy. In this context, the milling experiment variables were selected as two feed rates, two cutting speeds, and four cutting environments: dry, air, synthetic oil-based MQL, and LN2-assisted Cryo. Tool wear mechanisms, surface roughness/profile/topography, cutting performance (tool-chip interface temperature and energy consumption), chip shapes, microstructures, and micro-Vickers hardness of the machined surfaces were thoroughly analyzed to assess experimental observations. The Cryo medium reduces tool wear, surface roughness, cutting temperature, and cutting energy by 67 %, 61 %, 85 %, and 33 % in comparison with a dry environment, respectively. Abrasion, adhesion, and diffusion mechanisms were supposed to be the most dominant wear types following SEM observations. Besides, the Cryo environment concluded a reduction of grain size to ⁓ 4 µm in concomitant with an increase of micro-hardness ⁓ % 15. The whole observed outcomes agreed to a great extent with each other, asserting the effectiveness of the LN2 cooling protocol in improving machining characteristics of Inconel 718 superalloy.