Abstract
Strengthened by Oxygen doping, the single-phase body-center-cubic (BCC) TiZrHfNbO refractory high-entropy alloys (HEAs) become strong and ductile. However, phase stability at intermediate temperature and the effects of Oxygen addition on the deformation behavior during tensile tests need to be well understood. In the present work, the phase decomposition of (TiZrHfNb)100-xOx HEAs with Oxygen doping in the range of x=0, 0.5, 1, 1.5, 2 was examined at 873 K. The formation of hexagonal-close-packed (HCP) solid-solution precipitates in submicron size, enriched with Hf, Zr and O elements, were investigated by a combination of X-ray diffraction, transmission electron microscopy and atom probe tomography. Tensile tests of alloys annealed at both 1273 K and 873 K were conducted. It was found that doping Oxygen increased the yield strength and maintained ductility for alloys annealed at 1273 K, while formation of HCP precipitates after annealed at 873 K deteriorates the plasticity significantly. To unveil the deformation behaviors, in situ synchrotron X-ray diffraction experiments were applied in the current research. The single-crystal elastic constants and shear elastic anisotropy of HEAs with and without Oxygen doping were calculated and found similar to those of “Gum Metal” Ti alloy. Yet current HEAs possess higher BCC phase stability than “Gum Metal”, and no stress-induced phase transformation was detected during deformation.
Highlights
High-entropy alloys (HEAs), consisting of multi-principle elements with equi-atomic or near equiatomic ratio, have been attracting remarkable attention since the new concept of composition design was proposed (Yeh et al, 2004)
Of the HEAs developed to date, refractory HEAs are of special significance due to their outstanding mechanical properties at high temperatures and promising application potential in thermally-harsh environments, such as aerospace and petrochemical industries (Senkov et al, 2012; Senkov et al, 2013; Zhang et al, 2014; Pogrebnjak et al, 2015; Senkov and Semiatin, 2015; Miracle and Senkov, 2017; Vrtnik et al, 2017)
Recent investigations by Chen et al (2019) demonstrated that the HfNbTaTiZr refractory HEA decomposed into three phases, the body-centered-cubic (BCC) matrix, BCC precipitates enriched in Ta-Nb, and hexagonal-close-pack (HCP) precipitates enriched in Zr-Hf when annealed at 973 K even after a short-term annealing of 2.5 h
Summary
High-entropy alloys (HEAs), consisting of multi-principle elements with equi-atomic or near equiatomic ratio, have been attracting remarkable attention since the new concept of composition design was proposed (Yeh et al, 2004). Stability and Deformation Behavior of TiZrHfNbO applications To solve this issue, appropriate composition design and alloying, e.g., TiZrHfNb (Wu et al, 2014) and AlTiZrHfNb HEAs (Wu et al, 2018), could be promising approaches for realworld applications, considering these alloys exhibited great tensile ductility at ambient temperature. For the applications of these alloys at high temperatures, maintaining the high phase stability in a wide temperature range during a long-term service is crucial. Recent investigations by Chen et al (2019) demonstrated that the HfNbTaTiZr refractory HEA decomposed into three phases, the body-centered-cubic (BCC) matrix, BCC precipitates enriched in Ta-Nb, and hexagonal-close-pack (HCP) precipitates enriched in Zr-Hf when annealed at 973 K even after a short-term annealing of 2.5 h
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