PSI - Issue 23

Mattias Calmunger et al. / Procedia Structural Integrity 23 (2019) 215–220

217

M. Calmunger et al. / Structural Integrity Procedia 00 (2019) 000–000

3

View II

Fracture surface

View III

Initiation point

Initiation point

View I

Polished cross section

Marker

Marker

Fig. 1. Illustration of how the specimens were cut. A piece of material far away from the fracture surface was used to study general microstructure (view I). The fracture surface was cut through the crack initiation point and polished to allow investigation of the microstructure adjacent to identified features on the fracture surface (view II and III).

3. Results and discussion

3.1. General microstructure of the AM material

Figure 2 and 3 show cross sections from specimens built in the 0 ◦ and 90 ◦ directions, both tested at ∆ ε = 1 . 3 %. Both are displayed according to view I (see Fig. 1). Figure 2 and 3 contain ECCI images as well as a compound image consisting of an EBSD map overlayed on an ECCI image; in addition, the melt pool boundaries have been filled in using the LOM pictures described in section 2. Solidification occurs, at least partially, by the nucleation and growth of bundles of cellular dendrites which extend through several melt pools Wang et al. (2016). Note that the cellular dendrites, although visible in the ECCI image, cannot be resolved by the EBSD map, see Fig. 2. For the specimen tested in the 0 ◦ build direction at ∆ ε = 1 . 3 %, the crack propagation direction coincided with the build direction.

a)

Build direction

100 µm

b)

111

001

101

100 µm

Crack initiation occured from this side

Fig. 2. Specimen built in the 0 ◦ tested in LCF at ∆ ε = 1 . 3 %: a) ECCI image and b) EBSD map overlayed on the ECCI image. The melt pool lines have been outlined in b). Crack propagation direction coincided with the build direction.