Bcc Structure Research Articles

First-principles study of highly-compressed Sb: a stubborn body-centered cubic structure

We searched for plausible crystal structures and the entailing electronic profiles of highly-compressed Sb using an originally developed structure-search method and first-principles calculations based on the density functional theory. We report that the experimentally observed highest-pressure (59 GPa) close-packed body-centered cubic (bcc) structure remains the lowest-enthalpy structure at least up to 1000 GPa within the precision of our calculations. Any possibilities of complex structures with many atoms and distortions within the bcc phase, as in the case of the cI16 structure observed for high pressure P, were also safely ruled out. Careful investigations of the density of states (DOS) and phonon dispersions revealed that the bcc structure becomes more stable with increasing pressure. The DOS and phonon dispersions indicate that the stability of the bcc phase increases with increasing pressure. In understanding the strong stability of this stubborn bcc phase, we discuss the phonon and electronic profiles of Sb.

Nanoscale microstructures and novel hydrogen storage performance of as cast V47Fe11Ti30Cr10RE2 (RE = La, Ce, Y, Sc) medium entropy alloys

As classical BCC structure solid state hydrogen storage materials, vanadium-based solid solution alloys occupied a prominent position in the field of hydrogen storage materials due to their significant advantages such as the ability to absorb and desorb hydrogen with high capacity under moderate conditions. In this paper, RE-containing medium entropy BCC solid solution alloys were designed. The microstructure, phase composition and hydrogen storage properties of the medium entropy alloys were systematically studied. Microstructural analysis showed that nanoscale crystals were found in as-cast medium entropy alloys obtained by arc melting followed by natural cooling inside the furnace. This is different from the vanadium-based alloys that are often regarded as traditional coarse-grained alloys in the past decades. The V 47 Fe 11 Ti 30 Cr 10 RE 2 alloys can be fully activated by one cycle of hydrogen ab/de-sorption after pretreatment. The kinetic test shows that the time required for the as-cast RE-containing medium entropy alloys hydrogen uptake to 90% saturation is less than 100 s at room temperature. The alloys exhibit very excellent hydrogen absorption kinetic properties than reported alloys takes at least about 300 s. This is due to the fact that the present alloys are composed of nanocrystals with numerous interfaces and grain boundaries, and these defects can act as good channels for the diffusion of hydrogen atoms. The V 47 Fe 11 Ti 30 Cr 10 Y 2 alloy exhibits a maximum capacity of 3.41 wt% at 295 K. The thermodynamics of hydrogen ab/de-sorption and the hydrogen desorption under non-isothermal conditions were also studied in detail. • Nanoscale crystals were found in as cast RE-containing medium entropy BCC solid solution alloys prepared by arc melting. • The alloys have numerous interfaces and grain boundaries. • The time required for the alloys hydrogen uptake to 90% saturation is less than 100 s.

Evolution of Cu-rich phase in Al-modified ferrite stainless steel during short-term ageing

In this article, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy were used to characterize the precipitation behaviour of the Cu-rich phase in Al-free and 1Al Cu-bearing ferrite stainless steels; and further, the effects of Al addition on the precipitation and coarsening of the Cu-rich phase and its mechanism were analysed. The results show that Al increases the nucleation rate of the Cu-rich phase, and refines Cu-rich nanoprecipitates after ageing for 1 min. The Cu-rich phase with four crystal structures-BCC, 9R, twin FCC, and non-twin FCC were found in the Al-free sample during ageing. However, only Cu-rich phase with BCC and BCT structures were observed after Al addition. There are high-density edge dislocations in Al-containing Cu-rich nanoprecipitates. These dislocations can be used as a diffusion channel for solute atoms, increasing the coarsening rate of the Cu-rich phase. However, with the extension of the ageing time, dislocations in the Cu-rich phase will be annihilated owing to the thermal activation and the decrease of the Al concentration in the Cu-rich phase, which will lead to a decrease in the dislocation density in Al-containing Cu-rich phase. Finally, the promotion effect of Al on the coarsening of the Cu-rich phase is weakened.

