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

该奖项支持研究一种新的基于激光的添加剂制造技术，以制造具有在严重变形后恢复其原始形状的独特能力的材料，称为形状记忆合金。两个主要目标是建立对制造-结构-性能关系的基本理解，并定制潜在的微结构形态，从而确定形状记忆材料的响应。随着连续的金属粉末层的沉积和激光固化，零件被堆积起来。对于合金来说，温度或外力/应力促进了原子结构的变化，从而导致了固-固组织相变。通过在变形后颠倒外部刺激(加热/冷却或加载/卸载)的感觉，该转变发生在相反的情况下，并且块状材料恢复其原始形状。小规模形状记忆合金板材和棒材的几何形状将采用加法制造进行合成。这项工作用透射电子显微镜表征了热诱导和应力诱导的相变以及潜在的原子/微结构。通过温度循环和力学应力实验，结合局部位移/应变和温度的实时微观测量，直观地显示了变形过程中相变的演变。加法制造技术以具有成本效益、能源效率和环保意识的方式逐层构建计算机生成的3D模型几何图形。这项基础性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可变工艺参数的并行合成的能力。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。加法制造为近净形状构件的商业化制造提供了一种新的方法。这项工作是几何复杂的分层结构的基础-微米级的板和杆的几何形状是结构的积木。形状记忆合金层次化结构在民用、海军、汽车和航空航天结构的减震减振等方面具有广阔的应用前景。

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.