Evolution of microstructure and hardness in Hf25Nb25Ti25Zr25 high-entropy alloy during high-pressure torsion

Gubicza, Jenő and Heczel, Anita and Kawasaki, Megumi and Han, Jae-Kyung and Zhao, Yakai and Lábár, János (2019) Evolution of microstructure and hardness in Hf25Nb25Ti25Zr25 high-entropy alloy during high-pressure torsion. JOURNAL OF ALLOYS AND COMPOUNDS, 788. pp. 318-328. ISSN 0925-8388

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Abstract

A four-component equimolar high-entropy alloy (HEA) with the composition of HfNbTiZr and body-centered cubic (bcc) structure was processed by HPT at RT. The evolution of the dislocation density, the grain size and the hardness was monitored along the HPT-processed disk radius for different numbers of turns between ¼ and 20. It was found that most of the increase of the dislocation density and the refinement of the grain structure occurred up to the shear strain of ∼40. Between the strains of ∼40 and ∼700, only a slight grain size reduction was observed. The saturated dislocation density and grain size were ∼2.1 × 1016 m−2 and ∼30 nm, respectively. The saturation in hardness was obtained at ∼4450 MPa. These values were similar to the parameters determined in the literature for five-component HEAs processed by HPT. The analysis confirmed that the main component in the strength was given by the friction stress in the HPT-processed bcc HfNbTiZr HEA. It was also revealed that the contribution of the high dislocation density to the strength was significantly higher than the effect of the small grain size.

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