A general structural-property relationship in metallic glass - Charles Zeng

FEBRUARY 1, 2016

Structure-property relationship is a central topic in materials science. In crystalline materials, the well-defined lattice structure or defects enable us to describe their properties quantitatively. The structure of glass is basically featureless, very few rigorous laws are currently known for defining its ‘disordered’ structure. Establishing general and exact rules regarding structure-property relationships in glass remain elusive. A breakthrough has been made by a international team led by Dr. Qiaoshi Zeng, a staff scientist from HPSTAR. This team established a general rule correlating the bulk properties (volume V) with most prominent atomic structure information (principle diffraction peak position q1) for metallic glasses, i.e. V∝(1/q1)2.5. It is shown that the 2.5 power law is strictly followed by any metallic glass with its volume tuned by pressure and/or composition. This general 2.5 power law is attributed to the well constrained structure change/modification inevitably happened during pressure and/or composition tuning of metallic glasses, which brings new insight into the structure of metallic glasses. These results are just published by PNAS ( doi: 10.1073/pnas.1525390113).

Metallic glass is a new category of materials which combines disordered atomic-level structure and non-directional metallic bonding. As a result, metallic glasses could possess a combination of desirable properties of conventional oxide glass and crystalline metals, and even beyond. E.g. extremely high strength, hardness at room temperature and good formability at high temperature (above glass transition at ~ two thirds of melting temperature). Quantitative property-property correlations have been extensively observed in metallic glasses, which suggests possible common structural feature among them. However, due to the lack of knowledge about their atomic structure at various length scales, general quantitative relationship between atomic-level structures and the macroscopic properties of metallic glass is difficult to establish.

Recently, Zeng and his colleagues found that under compression, the volume (V) of a metallic glass changes precisely to the 2.5 power of its principle diffraction peak position (1/q1) by experiments [Phys. Rev. Lett. 112, 185502 (2014)] and simulations [Science 349,1306 (2015)]. Further, the current new study published in PNAS finds that this 2.5 power law holds even through the first order polyamorphic transition of a Ce68Al10Cu20Co2 MG. This transition is, in effect, the equivalent of a continuous “composition” change of 4f-localized “big Ce” to 4f-itinerant “small Ce”, indicating the 2.5 power law is general for tuning with composition. The exactness and universality imply that the 2.5 power law may be a general rule defining the structure of MGs.

“Although two similar non-cubic power laws have been reported with pressure tuning or composition tuning of metallic glasses by our group and by Dong Ma and his colleagues, respectively, no connection between these two power laws has been addressed. This puzzles the glass community,” said Dr. Zeng. “By studying a special metallic glass, the polyamorphic Ce-based metallic glass under high pressure, we could be able to combine pressure and composition tuning of metallic glass in one experiment for the first time. And this is the key point of this study to address the puzzle.”

Other co-authors in this team include HPSTAR’s Zhidan Zeng, Hongbo Lou, Wenge Yang, Hongwei Sheng, Ho-kwang Mao and Wendy Mao. This work was supported by NSFC under grand U1530402.

Caption: The sample volume of a Ce-based metallic glass during compression directly measured by in situ high pressure transmission x-ray tomography in a specially designed cross diamond anvil cell.

A schematic cartoon: Pressure and composition are found to have the same effects on the volume or density of metallic glass which follows a general strict 2.5 power law. Image is provided courtesy of Qiaoshi “Charles” Zeng.

Please find the full story at  http://www.pnas.org/content/early/2016/01/27/1525390113.

Other report of the work: https://www.gl.ciw.edu/content/2016/2/10/making-sense-metallic-glass