Page 41 - MSAM-2-2

Materials Science in Additive Manufacturing Tensile and fatigue properties of Ti6Al4V SLM parts

Figure 6. Left: Poor grinding of fatigue specimen. Right: Good grinding of fatigue specimen.

surface quality. When a surface is rough, there is a
reduction in tensile strength as these rough surfaces cause
stress concentrations that may lead to crack initiation and
propagation.

4.2.3. Impact of surface treatment on tensile
property

Finally, we compared sandblasted and non-sandblasted
specimens. Based on the experimental results, the tensile
strength of sandblasted specimens and non-sandblasted
specimens is negligible (0.8% difference for 30-μm layer
Figure 7. Graph of Log S versus Log N. thickness and −0.4% difference for 130-μm layer thickness).
Although it is expected for the sandblasted specimens to
have a better tensile strength due to better surface quality,
this may be due to experimental variability. In future, the
tensile tests should be repeated at least 3 times for each
parameter configuration.
Theoretically, vertical build orientation has poorer
mechanical properties as compared to horizontal build
orientation due to the weak interlay bonding strength
along the z direction and discreet grain structure across
layers along the z direction. However, in future, if
Figure 8. Left: Specimens printed in parallel causes more warping. Right: specimens are to be printed for fatigue testing validation
Specimen printed in diamond shape.
with default SLM printing parameters, the specimens
should be printed vertically. This reduces the need for any
horizontal orientation tend to produce parts with the form of support structure for the dog bone-shaped test
highest tensile strength as this orientation results in piece. Removing the need for supports reduces additional
the formation of a more continuous and aligned grain external factor of inconsistent and poor grinding. Even
structure. This orientation also typically results in the when the samples were sent for machining/milling,
lowest anisotropy. The specimens printed using vertical this additional need for machining not only wastes
build orientation have lower tensile orientation as there is resources, but may also induce microcracks within the
a less continuous grain structure, with each layer acting as structure. A disadvantage of vertical samples is that a tall
a potential weakness in the part. However, this orientation build requires a lot of metal powder for manufacturing
may be advantageous for parts that require high even if the excess could be recycled. Instead, another
compressive strength. As for a flat build orientation, it is method could be to use CT scans or X-rays to see the
theoretically supposed to have the best tensile strength out defects even before the fatigue testing so that any
of the three orientations. Although it is a microstructure scatter or discrepancies in results could be analyzed and
similar to the horizontally oriented specimens, it has a substantiated.
larger surface area with the build plate, meaning that
Severe warping could be seen on all printed products.
there is faster and more even cooling . This leads to the Heat treatment should be done to mitigate stress
[29]
reduction of residual stresses in the specimen, which may concentrations and reduce the warpage before removed
justify its better tensile strength.
from the base plate. There should be an optimized
In post-processing, we compared the effect of orientation to arrange the specimens on the plate such that
sandblasting on tensile strength. Sandblasting improves the entire substrate plate does not warp.

Volume 2 Issue 2 (2023) 8 https://doi.org/10.36922/msam.0912