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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

A B

Figure 13. Tensile properties of selective laser melting produced CoCrFeMnNi at 450 and 750 mm/s scanning speeds before and after heat treatment.
(A) Room temperature stress-strain curves; (B) ultimate tensile strength and elongation.

Figure 14. Microhardness results for selective laser melting-produced Figure 15. Energy absorption during Charpy test for selective laser
CoCrFeMnNi at 450 and 750 mm/s scanning speeds before and after heat melting-produced CoCrFeMnNi at 450 and 750 mm/s scanning speeds
treatment, along with the microhardness values reported in literature. [66-69] before and after heat treatment, along with the reported absorption
energies in literature [22,71] . Note that the DED result was obtained at 0°C.
[71]
by 15.6%, while that for the 750 mm/s samples increased
by 11.1%. The absorbed impact energy of both HT are cleavage facets whose presence indicates brittle type
and untreated samples are noticeably smaller than fracture [43,71] . Cleavage facets are surrounded by region
the energy absorbed by VIM-produced CoCrFeMnNi that consists of dimples and microvoid coalescence of a
(approximately 200 J) which, in turn, is half that of the submicron size. Abundance of dimple pattern is a typical
[22]
forged Al CoCrFeNi . On the other hand, Charpy results characteristic of ductile fracture, which is related to the
[70]
x
of the current study are significantly higher compared to coalescence of microvoids. The microvoids can form due to
CoCrFeMnNi sample made by DED whose impact energy decohesion between second-phase particle and matrix .
[43]
was measured to be only 50 J at 0°C . This toughness High magnification image in Figure 16B of dimple pattern
[24]
reduction of SLM-produced samples compared to the cast shows that they were formed by both normal and shear
samples can be attributed to the presence of defects, such ruptures. When the SEM electron probe hits inclined edge
as pores, impurities, and brittle, non-equilibrium phases. of a dimple, more of secondary electrons escape from it
The latter two were not observed in the present work but than from the flat surface of cleavage facets. This leads to
the existence of defects, such as LOF and micro-cracks, so-called edge effect leading to brighter appearance of the
described above may explain such toughness reduction. region that surrounds cleavage facets . Figure 16C and D
[72]
To better understand the impact behavior, fracture shows two cleavage facets whose size differs roughly by
surface images of 450 and 750 mm/s samples, both before an order of magnitude. The smaller one demonstrates
and after heat treatment, were studied. Higher magnification clearly defined cleavage steps, river pattern and dimples
SEM images reveal features that are characteristic for both surrounding the cleavage area, which are similar to the
ductile and brittle fracture. For instance, Figure 16A shows features observed on the fracture surface of AlCoCrCuFeNi
that vast area of fracture surface is dominant by large dark HEA . Besides, unmelted powder particles are observed
[71]
islands with average size of 50 – 150 μm surrounded by a on fracture surface of all studied samples. In most cases,
texture that appears brighter. The observed flat dark islands they are found in a colony of conglomerated particles,

Volume 2 Issue 1 (2023) 12 https://doi.org/10.36922/msam.42