6533b85bfe1ef96bd12bbb14

RESEARCH PRODUCT

Microstructure-process relationship and reactivity at the nanoscale : a molecular dynamics study of Ni, Ni-Al, and Ti-Al metallic systems

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The process-microstructure relationship is central in materials science because the microstructure will determine the properties of the materials developed by the processes. In our work, we focused on different metallurgical processes by adopting a description at the atomic scale. This approach allows us to detect the elementary mechanisms that are at the origin of the observed microstructures without having to postulate macroscopic mechanisms or estimate the associated parameters. In this respect, molecular dynamics simulations provide a tool for "in-situ" observation of metallic systems as long as an atomic interaction potential is available. The originality of our approach consists in modeling the characteristics of the processes at nanometric scales. In the context of powder metallurgy, we focused on the additive manufacturing of metallic materials and the activation of metallic powders by high-energy milling. We performed molecular dynamics simulations to understand the directional solidification processes at the nanoscale of a pure Ni polycrystalline metal in the context of additive manufacturing. Various microstructures were observed as a function of thermal conditions. Solidification and nucleation were also compared to classical solidification and nucleation theories to establish their validity at the nanoscale. We modeled the milling process by mechanical treatment with compaction and plastic deformation to observe the action of grinding balls on a binary mixture of powders. This approach allows us to understand the behavior of mechanically activated powders (Ti+Al and Ni+Al) by characterizing atom mobility, structural transformations and reactivity. We also studied the reactivity of a Ti-Al nanometric multilayer model similar to the materials obtained after high-energy milling. We have highlighted several elementary mechanisms responsible for their increased reactivity, such as dissolution at the Ti(solid)/Al(liquid) interfaces and the formation of an intermetallic (TiAl3).