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Monday, 14 January 2019 01:00cat

High-strength and ductile alloys developed in China

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Extremely strong and ductile multicomponent alloys Extremely strong and ductile multicomponent alloys

Researchers at the City University of Hong Kong (CityU) have developed an extremely strong but still ductile and flexible multicomponent alloys.

The research focuses on high-entropy alloys (HEAs), new type of materials that are produced by 5 or more metals. HEAs are currently very popular in material science due to their desirable mechanical properties for structural engineering. However, as common metals, they face the strength-ductility trade-off dilemma, a conventional approach that improving strength of an alloy results in loss of ductility (the ability of a material to undergo plastic deformation before rupture).

According to authors, the study addresses the significant problems derived from the strength-ductility trade-off dilemma by creating alloys both strong and ductile through massive precipitation of nanoscale particles.
"Most conventional alloys contain one or two major elements, such as nickel and iron to manufacture. However, by adding additional elements of aluminium and titanium to form massive precipitates in the FeCoNi-based alloy, we have found both the strength and ductility have significantly increased, solving the critical issue of the trade-off dilemma for structural materials," Professor Liu Chain Tsuan, University Distinguished Professor of the Department of Materials Science and Engineering at CityU, stated. "We are able to make a new high-entropy alloy called Al7Ti7 ((FeCoNi)86-Al7Ti7) with a superior strength of 1.5 gigapascals and ductility as high as 50% in tension at ambient temperature. Strengthened by nanoparticles, this new alloy is five times stronger than that of the iron-cobalt-nickel (FeCoNi)-based alloy," he added.

Strong alloys develop another deformation instability, known as the necking problem. When such a material experiences high stress, its behavior may become unstable and lead to local deformation (necking). The team found that by adding "multicomponent intermetallic nanoparticles" made of different element atoms, this phenomenon could be mitigated. Those complex nanoparticles consist of nickel, cobalt, iron, titanium and aluminium atoms and measure 30-50 nanometers.

According to Professor Liu, those alloys can function in temperatures from -200°C to 1000°C and therefore they can be utilized in other fields of engineering such as mechanical engineering, aeronautic systems and cryogenic devices.



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