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. 2019 Oct 25;12(21):3508.
doi: 10.3390/ma12213508.

Spinodal Decomposition and Mechanical Response of a TiZrNbTa High-Entropy Alloy

Tai-You Liu  1 , Jacob C Huang  1   2 , Wen-Shuo Chuang  1 , Hung-Sheng Chou  1 , Jui-Yu Wei  1 , Chih-Yeh Chao  3 , Yu-Chin Liao  4 , Jason S C Jang  4   5
Affiliations

Spinodal Decomposition and Mechanical Response of a TiZrNbTa High-Entropy Alloy

Tai-You Liu et al. Materials (Basel). .

Abstract

In this study, the effects of spinodal decomposition on the microstructures and mechanical properties of a TiZrNbTa alloy are investigated. The as-cast TiZrNbTa alloy possesses dual phases of TiZr-rich inter-dendrite (ID) and NbTa-rich dendrite (DR) domains, both of which have a body-centered cubic (BCC) structure. In the DRs of the as-cast alloy, the α and ω precipitates are found to be uniformly distributed. After homogenization at 1100 °C for 24 h followed by water quenching, spinodal decomposition occurs and an interconnected structure with a wavelength of 20 nm is formed. The α and ω precipitates remained in the structure. Such a fine spinodal structure strengthens the alloy effectively. Detailed strengthening calculations were conducted in order to estimate the strengthening contributions from the α and ω precipitates, as well as the spinodal decomposition microstructure.

Keywords: high entropy alloy; precipitate; spinodal decomposition; strengthening.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) The X-ray diffractometry (XRD) analysis of the as-cast and as-homogenized Ti25Zr25Nb25Ta25 alloys, (b) the enlargement of the (220) peak profile and the fitting curves for body-centered cubic (BCC)1 and BCC2 of the as-cast sample, and (c) the enlargement of the (220) peak profile.
Figure 2
Figure 2
(a) The scanning electron microscope (SEM) back-scattered image (BEI) of the as-cast Ti25Zr25Nb25Ta25 high-entropy alloy (HEA), and the corresponding composition mapping for (b) Ti, (c) Zr, (d) Nb, and (e) Ta. Note that the Nb mapping does not really expose the dendrites (DRs) and inter-dendrites (IDs) clearly. This may be attributed to the fact that the Lα X-ray energy of element Nb (~2.169 eV) is slightly larger than the M absorption edge energy of element Ta (~1.804 eV). Therefore, in the dendrite regions, the Lα X-ray energy of element Nb would be significantly absorbed, resulting in an underestimated amount of the element Nb.
Figure 3
Figure 3
(a) The SEM BEI of the as-homogenized Ti25Zr25Nb25Ta25 HEA, and the corresponding composition mapping for (b) Ti, (c) Zr, (d) Nb, and (e) Ta.
Figure 4
Figure 4
The compressive stress–strain curves of the as-cast and as-homogenized TiZrNbTa alloys.
Figure 5
Figure 5
Transmission electron microscopy (TEM) results of the NbTa-rich region in the as-cast alloy: (a) selected area diffraction pattern (SADP) of the [011] BCC zone axis; (b) dark-field image taken from the α spot, as highlighted by the red arrow in SADP; and (c) dark-field image taken from the ω spot, as highlighted by the yellow arrow in SADP.
Figure 6
Figure 6
(a) The TEM dark-field images, (b) the corresponding high-resolution TEM images, and (c) the HAADF-STEM image of the interconnected structure in the as-homogenized alloy.
Figure 7
Figure 7
STEM-EDS line scan result of the spinodal interconnected structure along the red line of Figure 6c in the as-homogenized alloy.
Figure 8
Figure 8
TEM results of the α and ω precipitates in the as-homogenized alloy: (a) SADP of the [012] BCC zone axis; (b) dark-field image taken from the α spot, as highlighted by the red circle in SADP; and (c) dark-field image taken from the ω spot, as highlighted by the yellow circle in SADP.
See this image and copyright information in PMC

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