INFORMATION:
This research was funded by the National Key R&D Program of China (No. 2017YFB0701604).
See the article:
T.-Y. Zhang, Y.-X. Gao, and S. Sun, Grain boundary segregation and relaxation in nano-grained polycrystalline alloys, Sci. China-Phys. Mech. Astron. 64, 224611 (2021), https://doi.org/10.1007/s11433-020-1614-5
The valuable contribution of stress to the thermal stability of nanograined polycrystalline alloys
2021-03-16
(Press-News.org) Nanograined metals and alloys, whose grain size is less than 100 nm, exhibit extremely high strength and high ductility, possessing excellent mechanical properties. Nanograined materials, however, have a large number of grain boundaries and hence high total grain boundary energy. At a temperature higher than a critical temperature, grains in nanograined materials will grow spontaneously to reduce the grain boundary energy, leading to thermal instability of the materials. A common approach to enhance the thermal stability is via grain boundary energy segregation, which thermodynamically lowers the grain boundary energy and kinetically pins the movement of grain boundaries, thereby enhancing the critical temperature of recrystallization. However, the role of mechanical stresses in the thermal stability has not been systematically studied yet.
A recently published paper entitled "Grain boundary segregation and relaxation in nano-grained polycrystalline alloys", in SCIENCE CHINA Physics, Mechanics & Astronomy, Vol. 62, Issue 2, 2021, systematically studies the thermal stability of nanograined alloys, by analytic investigation of three coupled behaviors between grain boundaries and crystalline grains among chemical concentrations and mechanical stresses. The three coupled behaviors are 1) the coupling between grain boundary stress and grain stress, 2) grain boundary segregation, and 3) the coupling between concentration and stress. Finally, a novel thermodynamic criterion is developed for the thermal stability of nanograined alloys, which shows stresses play an extremely role there. The authors of the paper are ZHANG Tong-Yi, GAO Yingxin and SUN Sheng from Materials Genome Institute, Shanghai University.
The thermodynamic energy is divided into the mechanical energy and the chemical energy and both are coupled each other. The analysis of mechanical energy considers the grain boundary eigen-stress and the eigen-strain induced by grain boundary segregation and develops a hybrid method to solve the eigen-stress and eigen-strain coupling problem. The chemical thermodynamics analysis considers the difference in the chemical potentials of pure elements in grain boundaries and in grains, and hence proposes a generalized McLean adsorption isotherm, which naturally includes the stress term. Based on the three coherent coupling effects, a novel criterion is developed for the thermal stability of nanograined alloys, and quantitatively and analytically expressed by the difference in molar free energy between a nanograined polycrystalline alloy and its single crystal counterpart. A positive or negative difference in molar free energy indicates the nanograined alloy is thermal unstable or stable.
Ni1-xMox binary alloys are taken as an example to illustrate, with figures, the theoretical results and the roles of each parameters involved in the analytic criterion. The present study shows that stresses play a vital role in the thermal stability of nanograined alloys. Any criterions without considering internal stresses would partially estimate the thermal stability of nanograined alloys.
ELSE PRESS RELEASES FROM THIS DATE:
HKUST researchers unlock the micro-molecular physiochemical mechanism of dental plaque formation
2021-03-16
An inter-disciplinary team of researchers led by Prof. Qian Peiyuan, Chair Professor at the Hong Kong University of Science and Technology (HKUST)'s Department of Ocean Science and Division of Life Science has unraveled how a novel microbial small molecule released by Streptococcus mutans (S. mutans) - a bacterium commonly found in the human oral cavity - is connected to dental caries development using a synthetic biology approach, offering new insights to the health impact of the human oral microbiota and facilitating future research on the prevention of tooth decay. The research findings were recently published in the prestigious scientific journal Nature Chemical Biology and reported by Nature as one of the research highlights.
Every wetted surface on our ...
State of the climate over the three gorges region of the Yangtze river in 2019
2021-03-16
The Three Gorges project, completed in 2009, is one of the world's largest hydropower projects. It has brought important social and economic benefits in flood control, power generation, shipping and water resources redistribution.
But how does such a large-scale water conservancy project affect the local climate, and is the response to climate change a relatively vulnerable one? The Three Gorges Project has been repeated questioned, especially whenever rainstorms, floods and drought hit the area around the reservoir area or its neighboring areas, since ...
Researchers discover intact plant fossils beneath Greenland's ice sheet for the first time
2021-03-16
Following a relocation of ice cores to the Copenhagen suburb of Rødovre in 2017, University of Copenhagen researchers found unopened boxes of ice cores dating back to 1966--the first ice cores drilled on Earth.
Analyses of the long-forgotten ice have now been completed and are presented in a new study with groundbreaking results.
Within the cores, which come from deep within the ice sheet at Camp Century, Greenland, the UCPH researchers and their Belgian and American colleagues became the first ever to find these millions of years old macrofossils.