Study on Stability and Elastic Properties of β-TiX (X=Nb, Ta) Alloys From First-Principles Calculations

In this article, the phase stability, elastic properties, and electronic structure of the β-TiX (X = Nb, Ta) alloy body-centered cubic (bcc) structure were systematically studied with the aid of first-principles calculations. The results show that the phase stability and elastic properties of the β-TiX alloys are closely related to the contents of alloying element X. For β-TiX alloys, the contents of Nb and Ta that satisfy their mechanical stability are 10% and 13%, respectively; at room temperature, both β-TiNb and β-TiTa alloys can reach a thermodynamically stable state when the content of Nb or Ta is 25%. In terms of elastic properties, the content of alloying element X is positively correlated with the elastic constant, Young’s modulus, and shear modulus of the β-TiX alloys. The elastic modulus reaches its minimum when the X content is 25%, and the smallest direction of Young’s modulus appears in the <111> direction. The calculation results of the electronic structure show that the bonding strength between the Ti atom and X atom increases with the content of alloying element X, which leads to improvement of phase stability and elastic modulus.

Formation of hypoeutectic structure and strengthening mechanism of Co4Cr1.5Fe1.5Ni5 high entropy alloy alloyed by Al

To reveal the phase formation mechanism and the strengthening mechanism, the AlxCo4Cr1.5Fe1.5Ni5 alloys (x = 1.0, 1.2, 1.4, 1.6, 1.8, 2.0) were prepared by arc melting. Phase formation and prediction, tensile properties, strengthening mechanism and deformation mechanism were researched in detail. Results show that the microstructure of AlxCo4Cr1.5Fe1.5Ni5 alloys changes from single FCC phases (x ≤ 1.4)) to FCC and BCC phases (x＞1.4), which was in good agreement with the calculated phase diagram (CALPHAD) prediction. The lower mixing enthalpy of Ni-Al leads to the segregation of Al element at the inter-dendritic region, which promotes the formation of BCC and FCC lamellar structure in hypoeutectic Al2Co4Cr1.5Fe1.5Ni5 alloy. The ultimate tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is 835 MPa, meanwhile the fracture strain is 31.8 %. The tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is attributed to the interface strengthening and the solid solution strengthening. The massive cross slip of dislocations in primary FCC phases and the dense dislocations blocked by the FCC-BCC interface increase the tensile strength. The interface barrier strength of the BCC-FCC interface in Al2Co4Cr1.5Fe1.5Ni5 alloy was estimated to be 3.9 GPa, which shows the higher barrier strength than conventional BCC-FCC interfaces. Coupled effects of the primary FCC and the lamellar structure of FCC and BCC phases will maintain good mechanical properties.

Structure and pressure dependence of the Fermi surface of lithium

We report studies of the Fermi surface (FS) of isotopically pure polycrystalline $^{7}\mathrm{Li}$ from ambient pressure to 4.7 GPa. Shubnikov--de Haas (SdH) oscillations at 300 mK in external magnetic fields up to 35 T are measured to map the spherical parts of the FS of lithium. Our ambient pressure data show that the principal SdH frequencies consist of three distinct peaks at $41.25\ifmmode\pm\else\textpm\fi{}0.05, 41.65\ifmmode\pm\else\textpm\fi{}0.05$, and $42.05\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{kT}$, which are theoretically consistent with the presence of two crystal structure domains exhibiting nearly spherical FS. The size of the spherical parts of the FS is compatible with bcc and fcc crystal structures. The measured frequencies at 41.25 and 42.65 kT present direct quantitative evidence for the spherical deformation of the FS in fcc Li. Our high-pressure data show that while the FS of Li deforms under compression, it remains mostly spherical up to 4.7 GPa and the pressure dependence of the SdH frequency is consistent with the theoretically calculated pressure dependence in the fcc structure. Finally, we find that the electron effective mass does not deviate under pressure significantly from its ambient pressure value.

Corrosion Behavior of Alx(CrFeNi)1-x HEA under Simulated PWR Primary Water.

