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The adhesion properties of powder particles could profoundly influence the quality of parts made by Additive Manufacturing (AM) processes. Accurate experimental characterization of adhesion and the spatial surface adhesion distribution of a single microparticle has been a significant challenge, due mainly to difficulties associated with the micro-scale handling/manipulation in a controllable manner and uncertainty in the nature of micro/nano-scale contacts. In current work, an approach for determining the spatial energy/adhesion distribution on the surfaces of single microparticles used in AM is introduced and demonstrated using Molybdenum (Mo) metal particles as model particles. Both ultrasonic base and Surface Acoustic Wave (SAW)-based excitation techniques coupled with laser Doppler vibrometry are utilized to excite and acquire the vibrational rocking motion and to drive the rolling motion of single Mo particles on a Silicon (Si) substrate in a controllable manner and, thereby determining the spatial adhesion distribution on the particle surfaces. Spatial surface energy distribution data of microparticles could be utilized in Discrete Element Method (DEM) simulations as a statistical input for simulating local powder bed dynamics with increased accuracy, which would potentially lead to more predictable AM processes. [ABSTRACT FROM AUTHOR]

At nano/micro-scales, the resistance of a particle to rolling is a critical factor in many applications and biological phenomena as it affects particle adhesion, motion and flow as well as particle manipulation (e.g. picking and placing of microparticles). In present work, a non-contact non-invasive experimental method is detailed and applied to determine the pre-rolling critical leaning angle (CLA) of single microparticles. Transient Rayleigh surface acoustic waves (SAW) are utilized as the excitation mechanism and interferometry and image processing as detection/monitoring and analysis techniques for capturing the micro/nano-scale dynamics of the microparticles. The CLA values for a set of 30 PSL (polystyrene latex) microparticles with a diameter of 14.9 ± 0.6 μm on a soda-lime glass substrate are reported. The CLA of the studied particles are determined to be between 0.9 and 7.8°. It is also observed that during a SAW field burst cycle, microparticles could change their drifting (rolling and/or sliding) directions, speeds and accelerations. The trajectory of a particle is often found to be non-linear. This nonlinear behavior is attributed to the inhomogeneity of the surface properties of the particles and the substrate as well as possible electric charge density, chemistry variations and potential contamination on surfaces. Moreover, the effect of electric charge (developed due to the triboelectric effect) on the particle drifting motion is investigated. It is found that the percentage of drifting particles is not only a function of the amplitude of the excitation field but also a function of possible electrostatic charges developed on the particles due to the drifting motion on the substrate. In addition to their potential uses in particle manipulation, removal and adhesion characterization, the reported results could be utilized in numerical simulations of microparticle motion and deposition. [ABSTRACT FROM AUTHOR]