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造的零件的热处理周期、微观结构和机械性能之间的关系。在本文研究的基于激光的增材制造技术中，粉末原料被运送到所需的位置，激光局部熔化粉末，使其与下面的材料融合，一次一层地构建组件。后续激光通道产生的热循环会影响底层材料的微观结构，从而影响部件的机械性能（例如强度和延展性）。在这里，我们将研究两种材料系统：一种是在冷却时发生扩散相变的钛合金，一种是在机械加载时发生无扩散变形相变的不锈钢合金。本研究旨在阐明热历史对增材制造材料的局部微观结构和力学性能的影响，并建立基于物理的塑性模型，该模型考虑了热历史、产生的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，允许生产定制设计的结构部件，用于无数应用，在这些应用中，开发锻造，铸造或成形金属部件的工具的成本无法保证少量所需（例如，国防部老化的飞机，船舶和潜艇的更换部件），在经济的过程中，比传统的减法制造浪费更少的材料。基础研究将导致完全集成计算模型的发展，其中加工参数（例如，激光功率，路径和速度）被确定，以产生具有特定机械性能的端网形状组件，为设计空间提供基础设施，几乎没有几何形状的限制，可以制造。

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.