close
Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2020 Mar 27;6(13):eaax4002.
doi: 10.1126/sciadv.aax4002. eCollection 2020 Mar.

Cooperative deformation in high-entropy alloys at ultralow temperatures

Muhammad Naeem  1 , Haiyan He  1 , Fan Zhang  2 , Hailong Huang  2 , Stefanus Harjo  3 , Takuro Kawasaki  3 , Bing Wang  1 , Si Lan  1   4 , Zhenduo Wu  1 , Feng Wang  5 , Yuan Wu  2 , Zhaoping Lu  2 , Zhongwu Zhang  6 , Chain T Liu  5   7 , Xun-Li Wang  1   8
Affiliations

Cooperative deformation in high-entropy alloys at ultralow temperatures

Muhammad Naeem et al. Sci Adv. .

Abstract

High-entropy alloys exhibit exceptional mechanical properties at cryogenic temperatures, due to the activation of twinning in addition to dislocation slip. The coexistence of multiple deformation pathways raises an important question regarding how individual deformation mechanisms compete or synergize during plastic deformation. Using in situ neutron diffraction, we demonstrate the interaction of a rich variety of deformation mechanisms in high-entropy alloys at 15 K, which began with dislocation slip, followed by stacking faults and twinning, before transitioning to inhomogeneous deformation by serrations. Quantitative analysis showed that the cooperation of these different deformation mechanisms led to extreme work hardening. The low stacking fault energy plus the stable face-centered cubic structure at ultralow temperatures, enabled by the high-entropy alloying, played a pivotal role bridging dislocation slip and serration. Insights from the in situ experiments point to the role of entropy in the design of structural materials with superior properties.

PubMed Disclaimer

Figures

Fig. 1
Fig. 1. Crystal structure and deformation behavior of CrMnFeCoNi alloy at low temperatures.
(A) Selected diffraction patterns at room temperature and at 15 K during deformation, showing a clean single-phase fcc structure. (B) True stress-strain curves at room temperature, 140 K, and 15 K. The trend of temperature fluctuations (right-hand axis) due to serrations at 15 K is also superimposed. (C) Two serrations are shown with temperature (plotted in reverse scale for better comparison) to illustrate details of serrated deformation. (D) Plots of strain-hardening rate (SHR) at three temperatures. (E) Scanning electron microscopy image of the fractured sample at 15 K showing the 45° wedge.
Fig. 2
Fig. 2. Lattice strain and texture development during deformation.
Evolution of the lattice strain and the normalized integrated intensity for (hkl)//LD grains at (A) room temperature, (B) 140 K, and (C) 15 K for CrMnFeCoNi alloy. Below room temperature, the lattice strains for (111)//LD and (222)//LD split at large deformations. The same goes for (200)//LD and (400)//LD. The macroscopic yield strengths σy at different temperatures are indicated by vertical dashed lines.
Fig. 3
Fig. 3. Deformation pathway of CrMnFeCoNi HEA at 15 K.
SFP and normalized integrated intensity of (111)//LD as a function of true stress are compared for room temperature and 15 K. Vertical dashed lines are drawn to pinpoint the changes in deformation behaviors in the 15 K dataset: (1) macroscopic yield point at σy,15K ~ 718 MPa; (2) start of SFs (σ ~ 1075 MPa); (3) first sign of serration (σ ~ 1270 MPa), followed by a rapid increase in SFP and change in the slope of texture development; and (4) massive serrations coincided with the saturation of texture (σ ~ 2000 MPa).
Fig. 4
Fig. 4. Electron microscopy results of fractured samples.
TEM images at room temperature showing the dislocation pileups (A), while the dark-field image also shows some sparse twins (B). The 15 K sample has a large number of SFs (C) and a very high density of closely spaced twins (D). An intersecting twinning network is formed at 15 K (E), while the SAD pattern in the inset shows the additional bright spots due to twinning. (F) HR-TEM taken from the 15 K sample shows deformation twins, with the twin boundaries marked.
Fig. 5
Fig. 5. Deformation diagram of fcc HEAs.
The critical strain at which the SFs and serrated deformation were activated. In quinary CrMnFeCoNi, the SFs are observed only at a strain value closer to fracture (36.8% in true strain) at 295 K, while at low temperatures, the SFs appear earlier, after ~22.2% at 140 K and ~15.8% at 15 K, respectively. The SFs form more easily in the quaternary CrFeCoNi alloy, where the SFs start at lower deformation strains for all three temperatures. The trend continues for the ternary CrCoNi alloy, where SFs begin to form even at an early stage of deformation at room temperature. The open symbols are the activation strain for serrations at 15 K (the data points are displaced to the left-hand side for clarity), which are substantially higher than the critical strains for SFs.
See this image and copyright information in PMC

References

    1. Suzuki A., Inui H., Pollock T. M., L12-strengthened cobalt-base superalloys. Annu. Rev. Mater. Res. 45, 345–368 (2015).
    1. Gumbsch P., Riedle J., Hartmaier A., Fischmeister H. F., Controlling factors for the brittle-to-ductile transition in tungsten single crystals. Science 282, 1293–1295 (1998). - PubMed
    1. Zhang Y., Zuo T. T., Tang Z., Gao M. C., Dahmen K. A., Liaw P. K., Lu Z. P., Microstructures and properties of high-entropy alloys. Prog. Mater. Sci. 61, 1–93 (2014).
    1. Gludovatz B., Hohenwarter A., Catoor D., Chang E. H., George E. P., Ritchie R. O., A fracture-resistant high-entropy alloy for cryogenic applications. Science 345, 1153–1158 (2014). - PubMed
    1. Li Z., Pradeep K. G., Deng Y., Raabe D., Tasan C. C., Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off. Nature 534, 227–230 (2016). - PubMed

LinkOut - more resources