Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion resistance and high mechanical properties that are maintained up to elevated temperatures (600-800 °C). However, these superalloys are classified as difficult-to-cut and therefore modelling and simulation of the machining processes has become a key in the machinability assessment of nickel based alloys. The reliability of Finite Element Models (FEM) largely depends on the quality of input parameters, one of the most relevant being the constitutive material model representing work material behavior under high strain, strain rate and tempera-tures.In order to develop a reliable material model, the present work deals with a complete characterization of Inconel 718. Uniaxial compression tests at testing temperatures close to those found in machining (21-1050 °C) and high strain rates (10°−10 2 s −1 ) were performed on the Gleeble 3500 testing machine. Moreover, the microstructural analysis and microhardness measurements of the testing samples were performed, in order to correlate the microstructural state with the mechanical properties of the Inconel 718. Based on this experimental work, a new coupled empirical model is proposed to describe the particular behaviour of nickel based alloys at elevated temperatures and high strain rates. This material behaviour model introduces softening phenomena as well as the coupling between the temperature and the strain rate known to occur experimentally, for machining FEM simulations with Inconel 718 superalloy.

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Titanium alloys are widely employed in many aerospace components due to their high strength-toweight ratio, good corrosion resistance and fatigue properties, maintained at relatively high temperatures. Nevertheless, machining these materials efficiently has become a challenge in a sector that demands high productivity rates and minimal manufacturing times. This work analyses the machinability of the α + β Ti-6Al-4V alloy in rough turning. Since oxygen is one of the elements that most affects the mechanical properties of titanium alloys, the aim is to understand its influence on the machinability of these materials. To do so, two different oxygen contents of 1200 and 2000 ppm are tested. A comprehensive material characterisation of both materials is carried out in order to clearly establish their differences: chemical composition, microstructure and mechanical properties (yield strength and hardness of the phases by nanoindentation). Machining trials consist of (i) tool life tests, which include a tool wear analysis, and (ii) cutting fundamental turning tests, in which the cutting forces and the chip form are studied. The work concludes that Ti-6Al-4V alloy with the highest oxygen content has the worst machinability (~15 % lower compared to lowO), due to its higher volume fraction of β + α s phase, slightly harder α p and greater yield strength, which generates higher mechanical and thermal tool wear. Thus, oxygen is a key composition element that should be controlled in machining titanium alloys, if robust results in tool life are expected to be obtained. Nomenclature Symbol Description UnitsMaterial characterisation T β Beta-transus temperature (phase transition) ºC ε True strain () σ True stress MPa UTS Ultimate tensile strength MPa YS Yield stress MPa YS 0.2 Yield stress for a plastic deformation of 0.2 % MPa Machining tests E Activation energy J mol −1 V b Average flank wear mm α Clearance angle°A c Contact area on the rake face mm 2 Q Cooling flow l min −1 P Cooling pressure bar * Irantzu Sacristan isacristan@mondragon.edu;

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