AsianScientist (Sep. 11, 2017) – In a study published in the journal Nature Communications, scientists in Japan have discovered a method to create single-crystal metal alloys that could lead to improved earthquake-resistant construction materials.
Most metals are made of a large number of crystals. However, for some metals, their properties are enhanced when they are in the form of a single crystal. Single-crystal metals are expensive to produce, thus limiting their widespread use in industries such as construction.
In this study, researchers from Tohoku University have found an economical way to create a single-crystal metal bar that is 70 centimeters in length and 15 millimeters in diameter. The alloy which they used, made of copper, aluminium and manganese, is a well-known shape memory metal that is easy to cut with machines. Increasing the size of the material’s crystals drastically enhances its elasticity, while altering its shape makes it quite strong.
To produce this large single-crystal metal bar, a ‘shape memory’ metal alloy, one that returns to its original shape after being deformed, is heated to 900°C then cooled to 500°C. This is the first step in the production process and is repeated five times.
The second round of treatment involves four cycles of heating to 740°C then cooling to 500°C. This is the crucial step in the formation of a single-crystal metal. Finally, the metal is heated once more to 900°C.
The entire process is inexpensive and takes advantage of a phenomenon known as ‘abnormal grain growth,’ wherein a metal’s multiple ‘grains,’ or crystals, grow irregularly, some at the expense of others, when exposed to heat. The resultant metal bar is very large compared to the sizes of current shape memory alloy bars, making it suitable for building and civil engineering applications, said Professor Toshihiro Omori of Tohoku University, the lead researcher in the study.
“Since the present technique is advantageous for mass production of single crystals because of the simplicity of the process, this finding opens the way for applications of shape memory single crystals for structural materials, such as for seismic applications in buildings and bridges,” said the researchers.
The article can be found at: Kusama et al. (2017) Ultra-large Single Crystals by Abnormal Grain Growth.
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Source: Tohoku University; Photo: Pixabay.
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