Mixing-enthalpy modulation on phase transformation in the gradient chemical core/shell high-entropy shape-memory alloys

Mixing-enthalpy modulation on phase transformation in the gradient chemical core/shell high-entropy shape-memory alloys

High-entropy alloys (HEAs) are of more chemical inhomogeneity than traditional alloys. How thermal effects perturb entropy and chemical fluctuations is a major scientific issue. In this study, selected benchmark phenomena revealed by in-situ synchrotron X-ray mapping demonstrates how local chemical...

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Main Authors: E-Wen Huang, Tu-Ngoc Lam, Zachary H. Aitken, Mao-Yuan Luo, Nien-En Chiang, Yuh Sun, Jo-Chi Tseng, Ching-Yu Chiang, Wan-Zhen Hsieh, Wen-Jay Lee, Yong-Wei Zhang, Peter K. Liaw, Che-Wei Tsai
Format: Article
Language:English
Published: Elsevier 2025-03-01
Series:Materials & Design
Subjects:
High-entropy shape-memory alloys
Phase transformation
Mixing enthalpy
Gradient structure
Core/shell structure
Online Access:http://www.sciencedirect.com/science/article/pii/S0264127525000437
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Summary:High-entropy alloys (HEAs) are of more chemical inhomogeneity than traditional alloys. How thermal effects perturb entropy and chemical fluctuations is a major scientific issue. In this study, selected benchmark phenomena revealed by in-situ synchrotron X-ray mapping demonstrates how local chemical gradients control temperature-dependent behaviors in HEAs. Specifically, the gradient chemical layers in the core/shell structure play an important role in the thermally-induced phase transformation of Cu15Ni35Ti50-x(HfZr)x high-entropy shape-memory alloys (HESMAs). The dendritic microstructure in Cu15Ni35Ti20(HfZr)30 exhibits the mixing enthalpy-driven pronounced composition inhomogeneity of an Ni-Hf-rich core and Cu-Zr-Ti-rich shell, demonstrated by thermodynamics calculations and second nearest-neighbor modified embedded atom method (2NN MEAM) formalism. The shell acts as an interfacial energy barrier for the stable martensitic transformation that occurred primarily in the effective Ni-Hf-rich core of the Cu15Ni35Ti20(HfZr)30. The temperature-dependent Gibbs-free energy agrees with the Cu movement, which widens the thermally-induced gradient layer of the elemental redistribution. Our findings are conducive to a potential design strategy of tailoring gradient chemical core/shell HEAs for stable high-temperature shape-memory applications.
ISSN:0264-1275

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