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Boko Park-Popular Science: Dr. Ashley Bucsek, the first author of these three papers and now a postdoctoral researcher at the University of Minnesota, said: However, this does not match its technical influence-only a few of these 20,000 SMA patents have been realized as commercially feasible products, and many other advanced materials are similar, and it takes decades from development to realization. One of the reasons for this gap between development and implementation is that researchers actually scrape the surface with traditional microscope technology, while most micro-mechanisms in SMAs are three-dimensional, out-of-plane and very sensitive to internal constraints. To make up for this gap, Bucsek and his colleagues put NiTi (the most widely used and available sma) under the most powerful 3d microscope of Cornell High Energy Synchrotron Light Source (CHESS) at Cornell University in upstate New York.
Specifically, the near-field and far-field high-energy diffraction microscope (HEDM) is used. Under the umbrella of three-dimensional X-ray diffraction technology, she can visualize the internal microstructure of materials in three dimensions, and its reaction is real-time. Although HEDM has been developed in the international and other synchrotron fields for more than ten years, the advanced material process of using HEDM to study low symmetric phase mixtures and large crystal size differences basically does not exist. Therefore, all three experiments need to develop new experimental, data analysis and data visualization technologies to extract the required information. Many results are surprising, revealing decades of debate in the field of SMA micromechanics. In SMAs, the highly symmetrical "austenite" phase is usually stable at high temperature, but if enough stress is applied or the temperature is lowered, it will become a low symmetrical "martensite" phase.
The first paper, Measuring the Microstructure of Stress-induced Martensite by Far-field High-energy Diffraction Microscope, was published in Journal of Crystallography A: Foundation and Progress, aiming at predicting the specific changes of martensite. By using this method, it is found that the martensite microstructure in SMAs seriously violates the prediction of the maximum deformation processing standard, which indicates that the widely accepted application of the maximum deformation processing standard needs to be revised in the case that SMAs may have engineering-grade microstructure characteristics and defects. The second experiment studies the load-induced twin rearrangement, or martensite reorientation, which is a reversible deformation mechanism. Through this mechanism, the material can bear large load and deformation without being damaged by crystal twinning rearrangement. In the macroscopic deformation zone, when they propagate in the microstructure, a series of specific twin rearrangement microscopic mechanisms will occur.
The results show that the strain localization in these bands leads to lattice bending as high as 15 degrees, which is of great significance for the maximum realization of elastic strain, analytical shear stress and twin rearrangement. These findings will guide future researchers to use twin rearrangement in new multiferroic technology. Solid-state drive is one of the most important applications of SMAs, and it has applications in many nano-electromechanical and micro-electromechanical systems, biomedicine, active damping and aerospace drive systems. The goal of the final experiment is the special large-angle grain boundary phenomenon in austenite grains under the action of SMAs. During the driving process, SMA is heated, cooled and reheated under constant load to induce the transformation from austenite to martensite and then to austenite. Electron microscope observation shows that austenite will rotate greatly when the sample is reheated, which is not conducive to output work and fatigue.
However, due to the small sample size required by the electron microscope, the observed rotations are very inconsistent and appear under the same load conditions, but they do not appear later, or appear after several cycles, but do not appear after thousands of cycles. The results show that under mild conditions, the rotation of these particles can only occur in one cycle. However, due to the small size and uneven rotation and dispersion, a volume is needed to observe them. Baksek's research funding comes from the National Science Foundation (NSF) postgraduate research scholarship. Aaron Taibner, her doctoral supervisor and co-author and associate professor of mining machinery engineering in rawlinson, won the 20 15 NSF career award. The additional funds needed to analyze data with high-performance computers come from the NSF XSEDE project. The paper work recorded by Dr. Baksek in these articles shows that it is very important to study the 3d structure of materials by using 3d technology.
This is the first time that she has been able to observe and understand this mechanism that has been hypothesized and debated for more than 50 years. Like most technologies, the biggest obstacle to adopting new materials is the fear of the unknown. This understanding will undoubtedly make these magical materials more widely accepted and applied, because it will enhance our confidence in the development certificate and qualified materials. The National Science Foundation also provides the operation of Cornell high-energy synchrotron light source for X-ray microscope measurement. Darren Pagan, a scientist, said: In her thesis work, Dr. Baksek developed a new creative method, applied HEDM method to the study of shape memory alloy system, and overcame the challenges related to data processing and interpretation, which made people have a new understanding of the micromechanics of shape memory alloy deformation!
Boko Park-Popular Science | Research/From: colorado school of mines
References: Material Express, Journal of Solid Mechanics and Physics, Journal of Crystals.
DOI: 10. 10 16/j . script Amat . 20 18. 1 1.043
DOI: 10. 10 16/j . jmps . 20 18. 12.003
DOI: 10. 1 107/20532733 1800880 x
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