High-entropy alloys (HEAs) have great potential as accident-tolerant fuel (ATF) cladding. Aluminum-forming duplex (BCC and FCC) stainless-steel (ADSS) is a candidate for ATF cladding, but the multiphase composition is detrimental to its corrosion resistance. In this paper, two single-phase HEAs were prepared by adjusting the content of each element in the ADSS alloy. The two HEAs were designed as Al0.05(CrFeNi)0.95(FCC) and Al0.25(FeCrNi)0.75(BCC). Their corrosion behavior under simulated pressurized water reactor (PWR) primary water was investigated. The corrosion products and corrosion mechanisms of these two HEAs were explored. The results show that the corrosion resistance of HEA alloys containing FCC is better than that of BCC and ADSS alloys. At the same time, the reason why the BCC structure composed of these four elements is not resistant to corrosion is revealed.

Lu37Ru16.4In4 – coloring and vacancy formation in a new structure type closely related to a 8 × 8 × 8 bcc superstructure

Abstract The lutetium-rich intermetallic compound Lu37Ru16.4In4 was synthesized by induction melting of the elements in a sealed tantalum ampoule and subsequent annealing. The Lu37Ru16.4In4 structure was refined from single crystal X-ray diffractometer data: new type, I a 3 ‾ d $Ia\overline{3}d$ , a = 2756.21(11) pm, wR2 = 0.0579, 3056 F 2 values and 92 variables. The superstructure formation of Lu37Ru16.4In4 is discussed on the basis of a group–subgroup scheme starting from the bcc structure as the aristotype.

Low-temperature growth of In2O3 films on a-plane sapphire substrates by pulsed laser deposition

High-quality body-centered cubic In2O3 films were grown on a-plane sapphire substrates at a temperature range of 100–600 °C by pulsed laser deposition. The structure, optical, and electrical properties were studied by X-ray diffraction, Raman spectroscopy, spectrophotometer, and Hall effect. The obtained In2O3 films have a bcc structure, a high carrier concentration range of 1 × 1019–9 × 1020 cm−3, a mobility range of 8 to 30 cm2V−1s−1, and a wide bandgap of 3.7–3.9 eV. The change of substrate temperature affects the crystalline quality, transmittance, carrier concentration, mobility, and bandgap value of In2O3 films. We believe that the low-temperature growth of high-quality In2O3 films can make In2O3 more widely used in various semiconductors devices.

Effect of Cu and Co addition on non-isothermal crystallization kinetics of rapidly quenched Fe-Sn-B based alloys

Crystallization kinetics of rapidly quenched Fe-Sn-B alloys under non-isothermal conditions were studied using differential scanning calorimetry. Formation of crystalline phases was analyzed by X-ray diffraction. Nominal chemical compositions were Fe81Sn7B12, (Fe3Co1)81Sn7B12 and (Fe81Sn7B12)99Cu1. Alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. Mechanism of crystallization was studied under framework of the Johnson-Mehl-Avrami-Kolmogorov model. Alloys exhibit two stages of crystallization. Results show decrease in activation energy of the first stage of crystallization with addition of Cu and increase with addition of Co. Crystallization mechanism of the first stage of crystallization for Fe81Sn7B12 and (Fe81Sn7B12)99Cu1 alloy starts as growth with increasing nucleation rate and continues as growth with decreasing nucleation rate. Addition of Co changes mechanism of crystallization. Which in case of (Fe3Co1)81Sn7B12 alloy starts as a growth with increasing nucleation rate. Then changes to growth with decreasing nucleation rate. After which nucleation rate decreases to zero. Rest of crystallization stage is governed by growth of pre-existing nuclei. In the first stage of crystallization α-Fe phase with bcc structure crystallizes from amorphous matrix. In the second stage of crystallization the remaining amorphous matrix crystalizes into tetragonal Fe2B phase and hexagonal FeSn phase. After the first stage of crystallization, 50 % to 55 % volume of studied alloys were crystalized. Addition of Cu decreases crystalline size of α-Fe crystallites by 60 % and decreases concentration of Sn in α-Fe phase by 0.8 at. %. Addition of Co doesn't affect the size of α-Fe crystallites and decreases the concentration of Sn in α-Fe phase by 1.7 at. %.

