On the evolving nature of c/a ratio in a hexagonal close-packed epsilon martensite phase in transformative high entropy alloys

Abstract

Activation of different slip systems in hexagonal close packed (h.c.p.) metals depends primarily on the c/a ratio, which is an intrinsic property that can be altered through alloying addition. In conventional h.c.p. alloys where there is no diffusion-less phase transformation and associated transformation volume change with deformation, the c/a ratio remains constant during deformation. In the present study, c/a ratio and transformation volume change of h.c.p. epsilon martensite phase in transformative high entropy alloys (HEAs) were quantified as functions of alloy chemistry, friction stir processing and tensile deformation. The study revealed that while intrinsic c/a is dependent on alloying elements, c/a of epsilon in transformative HEAs changes with processing and deformation. This is attributed to transformation volume change induced dependence of h.c.p. lattice parameters on microstructure and stress state. Lower than ideal c/a ratio promotes non-basal pyramidal 〈c + a〉 slip and deformation twinning in epsilon phase of transformative HEAs. Also, a unique twin-bridging mechanism was observed, which provided experimental evidence supporting existing theoretical predictions; i.e., geometrical factors combined with grain orientation, c/a ratio and plastic deformation can result in characteristic twin boundary inclination at 45–50°.

Tb- and Eu-doped yttrium oxyselenides as novel absorber layers for superstrate thin-film photovoltaics: improved spectral optical absorption and green–red phosphor activation

“…40 The c / a shows that the bond (distance) between the metal atoms and the anions will be longer in the doped nanomaterials especially for YOSe:Eu. 41,42 By using DIAMOND software, the crystal structures were simulated using the calculated lattice constants and the obtained structures are displayed in Fig. 5.…”

“…It is important to point out that for hexagonal crystal structures, a c/a value of 1.63 entails that the distances between the atoms are equal. 41 The c/a of the nanomaterials deviated from this value with values higher than 1.63 which indicates longer bond lengths. Fig.…”

Correlating work hardening with co-activation of stacking fault strengthening and transformation in a high entropy alloy using in-situ neutron diffraction

“…It is known that both strain and www.nature.com/scientificreports/ temperature will affect the structure. Recent studies demonstrated that processing or tensile deformation can lead to changes in both lattice constants a and peak broadening 23,36 . Consistent with the expectation based on previous studies 23,36 , during tensile deformation, both conditions exhibited increases in lattice spacings.…”

“…Recent studies demonstrated that processing or tensile deformation can lead to changes in both lattice constants a and peak broadening 23,36 . Consistent with the expectation based on previous studies 23,36 , during tensile deformation, both conditions exhibited increases in lattice spacings. Importantly, the differences in the evolution of lattice spacing support the idea that the L SF would behave differently in response to deformation.…”

Regulating the Nanosize Effect of LiCoO2 for High-Performance Battery-Supercapacitor Hybrid Devices

“…Further characterization by high-resolution transmission electron microscopy (HRTEM, Figure S2) reveals in-plane lattice grown along with a specific direction for SC-LCO, showing single-crystalline nature, while the irregular lattice orientation in NC-LCO indicates the nanopolycrystalline structure. The larger c / a ratio of SC-LCO in X-ray powder diffraction (XRD) pattern demonstrates enhanced 2D character (Figure d) . The I (003) / I (104) (Table S1) in SC-LCO (9.74) is significantly higher than NC-LCO (1.43), deriving from the preferential growth of the (003) plane .…”