High-throughput Alloy Development for Additive Manufacturing via 3D-Extreme High-speed Laser Material Deposition (3D-EHLA)

增材制造（AM）技术是个性化和资源高效生产高功能部件的关键推动因素。今天，由于缺乏高性能的AM材料，AM技术无法充分发挥其潜力，这些材料利用了工艺固有的条件，例如极高的加热和冷却速率。因此，必须设计新的高通量方法，以允许开发新的AM适合材料的敏捷和有效的方式。激光材料沉积（LMD）及其变体超高速激光材料沉积（EHLA）等可原位混合多种材料/元素的工艺非常适合对多种合金进行资源高效和自动化测试。EHLA的创新（专利FhG/RWTH亚琛，2015）在于粉末颗粒不像传统的激光材料沉积（LMD）那样在基材上的熔池中熔化，而是在基材上方熔化（图1）。这使得层厚度从10-300微米的工艺速度高达200米/分钟。由于这些特性，在凝固过程中的冷却速率可以变化到约100微米的范围内的高度。10^2-10^4K/s（常规LMD）和约10^4和10^6 K/s（EHLA），通过不同的加工速度沿着，以及定制的强度、激光功率和系统技术。因此，可以专门调整材料设计方面（例如，偏析），以影响失效机制（例如，TRIP）。目前，由于表面速度较高，EHLA的应用仅限于旋转对称样品。然而，Fraunhofer ILT最近的发展表明，EHLA也适用于非旋转设置。通过这样的设置，也可以研究关键区域，例如反转点（增加的热输入和冷却/固化条件的改变）。这种高速和全3D功能的结合使应用的3D-EHLA机器还可以模拟其他AM技术（例如激光粉末床融合）。该机器将能够同时处理多达8个（初级）粉末材料，在5g加速度下的处理速度高达200 m/min。为了通过应用不同的温度曲线（通过定制的强度）来控制熔体的形成和固化，可以将不同的光学器件集成到加工头中。此外，许多用于材料表征和过程观察的设备（例如，高速摄像机、比率高温计、激光诱导击穿光谱等）将成为设置的一部分，以实现过程条件的即时反馈。因此，这款独一无二的设备不仅涵盖了LMD的高通量材料开发，还提供了模拟各种AM工艺的机会（通过控制10^2-10^6K/s的局部冷却条件以及适应的工艺策略）。与LMD/EHLA的原位材料混合能力一起，这使得AM材料开发迈出了全新的一步（图1）。

Additive Manufacturing (AM) technologies are a key enabler of individualized and resource-efficient production of highly functional parts. Today, AM technologies cannot reach their full potential due to the lack of high-performance materials for AM which exploit the process-inherent conditions such as extremely high heating and cooling rates. Thus, novel high-throughput approaches have to be designed to allow an agile and efficient way of developing new AM-suited materials. Processes with the possibility of in-situ mixing multiple materials/elements such as Laser Material Deposition (LMD) and its variant Extreme High-speed Laser Material Deposition (EHLA) are extremely suitable for the resource-efficient and automatable testing of numerous alloys. EHLA's innovation (Patent FhG/RWTH Aachen, 2015) lies in the fact that the powder particles are not molten in the melt pool on the substrate, as in conventional Laser Material Deposition (LMD), but above it (fig. 1). This enables layers with thicknesses from 10-300µm at process speeds of up to 200m/min. Due to these characteristics, the cooling rates during solidification can be varied to high degree in the regime of approx. 10^2-10^4K/s (conventional LMD) and approx. 10^4 and 10^6K/s (EHLA) by different process speeds along with tailored intensity, laser power and system technology. Hence, material design aspects, e.g. segregations can be specifically adjusted to influence failure mechanisms (e.g. TWIP, TRIP). So far, the application of EHLA is limited to rotationally symmetrical samples due to the high surface speeds. Yet, recent developments at Fraunhofer ILT shows that EHLA is also applicable in a non-rotational setup. With such a setup critical areas, e.g. reversal points (increased heat input and change of the cooling/solidification conditions) can be investigated, too. This combination - high speed and full 3D-capability - allows the applied-for 3D-EHLA machine also to emulate other AM technologies (e.g. Laser-Powder Bed Fusion). The machine will be able to process up to 8 (elementary) powder materials synchronously with process speed up to 200m/min at 5g acceleration. To control melt formation and solidification by applying different temperature profiles (by means of tailored intensities) different optics can be integrated into the processing head. Furthermore, numerous devices for material characterization and process observation (e.g. high-speed camera, ratio pyrometer, laser-induced breakdown-spectroscopy, etc.) will be part of the setup to enable instant feedback of the process conditions. Thus, this one-of-a-kind machine covers not only the high throughput material development for LMD but offers the opportunity to emulate various AM processes (by the control of the local cooling conditions from 10^2-10^6K/s together with adapted process strategies). Together with the in-situ material mixing capability of LMD/EHLA this enables a whole new step for the material development in AM (fig. 1).