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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

A B

C D E

Figure 16. Fracture surface analysis of a 450 AB Charpy sample after testing. (A) Overall observation showing large amount of cleavage facets; (B) a region
with dimples formed by normal and shear fractures; (C) a large cleavage facet; (D) a small cleavage facet; (E) colonies of unmelted particles inside a void.

inside either large voids or wide cracks, as shown in A B
Figure 16E. These colonies of unmelted powder particles
are surrounded by a smooth surface without cleavage steps
or river pattern suggesting that the cause of fracture in the
vicinity of unmelted powder particles is LOF.
Figure 17 shows low magnification image of surface of
the 450 and 750 samples before and after heat treatment.
There is a clear difference between the fracture surface
morphology before and after heat treatment. The amount
and size of cleavage facets of the HT sample are smaller C D
compared to the AB sample while more ductile dimples
can be observed on the surface of the HT sample. Both
materials have lots of slightly curved deep cracks with their
concave up direction pointing toward the deposit direction.
Their positions are generally aligned with a straight line
orthogonal to the deposition direction (marked as dashed
line), which suggests that they are situated on the same
deposited layer. In addition, almost all such cracks are free
of unmelted powder particles. The fact that these cracks
are found in HT samples as well suggests that the chosen Figure 17. Fracture surface of (A) 450 AB, (B) 450 HT, (C) 750 AB, and
heat treatment is not effective for the reduction of these (D) 750 HT Charpy samples showing wide cracks originated on lack of
defects, and perhaps hot isostatic pressing (HIP) treatment fusion defects.

Volume 2 Issue 1 (2023) 13 https://doi.org/10.36922/msam.42