Anti-Invar in Fe-Ni
1994; American Institute of Physics; Volume: 75; Issue: 10 Linguagem: Inglês
10.1063/1.356761
ISSN1520-8850
AutoresM. Acet, Thomas Schneider, H. Zähres, E. F. Wassermann, Werner Pepperhoff,
Tópico(s)Metallurgical and Alloy Processes
ResumoAnti-Invar behavior in a material can be characterized by an anomalously large and a weak temperature-dependent thermal-expansion coefficient, when compared to the respective Grüneisen lattice expansion. It is just the opposite of the Invar effect, which is characterized by an anomalously small thermal-expansion coefficient. Common to Invar and anti-Invar is the fact that both posess moment-volume instabilities. Anti-Invar is observed in the paramagnetic state. It occurs in γ-Fe and in a number of 3d fcc binary and ternary alloys. In FexNi100−x alloys it is observed in the concentration range 70≤x≤100 at. % within the fcc stability range. The effect vanishes as the Invar concentration, x=65 at. %, is approached. To examine the valence electron concentration dependence of the anti-Invar effect the thermal expansion has been measured in the fcc state of FexNi100−x for 63≤x≤100 at. %. Using a model based on moment-volume instabilities in conjunction with a thermal activation process the size of the anti-Invar effect in these alloys has been determined. The volume enhancement is found to decrease with increasing Ni concentration from 2.8% in γ-Fe to 0% at x=65 at. %.
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