Louis-Philippe Lefebvre

Characterizing powder feedstock is crucial for ensuring the quality and reliability of parts produced through metal additive manufacturing (AM). The morphology of particles impacts the flowability, packing density, and spreadability of powders, affecting productivity and part quality. A new methodology has been developed to classify particle morphological features in AM powder feedstocks, such as spherical or elongated shapes, and the presence of satellites and facets. This approach uses multiple descriptors for quantitative evaluation. The results from shape descriptors can vary based on image resolution, gray/color thresholding, and software algorithms. There are various commercial systems available for characterizing particle shape, some of which use images taken of static particles, while others use images of particles in motion. This diversity can lead to differences in powder characterization across laboratories with different equipment and methods. This paper compares results from a particle classification approach using two software programs that work with metallographic images with those from an automated static particle analyzer. While traditional methods offer higher resolution and precision, this study shows that automated systems can achieve similar particle shape classification using different shape descriptors and thresholds.

Characterizing powder feedstock is crucial for ensuring the quality and reliability of parts produced through metal additive manufacturing (AM). The morphology of particles impacts flowability, packing density, and spreadability of powders, affecting productivity and part quality. A new methodology has been developed to classify particle morphological features in AM powder feedstocks, such as spherical or elongated shapes, and the presence of satellites and facets. This approach uses multiple descriptors for quantitative evaluation. The results from shape descriptors can vary based on image resolution, grey/colour thresholding, and software algorithms. There are various commercial systems available for characterizing particle shape, some of which use images taken of static particles, while others use images of particles in motion. This diversity can lead to differences in powder characterization across laboratories with different equipment and methods. This paper compares results from a particle classification approach using two software programs that work with metallographic images with those from an automated static particle analyzer. While traditional methods offer higher resolution and precision, the study shows that automated systems can achieve similar particle shape classification using different shape descriptors and thresholds.

Additive manufacturing (AM) processes are using powders with different particle size distributions. However, a significant fraction of metallic powders produced for AM do not have the appropriate particle size distribution to be used in AM processes. Consequently, high-quality powders are out of AM specifications and cannot be used in AM processes. This directly impacts the cost and sustainability of many AM processes. There are opportunities to adapt and develop processes to take advantages of the fine microstructures of these rapidly solidified powders. This presentation provides examples of microstructure and properties of materials produced using AM by-products. The effect of the particle size and consolidation techniques on the properties of the materials is presented and discussed.

It is recognized that humidity affects the properties of metallic powders (e.g., flowability, density, composition). Although standards exist to evaluate the water content in various materials, there is presently no standard method validated or specifically adapted for the evaluation of the water content in metallic powders. This article evaluates the water content in titanium powders using different techniques (gravimetry, Karl Fischer titration, quantification of volatiles with a relative humidity sensor). The effect of measurement conditions, particle size, and types of powder were investigated. The results showed that the adsorption of water is a function of the relative humidity in the environment and the characteristics of the powders. The relative humidity in the laboratory has, however, limited effect if the exposure of the powder to the environment is limited prior to the measurements. Water adsorption/desorption is a function of the surface area of the powder. The measured values were underestimated as the methods used (i.e., heating at temperature lower than 275°C) did not allow recovering all the water from the powders (i.e., chemisorb water is strongly bonded to the surface and cannot be completely desorbed at temperatures lower than 275°C). Although some variability has been observed, the measurement of volatiles with the relative humidity sensor allowed discriminating powders with water contents ranging from 0 to 108 ppm. The amount of water measured using the gravimetric technique was not sensitive enough to precisely monitor the small amount of water adsorb/desorb on the powders investigated in this study. Additional studies are needed to assess the variability and reproducibility of the results and evaluate the techniques on other types of metallic powders.

Bioactive glasses (BG) possess significant bone-bonding and osteogenic properties that support their use for bone defects repair in orthopaedic and dental procedures. Recent advancement enables the manufacturing of BG-based scaffolds providing structural support during bone regeneration. Despite the wide number of studies on BG and BG-based materials, little information on their aging mechanisms and shelf life is available in the literature. In this study, the evolution of chemical species on BG-based foams was investigated via accelerated tests in the presence of CO₂ and humidity. The aging process led to the formation of carbonates (Na₂CO₃ and CaCO₃) and hydrocarbonates (NaHCO₃). The amount and composition of nucleated species evolved with time, affecting the structure, properties, and bioactivity of the scaffolds. This study provides a first structured report of aging effects on the structure and chemico-physical properties of bioactive glass-based scaffolds, offering an insight about the importance of their storage and packaging.