Diffusion Behaviour of C Element in TiNiCuZrNbTa Refractory High-entropy Alloy

WANG Jiawei; SHAO Zexi; WU Bintao; XIA Mingxu

doi:10.3969/j.issn.1674-6457.2025.12.004

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Journal of Netshape Forming Engineering ›› 2025, Vol. 17 ›› Issue (12) : 35-44. DOI: 10.3969/j.issn.1674-6457.2025.12.004

Advanced Forming Engineering of High-Entropy and Amorphous Alloys

Diffusion Behaviour of C Element in TiNiCuZrNbTa Refractory High-entropy Alloy

WANG Jiawei¹, SHAO Zexi², WU Bintao^1,*, XIA Mingxu¹

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Abstract

To advance the regulation of TiNiCuZrNbTa refractory high-entropy alloy (RHEA) properties, the work aims to investigate C diffusion in various phase structures and its impact on the microstructural hardness. A TiNiCuZrNbTa RHEA cladding layer was fabricated on a copper substrate via laser cladding with polyvinyl alcohol (PVA) as carbon source. The effects of C on the microstructure, phase composition, and hardness across the bottom, middle, and top regions of the alloy were systematically studied. The top region at the cross section of the alloy primarily exhibited fine equiaxed grains, with Zr-rich phases forming dendritic networks and fine Ta/Nb particle phases dispersed within the matrix. Conversely, with the gradual decrease in solidification rate, the middle region featured coarse dendritic structures, where Ta/Nb phases manifested as dots or fine strips concentrated at dendrite arm intersections. The bottom region, adjacent to the substrate, experienced a higher thermal gradient during solidification, resulting in the formation of columnar crystals perpendicular to the interface, exhibiting a structural transition towards the coarser dendritic morphology of the middle region. In the different phases of the alloy, strong carbide-forming elements (Ti, Zr, Ta) combined with C to generate dispersed carbide particles, enhancing the strength. Notably, oxygen (O) promoted C diffusion across phases via a “mediated diffusion” mechanism. Along the build direction of the cladding layer, the hardness near the copper substrate measured approximately 465HV. With the increasing C content, the hardness rose correspondingly, reaching approximately 527HV in the cladding layer. Within this RHEA system, the C concentration in each phase escalates along the cladding layer. Optimal C diffusion in different phases facilitates solid solution and dispersion strengthening, effectively impeding dislocation movement and enhancing surface hardness.

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refractory high-entropy alloy (RHEA) / laser cladding / microstructure / C diffusion / microhardness

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WANG Jiawei, SHAO Zexi, WU Bintao, XIA Mingxu. Diffusion Behaviour of C Element in TiNiCuZrNbTa Refractory High-entropy Alloy[J]. Journal of Netshape Forming Engineering. 2025, 17(12): 35-44 https://doi.org/10.3969/j.issn.1674-6457.2025.12.004

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Funding

Joint Funds of the National Natural Science Foundation of China (U24A2006); Ningxia Natural Science Foundation for Outstanding Young Scholar (2024AAC04002)