PSI - Issue 19

S. Periane et al. / Procedia Structural Integrity 19 (2019) 415–422

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S.Periane et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction

Super alloys are high-temperature materials used in turbines, rockets and heat exchangers. The first and foremost property was its ability to withstand loading at an operating temperature close to its melting point. In general superalloys which were of fcc matrix did not give strength but in addition, there was a presence of special strengthening phases, usually called as precipitates by Matthew J (2002). Aerospace industry showed more interest in the potential use of additive manufacturing for the production of super alloys by Carter L (2014). The Selective Laser Melting (SLM) was providing an ideal means for manufacturing complex geometrical features. Although the components were fabricated to the net shape in additive manufacturing, machining was required to meet the geometrical tolerances. The main factors that affect the cutting tool performance were high hardness, wear strength, the low thermal conductivity of the superalloys by Li L et al. (2002). The material used in this work was vertical oriented rectangular Inconel718 sample with the dimensions of 60mm by 10mm by 7mm modelled using magics software and fabricated by Selective Laser Melting (SLM). For the machining operation the cutting tool insert is 390R-070204E-ML 1040 grade with (Ti, Al)N 2 PVD coating from Sandvik. The reinforced strengthened cutting edge has a good stability for a wide range of cutting speed and feed conditions. The four point bending fatigue test was conducted using Instron 8872 equipped with servohydraulic actuator. The machine is completely controlled from computer via console software. 2. Materials and methods The fatigue samples were modelled using Materialise magics builds processor shown in figure 1 (a) and then fabricated by SLM 125 HL machine. From the fabrication point of view, a maximum of 24 samples can be fabricated in one pattern for the vertical orientation samples. The building duration is about 16 hrs and 30 mins and a distance of 12 mm was maintained between each sample shown in figure 1 (c). The powder used for fabrication was gas atomized fine pre alloyed Inconel 718 shown in figure 1 (b) composing of 55% Ni, 21% Cr, 1.0% Co, 0.20% Al, 5.5% Nb, 3.3% Mo, 1.15% Ti and balance is Fe in weight percentage. The video granulometry analysis of the Inconel 718 powder was done using Horiba Camsizer X2. The laser power used for the fabrication is 100 W with scanning speed ranging from 100 to 1200 mm/s. The hatch distance of 120 µm, spot size 40µm and layer thickness of 50 µm with minimum scanning time of 12 seconds. The fabrication was done in a controlled nitrogen atmosphere at a preheated temperature of 200°C using stripes pattern. Since the samples after SLM fabrication has more porosity with a density of 99.97%, to attain 99.99% density the samples were subjected to Hot Isostatic Pressing (HIP) and then Aeronautic Heat Treated (AHT). After performing these two different heat treatments the samples were machined. 3. Experimental methods

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b) c) Fig. 1. (a) CAD model; (b) SEM image of Inconel 718 powder; (c) SLM fabricated samples