In Situ Characterization of Effect of Rapid Thermal Cycling During Additive Manufacturing on Deformation-Induced Transformations and Micro-Mechanical Properties

该奖项支持金属材料增材制造的基础研究，其主要目标是揭示通过增材制造制成的零件的热加工周期，微观结构和机械性能之间的关系。在这里研究的基于激光的增材制造技术中，粉末原料被输送到所需的位置，激光局部熔化粉末，将其融合到下面的材料中，一次一层地构建组件。由后续激光通过产生的热循环影响下面材料的微观结构，并因此影响机械性能（例如，强度和延展性）。在这里，两种材料系统将被检查：钛合金，在冷却时进行基于扩散的相变，和不锈钢合金，在机械载荷时进行无扩散变形诱导相变。这项研究旨在：阐明热历史对增材制造材料中局部微观结构和力学性能的影响，并开发基于物理的塑性模型，该模型考虑了热历史、所得微观结构和微观结构演变对局部塑性性能的影响。增材制造具有改变美国制造业的巨大潜力，允许生产用于无数应用的定制设计的结构部件，其中开发用于锻造、铸造或形成金属部件的工具的成本对于所需的小数量来说是不必要的（例如，老化的国防部飞机、船舶和潜艇的替换零件），与传统的减材制造相比，以更少的浪费材料的经济程序。 基础研究将导致开发完全集成的计算模型，其中处理参数（例如，激光功率、路径和速度）被确定以生产具有特定机械性能的最终净形状部件，从而为设计空间提供基础结构，而实际上对可制造的几何形状没有限制。

This award supports fundamental research on additive manufacturing of metallic materials, in which the primary goal is to uncover the relationships between thermal processing cycles, microstructure, and mechanical properties in parts made through additive manufacturing. In the laser-based additive manufacturing techniques studied here, a powder feedstock material is delivered to a desired location, and a laser locally melts the powder to fuse it to the material below, building up a component one layer at a time. The thermal cycles generated by the subsequent laser passes affect the microstructure of the underlying material, and therefore the mechanical properties (e.g., strength and ductility) of the component. Here, two materials systems will be examined: a titanium alloy that undergoes diffusion-based phase transformation upon cooling, and a stainless steel alloy that undergoes diffusionless deformation-induced phase transformation upon mechanical loading. This research aims to: elucidate the effect of thermal history on the local microstructure and mechanical properties in additive manufactured materials, and develop physically based plasticity models that take into account the effect of thermal history, resulting microstructure, and microstructural evolution on the local plasticity properties.Additive manufacturing has great potential to transform U.S. manufacturing, allowing for the production of custom-designed structural components for countless applications where the cost to develop tools for forging, casting, or forming of metal components is not warranted for the small number required (e.g., replacement parts for aging Department of Defense airplanes, ships, and submarines) in an economical procedure with less waste material than traditional subtractive manufacturing. Fundamental research will lead to the development of fully integrated computational models in which the processing parameters (e.g., laser power, path, and speed) are determined to produce an end net shape component with specified mechanical properties, providing the infrastructure for a design space with practically no limitations on geometries that can be fabricated.