These include TiZrHfCoNiCu (see pictures), an alloy of titanium, zirconium, hafnium, cobalt, nickel and copper. The scientists are thus working on high entropy shape memory alloys (HE-SMA). Researchers at the IW are going one step further and applying the described principle of high entropy alloys on the special field of shape memory alloys (SMA). The Cantor and Senkov alloys, which are named after their discoverers, are particularly well known as pioneering alloy systems in this respect. Unusual phenomena in microstructure and mechanical properties that cannot be achieved in conventional alloys are revealed. This new concept of alloy design opens up a huge range of possible combinations with considerable technological potential. However, IW studies in this area have been able to demonstrate, despite the supposed chaos, a form of order that is somewhere between the classical order in conventional alloys and a chaotic distribution of elements. This means that it is not a single element determines the order in the material and the resulting properties, but rather the large number of elements with a random occupation of the lattice sites. The new class of high-entropy alloys (HEA) refers to metals with five or more elements in almost the same concentration.

The main element also determines the crystal lattice and thus the regular internal arrangement of the atoms in a material.īut what happens when there is no single main element alone, but instead there are five or more elements that together take the main role? Researchers at the Institute of Materials Science (IW) at Leibniz University Hannover are precisely investigating this question and are working on so-called high entropy alloys as part of the Priority Program 2006 of the German Research Foundation (DFG). The main element as the basis determines the overall properties of a material, such as strength, ductility and hardness these properties can be improved within certain limits by the addition of secondary elements. In steels, iron as the main element usually has a mass fraction of more than 90%. Metallic materials such as steels or aluminum alloys, which are conventionally used in a wide range of applications, consist mainly of one main element and some important secondary elements in low concentrations. For further developments in almost all technological areas, the materials used must therefore also become more efficient. Whether in electrical engineering, power generation, transportation or aerospace – the fundamental physical properties of all technical components are generally determined by the selection of the right materials.

High entropy