A new theory of iron–nickel alloy solidification has been proposed. Regulating the process of creating Invar (iron–nickel, Fe–Ni) could bring about a more uniform structure, controlled characteristics, and improved properties in the final product.
Who
Physicists at the Ural Federal University (UrFU) have determined that oncoming flow plays an important role in the technology for creating Invar products, namely in the solidification process. When an alloy cools, the liquid layer flows on top of the solidified layer.
Dmitry Alexandrov, Head of the Ural Federal University’s Laboratory of Multi-Scale Mathematical Modeling, gave the following analogy to explain the process to phys.org: “When the water freezes, it pushes out all the dirt. You could put a piece of ice in your mouth, it will be clean. Approximately the same happens with melts during cooling. Only they do not push out all the impurities, just some of them. Some of the impurities come out and some remain in the melt. What remains in the melt fills the gaps between the crystals that solidify and the voids that remain. Thus, the alloys are heterogeneous: one tiny piece is enriched, while the neighboring piece is not. And this affects the properties of the finished product.”
Why it matters
Nickel and iron alloys are used to create high-precision instruments, including clocks, seismic sensors, chip substrates, valves and engines in aircraft, and instruments for telescopes – all fields where precision is paramount.
The term “Invar” comes from the word “invariable”, referring to the key property of the alloy, which doesn’t expand or contract due to changes in temperature. Any impurities have the potential to affect this property.
“The practical significance of the theoretical work conducted by the Ural scientists is that even purer Invar alloys than those currently being produced could be obtained. Purity levels play a big role in their application. For example, purer alloys can be used to produce more reliable containers for storing liquefied natural gas. It appears likely that Russian researchers will develop a whole line of innovative invars over the next few years” – Comment by Leonid Khazanov / Consultant – Metals and technologies // Science columnist specializing in metals, the fuel and energy sector, and industry trends. PhD in economics. Consults foreign companies on investments in Russian mining locations and factories. 
