26 - Understanding ageing mechanism of Al-based metallic powders: probing grain/grain interactions with Atomic Force Microscopy

Abstract

Metallic powders utilized in additive manufacturing (AM) hold substantial value due to their production expenses and the specific requirements associated with the industrial sectors they serve, such as biotechnology and aeronautics. In addition to the process parameters, the quality of final components in AM also depends on the quality of the powder and their processability. Among the powder characteristics that have to be carefully controlled for AM one can found geometrical ones (particle size distribution, sphericity), chemical composition (bulk and surface), and their rheological properties which come out from the previous ones. These properties directly influence thermal properties and flowability of the powders. Despite the increasing optimization of AM processes, their profitability remains limited to a select few applications, necessitating ongoing research to ensure their sustainability. One area of focus for improvement lies in material costs, with three key considerations: the reuse of unmelted powder in the production of parts, the recycling of powders that have been compromised during the AM process, and the management of storage & ageing of metallic powders. In the context of resource efficiency, powder storage stands out as a significant challenge for AM. Indeed, it has been observed that storage of metallic powders may lead to changes in the surface chemistry of the grains and consequently to the alteration of the rheological properties of the powder due to lower interparticle forces. As a result, this alteration reduces the economic interest of AM while increasing its environmental cost, even with the possibility of recycling. The main objective of this study is to understand the relationship between the surface properties of aged individual Al-based alloy grains and the macroscopic rheological properties of a powder, with a focus on the understanding of ageing mechanisms. A method for determining the grain/grain interactions and their modifications with ageing has been developed. This method is based on the measurement of adhesion forces between individual grains as a function of ageing conditions using Atomic Force Microscopy (AFM). The proposed method provides a deeper understanding of how particle micro and nano roughness and the formation of both oxides and hydroxides impact adhesion. The results obtained are subjected to critical discussion, considering the insights derived from the analysis of microstructures. This work should allow a better understanding of powder ageing and therefore help the AM community to develop reliable processes for storage and use of metallic powders.

Speaker

Yassine Lakroune

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Conference

26 - Understanding ageing mechanism of Al-based metallic powders: probing grain/grain interactions with Atomic Force Microscopy

Date/Time

21/03/2024

11:25 am -11:45 am

Location

Room 6