PSI - Issue 13

Catrin M. Davies et al. / Procedia Structural Integrity 13 (2018) 1384–1389 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 4: (a) Schematic illustration of SEN(B) geometry (b) illustration of the SEN(B) finite element model mesh.

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Fig. 5: Tensile data employed in the FE analysis representing the AB and heat treated conditions in the vertical and horizontal orientations.

4. Results 4.1. Charpy Imapct Energy and Hardness Values

The influence of sample build orientation and heat treatment on the Charpy impact energy is shown in Table 1 and the corresponding average harness values are given in Table 2. Generally it can be seen that the Charpy impact energy for samples orientated in the vertical direction are around a factor of 3 less than that in the horizontal orientation. This suggests that crack growth parallel to the build layers requires much less energy than when the crack growth through the layers, and that the interface between the build layers are a source of weakness. However, crystallographic orientation and texture may also be a factor. It would be expected that heat treatment to higher temperatures would soften the material and thus increase its toughness. This is true when comparing the horizontal AB to 700 °C data, where the impact energy increases by around 40% after heat treatment. However for the 900 °C horizontal data significant variability is seen. Though one of the three 900 °C horizontal samples tested showed the highest impact energy two other samples have impact energies comparable to the AB conditions. This may be due to natural variability in Charpy impact toughness values together with the presence of porosity in these two samples. Note that the vertic al samples’ toughness appear to be unaffected by heat treatment, signifying that there is a weakness in this orientation, as previously discussed. The average hardness values of six measurements and an estimate in the error in the mean values are shown in Table 2. The hardness value maybe considered more of a volumetric measurement and therefore there is no significant variation in the hardness of the horizontal and vertically orientated samples. Furthermore the hardness does appear to decrease with the heat treatment temperature. However, more tests are required to ascertain these trends.