Impact of atomization gas on characteristics of stainless steel powder feedstocks for additive manufacturing
Open Access
- Author:
- Gao, Mingze
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 20, 2020
- Committee Members:
- Todd Palmer, Thesis Advisor/Co-Advisor
Jayme Scot Keist, Committee Member
Andrea Paola Arguelles, Committee Member
Reginald Felix Hamilton, Committee Member
Bellamarie Ludwig, Special Signatory
Judith Todd Copley, Program Head/Chair - Keywords:
- Powder Characterization
Powder Rheology
316L Stainless Steel
Discrete Element Modeling
Additive Manufacturing - Abstract:
- Powders are primary feedstock materials for most of additive manufacturing processes. The characteristics of powder are essential for bulk powder behaviors, such as flow and packing, and can eventually impact the quality of the fabricated components. Even though the characteristics of powder are closely related to its atomization conditions, the impact of atomization gas on the powder characteristics has not been sufficiently studied. The characteristics of three 316L austenitic stainless-steel powders, gas atomized with nitrogen or argon, were investigated. The particle size distributions of the powders are nearly identical. Even though there is no obvious difference in SEM images of the powders, particle morphology was quantified in details, such as convexity, aspect ratio and circularity, to explore if there are subtle differences in the powders. Convexity and circularity showed no considerable difference. Compared with nitrogen atomized powders, argon atomized powder has 10% more particles with aspect ratio close to one, which indicates there are 10% more highly spherical particles in argon atomized powder. Particles were found to be less spherical as the particle size increases from 10 to 35µm, and this trend is observed on all the powder samples. Traditional powder packing measurements, apparent density and tap density, indicated that argon atomized powder exhibits slightly higher packing density compared with nitrogen atomized powders. Even though traditional flowability measurements, flow rate and angle of repose, showed no difference in the powders, rheological flowability measurements showed considerable differences. Argon atomized powder showed 5 degrees lower avalanche angle, which can be correlated to the 10% more highly spherical particles. It was also demonstrated that particles with lower aspect ratio exhibit higher interparticle force by numerical simulations. Internal porosity in powder particles was found to impact basic flow energy measurements. Due to the exist of internal porosity, the true volume of the powder is reduced, and less energy is needed to keep the powder flowing. The local void size distribution of powder bed was accessed by micro-CT. Permeability of powder bed tends to be more dependent on the local void size than bulk packing density, and the difference in local void size can be correlated to a small difference in particle size.