Page 17 - MSAM-2-1

Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

A B

Figure 11. Tafel potentiodynamic polarization curves of selective laser melting-produced CoCrFeMnNi at 450 and 750 mm/s scanning speeds at AB
conditions (A) and HT conditions (B).

However, the tensile properties are lower compared
with the highest ultimate tensile strength and elongation
achieved by the traditional casting process, which were
reported to be 763 MPa and 57%, respectively.
3.4.2. Microhardness
Microhardness results for all four conditions, along with
the reported values in literature are shown in Figure 14.
It appears that the scanning speed does not affect the
microhardness of as-built samples. Both 450 AB and
750 AB conditions have practically the same hardness at
about 237 HV. In contrast, the microhardness after heat
treatment is significantly smaller for both 450 HT and 750
Figure 12. Summary of corrosion potentials for selective laser melting- HT conditions. However, the effect of heat treatment on
produced CoCrFeMnNi at 450 and 750 mm/s scanning speeds before and the 750 mm/s sample in terms of microhardness was more
after heat treatment.
pronounced. The hardness of the 750 AB sample decreased
by 15% while that of 450 AB sample decreased by only
strength after heat treatment is usually associated with 8.6% after heat treatment. Note that the microhardness
either the Hall-Petch effect , which establishes the inverse values for as-built materials are modestly higher than
[13]
relationship between grain size and tensile strength, or the hardness of 212 HV1 reported for SLM produced
with the formation of precipitates such as carbides along CoCrFeMnNi , and even higher compared to the DED
[66]
the grain boundaries and plate-like martensitic phases produced CoCrFeMnNi (195 HV5) and the cast and
[67]
which contribute to stress concentration , or with homogenized (C&H) CoCrFeMnNi (160 HV1) . In
[64]
[68]
residual stress caused by lattice distortion . The more addition, the obtained microhardness values are close to
[13]
obvious increase in ductility after heat treatment can be that reported for the same HEA produced by arc melting
attributed to the increase of grain size and reduction of and drop casting with cold rolling (AMDC&CR) of 21%
small-angle misorientation (shown in Figure 8), which is reduction (222 HV0.3) .
[69]
a clear indication of release of residual strain induced by
SLM process, and restoration of ductility. Note that the 3.4.3. Impact fracture
obtained tensile properties are in general on par with the The Charpy test results are depicted in Figure 15. Similar
reported values from SLM and laser DED processes under to the microhardness results, the laser scanning speed
the as-built condition. For instance, an ultimate tensile has little effect on how much energy has been absorbed
strength value of 601 MPa was achieved for SLM produced by 450 AB and 750 AB conditions. Both have almost the
CoCrFeMnNi without heat treatment , and an ultimate same value of 140 J. However, heat treatment generates
[65]
tensile strength value of 660 MPa was reported for laser noticeable influence on the impact fracture results - the
DED-produced CoCrFeMnNi without heat treatment . energy absorption for the 450 mm/s samples increased
[18]

Volume 2 Issue 1 (2023) 11 https://doi.org/10.36922/msam.42