PSI - Issue 18

Mirco Peron et al. / Procedia Structural Integrity 18 (2019) 538–548 Author name / Structural Integrity Procedia 00 (2019) 000–000

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behaviour in order to understand the different mechanical behaviour. 2. Materials and methods 2.1. Materials and environment

AZ31 Mg alloy was supplied in form of commercially available bars. The microstructure of the material in the as received condition is shown in Figure 1 and consists of a quite homogeneous α matrix. The initial grain size was measured by linear intercept method and resulted equal to 13.2 ± 8 μm.

Figure 1. Microstructure of the AZ31 alloy in the as-received condition.

The test medium was a simulated body fluid (SBF) prepared according to Ref. (Kokubo and Takadama 2006) and whose composition is reported in Table 1.

Table 1. Reagents and their quantities for preparation of 1000 ml of the SBF solution according to (Kokubo and Takadama 2006).

Reagents

Amount 8.035 g 0.355 g

NaCl

NaHCO 3

KCl 0.225 g K 2 HPO 4 ꞏ3H 2 O 0.231 g MgCl 2 ꞏ6H 2 O 0.311 g 1.0 M -HCl 39 ml CaCl 2 0.292 g Na 2 SO 4 0.072 g Tris 6.118 g

2.2. Atomic Layer Deposition The deposition of a ZrO 2 layer was performed in a commercial ALD reactor (Savannah S200, Veeco Instruments Inc., Massachusetts, USA) through successive cyclic reactions between Tetrakis (dimethylamino) zirconium (TDMAZ) and deionized water (H 2 O) at 160 °C with 926 cycles for a total thickness of 100 nm. Each cycle was composed of two parts. The first part consisted of a 250-ms TDMAZ precursor pulse and a 10-s Hi-purity N 2 purge with a flow rate of 20 sccm to remove residual reactants and by-products from the chamber so as to prevent any additional chemical vapor deposition reactions. The second part comprised a 150-ms H 2 O precursor pulse and a 15-ms Hi-purity N 2 purge.