This alloy is kinky: It just won't crack or bend at extreme temperatures

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The alloy's resilience to bending and fracture across an enormous range of conditions could open the door for a novel class of materials for next-generation engines.

This new class of metals is known as refractory high or medium entropy alloys. (Photo: Representative Image)

New Delhi,UPDATED: Apr 23, 2024 15:55 IST

Metals have a habit of cracking under extreme temperatures due to kinking or bending of the crystals at the atomic level. Not anymore.

Scientists have developed a metal alloy that has impressive strength and toughness at both extremely hot and cold temperatures, a combination of properties that seemed so far to be nearly impossible to achieve.

The alloy can withstand kinking, a type of deformation or distortion that occurs in metal materials, particularly in thin sheets or wires. When a metal undergoes kinking, it forms a sharp bend or twist, often resulting in localised areas of severe plastic deformation. This deformation can compromise the structural integrity and mechanical properties of the metal.

The metal is made from a combination of iobium, tantalum, titanium, and hafnium. Researchers said that the alloy's resilience to bending and fracture across an enormous range of conditions could open the door for a novel class of materials for next-generation engines that can operate at higher efficiencies.

The findings have been published in the journal Science, which states this new class of metals is known as refractory high or medium entropy alloys. This material structure map shows kink bands formed near a crack tip during crack propagation (from left to right) in the alloy at 25 C, room temperature. (Photo: Berkeley Lab)

The alloy to a distinctive category known as refractory high or medium entropy alloys (RHEAs/RMEAs). Unlike conventional alloys comprising one primary metal with trace elements, RHEAs/RMEAs blend nearly equal proportions of metallic elements with exceptionally high melting points, yielding unique properties still being deciphered by scientists.

Ritchie's team has focused on these alloys due to their potential for high-temperature applications.

Previous investigations revealed RHEAs/RMEAs to be robust yet exceedingly low in fracture toughness. Thus, the unexpected discovery of an RMEA alloy exhibiting remarkably high toughness was surprising.

This specific alloy, comprising niobium, tantalum, titanium, and hafnium (Nb45Ta25Ti15Hf15), surpassed even cryogenic steel in toughness at room temperature.

However, practical applications demand consideration of extreme temperatures. Strength and toughness assessments were conducted at temperatures ranging from -196C to 1200C. Remarkably, the alloy maintained considerable strength across this spectrum, with fracture toughness remaining high.

Further analysis revealed the alloy's extraordinary toughness, attributed to a rare defect known as a kink band. These bands, form within the crystal structure under stress, redirect force, impeding crack propagation and mitigating fracture. Contrary to expectations, the presence of kink bands enhanced toughness rather than diminishing it.

While promising, the unique alloy still requires extensive research and testing before practical applications, such as in aerospace components, can be realised. Understanding its atomic structure and mechanical behaviour is imperative for harnessing its full potential.

Published By:

Sibu Kumar Tripathi

Published On:

Apr 23, 2024