PSI - Issue 53

Serhii Lavrys et al. / Procedia Structural Integrity 53 (2024) 246–253 Serhii Lavrys et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Materials and methods AM Ti6Al4V titanium alloy samples were fabricated by selective laser melting method using a Concept Laser M2 equipment (3D Metal Tech LLC, Kyiv, Ukraine). Ti6Al4V titanium alloy powders (CL 41TI ELI) were supplied by GE Additive Concept-Laser GmbH (Lichtenfels, Germany) (Table 1). Conventional wrought Ti6Al4V samples with the same chemical compositions were acquired from a commercial supplier to compare their microstructure and anti corrosion characteristics with the AM samples. The chemical compositions of the Ti6Al4V powders and wrought samples are listed in Table 1 based on the supplier data sheets. As can be seen, the chemical compositions of the samples are nearly equivalent, enabling an accurate comparison.

Table 1. Chemical composition (wt.%) of Ti6Al4V titanium alloy powders for AM and wrought samples (based on the supplier's data sheet) Samples Al V Fe C N O H Ti Content, [wt.%] Powder (AM) 5.5…6.5 3.5…4.5 ≤ 0.25 ≤ 0.08 ≤ 0.03 ≤ 0.13 ≤ 0.012 balance Wrought 5.3…6.8 3.5…5.3 ≤ 0. 60 ≤ 0.10 ≤ 0.05 ≤ 0.20 ≤ 0.015 balance

Post HT for AM Ti6Al4V titanium alloy was carried out according to the following regime: 1. HT800°C: heating to 800°C, holding for 2 h, cooling to 500 ° C, holding for 0.5 h, furnace cooling to room temperature. Heat treatment was carried out in a vacuum at P = 10 – 3 Pa. 2. HT850°C: heating to 850°C, holding for 2 h, cooling to 750 °C, holding for 0.5 h, furnac e cooling to room temperature. Heat treatment was carried out in a vacuum at P = 10 – 3 Pa. The phase composition of surface layers was determined by X-ray diffraction (XRD) analysis using DRON-3.0 diffractometer in monochromatic CuK α radiation with Bragg – Brentano focusing. The surface microhardness was measured by means of Vickers indenter with a load of 50 g for 15 s. The metallographic analysis was performed using an «Epiquant» digital optical microscope. To reveal the microstructure the Kroll's reagent (3 mL of HF, 6 mL of HNO 3 , and 91 mL of H 2 O) was used. The electrochemical tests of AM and wrought Ti6Al4V alloys were carried out in 20 wt.% hydrochloric acid. Open circuit potential (OCP) was measured for two hours. The potentiodynamic polarization curves were recorded using an VersaSTAT 3 potentiostat-galvanostat in the range of potentials – 1.0...2.5 V vs. Ag/AgCl with a scan rate of 2 mV/s. The surface of the working electrode was covered with epoxy resin, leaving working surface of 1 cm 2 . The polarization characteristics were determined from the polarization curves by the Tafel extrapolation method. The electrochemical impedance spectroscopy (EIS) measurements were conducted at OCP conditions. The frequency range was from 10 – 2 to 10 4 Hz with a potential perturbation of 10 mV peak to peak. The EIS spectra were analyzed by Zview software. For the static immersion tests the samples with the dimensions of 10×10×20 mm were used. The weight of the samples was determined using an analytical OHAUS balance with an accuracy of ±0.1 mg. After the static immersion, the average corrosion rate of titanium sample was calculated according to ASTM Standard G31-72(2004) by an equation 1. The morphology of corroded specimens was observed by ZEISS EVO 40XVP scanning electron microscope (SEM).

A T D K W   

(1)

rate Corrosion

=

where K is a constant (8.76×10 4 ), W – weight loss in g, A – the exposed area of the specimen in cm 2 , T – the exposure time in hour, and D – the density in g/cm 3 .