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Tsuru, Tomohito; Han, S.*; Chen, Z.*; Lobzenko, I.; Inui, Haruyuki*
Materia, 63(10), p.695 - 702, 2024/10
VNbMoTaW, a typical high-entropy alloy with the BCC phase, is composed of metals with high melting points, and is called a reflectory high-entropy alloy. TiZrNbTaHf, which are also known as typical high-entropy alloys with the BCC phase, are also single phase and have a melting point 500 
C lower than that of VNbMoTaW, but are known to exhibit excellent ductility at low temperatures below room temperature. Understanding what properties govern the mechanical properties is essential for designing alloys such as high-temperature resistant alloys with excellent high-temperature strength and low-temperature ductility. Given that both VNbMoTaW and TiZrNbTaHf are single-phase alloys, the key lies in the relationship between the constituent elements and the properties underlying the deformation, such as dislocations. This paper presents the results of the differences in mechanical properties of these two refractory high-entropy alloys, using experimental, theoretical, and computer simulations to investigate the key factors controlling ductility and strength.
Tsuru, Tomohito; Han, S.*; Matsuura, Shutaro*; Chen, Z.*; Kishida, Kyosuke*; Lobzenko, I.; Rao, S.*; Woodward, C.*; George, E.*; Inui, Haruyuki*
Nature Communications (Internet), 15, p.1706_1 - 1706_10, 2024/02
Times Cited Count：31 Percentile：98.70(Multidisciplinary Sciences)Refractory high-entropy alloys (RHEAs) have attracted attention because of their potential for use in ultrahigh-temperature applications. Unfortunately, their body-centered-cubic (BCC) crystal structures make them more brittle than the ductile and fracture-resistant face-centered-cubic (FCC) HEAs. RHEAs also display significantly lower creep strengths than a leading Ni-base superalloy and its FCC matrix. To overcome these drawbacks and develop RHEAs into viable structural materials, improved fundamental understanding is needed of factors that control strength and ductility. Here we investigate two model RHEAs, TiZrHfNbTa and VNbMoTaW, and show that the former is plastically compressible down to 77 K, whereas the latter is not below 298 K. We find that hexagonal close-packed (HCP) elements in TiZrHfNbTa lower its dislocation core energy, increase its lattice distortion, and lower its shear modulus relative to VNbMoTaW whose elements are all BCC, leading to the formers higher ductility and modulus-normalized yield strength. Consistent with our yield strength models, primarily screw dislocations are present in TiZrHfNbTa after deformation, but equal numbers of edge and screw segments in VNbTaMoW. Dislocation cores are compact in VNbTaMoW and extended in TiZrHfNbTa, and different macroscopic slip planes are activated in the two RHEAs, which we attribute to the concentration of HCP elements. Our findings demonstrate how electronic structure changes related to the ratio of HCP to BCC elements can be used to control strength, ductility, and slip behavior to develop the next generation of high-temperature materials for more efficient power plants and transportation.
Nb with the L1
structureOkamoto, Norihiko*; Takemoto, Shohei*; Chen, Z. M. T.*; Yamaguchi, Masatake; Inui, Haruyuki*
International Journal of Plasticity, 97, p.145 - 158, 2017/10
Times Cited Count：14 Percentile：52.40(Engineering, Mechanical)Tsuru, Tomohito; Lobzenko, I.; Han, S.*; Chen, Z.*; Kishida, Kyosuke*; Inui, Haruyuki*
no journal, ,
In this study, the effect of the constituent elements on the mechanical properties of the ternary BCC medium entropy alloy (MEA) model was investigated by the first-principles calculation. For NbTiZr with different composition as BCC-MEA, we construct an atomic model with random solid solution and short-range ordered (SRO) structure obtained from Monte Carlo analysis. For each of the Random structure and SRO structure, various bulk properties related to the formation of the SRO, mean square atomic displacement (MSAD), elastic properties, stacking defects, twins, etc. are investigated. The formation energy and distribution of dislocation dipoles were evaluated by first-principles calculation of the dislocation structure, and the influence of Group 4 elements was examined.
