On Zero or Negative Thermal Dilatation and Phase Transformations in Cold-Worked Fe–Ni Invar Alloys

Abstract

The effect of cold-swaging on the low thermal dilatation in the Fe–Ni Invar alloys, especially the negative dilatation of the 36%Ni alloy, was investigated by the X-ray and magnetic measurements as well as the thermal expansion measurements in the directions perpendicular and parallel to the swaging direction. Anomalies of the α→γ transformation were found in the irreversible alloy, which behaves as including higher A_f-points or lower nickel contents. The γ-phase alloy after this transformation includes presumably lower Curie points. For the 36%Ni alloy, a swelling portion was found in the magnetic susceptibility in the para-process versus temperature curve in a lower temperature range, which is in agreement with the range of the negative dilatation. To explain such a state, a shear mechanism was discussed.