Novel 3D printing strategies to produce high performance, nanostructured steels

提高金属合金的力学性能是工程界长期致力于的工作。更坚固和更坚韧的金属有利于更高效的运输，更安全的基础设施，并减少几个工业部门的检修。改善金属机械性能的一种常见方法是赋予它们复杂的纳米级结构。可以采用无数不同的制造工艺来生产纳米结构金属。然而，它们都存在可伸缩性有限的问题，这阻碍了它们在结构应用中的使用。在本论文中，我将探索利用激光粉床熔化(LPBF)技术来制备块体高性能纳米结构合金的可能性。LPBF是一种添加剂制造工艺，它依赖于将金属原料小范围熔化和凝固成三维零件。通过微调激光参数，有可能操纵材料的热历史，并在纳米级设计材料的凝固结构。为了展示这项技术提供的机会，我将重点介绍17-4PH马氏体不锈钢。我将采用的LPBF策略旨在控制材料在冷却时将保留的母相，以及决定合金机械性能的强化富铜纳米沉淀物和亚微米凝固单元的出现。值得注意的是，这些结构可以在常规和LPBF中形成，通过长期的专业热处理生产17-4PH。然而，这种额外的后处理步骤的时间和成本对于LPBF的可扩展性是令人望而却步的。因此，我的部分工作还将侧重于在没有后处理的情况下实现这种结构控制，从而产生更具成本效益和可持续的制造方法。

Improving the mechanical performance of metal alloys is a longstanding effort in engineering. Stronger and tougher metals are conducive to more efficient transportation, more secure infrastructure, and reduced overhauling in several industrial sectors. One common approach to improve the mechanical behaviour of metals is to impart them with a complex, nanoscale structure. A myriad of different manufacturing processes may be employed to produce nanostructured metals. However, they all suffer from limited scalability, which hampers their use in structural applications. In this thesis, I will explore the possibility of using laser powder bed fusion (LPBF) technology to produce bulk high-performance nanostructured alloys. LPBF is a class of additive manufacturing processes which relies on small scale melting and solidification of a metal feedstock into a 3-D part. By fine-tuning the laser parameters it is possible to manipulate the thermal history of the material and engineer the material's solidification structure at nanoscale. To showcase the opportunities offered by this technology, I will focus on 17-4 PH martensitic stainless steel. The LPBF strategies which I will employ will aim at controlling the parent phase that the material will retain upon cooling, as well as the occurrence of the strengthening copper-rich nanoprecipitates and submicron solidification cells which dictate the alloy's mechanical performance. Notably, these structures can be formed in conventional and LPBF produced 17-4 PH through long specialised heat treatments. However, the time and cost of this additional post processing step is prohibitive to the scalability of LPBF. Part of my work will thus also focus on achieving this structural control without post-processing, leading to a more cost-effective and sustainable manufacturing approach.