Thermal Expansion Coefficient of Fe-Ni(fcc) Alloys

The thermal expansion coefficient, α, was measured over the range from 800℃ to room temperature for Fe-Ni(fcc) alloys. The results obtained are as follows : (1) On the temperature vs. α curve, a peak appears at the Curie temperature, T_c, in the composition range above 42% of Ni but none in the range of 42-30% of Ni. (2) T_c of the alloys with more than 42% of Ni is present in the γ phase at a temperature higher than the upper limit for (α+γ) mixture phase in the equilibrium diagram. (3) the value of α_P obtained from α by climinating the magnetic contribution shows a minimum in the Invar range as in the case of α. This may suggest that the interatomic cohesive force must be considered in addition to the magnetic effect in making clear the origin of Invar property