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

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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.