The fossils are large enough to be seen without a microscope.
"We pinched ourselves over the treasure we'd found! Because within the cores, ...
Consumption of added sugar doubles fat production
2021-03-16
Sugar is added to many common foodstuffs, and people in Switzerland consume more than 100 grams of it every day. The high calorie content of sugar causes excessive weight and obesity, and the associated diseases. But does too much sugar have any other harmful effects if consumed regularly? And if so, which sugars in particular?
Even moderate amounts of sugar increase fat synthesis
Researchers at the University of Zurich (UZH) and the University Hospital Zurich (USZ) have been investigating these questions. Compared to previous studies, which mainly examined the consumption ...
Study: 94% of older adults prescribed drugs that raise risk of falling
2021-03-16
BUFFALO, N.Y. - Nearly every older adult was prescribed a prescription drug that increased their risk of falling in 2017, according to new University at Buffalo research.
The study found that the percentage of adults 65 and older who were prescribed a fall- risk-increasing drug climbed to 94% in 2017, a significant leap from 57% in 1999. The research also revealed that the rate of death caused by falls in older adults more than doubled during the same time period.
Even minor falls may be dangerous for older adults. Falls that are not fatal can still result in injuries - such as hip fractures and head traumas - that may drastically lower remaining quality of life. Each year, nearly $50 billion is spent on medical costs related to fall injuries ...
A new way to measure human wellbeing towards sustainability
2021-03-16
From science to implementation: How do we know if humankind is moving in the right direction towards global sustainability? The ambitious aim of the SDGs is a global call to action to end poverty, protect the planet, and ensure all people enjoy peace and prosperity by 2030. To monitor progress towards these goals, a set of over 220 indicators is used, but there is a danger that one can no longer see the forest for the trees. A single comprehensive indicator to assess the overall progress is needed. In a new paper published in the Proceedings of the National Academy of Sciences (PNAS), IIASA researchers and colleagues from the University of Vienna, the Vienna Institute of Demography (Austrian Academy of Sciences), and the Bocconi ...
Smart quantum technologies for secure communication
2021-03-16
Researchers from Louisiana State University have introduced a smart quantum technology for the spatial mode correction of single photons. In a paper featured on the cover of the March 2021 issue of Advanced Quantum Technologies, the authors exploit the self-learning and self-evolving features of artificial neural networks to correct the distorted spatial profile of single photons.
The authors, PhD candidate Narayan Bhusal, postdoctoral researcher Chenglong You, graduate student Mingyuan Hong, undergraduate student Joshua Fabre, and Assistant Professor Omar S. Magaña?Loaiza of LSU--together with collaborators Sanjaya Lohani, Erin M. Knutson, ...
Ancient light illuminates matter that fuels galaxy formation
2021-03-16
ITHACA, N.Y. - Using light from the Big Bang, an international team led by Cornell University and the U.S. Department of Energy's Lawrence Berkeley National Laboratory has begun to unveil the material which fuels galaxy formation.
"There is uncertainty on the formation of stars within galaxies that theoretical models are unable to predict," said lead author Stefania Amodeo, a Cornell postdoctoral researcher in astronomy in the College of Arts and Sciences, who now conducts research at the Observatory of Strasbourg, France. "With this work, we are providing tests for galaxy formation models to comprehend galaxy and star formation."
The research, "Atacama Cosmology Telescope: Modeling the Gas Thermodynamics ...
Not just CO2: Rising temperatures also alter photosynthesis in a changing climate
2021-03-16
CHAMPAIGN, Ill. -- Agricultural scientists who study climate change often focus on how increasing atmospheric carbon dioxide levels will affect crop yields. But rising temperatures are likely to complicate the picture, researchers report in a new review of the topic.
Published in the Journal of Experimental Botany, the review explores how higher temperatures influence plant growth and viability despite the greater availability of atmospheric CO2, a key component of photosynthesis.
Excessive heat can reduce the efficiency of enzymes that drive photosynthesis and can hinder plants' ability to regulate CO2 uptake and water loss, the researchers write. Structural features can make plants more - or less - susceptible to heat stress. Ecosystem attributes - such as the size ...
New research adds to evidence that POTS may be an autoimmune disorder
2021-03-16
The symptoms of postural orthostatic tachycardia syndrome, or POTS, can be as varied as they are confounding.
There can be fatigue, pain, bleeding disorders and anxiety. Heart palpitations and lightheadedness are common. Some patients experience gastrointestinal issues or brain fog. For the most severely affected, the simple act of standing up can send them crumpling into unconsciousness.
Though likely much more common than once thought, POTS remains something of a mystery. Many physicians have never heard of it. There's no lab test to confirm a diagnosis and no treatment to cure the condition.
That could all be ...