Physicists of the Ural Federal University (UrFU) have created a theory for the hardening of iron-nickel (Fe-Ni) alloys (Invar). They determined that the incoming flux plays an important role in the technology of creating reverse products, namely in the solidification process: when the alloy cools, the liquid layer flows over the solid layer. If this process is regulated, it is possible to control the properties of the alloy, obtaining a more uniform structure and, accordingly, improving the properties of the final product.

The work of scientists is significant, since nickel-iron alloys are used to create high-precision instruments: clocks, seismic sensors, chip substrates, valves and actuators in airframes, instruments for telescopes. Calculations will help to create an alloy of the required structure, which will affect the quality of the final products. Description of the fusion model and behavior, as well as analytical calculations, were published by the scientists in the journal Scientific Reports.

“Let me explain the work with the help of an analogy. When the water freezes, it pushes out all the dirt. So you can take a piece of ice in your mouth, it will be clean. Almost the same thing happens with melting during cooling. Except that they do not expel all the impurities but some. Some The impurities come out and some dissolve. What remains in the melt fills the gaps between the crystals that solidify and the voids left. Thus, the alloy is heterogeneous: one small piece is enriched, while the adjacent piece is not. Says Dmitry Alexandrov, head of the Laboratory for Multiscale Mathematical Modeling at Ural University FEMA, it affects the properties of the final product.

The main thing that scientists have shown are the processes in the biphasic layer: a layer in which there are both solid and liquid phases, inside of which there is a transition from a liquid to a solid.

“This layer completely changes the crystallization scenario. Thus, for example, the temperature at each point of this layer is lower than the crystallization temperature, and the crystals and dendrites release phase-shift heat and thus partially compensate for the supercooling. In addition, the growing solid phase Displaces dissolved impurities, lowering the crystallization temperature. These processes lead to the formation of complex branched solid-phase structures, the gaps between which are filled with a liquid with a higher concentration of impurities,” says Lyubov Turupova, senior researcher in the Laboratory for Mathematical Modeling of Physical and Chemical Processes at UrFU.

reference

Invar – from the word “unchanged”, as the alloy almost does not expand or contract when the temperature changes. The first alloy Invar was discovered by the Swiss scientist Charles Edouard Guillaume in 1896. In 1920 he was awarded the Nobel Prize in Physics for it.

Nickel-iron alloys are used when particle dimensional stability of finished parts is required: in precision instruments, clocks, valves, etc. One of the element’s first applications is rods for pendulum clocks. At the time the pendulum clock was invented, it was the most accurate chronometer in the world. Today, Invars are also used in astronomy, as components that support size-sensitive optics for astronomical telescopes.

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