Effect of Heat Treatments on Magnetic Properties and Thermal Expansion Behavior in Two Distinct Types of Fe-Ni Invar Alloys

The casting process of Fe-Ni Invar alloy could drastically affect magnetic properties and thermal expansion. We have observed analogous trends of saturation magnetization and thermal expansion coefficient in two distinct types of casted samples, as we perform post-annealing at different temperatures. X-ray diffraction measurements show that all the alloys remain in the same face-centered cubic structure after different heat treatments without phase transformation. With the help of X-ray diffraction and differential thermal analysis, we have inferred that these changes in properties might be induced by magnetic lattice transitions and analyzed the possible reason for property differences in samples. This work delivers a perspective on the relationships between thermal expansion, magnetic properties, and heat treatments, which could help to improve the industrial assembly line design.