21 April 2020

Undergraduates help to develop new alloy

- Undergraduate students participate in cutting-edge research
- Theoretical predictions of microstructures used for novel alloy design
- New alloy showed improved oxidation resistance, low density and low cost compared to similar alloy systems

Microstructure of an alloy based on titanium, vanadium, chromium, zirconium and silicon

Undergraduates from the Department of Materials Science and Engineering have contributed to the development of a new High Entropy Alloy, demonstrating that in our discipline, advances can be made at any stage in your career.

The students, all of whom graduated in 2017, were part of the MEng Materials Science and Engineering (Research) programme in the Department, and they worked on the research project as part of an assessed unit during their course.

Under the watchful eye of Professor Russell Goodall, the students developed a brand new alloy composition, in work that has shown how Chvorinov’s rule may be used to investigate the potential for a selected combination of elements to form a useful alloy.

High Entropy Alloys are multicomponent alloys where (typically five or more) elements are combined in equal, or roughly equal, quantities. Successful combination of the elements leads to the formation of just a few (or even a single) simple structured phases, and the alloys possess unusual yet useful properties. Semi-empirical methods are used to predict the phases present, but variability may arise during alloy synthesis.

However, greater predictability is achieved using knowledge of the effective solidification temperature, which can be hard to predict for alloys which have never been made before. In this work, the researchers used Chvorinov’s rule for solidification time to predict the solidification temperature and hence help to design the new alloy system.

In this instance, researchers were combining titanium, vanadium, chromium, zirconium and silicon to produce a multiphase alloy. This combination was based on an existing HEA (TiVCrZrNb), and substituting niobium with silicon because the former was most expensive and most dense, and silicon is known to form silicide intermetallics which are temperature‐stable, has a relatively low density and cost, and can improve oxidation resistance in a variety of alloys by forming a protective oxide layer of SiO2.

Microstructure of an alloy based on titanium, vanadium, chromium, zirconium and silicon showing the presence of the different elements
Energy-dispersive X-ray spectroscopy (EDS) maps for TiVCrZr-Six alloys showing the distribution of each element (the top row shows maps for x = 0, the middle row shows maps for x = 0.5, and the bottom row shows maps for x = 1.0)

The outcome of the work was that an alloy was produced that, while not strictly an HEA, has the potential to be tailored to be suitable for a range of different applications, especially those with mechanical requirements. However, the purpose of the work was to demonstrate that Chvorinov’s rule can be used as a means of predicting the microstructure of the resultant alloys, as this could be applied to the design of many novel alloys.

Professor Goodall sums this work up: ‘This research project has made a valuable contribution to understanding the methods used in the development of new alloys. Moreover, it has shown that undergraduates are able to participate and contribute to genuine cutting edge research activities.

‘Many of the students who co-authored the paper, published in Metals, have gone on to PhD studentships either at the University of Sheffield or elsewhere, and all have a publication to their names before they have launched their research career.’

The authors of the paper who undertook the work as part of their undergraduate degree were Maximillian Bloomfield, Bethany Jim, George Kerridge, Jem Pitcairn, Michael Schobitz, Lorna Sinclair, Silvija Zilinskaite. They were supported in their work by Professor Goodall, Dr Zhaoyuan Leong and PhD student Yuhe Huang. The full article can be found here: https://www.mdpi.com/2075-4701/10/3/317

Image: student working; Text: Futures. Sheffield Made.

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