In the thermo-electromotive force versus temperature curve, when the ordered specimen is heated from room temperature, the thermo-electromotive force value suddenly decreases at 550°,and gradually from 550° to 730°. In the thermal expansion coefficient versus temperature curve, the thermal expansion coefficient suddenly reaches the maximum at 730°, then it decreases as the temperature goes down, but shows a distinct increase in a small degree at about 550°. In X-ray investigation, it has been discovered that FeCo alloy has body-centered cubic lattice in all the ranges of the process of superlattice formation. In the lattice constant versus temperature test by X-ray analysis at high temperature, it has been discovered that changes take place at 550° and 730°, and these changes correspond to the total expansion diagram. When FeCo alloy is quenched from higher temperature than 730°, it shrinks abnormally on the way of quenching process.
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