Page 38 - MSAM-2-2

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

2.5.1. Optical microscope Table 3. Key process parameters for Ti6Al4V specimens

Samples were observed under the light optical microscope Layer thickness Hatch distance Laser power Scanning speed
Olympus SZX16. The specimens were observed under ×0.7 30 μm 120 μm 280 W 1475 μm/s
magnification so that the entire fractured surface can be 550 W
captured and analyzed. As the fractured specimen is about 130 μm 150 μm 1000 μm/s
10-cm tall, the microscope had to be balanced on 2 metal
blocks so that the minimum focal length is appropriate for Table 4. Tensile measurements of Ti6Al4V specimens
the specimen. The specimen was placed on a plasticine Specimen Ultimate tensile Young’s
block to keep it in place during the microscopy. strength (MPa) modulus (GPa)

2.5.2. Laser scanning microscope 30-V-N 1145.43 109.70
30-V-SB 1185.75 106.00
Laser scanning microscope LEXT OLS4100 was used
to observe the more minute details on fractured surface, 30-H-N 1150.64 90.12
which cannot be achieved with optical microscope. The 30-H-SB 1129.38 152.49
specimens were observed under ×5, ×10, ×20, ×50, and 130-V-N 1130.92 106.53
×100 magnifications. Keyence Laser Scanning Microscope 130-V-SB 1016.93 (slipped)
was also used to quantify surface roughness. 130-H-N 1071.5 96.63

2.5.3. Scanning electron microscope 130-H-SB 1082.82 80.34
Notes: “V” stands for building the specimen in the vertical direction;
Scanning electron microscope JEOL 5600LV was used “H” stands for building the specimen in the horizontal direction;
to observe the fractured surface with extremely high “N” stands for testing the samples as as-build condition; “SB” stands for
resolution. For this experiment, samples were observed in testing the samples after sandblasting
up to 3000× magnification. To fit the vacuum chamber to
observe the fractured surface, the specimen had to be cut with 30-μm layer thickness is 1140.0 ± 15.0 MPa. The
into a 1 cm-by-1 cm cube. This was cut using CUTLAM average UTS of specimens printed vertically with 30-μm
micro 1.1 metallography cutting machine with a diamond layer thickness is 1165.6 ± 28.5 MPa. The average UTS
wheel cutter. of specimens printed horizontally with 130-μm layer
thickness is 1177.2 ± 8.0 MPa. The average UTS of
3. Results specimens printed vertically with 130-μm layer thickness

3.1. Relative density is 1073.9 ± 80.6 MPa. The average UTS of specimens with
as-build condition printed with 30-μm layer thickness is
The relative density of both Ti6Al4V samples built with 1148.0 ± 3.7 MPa. The average UTS of specimens with
30-μm and 130-μm layer thicknesses was measured with sandblasted condition printed with 30-μm layer thickness
the optical microscope. Key process parameters for both is 1157.6 ± 39.9 MPa. A 0.8% increase in average UTS
layer thicknesses are listed in Table 3. The same key process was observed when specimens were printed in 30-μm
parameters were used to produce the rest tensile and layer thickness. The average UTS of specimens printed
fatigues samples. horizontally with 130-μm layer thickness is 1101.2 ± 42.0
The density of Ti6Al4V samples built by 30-μm layer MPa. The average UTS of specimens printed vertically
thickness is 99.97 ± 0.02 % (n=8). The density of Ti6Al4V with 130-μm layer thickness is 1049.9 ± 46.6 MPa. A 0.4%
samples built by 130-μm layer thickness is 99.96 ± 0.02 % decrease in average UTS was observed when specimens
(n=8). were printed in 130-μm layer thickness.

3.2. Tensile property A t-test with two-sample assuming unequal variances
was run for tensile properties of the samples between
The tensile properties of both Ti6Al4V samples built by those built in 30-μm layer thickness and those built in
30- and 130-μm layer thicknesses are given in Table 4. 130-μm layer thickness. After calculation, the test statistic
Both UTS and Young’s modulus of all tensile samples were was obtained as 2.944. The one-tail p-value (T ≤ t) is
measured and recorded. 0.0211 and two-tail p-value (T ≤ t) is 0.0422. Since the

The average UTS of specimens with 30-μm layer two-tail p-value (T ≤ t) is 0.0422, which is more than 0.01,
thickness is 1152.8 ± 23.8 MPa. The average UTS of the null hypothesis is accepted, and it is assumed that no
specimens with 130-μm layer thickness is 1075.5 ± 46.8 significant difference exists between the two groups of
MPa. The average UTS of specimens printed horizontally samples.

Volume 2 Issue 2 (2023) 5 https://doi.org/10.36922/msam.0912