PSI - Issue 18

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

544

7

3.3. Slow strain rate tests The engineering stress-strain curves for the bare and coated AZ31 samples tested in air and in SBF are reported in Figure 6 a and b, respectively. In addition, Table 3 compares the UTS and elongation at failure values obtained from the curves in Figure 6. a) b)

Figure 6. Engineering stress-strain curves of bare (a) and coated (b) AZ31 samples tested in air and SBF at 37°C and strain rate of 3.5ꞏ10 -6 s -1 .

Table 3. Mechanical properties of bare and coated samples from Figure 6.

In Air

In SBF

Surface

UTS (MPa) 256.3± 8.7 253.6± 5.6

Elongation at failure (%)

UTS (MPa) 233.3 ± 1.9 246.8± 1.0

Elongation at failure (%)

Bare

24.5 ± 0.7 24.1 ± 0.5

6.1 ± 0.3 19.7 ± 0.2

Coated

The surface characteristics did not influence the AZ31 mechanical properties when tested in air, being both the bare and coated samples characterized by an excellent and comparable combination of strength and ductility. On the other hand, the coated samples were characterized by a considerably higher elongation to failure than the bare counterparts when tested in SBF, indicating thus a lower tendency to suffer of embrittlement in SBF. To quantify the SCC susceptibility of the bare and coated samples, the I UTS and I Ɛ indices were evaluated and are reported in Figure 7.

Figure 7. SCC indices for the bare and coated AZ31 samples.

The SCC indices of the coated samples are lower than those of the bare samples. This suggests that a higher resistance to SCC in SBF is provided by the 100 nm thick ZrO 2 coating.