Journal of Materials Processing Technology 211 (2011) 1590–1598 Contents lists available at ScienceDirect Journal of Materials Processing Technology j o ur nal ho me p age : www.elsevier.com/locate/jmatprotec Dry machining of Inconel 718, workpiece surface integrity A. Devillez, G. Le Coz, S. Dominiak, D. Dudzinski ∗ Laboratoire d’Etudes des Microstructures et de Mécanique des Matériaux, UMR CNRS No. 7239, Université de Metz, Ile du Saulcy, 57045 Metz, France a r t i c l e i n f o Article history: Received 6 January 2010 Received in revised form 15 April 2011 Accepted 25 April 2011 Available online 6 May 2011 Keywords: Inconel 718 Dry machining Surface integrity Cutting forces Roughness Residual stresses Microhardness a b s t r a c t In the machining of Inconel 718, nickel based heat resistant superalloy and classified difficult-to-cut material, the consumption of cooling lubricant is very important. To reduce the costs of production and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This goal can be achieved by using coated carbide tool and by increasing cutting speed. The present paper firstly reviews the main works on surface integrity and especially residual stresses when machining Inconel 718 superalloy. It focuses then on the effect of dry machining on surface integrity. Wet and dry turning tests were performed at various cutting speeds, with semi-finishing conditions (0.5 mm depth of cut and 0.1 mm/rev feed rate) and using a coated carbide tool. For each cutting test, cut- ting force was measured, machined surface was observed, and residual stress profiles were determined. An optimal cutting speed of 60 m/min was determined, and additional measurements and observations were performed. Microhardness increment and the microstructure alteration beneath the machined sur- face were analysed. It is demonstrated that dry machining with a coated carbide tool leads to potentially acceptable surface quality with residual stresses and microhardness values in the machining affected zone of the same order than those obtained in wet conditions when using the optimised cutting speed value; in addition, no severe microstructure alteration was depicted. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nickel based superalloys are widely employed in the aerospace industry, in particular in the hot sections of gas turbine engines; this is due to their high temperature strength and high corrosion resis- tance. They are known as being among the most difficult-to-cut materials. In machining difficult-to-cut materials, the consumption of cooling fluids remains very important. The coolant acquisition, use, disposal and the cleaning of the machined components lead to significant costs, up four times the one of consumable tooling used in cutting operations. The goal for the machining manufacturers is then to move toward dry cutting by eliminating or minimising the cutting fluids use and to improve material removal rate with high speed machining. In the following, attention is focussed on the Inconel 718 alloy. Due to the low machinability of this material, the worked surface and subsurface are easily affected or damaged during the machin- ing operations. To ensure the better surface integrity, a special care must be taken when choosing cutting conditions, tool material and geometry, and tool coating. Surface integrity is important for the components submitted to high thermal and mechanical loads during their use (Axinte and Dewes, 2002). Structures in aerospace applications are subjected ∗ Corresponding author. Tel.: +33 387 374 286; fax: +33 387 315 366. E-mail address: daniel.dudzinski@univ-metz.fr (D. Dudzinski). to severe conditions of stress, temperature and hostile environ- ments. Section size is continually reduced in order to minimise weight; then, surface condition has an ever-increasing influence on the performances of the components. Service histories and fail- ure analyses of dynamic components show that severe failures, produced by fatigue, creep and stress corrosion cracking, almost always start or nucleate on or near the surface of components and their origins depend to a great extent on the surface quality. Hence, much attention should be paid to surface characteristics of compo- nents, that was pointed first by Field and Khales (1971) and then by Arunachalam et al. (2004) about machining Inconel 718. Overheating/burning, surface irregularities, Build-Up-Edges or deposits of debris, macro- and microcracks, cavities, microdefects such as laps and inclusions, metallurgical alterations including microstructural distortion, phase transformations, heat affected layers, tensile residual stresses are the main problems identified. Such changes occur due to thermal and mechanical loads during machining. Surface integrity involves surface finish (roughness and waviness), macro- and microstructure and hardness of the surface, microhardness variations, structural changes in the machined sur- face layer and residual stresses (Field and Khales, 1971). Brinkmeier et al. (1982) gave a good overview of the subject of residual stresses, their measurement and causes in machining processes. Guo et al. (2009) presented an interesting review of the state-of- art on surface integrity characterization and prediction, especially the characteristics of residual stresses in machining of hardened steels and of difficult-to-cut alloys. 0924-0136/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2011.04.011