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Materials Science in Additive Manufacturing Bi-modal powder spreading behavior of ceramics

resolution of 0.001 mm was used to record the dimensions significant when p<0.05. If the data failed the normality
of the printed samples. The mass of the samples was check, group medians were compared with a Kruskal–
measured on a scale with a resolution of 0.001 g. Based Wallis one-way ANOVA on ranks to determine whether
on the recorded dimensions and mass, and the theoretical significant differences existed.
density of the alumina, the relative density of the samples
was calculated from Equation VIII: 3. Results and discussion
m s 3.1. Powder morphology and flowability
V
ρ = ρ alumina (VIII) After analyzing the apparent density and tap density, the
R
Hausner ratio and Carr’s index of the unimodal powders
where ρ is the relative density, m is the mass of the were calculated. Furthermore, the angle of repose was
s
R
sample, V is the volume of the sample, and ρ alumina is the measured for the powders. Figure 3 depicts all the values.
theoretical density of alumina, which is 3.96 g/cm . Hausner ratio, Carr’s index, and the angle of repose
3
increased as the powder size and temperature decreased.
2.7. Statistical analysis Except for the 1 µm powder, all the other powders showed
All statistical analyses were performed in Minitab passable flowability at elevated temperatures in terms
67
(version 21.2, Minitab LLC, State College, PA, USA). Prior of the Hausner ratio as classified by Kaleem et al. In
to hypothesis testing, the Shapiro-Wilk test (α = 0.05) addition, 1 µm powder has the lowest change in Hausner
was applied to each data set to verify normality. When ratio due to temperature change while displaying poor
the normality assumption was held, group differences in flowability at both temperatures. This smaller change for
powder size distribution, powder bed packing density, and 1 µm powder can be attributed to the agglomeration of the
green part relative density were evaluated with a one-way smaller powder, which then acts as a larger particle. On the
analysis of variance (ANOVA) conducted at a global two- contrary, the 20 µm powder exhibits excellent flowability
sided significance level of α = 0.05; effects were considered at elevated and room temperatures. In addition, the

A B

C D

Figure 3. Different mechanical characteristics. (A) Hausner ratio, (B) angle of repose (AOR), (C) relative density, and (D) Carr’s index, of alumina powders
of varied sizes: 1 µm, 5 µm, 10 µm, and 20 µm. Note: X indicates the unsuccessful data collection of AOR for 1 µm powder at room temperature

Volume 4 Issue 2 (2025) 6 doi: 10.36922/MSAM02510016