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Abstract Elastic stability is the basis for understanding structural responses to external stimuli in crystalline solids, including melting, incipient plasticity and fracture. In this work, elastic stability is investigated in a series of high-entropy alloys (HEAs) using in situ mechanical tests and atomic-resolution characterization in transmission electron microscopy. Under tensile loading, the HEA lattices are observed to undergo a sudden loss of ordering as the elastic strain reached ∽ 10%. Such elastic strain-induced amorphization stands in intrinsic contrast to previously reported dislocation-mediated elastic instability and defect accumulation-mediated amorphization, introducing a form of elastic instability. Together with the first principle calculations and atomic-resolution chemical mapping, we identify that the elastic strain-induced amorphization is closely related to the depressed dislocation nucleation due to the local atomic environment inhomogeneity of HEAs. Our findings provide insights for the understanding of the fundamental nature of physical mechanical phenomena like elastic instability and incipient plasticity.

Common wisdom to improve ductility of bulk metallic glasses (BMGs) is to introduce local loose packing regions at the expense of strength. Here the authors enhance structural fluctuations of BMGs by introducing dense local packing regions, resulting in simultaneous increase of ductility and strength.

Qinghai is located in a permafrost region, which belongs to the continental climate zone of the the Qinghai-Tibet Plateau. At the same time, freezing-thawing cycles are common destructive factors for roadbeds and foundations. In order to examine the effects of freezing-thawing cycles on actual projects in Qinghai and reveal the mechanisms of freezing-thawing cycles on damage of the projects, the freezing-thawing cycle test, unconfined compressive strength test and electron microscope scanning test of the undisturbed loess and remolded loess in the Xining area of Qinghai are conducted to analyze the influence of different freezing-thawing temperatures and different freezing-thawing cycles on the strength and microstructure of the undisturbed loess and remolded loess. The results show that when the loess undergoes 0-6 freezing-thawing cycles, the strength of the undisturbed loess and remolded loess gradually decreases. After 8-10 freezing-thawing cycles, the unconfined compressive strength of the loess first increases and then tends to be basically stable. The strength of the undisturbed loess decreases with the decrease of the freezing and thawing temperature. However, the strength of the remolded loess first increases and then decreases with the decrease of temperature. From a microscopic point of view, the decrease in freezing-thawing temperature and the increase in the number of freezing-thawing cycles both lead to the decomposition of large loess particles into small particles, and the arrangement of the particles has changed. The results are of reference value for actual project construction and construction in the Xining area of Qinghai.

Loess, a collapsible soil, is widely distributed in the Qinghai–Tibet Plateau in China. In the meantime, loess is a sustainable and green building material that is widely used in traditional residential buildings. However, previous studies have focused on the properties of loess itself, ignoring the influence of climatic conditions on loess buildings, as well as a series of engineering problems such as soil spalling caused by freezing and thawing, cold cracks in walls, and settlement deformation of foundation. This research presents a series of laboratory tests on both undisturbed and remolded loess. The tests investigated changes in the unconfined compressive strength (UCS) of both types of loess after different freeze–thaw cycles. The freeze–thaw-induced changes to the internal structures of the loess were also investigated using a scanning electron microscope (SEM) and X-ray diffraction test (XRD). The test results showed that: (1) with increasing freeze–thaw cycles, the UCS of both the undisturbed and remolded loess appeared to first increase and then decrease, and the stress–strain curves showed a stronger strain-softening tendency. (2) The compressive strength of undisturbed loess is higher than remolded loess. (3) SEM analysis showed that the large particles inside the loess sample were gradually broken down into small particles, which led to an accumulative increase in fine particles and a decrease in the porosity. With the increase in the number of freeze–thaw cycles, the particles inside the soil become denser, and the strength increases. (4) Freezing and thawing have less effect on loess minerals. (5) The conclusion can provide a reference value for the protection of loess buildings in Qinghai and the management of freeze–thaw disasters.