Influência dos parâmetros de corte sobre a integridade superficial do Inconel 718 torneado sob condição criogênica

Abstract

Nickel alloys such as Inconel 718 have been widely used in the aerospace, oil & gas and chemical industries, due to their excellent properties that combine high creep resistance and high mechanical strength, fatigue and corrosion. However, these properties make these alloys extremely difficult to machine due to high heat generation during material removal, occurring a quick cutting tool wear that produces a detrimental effect on the surface integrity, reducing fatigue life of machined component and low productivity. For these reason, the aim of this work was the evaluation of the influences of cutting parameters on the surface integrity of the Inconel 718 turned under cryogenic condition using liquid nitrogen (LN2) in high cutting speed. The whisker reinforced ceramic tool was used for resisting at high speed cutting, associated with aspects of surface integrity in terms of roughness Ra, residual stresses, microhardness and white layer as well as cutting forces. Central composite design was chosen as factorial planning for the independent variables as cutting speed, feed rate and depth of cut to carry out of the experiments. Cryogenic cooling resulted in average cutting force of 267 N, where penetration force was higher. The roughness Ra was of 0.52 μm, influenced by feed rate and depth of cut. Regarding to residual stresses measurement, higher tensile residual stresses with LN2 and dry conditions were 1394 MPa and 1237 MPa in the circumferential direction respectively, influenced by depth of cut. Small microhardness changes occurred until 0.3 mm from beneath machine surface and presence of white layer was not noticed. Although tensile residual stresses were slightly higher using LN2 in relation to dry machining on surface, LN2 resulted in higher compressive residual stresses on subsurface, which can improve fatigue life of machined components in high cutting speed. The results showed that lower cutting parameters tend to present the best results regarding the aspects of cutting force and surface integrity.