Richard D. James from the University of Minnesota works as a Mercator Fellow on shape memory materials at Kiel University
Often stents are used for the treatment of circulatory disturbances of the heart. These ultrathin metallic tubes keep the vessels open and the blood flowing. In many cases they are made out of shape memory alloys that can return to a “memorized” original state after deformation. This way, a stent inserted into a tiny plastic tube at the end of guidewire can expand to the shape of a stent when deployed in a coronary artery. These superelastic materials used in numerous medical and industrial applications require a sufficient lifetime.
Ceramics are considered by most researchers to be far too brittle to serve as shape memory materials. With the support of a high-risk Reinhart Koselleck-Project of the German Research Foundation (DFG) Professor Eckhard Quandt, from Kiel University and Professor Richard D. James from the University of Minnesota believe that this conventional wisdom may be unjustified. Now Quandt has won a Mercator Fellowship of the DFG for James to expand on this work. The internationally renowned expert on shape memory materials will work on the project as a Mercator Fellow for a total period of one year. Together they want to drive further the development of new materials for other applications in medicine, industry and energy.
Why are the phases of deformation reversible?
Triggered by temperature and stress shape memory materials can change between different states. Thereby they pass several crystalline phase transformations. Since these are reversible, these materials can return to former states. “I want to understand the full set of physical principles that govern reversibility and how these phases can fit togetherin many wayswithout stressed transition layers”, outlines Professor Richard D. James from the Department of Aerospace Engineering Mechanics at the University of Minnesota. James and Quandt call this characteristic of some phases “Supercompatibility”. They have studied it with the focus on shape memory materials for some years and now they want to intensify their cooperation.
Shape memory materials made of ceramics could withstand even high temperatures
“In our current project, we want to figure out the range of factors that influence the lifetime of shape memory materials and how we could optimize them. This way we could develop new materials that allow new applications in medicine and industry”, Quandt, Professor for Inorganic Functional Materials, explains. In his Reinhart Koselleck-Project on Crystallographically Compatible Ceramic Shape Memory Materials he is working on shape memory materials made of ceramics that could be especially advantageous: Unlike metal materials,they could also be used at high temperatures, for examples as an actuator in engines. However, their phase transformations are not reversible enough so far, so more research is necessary.
Another main topic of the research cooperation of James and Quandt on shape memory materials is the phenomenon hysteresis: when you cool a material it transforms at one temperature and when you heat it back up again it transforms at a higher temperature. It has been known for a while that the hysteresis can be nearly eliminated if you satisfy a certain condition on the transformation matrix. Quandt and James conjecture that this works even better when supercompatibility is fulfilled. During the term of the Mercator fellowship they plan to examine theories like that.
Based on long-standing cooperation
A much-noticed paper in the leading journal Science was the starting point for closer collaborations between James and Quandt. Here Quandt reports on an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. His working group was successful in developing a process to develop well-defined pure polycrystalline materials, that can also be used for shape memory materials. “With high-quality materials you can study each factors’ impact on its fatigue much more precisely”, Quandt explains. The possibility to produce high-quality materials by thin film technology has already spawned a successful spin-off company.
Mercator Fellow James, one of the international leading theorists for shape memory materials, is now collaborating with the project. During the last years some joint publications have already been published, also in cooperation with the Research Training Group 2154 “Materials for Brain” at Kiel University. Both scientists are optimistic, they can take this research area one major step forward.
Richard D. James is an engineer and mathematician at the University of Minnesota. He received his PhD 1979 at Johns Hopkins University in Mechanical Engineering. As a postdoc he worked at the University of Minnesota and since 1981 as an Assistant Professor at Brown University. 1985 he became Associate Professor and 1991 Professor at the University of Minnesota. 1998 he became Distinguished McKnight University Professor, 2001 Russell J. Penrose Professor. He was awarded numerous prizes, for example the renowned Vannevar Bush Faculty Fellowship, the William-Prager-Medal, the Warner-T. Koiter-Medal, the Theodore von Kármán Prize and the Humboldt Research Award. One of his main research interests are phase transformations in materials - especially shape memory and multiferroic materials – and the development of mathematical methods for the analysis of materials at atomic and continuum scales.
The programme “Mercator Fellows” of the DFG enables an intensive and long-term exchange with researchers in Germany and abroad. Fellows will partially be on site but will remain in contact with project participants even after their stay to add significant value to a research project. The Reinhart Koselleck-Projects of the DFG offers the possibility to implement innovative and high-risk research projects.
Details, which are only a millionth of a millimetre in size: this is what the priority research area "Kiel Nano, Surface and Interface Science – KiNSIS" at Kiel University has been working on. In the nano-cosmos, different laws prevail than in the macroscopic world - those of quantum physics. Through intensive, interdisciplinary cooperation between physics, chemistry, engineering and life sciences, the priority research area aims to understand the systems in this dimension and to implement the findings in an application-oriented manner. Molecular machines, innovative sensors, bionic materials, quantum computers, advanced therapies and much more could be the result. More information at www.kinsis.uni-kiel.de