Powders by design for additive manufacture through multi-scale simulations

选择性激光熔化工艺是一种很有前途的大规模增材制造（或3D打印）技术，可以快速生产原型，最近还可以小批量生产重量敏感/多功能部件，几乎可以任意复杂。该工艺在每个周期中通过三个主要阶段逐层构建最终部件：(1)在制造表面沉积一层细粉末（典型晶粒尺寸约为0.03 mm），形成薄薄的粉末床，其厚度仅略高于平均晶粒尺寸；(2)根据最终产品的三维计算机模型，激光束在特定位置熔化粉末床；(3)粉末颗粒冷却凝固后在这些位置熔合，形成一层最终产品。总的来说，与传统制造技术相比，选择性激光熔化工艺和增材制造提供了几个优势，例如更大的设计自由度，产品的大规模定制和个性化，复杂几何形状的生产以提高性能和降低劳动力成本，减少宝贵材料的浪费，以及新的商业模式和供应链。然而，也存在一些挑战。例如，缺乏对粉末颗粒形状对潜在物理过程的影响的理解，迫使该行业要求大多数单个粉末颗粒是球形的。这种严格的要求增加了粉末（原材料）的成本，从而增加了生产成本，阻碍了新工艺的开发和新材料的引入。为了解决这个问题，需要高质量的过程模拟研究软件来补充实验并使新的科学发现和创新成为可能。目前的研究计划通过提供一种新的计算包来解决这一技术需求，该计算包能够模拟选择性激光熔化过程中各种复杂的物理现象。为了实现这一目标，高性能计算将用于跟踪系统中单个颗粒的运动，它们与激光束的相互作用以及它们的相位变化。然后，该计算包将用于揭示粉末颗粒形状对床内激光束的吸收和散射以及随后的快速熔化过程的复杂影响。此外，假设表面带有小夹杂物的细长或卫星球形颗粒（通常存在于粉末中并且通常被认为是不受欢迎的颗粒形状），如果仔细选择它们的数量密度，实际上可以改善工艺。这一假设将在这里首次得到验证，这将大大降低选择性激光熔化的原材料成本，从而使这一使能技术得到更广泛的采用。

The selective laser melting process is a promising large-scale additive manufacturing (or 3D printing) technique that allows for rapid production of prototypes, and lately for weight-sensitive/multi-functional parts at small volumes, with almost arbitrary complexity. The process builds the final parts layer-upon-layer by going through three main stages during each cycle: (1) deposition of a layer of fine powder (with a typical grain size of approximately 0.03 mm) on a fabrication surface to form a thin bed of powder, which is only marginally thicker than the average grain size; (2) a laser beam then melts the powder bed at specific locations, based on a 3D computer model of the final product; (3) the powder grains then fuse at those locations after cooling and solidifying to produce a layer of the final product.In general, the selective laser melting process and additive manufacturing provide several advantages compared to conventional manufacturing techniques, such as greater design freedom, mass customisation and personalisation of products, production of complex geometries to improve performance and reduce labour costs, decreased wastage of precious materials, and new business models and supply chains. However, several challenges also exist. For example, a lack of understanding of the impact of powder grain shape on the underlying physical processes has forced the industry to require the majority of individual powder grains to be spherical. Such a stringent requirement increases the cost of powder (raw material), which consequently increases the production cost and hinders the development of new processes and the introduction of new materials. To address this issue, high-quality research software for process simulation is required to complement experiments and to enable new scientific discoveries and innovations. The present research programme addresses this technological need by providing a novel computational package capable of modelling various complex physical phenomena underlying the selective laser melting process. To achieve this, high-performance computing will be used to track the motion of individual grains in the system, their interaction with a laser beam, and their phase changes. This computational package will then be used to uncover the complex impact of powder grain shapes on the absorption and scattering of a laser beam within the bed and the following rapid melting process. Furthermore, it is hypothesised that elongated or satellite-spherical particles with small inclusions on their surfaces (grain shapes which are commonly present in powders and are generally considered undesirable) can, in fact, improve the process if their number densities are carefully selected. This hypothesis will be tested here for the first time, which can greatly reduce the cost of raw materials for selective laser melting, which results in wider adoption of this enabling technology.