Abstract
Body-centred cubic refractory multi-principal element alloys (MPEAs), with several refractory metal elements as constituents and featuring a yield strength greater than one gigapascal, are promising materials to meet the demands of aggressive structural applications1,2,3,4,5,6. Their low-to-no tensile ductility at room temperature, however, limits their processability and scaled-up application7,8,9,10. Here we present a HfNbTiVAl10 alloy that shows remarkable tensile ductility (roughly 20%) and ultrahigh yield strength (roughly 1,390 megapascals). Notably, these are among the best synergies compared with other related alloys. Such superb synergies derive from the addition of aluminium to the HfNbTiV alloy, resulting in a negative mixing enthalpy solid solution, which promotes strength and favours the formation of hierarchical chemical fluctuations (HCFs). The HCFs span many length scales, ranging from submicrometre to atomic scale, and create a high density of diffusive boundaries that act as effective barriers for dislocation motion. Consequently, versatile dislocation configurations are sequentially stimulated, enabling the alloy to accommodate plastic deformation while fostering substantial interactions that give rise to two unusual strain-hardening rate upturns. Thus, plastic instability is significantly delayed, which expands the plastic regime as ultralarge tensile ductility. This study provides valuable insights into achieving a synergistic combination of ultrahigh strength and large tensile ductility in MPEAs.
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The data that support the findings of this study are available from the corresponding authors upon request.
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Acknowledgements
This research was supported by the National Key R&D Program of China (grant no. 2021YFA1200201), Beijing Outstanding Young Scientists Projects (grant no. BJJWZYJH01201910005018), Basic Science Center Program for Multiphase Evolution in Hypergravity of the National Natural Science Foundation of China (grant no. 51988101) and the Natural Science Foundation of China (grant nos. 52071003, 91860202). The methodology of high-energy synchrotron X-ray scattering was supported by the National Key Basic Research Program of China (grant no. 2020YFA0406101), Beijing Nova Program (grant no. Z211100002121170), Beijing Municipal Education Commission Project (grant no. PXM2020_014204_000021), China Postdoctoral Science Foundation (grant no. 2022M720311), ‘111’ project (grant no. DB18015) and the Hong Kong Research Grant Council with CityU grant no. 21205621. We also thank Y. Du and F. Liu for discussions on spinodal decomposition and the phase diagram.
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X.H., S.M. and Z.A. designed the study. Z.A., T.Y., B.C., L.Z., R.W., Z.W., B.Z., R.S., J. Zhang, C.S., Y.R., C.L., X.W., L.S., A.L. and J. Zhao carried out the main experiments under the supervision of X.H., S.M. and Y.R. The data were analysed by Z.A., S.M., X.H., Z.Z., Y.C., Z.L., F.R., H.L., W.L., Z.W., L.Y., F.H., C.-T.L. and X.Z. All authors contributed to the discussion of the results and commented on the manuscript. The draft was written by Z.A., S.M. and X.H. X.H. finalized the paper.
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Extended data figures and tables
Extended Data Fig. 1 Mechanical properties of the annealed HNTVAx (x = 0, 5, 10, 15) alloys.
a, True stress–true strain curves of the four alloys. b, Yield strength against mixing enthalpy of the four alloys. c, Ductility (true strain) against mixing enthalpy of the four alloys.
Extended Data Fig. 2 L-CF structure in the annealed HNTVA10 alloy.
a, STEM-HAADF images of annealed HNTVA10 samples cut from three orthogonal directions. b, Three-dimensional (3D) constructed STEM-HAADF image. c, STEM-HAADF images of L-CFs taken at different tilt angles. d, A 3D constructed image showing the interlocking structure of L-CFs.
Extended Data Fig. 3 Microstructure of the HNTVAx (x = 0, 5, 10, 15) alloys.
(a-d), SEM secondary electron images of cast HNTVA0, HNTVA5, HNTVA10, and HNTVA15 alloys, showing dendrite structure. (e-f), STEM-HAADF image of the cast HNTVA0, HNTVA5, and HNTVA10 alloys, showing L-CFs heterogeneous solid solution structure. The inset shows the corresponding SAED pattern. h, TEM image of the cast HNTVA15 alloy, showing B2 structure. The inset shows the corresponding SAED pattern. (i-l), SEM secondary electron images of the homogenized HNTVA0, HNTVA5, HNTVA10, and HNTVA15 alloys. (m-o), EBSD-IPF images of the HNTVA0, HNTVA5, and HNTVA10 alloys after cold-rolling and annealing at 1200 °C for 5 min. p, EBSD-IPF image of the HNTVA15 alloy after annealing at 1200 °C for 5 min. (q-s), HAADF-STEM images of the HNTVA0, HNTVA5, and HNTVA10 alloys after cold-rolling and annealing at 1200 °C for 5 min, showing L-CF heterogeneous microstructure. t, TEM image of the annealed HNTVA15 alloy, showing B2 structure.
