Abstract
A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution appears after 50 h of milling. The grain size was 10 nm after 150 h of milling. Microstructure parameters were calculated by the Rietveld fitting of the X-ray Diffraction patterns. Magnetic characterizations of milled and annealed powders at 650 °C for 1 h were investigated. The heat treatment improves the magnetic properties of the milled powders by enhancing the saturation magnetization value from 94.31 to 127.30 emu/g and decreasing the coercivity from 49.07 to 29.57 Oe. The cohabitation of the FCC phase with the equilibrium crystalline phases observed after annealing is responsible of this magnetic softening. The as-milled powder was also consolidated by spark plasma sintering at 750 and 1000 °C. The obtained specimen consolidated at 750 °C improved the coercivity to 25.06 Oe and exhibited a compressive strength of 1062 Mpa and Vickers hardness of 518 ± 14 HV, with a load of 2 kN. The nanoindentation technique with the Berkovich indentor gave hardness and indentation elastic modulus of 6.3 ± 0.3 Gpa (~640 HV) and 111 ± 4 Gpa for samples consolidated by SPS at 750 °C.
Highlights
High-entropy alloys (HEAs) are a new field of metal alloys, discovered by Yeh et al [1]
The FeCoNiB0.5Si0.5 HEA alloy was successfully synthesized by mechanical alloying with a single solid solution structure, while the thermo-dynamic criteria for obtaining such a phase were not respected
The heat treatment of the as-milled FeCoNiB0.5Si0.5 HEA produced a material with softer magnetic properties
Summary
High-entropy alloys (HEAs) are a new field of metal alloys, discovered by Yeh et al [1]. The quinary system Fe25Co25Ni25(B,Si)25 [7] and the senary Fe25Co25Ni25(P,C,B)25 [8] high-entropy bulk metallic glasses (HE-BMGs) were synthesized by the copper mold casting method. They exhibited good soft magnetic and mechanical properties. The Fe25Co25Ni25(B,Si) system was already synthesized as a high-entropy bulk metallic alloy by the copper mold casting method and it showed excellent mechanical and magnetic properties [7]. Many bulk alloys and bulk high-entropy alloys have been consolidated by spark plasma sintering (SPS) of as-milled powders [15,16,17,18].
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