Nanoparticle additivation of powders for laser additive manufacturing of oxide-dispersion strengthened steels: a joint experimental and numerical study

粉末激光增材制造（LAM）是生产氧化物弥散强化（ODS）钢3D零件的潜在突破性技术。然而，目前用作激光粉末床熔合（LPBF）和定向能量沉积（DED）的LAM方法的原料的ODS粉末不适合于激光加工，并且阻碍了这些技术的进一步发展。因此，拟议的联合项目旨在通过引入在金属粉末上分散纳米颗粒的新颖且通用的方法来开发用于LAM的新型铁铬基粉末。胶体氧化物纳米颗粒通过液体中的脉冲激光破碎产生，并通过pH控制的静电相互作用吸附在钢粉载体上。在LAM处理这些粉末之后，所形成的纳米内含物应通过Orowan机制强化打印材料。然而，这些纳米夹杂物的尺寸和分布强烈地依赖于熔池物理和熔池中的纳米颗粒运动学，因此对加工方法（LPBF或DED）和工艺参数敏感。为了理解和控制纳米粒子分散在LAM过程中，非等温相场熔池模拟结合一种新的纳米粒子运动学模型将开发调查的时空分布的纳米粒子和耦合物理，如质量/热传递，熔池动力学和再凝固的影响。耦合模型的有限元实现允许在空间和时间分辨的熔池尺度上的熔化再凝固动力学和微观结构的数值模拟。 纳米、微米和宏观尺度的深入材料分析也将分别应用于材料合成链及其在LAM之前和之后的变化，以将材料设计与其加工性能和合金的最终零件性能相关联。模拟和表征的微观结构信息，如纳米夹杂物的距离和尺寸，特别是它们对粉末复合材料和工艺类型和参数的依赖性，将进一步用于估计和优化打印材料的机械性能。由于我们方法的基本材料科学性质，我们项目的潜在影响不仅限于消耗臭氧层物质钢。它还将有助于对如何实现粉末的机械理解，这些粉末通过LAM构建部件内的高度分散的纳米夹杂物来增强材料。

Powder-based laser additive manufacturing (LAM) is a potential breakthrough technology for the production of 3D parts made of oxide dispersion-strengthened (ODS) steel. However, the ODS powders currently used as feedstock for the LAM methods of laser powder bed fusion (LPBF) and directed energy deposition (DED) are unsuitable for laser processing and prevent these technologies from further development. Therefore, the proposed joint project aims at developing a new iron-chromium-based powder for LAM by introducing a novel and versatile method of dispersing nanoparticles on metal powders. Colloidal oxide nanoparticles are produced by pulsed laser fragmentation in liquids and are adsorbed on steel powder supports via pH-controlled electrostatic interaction. After LAM processing these powders, the formed nanoinclusions should strengthen the printed material through the Orowan mechanism. However, the size and distribution of these nanoinclusions depend strongly on the melt pool physics and the nanoparticle kinematics in the melt pool and are thus sensitive to the processing method (LPBF or DED) and process parameters. For understanding and controlling the nanoparticle dispersion during LAM, non-isothermal phase-field melt pool simulations combined with a novel nanoparticle kinematic model will be developed to investigate the spatio-temporal distribution of nanoparticles and their influence on coupled physics, such as mass/heat transfer, melt pool dynamics, and resolidification. The finite element implementation of the coupled models allows numerical simulations of the melting-resolidification kinetics and microstructure on spatially and temporally resolved melt pool scales. In-depth material analytics on the nano, micro, and macro-scale will also be employed on the chain of materials synthesis and its change before and after LAM, respectively, to correlate material design with both its processability and the resulting part properties of the alloy. The simulated and characterized microstructural information, such as the distance and the size of the nanoinclusions and particularly their dependency on the powder composites and the process type and parameter, will be further used to estimate and optimize the mechanical properties of the printed materials. Due to the fundamental materials science nature of our approach, the potential impact of our project is not limited to ODS steels. It will also contribute to a mechanistic understanding of how to achieve powders that lead to material strengthening by highly dispersed nanoinclusions within a LAM-built part.