GIFT researchers have developed a method to extend a 10 mm metal sample to 200 mm without breaking it.
Prof. HyoungSeop Kim, Chong Soo Lee, Zargaran Alireza and their research team published the result of their research on a nanocrystalline high-entropy alloy material that was processed by high-pressure torsion and that can be extend in length to 2,000% of its original length.
Under certain conditions, such as high temperatures and very slow strain rates, some materials can stretch 300 to 500% until they tear or break. This property is called superpl asticity. Super-plastic materials can be used to form complexly-shaped parts such as those required for aircraft, space launch vehicles, and automobiles, but that are difficult to make with conventional molding processes. However, superplasticity occurs mostly at a slow deformation rate, so the molding time is long and as a result the processing cost is high.
The research team sought to overcome the limitations of existing materials by achieving superplasticity using a high-entropy alloy that has excellent thermal stability. High-entropy alloys were formed by using high-pressure torsion processing to form ultra-fine nanocrystals, an important prerequisite for superplasticization; the process inhibited grain growth at high temperatures.
This alloy achieved a world-class stretch rate of up to 2,000% under 5% high-speed strain per second, which is faster than the super-plastic process speed that was only 0.01 to 0.1% per second. This result can reduce molding time and cost compared to the existing superplasticizing process.
The results of the research were recently published in the science journal ‘Nature Communications’. Prof. HyoungSeop Kim said, “This study is the highest level of superplastic properties of metal materials reported so far.” It is expected to be a key element.