Invar effects in FeNiCo medium entropy alloys: From an Invar treasure map to alloy design

Abstract

To facilitate the understanding of Invar effects and design of FeNiCo-base Invar alloys characterized by low thermal expansion coefficient (TEC), we investigated the magnetic and thermal expansion behavior of an equiatomic prototype medium entropy alloy FeNiCo and a non-equiatomic (super Invar) Fe 63 Ni 32 Co 5 (at. %) reference alloy by means of experiments and ab initio calculations. Both alloys consist of a single face-centered cubic phase with fully recrystallized microstructure in the homogenized state. Large spontaneous volume magnetostriction is observed in both alloys below their respective Curie temperatures. The Invar effect in the non-equiatomic Fe 63 Ni 32 Co 5 alloy is of step-type with nearly zero TEC over a wide temperature range (from room temperature to 120°C) below its Curie temperature. The equiatomic FeNiCo alloy shows a peak-type Invar effect in a very narrow temperature range (from ∼675°C to ∼730°C) with relatively low TECs. The equiatomic FeNiCo alloy shows both higher saturation magnetization and Curie temperature than the non-equiatomic Fe 63 Ni 32 Co 5 alloy. The relationships among magnetic behavior, spontaneous volume magnetostriction and Invar effects for a wider array of metallic alloys are discussed mainly based on Masumoto's rule combined with Wohlfarth's itinerant electron theory. An Invar alloy search map is constructed based on the present results and available literature data to visualize the relationships among saturation magnetization, Curie temperature and thermal expansion coefficient for a wide range of Invar alloys. Based on this treasure map a design route for further developments of new Invar alloys by tuning their magnetic properties is discussed.

Effects of Cr/Ni ratio on physical properties of Cr-Mn-Fe-Co-Ni high-entropy alloys

“…This implies that the alloys with low Cr concentrations may show a magneto-volume effect. For added perspective, the ω s values of the investigated alloys ( ∼1 -2%) are smaller than those previously found in equiatomic FeCoNi and the super Invar Fe 63 Ni 32 Co 5 alloy (2.6 and 4.1%) [92] , which is consistent with the much smaller impact on expansion found for the present alloy.…”

Unveiling the mechanism of abnormal magnetic behavior of FeNiCoMnCu high-entropy alloys through a joint experimental-theoretical study

“…The mechanical properties of HEAs have been extensively studied [12][13][14][15][16][17] but their functional properties are less explored. Most recent studies on functional properties of HEAs have addressed thermal, electrical, and magnetic properties, yet detailed studies on the underlying mechanisms are still rare [18][19][20][21][22][23][24][25][26]. While as an example for specific functional properties the resistive and superconducting properties of a TaNbHfZrTi HEA with a critical temperature of 7.3 K have been addressed [20], long term benefits could arise from HEAs with combinations of good mechanical and functional properties.…”

Dislocation-induced breakthrough of strength and ductility trade-off in a non-equiatomic high-entropy alloy

“…Only for Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , the FiM state shows a slightly lower total energy as the AFM state (by about ~4 meV/atom). We also estimate T c for the investigated alloys in the AFM state based on the mean-field approximation [52][53][54] . The obtained T c are all within a range of 200~350 K i.e.…”