Twisting technique creates submicron ‘anti-crash wall’

A combined team of metallurgists, materials scientists and engineers from the Chinese Academy of Sciences, Shandong University and the Georgia Institute of Technology has developed a way to make stainless steel more resistant to metal fatigue. In their study published in the journal Science, the group developed a new twisting technique that functions as an “anti-crash wall” in the steel, giving it much more strength and resistance to cyclic creep.

Metal can experience fatigue when bent many times, leading to breaking. When this occurs in critical applications, it can result in catastrophic accidents such as bridge failures. Because of that, scientists have for many years been working to reduce or prevent stress levels in metals. In this new effort, the researchers found a way to dramatically improve the strength of a type of stainless steel while also boosting its resistance to what is known as cycle creep, where fatigue occurs due to ratcheting, a form of repeated bending.

The new technique involved repeatedly twisting a sample of 304 austenitic stainless steel in a machine in certain ways. This led to spatially grading the cells that made up the metal, resulting in the build-up of what the team describes as a submicron-scale, three-dimensional, anti-crash wall. Under a microscope, the researchers found an ultra-fine, sub-10 nanometer, coherent lamellar structure that slowed dislocation by preventing stacking faults.

Using other instruments, the team found that the reason the metal exhibits such improvements is due to the walls that are built up during twisting, behaving like springs, allowing the metal to absorb impacts, making the entire piece of metal more uniform in its ability to resist cycle creep.

In testing the metal after treatment, the research team found it boosted its strength by a factor of 2.6 while also cutting strain due to ratcheting by two to four orders of magnitude compared to untreated stainless steel. Such improvements, the team claims, could allow products made using the metal to be up to 10,000 times more resistant to fatigue. That makes it eligible for special applications, such as those that are needed for the aerospace industry.

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