PSI - Issue 53

A. Teixeira et al. / Procedia Structural Integrity 53 (2024) 352–366 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental procedures 2.1. Workpiece material and cutting inserts 2.1.1. Workpiece material

The Inconel 718 alloy was supplied in the form of 3 cylindrical rods with a length of 120 mm and diameter of 50 mm. The alloy was subjected to a heat treatment according to the AMS 5663 standard: solution annealing at 968°C followed by rapid cooling in water, and precipitation hardening at 718°C for 8 hours, and then subjected to a furnace cooling until reaching 620ºC. The material is then held at 620 ºC for a total aging time of 18 hours. The chemical composition was evaluated by arc/spark optical emission spectrometry using a spark emission spectroscopy, the SPECTROMAXx metal analyser equipment. The results obtained by the analysis are presented in Table 1, allowed to verify that the chemical composition of the alloy is within the range established by the standard.

Table 1. Chemical composition (wt %) of IN718 alloy.

Element

Ni

Cr

Fe

Nb

Mo

Ti

Al

C

Si

Percentage (wt%)

54.30

17.63

17.77

4.89

2.92

0.907

0.552

0.321

0.149

The workpiece material’s microstructure was also evaluated. Samples from the material were cut and hot-mounted in thermoset resin, to then be subjected to grinding and polishing operations. After polishing, samples were etched with Kallings reagent, and then were observed through a metallurgical microscope OLYMPUS PMG3. Etching enabled the visualisation of different phases and grain structures, as shown in Fig. 1. Fine precipitates along the γ matrix were found which are responsible for strengthening Inconel 718.

Fig. 1. Optical microscopy image of the INCONEL 718 after chemical etching.

In addition to microstructure characterization, compression tests were devised and carried out. This was performed to obtain the stress-strain curves, that portray the material’s behaviour under extreme deformation levels. These curves can also be used to calibrate the material’s model in the simulation software. To perform these compression tests, circular cylinders, having 6 mm diameter and 10 mm in height, were cut from the workpiece material, using wire electric discharge machining (EDM). These test specimens were then placed in a compression electromechanical testing machine (INSTRON 5900R), with force and displacement values being acquired by a load cell connected to a data acquisition system and a computer. 2.1.2. Cutting inserts Cutting insert CNMG 120402-GSF is a WC tool coated with TiAlSiN having a chemical composition of 51% Ti; 18% Al; 28% N; 3% Si and a 3 µm thickness. Cutting insert has 7% of Co content, 1-2% of γ phase (mainly composed by TaC, NbC and TiC) with the remaining being WC, and has a grain size of approximately 0.8 µm. This insert has a