Fatigue behavior of NiTi architectured materials obtained by additive manufacturing
Researchers
Research areas
Shape Memory, Additive Manufacturing, Mechanical Characterization, Fatigue, Design
Project brief
Background:
The superelastic and shape memory effects of NiTi alloys are phase transformation processes that make them excellent candidates for applications in the transport, space and medical sectors. Superelasticity (SE) allows an alloy to deform reversibly over very large deformation ranges, reaching up to 10% of recoverable strain. This effect allows the material to be used as a high damping metal, given its outstanding dissipating capabilities, or in bone replacement thanks to its similar mechanical behaviour and biocompatibility. The shape memory effect (SME) on the other hand, is the ability of a part to recover its original shape, even after significant deformation, by heating. This allows for example the development of light weight actuators that deploy solar panels on satellites simply by heating a shape memory component.
As it can be seen, applications cover a wide range of fields, from medical applications (stents, endodontic files, flexible glasses) to smart wheels for cars and even in the space industry for the superelastic wheels on the Mars rover. What remains limiting, however, is the difficulty of shaping and machining NiTi alloys. This means that complex shapes are difficult to obtain, limiting its production to wires and plates.
Over the last decades, the use of additive manufacturing technology has been implemented as a way to overcome these limitations. This allows the manufacture of complex parts such as architected structures, producing superelastic or shape memory metamaterials that combine the properties of the material and those of the structures. These structures could further the range of application of NiTi, such as in the field of advanced mobility, to absorb shocks or vibrations, or to create deployable structures or customised medical implants.
Research Methodology:
The main objective of this research project will be to determine the impact of process parameters on the mechanical behaviour of architectured NiTi obtained by selective laser melting (SLM). Therefore, a methodology will be developed to:
(1) understand the microstructures of architectured materials obtained by SLM technology using different microstructure characterization techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD);
(2) characterize the quasi-static and fatigue behaviour of lattice structures produced by metallic additive manufacturing;
(3) identify the damage mechanisms at the local scale and the link with the microstructure by performing in-situ mechanical testing under synchrotron radiation.
Expected Outcomes:
As a result of this research, it is expected to
(1) achieve a better understanding of the influence of process parameters on the microstructure (grain size and shape, precipitates, texture, etc), transformation temperatures and geometric deviation of lattice structured NiTi;
(2) manufacture and characterize the mechanical behaviour of superelastic lattice structured NiTi;
(3) develop a design process that allows to predict and tune the mechanical response of a SLM manufactured NiTi component for shape memory or superelastic behaviour.