Excellent strength-ductility combination of Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy at cryogenic temperatures

In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and annealing processes.The recrystallized sample is revealed to exhibit an excellent combination of strength and ductility over a wide temperature range of 4.2–293 K.With decreasing temperature from 293 to 77 K,the ductility and ultimate tensile strength(UTS)gradually increase by 30% to 95% and 137% to 1020 MPa,respectively.At the lowest temperature of 4.2 K,the ductility keeps 65% and the UTS increases by 200% to 1300 MPa,which exceed those published in the literature,including conventional 300 series stainless steels.Detailed microstructural analyses of this alloy reveal a change of deformation mechanisms from dislocation slip and nano-twinning at 293 K to nano-phase transformation at 4.2 K.The cooperation and competition of multiple nano-twinning and nano-phase transformation are responsible for the superior tensile properties at cryogenic temperatures.Our study provides experimental evidence for potential cryogenic applications of HEAs.

Self-standing oxygen-deficient a-MoO_(3-x)nanoflake arrays as 3D cathode for advanced all-solid-state thin film lithium batteries

Compared with the planar two-dimensional(2D)all-solid-state thin film batteries(TFBs),threedimensional(3D)all-solid-state TFBs with interdigitated contact between electrode and electrolyte possess great advantage in achieving both high energy and power densities.Herein,we report a facile fabrication of vertically aligned oxygen-deficient a-MoO3-x nanoflake arrays(3D MO_(x))using metal Mo target by direct current(DC)magnetron sputtering.By utilizing the 3D MO_(x)cathode,amorphous lithium phosphorus oxynitride solid electrolyte,and lithium thin film anode,3D solid-state TFBs have been successfully fabricated,exhibiting high specific capacity(266 mAh g^(-1)at 50 mA g^(-1)),good rate performance(110 mAh g^(-1)at 1000mA g^(-1)),and excellent cycle performance(92.7%capacity retention after 1000 cycles)in comparison with the 2D TFBs using the planar MO_(x)thin film as cathode.The superior electrochemical performance of the 3D TFBs can be attributed to the 3D architecture of the cathode,maximizing the cathode/electrolyte interface while retaining the short Lit diffusion length.The charge/discharge measurements of the 3D MO_(x)cathode in liquid electrolyte,however,exhibit fast capacity fading,demonstrating the advantage of using transition metal oxide as cathode in solid-state batteries.

Relationship Between the Strengthening Effect and the Morphology of Precipitates in Al–7.4Zn–1.7Mg–2.0Cu Alloy

The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes accordingly with the change of the average thickness–diameter ratio of precipitates. The GPII zones are mainly responsible for the first and also the highest hardness peak. They grow in diameter and keep 7-atomic-layer in thickness. Once the thickness changes, the phase transformation from GPII zone to g0 or g-precursor would occur. The resultant metastable g0 and g-precursor precipitates grow in both diameter and thickness, but much faster in the former. After the first hardness peak,the metastable g0 precipitates and g-precursor, coexisting with part of GPII zones, are counted as the main hardening precipitates.