Additive Manufacturing of Near-Net Shape and Fully Dense Shape Memory Alloys

该奖项支持研究一种新型的基于激光的增材制造技术，以制造具有在严重变形后恢复原始形状的独特能力的材料，称为形状记忆合金。两个主要目标是开发一个基本的理解的制造结构性能的关系，并定制底层的微观结构形态，从而形状记忆材料的响应。零件通过连续的金属粉末层沉积和激光固化而形成。 对于合金，温度或外力/应力促进原子结构变化，引起固-固微观结构相变。 通过在变形后反转外部刺激（加热/冷却或加载/卸载）的感觉，转变反向发生，并且散装材料恢复其原始形状。 小规模形状记忆合金板和杆几何形状将使用增材制造合成。 这项工作的特点都是热诱导和应力诱导相变，以及底层的原子/微观结构，使用透射电子显微镜。 通过结合温度循环和机械应力实验与局部位移/应变和温度的实时微尺度测量来可视化变形过程中的转变的演变。 增材制造技术以具有成本效益、节能和环保意识的方式逐层构建3D计算机生成的模型几何形状。 本基础研究的材料设计方面利用了该技术并行处理不同粉末混合物和并行合成可变工艺参数的能力。 这将决定加工参数、微观结构和形状记忆行为之间的基本关系。 增材制造提供了一种商业化制造近净形结构的新方法。 这项工作是几何复杂的层次结构的基础-微米尺度的板和杆的几何形状是结构的构建块。 形状记忆合金分级结构在实际应用中具有广阔的前景，包括用于民用、海军、汽车和航空航天结构的地震和冲击缓解以及振动阻尼。

This award supports the study of a novel laser-based additive manufacturing technique to fabricate materials with unique ability to return to its original shape after severe deformation, referred to as shape memory alloys. Two primary objectives are to develop a fundamental understanding of the manufacturing-structure-property relationships and to tailor the underlying microstructural morphology and thus the shape memory material response. Parts are built-up as successive metallic powder layers are deposited and laser consolidated. For the alloys, temperature or external force/stress facilitates an atomic structure change that begets a solid-solid microstructure phase transformation. By reversing the sense of external stimuli (heating/cooling or loading/unloading) after deformation, the transformation happens in reverse and the bulk material recovers its original shape. Small-scale shape memory alloy plate and rod geometries will be synthesized using additive manufacturing. This work characterizes both the thermal-induced and stress-induced phase transformations as well as underlying atomic-/microstructure using transmission electron microscopy. The evolution of the transformation during deformation is visualized by combining temperature cycling and mechanical stressing experiments with real-time micro-scale measurements of localized displacement/strain and temperature. The additive manufacturing technique builds 3-D computer generated model geometries layer-by-layer in a cost-effective, energy efficient, and environmental conscious manner. The materials design aspect of this fundamental study takes advantage of the capabilities of the technique for parallel processing of diverse powder mixtures and parallel synthesis with variable processing parameters. This will determine fundamental relationships between processing parameters, microstructure, and shape memory behavior. Additive manufacturing offers a novel approach to commercially manufacture near-net shape constructs. The work is the foundation for geometrically complex hierarchical structures - micrometer scale plate and rod geometries are structural building blocks. Shape memory alloy hierarchical structures are promising for practical applications including earthquake and impact mitigation and vibration damping for civil, naval, automotive, and aerospace structures.