#single crystals

A new heating method for certain metals could lead to improved earthquake-resistant construction materials.

Tohoku University researchers and colleagues have found an economical way to improve the properties of some ’shape memory’ metals, known for their ability to return to their original shape after being deformed. The method could make way for the mass production of these improved metals for a variety of applications, including earthquake-resistant construction materials.

Most metals are made of a large number of crystals but, in some cases, their properties improve when they are formed of a single crystal. However, single-crystal metals are expensive to produce.

Researchers have developed a cheaper production method that takes advantage of a phenomenon known as ‘abnormal grain growth.’ By using this method, a metal’s multiple 'grains’, or crystals, grow irregularly, some at the expense of others, when it is exposed to heat.

The team’s technique involves several cycles of heating and cooling that results in a single-crystal metal bar 70 centimetres in length and 15 millimetres in diameter. This is very large compared to the sizes of current shape memory alloy bars, making it suitable for building and civil engineering applications, says Toshihiro Omori, the lead researcher in the study.

A laser compressing an aluminum crystal provides a clearer view of a material’s plastic deformation, potentially leading to the design of stronger nuclear fusion materials and spacecraft shields.

Imagine dropping a tennis ball onto a bedroom mattress. The tennis ball will bend the mattress a bit, but not permanently – pick the ball back up, and the mattress returns to its original position and strength. Scientists call this an elastic state.

On the other hand, if you drop something heavy – like a refrigerator – the force pushes the mattress into what scientists call a plastic state. The plastic state, in this sense, is not the same as the plastic milk jug in your refrigerator, but rather a permanent rearrangement of the atomic structure of a material. When you remove the refrigerator, the mattress will be compressed and, well, uncomfortable, to say the least.

But a material’s elastic-plastic shift concerns more than mattress comfort. Understanding what happens to a material at the atomic level when it transitions from elastic to plastic under high pressures could allow scientists to design stronger materials for spacecraft and nuclear fusion experiments.