PSI - Issue 7

C. Garb et al. / Procedia Structural Integrity 7 (2017) 497–504 C. Garb et Al. / Structural Integrity Procedia 00 (2017) 000–000

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tomography (CT) analyses of all three specifications (Table 2) are executed to support the characterization of the occurred micropore shapes and sizes in the several specimen location volumes. In Fig. 5 a shrinkage pore of the fractographic analyses from cc AlSi8 Sr T6 Pos. 2 is shown. Fig. 6 depicts an example of a micropore from the CT analyses reflecting the complex shape of a shrinkage pore. At room temperature, all tested specimen indicate a crack initiation induced by micropores or respectively, a defect induced failure.

Fig. 5 SEM-picture of a shrinkage pore, a max = 407 µm

Fig. 6 CT-picture of a shrinkage pore, a max = 640 µm

The fractographical results of the specimens tested at 150 °C reveal a different failure mechanism allocation. The specification ch AlSi8 Sr T5 Pos. 1 shows a significant change of the failure mechanism, whereby over 46 % of the specimens highlight a slip band induced failure. For cc AlSi8 Sr T6 Pos. 1, over 11 % of the specimen exhibit slip band induced failure, only the cc AlSi8 Sr T6 Pos. 2 exclusively shows defect induced crack-initiation at the fractographical surface of the specimen.

Fig. 7 Comparison of the causes of failure of the different specifications at room temperature and 150 °C

Fig. 8 Comparison of the different micropore sizes of the specifications for room temperature (RT) and 150 °C

In addition, considering the results of the quasi-static tests, listed in Table 2 and Table 3, the elongating at break A reveals a significant increase at 150 °C for ch AlSi8 Sr T5 Pos. 1 and cc AlSi8 Sr T6 Pos. 1, but stays at the same level for cc AlSi8 Sr T6 Pos. 2. It should be also taken into account that the specification 1 differs in the heat treatment compared to specification 2 and 3, so there is not only a specimen location and component difference, but also a difference in the material properties. In Fig. 7 the shares of the different failure mechanism are displayed, comparing the three specifications at room temperature and 150 °C. Every detected micropore, which causes a failure of the specimen, is measured and the results of the failure induced defect sizes are listed in Table 4. These results are displayed and compared in Fig. 8. Examples for occurred slip bands on fractographical surfaces of the