Effects of mixing enthalpy and cooling rate on phase formation of Al <inf>x</inf> CoCrCuFeNi high-entropy alloys
Artikel i vetenskaplig tidskrift, 2019

We investigated the influence of mixing enthalpy and cooling rate on phase formation and selected the melt-spun Al x CoCrCuFeNi (x = 0, 0.1, 0.5, 0.8 and 1.0 in molar ratios) high-entropy alloys (HEAs) as a model system. The mean mixing enthalpy (ΔH mix ) of the alloy system is tuned from positive to negative by increasing Al molar ratios while the mixing entropy (ΔS mix ) only has an insignificant variation. Microstructure analyses revealed that the dominant phase in the Al x CoCrCuFeNi HEAs changes from a face-centered cubic (FCC) to body-centered cubic (BCC) structure with the variation of the ΔH mix . Accompanying with phase changing, the lattice constant of the FCC phase increases linearly with Al molar ratio regardless of cooling rate, indicating that the lattice expansion caused by the substitutional alloying of Al plays an important role in the phase evolution, in addition to the effect of the ΔH mix . The increasingly negative enthalpy ΔH mix with Al addition also leads to more pronounced phase separation with the formation of ordered intermetallic phases in the BCC-dominant HEAs than the FCC-dominant ones. Interestingly, when the magnitude of the mean ΔH mix is small, both the coarsening of Cu-rich nanophase and decomposition of the solid-solution phase in the Al 0.5 CoCrCuFeNi HEA are suppressed. This observation is in line with thermodynamic predictions that a weak ΔH mix benefits the stabilization of the solid-solution phase.

Cooling rate

High-entropy alloys

Mixing enthalpy

Phase stability

Phase decomposition

Författare

X. Xu

Tohoku University

Sheng Guo

Chalmers, Industri- och materialvetenskap, Material och tillverkning

T. Nieh

City University of Hong Kong

University of Tennessee

C. T. Liu

City University of Hong Kong

A. Hirata

Tohoku University

M. W. Chen

Johns Hopkins University

Tohoku University

Materialia

2589-1529 (eISSN)

Vol. 6 100292

Ämneskategorier

Fysikalisk kemi

Livsmedelsteknik

Metallurgi och metalliska material

DOI

10.1016/j.mtla.2019.100292

Mer information

Senast uppdaterat

2019-04-10