Today, the body of an ordinary family car consists of 193 different types of steel. The steel for each part of the car has been carefully selected and optimised. It is important, for example, that all parts are as light as possible because of the fuel consumption, whereas other parts of the car have to be super strong in order to protect passengers in a collision.
Super strong nanostructured metals are now entering the scene, aimed at making cars even lighter, enabling them to stand collisions in a better way without fatal consequences for the passengers. Research into this field is being conducted worldwide. Recently, a young PhD student from the Materials Research Division at Risø DTU took research a step further by discovering a new phenomenon. The new discovery could speed up the practical application of strong nanometals and has been published in the highly esteemed journal "Proceedings of the Royal Society" in London in the form of a paper of approx. 30 pages written by three authors from Risø DTU.
The research task of the young student, Tianbo Yu, is to determine the stability in new nanostructured metals, which are indeed very strong, but also tend to become softer, even at low temperatures. This is due to the fact that microscopic metal grains of nanostructured metals are not stable - a problem of which Tianbo Yu's discovery now provides an explanation.
The fine structure consists of many small metal grains. The boundaries between these metal grains can move, also at room temperature. At the same time a coarsening of the structure takes place and the strength of the nanometal is consequently weakened. Tianbo Yu's has now shown that the boundaries of the grains can be locked, when small particles are present and that the solution is technologically feasible. This has paved the way for car components to be made of nanometals.
"We are cooperating with a Danish company and also a Danish consulting engineering company with the purpose of developing light and strong aluminium materials with a view to their application in light vehicles where especially deformation at high rate as in a collision is in focus. The new findings will be included in this work," says Dorte Juul Jensen, head of division and Dr. Techn. She is happy that the excellent findings also have practical applications.
Tianbo Yu comes from Tsinghua University in Beijing – a leading university within technical scientific research. His studies in Denmark have been financed by the Danish National Research Foundation, which also supports a Danish-Chinese basic research centre in the Materials Research Division, where Tianbo Yu is now employed.
Tianbo Yu is a dedicated and talented researcher, who wishes to pursue a research career in Denmark. His wife is a student at RU (Roskilde University) and along with their studies, they both have decided to put a lot of effort into learning Danish; and they have become good at it. – All in all, a success for science as well as globalisation.
Smaller metal grains result in stronger metals
Nanometals contain very small metal grains - from 10 to 1,000 nanometers. One nanometer is a millionth of a millimetre. The smaller the metal grains become, the stronger the metal becomes. The metal becomes twice as strong, for example, if the individual metal grains are made four times smaller. That is why the materials scientists work to reduce the size of the individual metal grains. In steel and aluminium, the particles have been reduced to below 1 micrometre, which is one thousandth of a millimetre. There is a great interest in nanometals worldwide. Nanometals are super strong and their super strength can be combined with other desired properties, too.
A good example of a super strong nanometal is the thin steel wires used in grand pianos and for strengthening lorry tyres and containers, which have to withstand an extremely high pressure. Actually, they have been known for many years, but now they have become the subject of scientists' renewed and strong interest.
Scientists are not only interested in the size of the metal grains. The interfaces between the individual metal grains are also important to a number of properties. A special type of grain boundaries, so-called twin boundaries, provides both strength and good electrical conductivity. This paves the way for producing thinner wires, thereby reducing material consumption.