Annealing (glass)

High entropy alloys

Metallurgy

Materials science

Carbide

Lamellar structure

Refractory metals

Thermodynamics

Physics

Alloy

Microstructure

Eutectic system

Composite material

Isothermal process

Journal of Material Science and Technology

The microstructure and mechanical properties of as-cast and isothermally annealed CxHf0.25NbTaW0.5 (x=0, 0.05, 0.15, 0.25) refractory high-entropy alloys (RHEAs) were studied. Both the as-cast and annealed RHEAs consisted of disordered body-centered cubic solid solution phase and metal carbide (MC) phase with a face-centered cubic crystal structure (Fm-3m space group). The primary carbides were enriched with Hf and C elements and tended to form lamellar eutectic-like microstructure in the interdendrites. The lamellar eutectic-like structure in the interdendrites would be formed from the decomposition of sub-carbide M2C under the influence of Hf element. After isothermal annealing, slatted carbides were precipitated on the matrix, and the distribution became more uniform with high C content. The formation of carbides strongly influenced the mechanical properties both at room and high temperatures. The yield strength values of C0.25Hf0.25NbTaW0.5 RHEA at 1473 and 1673 K were 792 and 749 MPa, respectively. The result had exceeded the high temperature mechanical properties of currently known RHEAs. Moreover, this RHEA exhibited high-temperature performance stability and excellent plasticity, exceeding 30 and 50% at room and elevated temperatures (above 1273 K), respectively. During thermal deformation, carbon-containing RHEAs obtained more severe work hardening than that of ACH0 RHEAs, and required greater dynamic recrystallization to achieve the dynamic equilibrium.

Microstructure and mechanical properties of C Hf0.25NbTaW0.5 refractory high-entropy alloys at room and high temperatures