Extended Data Fig. 4 Microstructure of the annealed HNTVAx (x = 5, 10, 15) alloys.
a, XRD patterns showing the phase of the annealed HNTVA5, HNTVA10, and HNTVA15 alloys. All three alloys exhibit a BCC structure. b, Zoomed-in view of the (310) peak of the HNTVA10 alloy reveals that it is an overlap of two peaks, indicating the presence of two BCC variants in this alloy.
Extended Data Fig. 6 STEM-HAADF images show dislocation pinning in the annealed HNTVA10 alloy.
a, Low-magnification STEM-HAADF image showing dislocation pinning (red arrow). b-c, Continuously magnified STEM-HAADF images showing the dislocation pinning structure down to the atomic scale. d, Integrated intensity of each atomic column in the pink box of c, showing the existence of M-CFs (black dashed cycles represent the light atoms and solid cycles represent the heavy atoms) around the dislocation pinning structure.
Extended Data Fig. 7 Atomic-resolution STEM-HAADF image and the corresponding energy-dispersive Xray spectroscopy (EDS) maps for individual elements of Hf, Nb, Ti, V, and Al in the annealed HNTVA10 alloy, taken with \([11\bar{1}]\) zone axis.
The yellow symbol “⊥” marks out the dislocation, white circle lines marked out the M-CFs by V-enriched column.
Extended Data Fig. 8 TEM and STEM-HAADF images show the dislocation configuration of the annealed HNTVA10 alloy at a tensile strain of 5%.
a, TEM image showing the dislocation dipole walls, which indicate dislocation cross-slip. b, TEM image showing the dislocation cross-slip from the primary slip band (yellow dashed line). The red arrows show the tangled dislocations and the interaction structure, indicating dislocation pinning and sluggish motion. c, Atomic-resolution STEM-HAADF image showing edge dislocations, indicating a substantial increase in dislocations at heterointerfaces.
Extended Data Fig. 9 Mechanical behavior and microstructural analysis of the annealed HNTVA10 alloy during in situ tensile testing through SEM at room temperature.
a, Scanning electron microscopy, sample dimensions and the Gatan microtension tester used in the tension tests. b, Stress–strain curves of the HNTVA10 sample. The inset SEM image shows the sample micrographs before and after the tensile test. c-e, SEM images of the slip traces on the sample surfaces of the different interrupted strains. The schematic below illustrates the slip traces, slip system and Schmid factor. Regarding the dislocation substructure during tensile testing, dipolar walls that mainly contain a high density of primary dislocation dipoles are observed, suggesting a typical cross-slip to form a wavy slip line (red arrow). With increasing strain, an additional slip system is activated, resulting in the formation of highly dense straight slip line (pink arrow) in different directions.
Extended Data Fig. 10 Relationship between enhanced yield strength and Al content and mixing enthalpy.
a, Effect of Al content on the yield strength. b, Effect of mixing enthalpy on the yield strength, showing the increment of yield strength as the negative mixing enthalpy becomes more negative, and exhibiting a quasi-linear trend, such as, Zr1.2V0.8NbTi3.6Alx (~27 MPa/(kJ/mol))37, (NbTiZr)100−xAlx (~27 MPa/(kJ/mol))38, (TiZrHfNb)100−xAlx (~28 MPa/(kJ/mol))39, and Ti3Zr1.5NbVAlx (~28 MPa/(kJ/mol))40. However, some scattered data points are also observed, for instance, (NbTiV)100−xAlx (~10 MPa/(kJ/mol))41.
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Supplementary Figs. 1–20, Tables 1–3, Notes 1–4 and references.
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An, Z., Li, A., Mao, S. et al. Negative mixing enthalpy solid solutions deliver high strength and ductility. Nature 625, 697–702 (2024). https://doi.org/10.1038/s41586-023-06894-9
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DOI: https://doi.org/10.1038/s41586-023-06894-9
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