Ultrahard BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy formed by nanoscale diffusion-induced phase transition

In the current work, the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy (nc-HEA) with ultra-high hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite. First, a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite (nc-HEAC) was prepared by a laser source inert gas condensation equipment (laser-IGC). The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals. Then, the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase. With the increase of the annealing temperature, element diffusion intensifies, and the AlCoCrFeNi phase undergoes a phase transition from FCC to BCC structure. Finally, the BCC-AlCoCrFeNi bulk nc-HEA with high Al content (up to 50 at.%) was obtained for the first time. Excitingly, the nc-HEAC (Al-40%) sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500 °C for 1 h. We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing, and the corresponding micro-mechanisms in different annealing stages are revealed. The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs, which opens a new pathway for the design of high-performance nanocrystalline alloy materials.

Effect of Al content on the microstructure and properties of CoCrCuFeNiMoAlx high entropy alloy

A new multi-principal Co-Cr-Cu-Fe-Ni-Mo-Al high entropy alloy with good mechanical properties and corrosion resistance was prepared. For the phenomenon of Cu segregation, we report a strategy to tailor the existing form of Cu in HEA from undesired large-scale segregation to uniform distribution in the solid solution phase. The effects of the Al content on the microstructure, mechanical properties and corrosion behavior of CoCrCuFeNiMoAlx (x = 0, 0.32, 0.67, and 1.0) alloys were studied. The results show that when Al content is low, Cu segregation phenomenon is serious, and the microstructure of the alloy is FCC structure and a little BCC structure. With the increase of Al content, the microstructure is gradually transformed into BCC structure, and the Cu segregation phenomenon is improved. In addition, with the increase of Al content, the mechanical properties of the alloy are improved to some extent. According to the experimental results, the hardness increased by 30.4 %and the compressive strength increases by 22.9 %. Moreover, an increasing Al content had a positive influence on the corrosion resistance of the alloy, increased corrosion potential of the alloy and reduced corrosion current.

Microstructure and mechanical properties of NixFeCoCrAl high-entropy alloys

The microstructure and tensile properties of NixFeCoCrAl high-entropy alloys (HEAs) were investigated. The results indicated that the microstructure of NixFeCoCrAl HEAs can be tuned from a single body-centered cubic (bcc) structure, to a bcc/face-centered cubic (fcc) eutectic dual-phase structure, and finally to a single fcc structure by increasing the Ni element content. An ultimate tensile strength of 1534 MPa was achieved in the Ni1.71FeCoCrAl HEA (N30 alloy) with a bcc/fcc dual-phase structure. On the other hand, the fcc NixFeCoCrAl HEAs with relatively-higher Ni content tend to have good ductility. Typically, the fcc Ni4FeCoCrAl HEA (N50 alloy) has a good combination of tensile strength and ductility. The underlying reasons for the achievement of high strength and large ductility of the NixFeCoCrAl HEAs were analyzed and discussed based on the chemical compositions and related microstructures.

Understanding crystal structure roles towards developing high-performance V-free BCC hydrogen storage alloys

Current bottlenecks in the supply and high cost of V have negatively impacted their application. There is great interest in developing V-based hydrogen storage alloys that use less or free V. Here, we investigate the role of V in deliberately designed V-based alloys. Our results affirm that V plays an undeniable role in enhancing hydrogen storage properties. It is found that V maintains the stable single BCC structure but leads to more residual hydrogen (1.4 wt%) because of the high stability of the dihydride and smaller hydriding rate because of the small lattice parameter, which offers unexpected but encouraging perspectives towards reducing the need of V in such alloys. Mo substitution for V effectively alleviates the higher residual hydrogen to achieve a high dehydriding capacity of 2.5 wt%. Moreover, the suction-cast (Ti0.46Cr0.54)97.5Mo2.5 alloy, which keeps BCC structure after suction-cast process and contains a low-Mo content, also exhibits dehydriding capacity of 2.3 wt%. The enthalpy change as well as dehydriding capacity of V-Free alloys obtained were similar to those reported V-based alloys. These findings are attractive for developing new V-free BCC hydrogen storage alloys and higher hydrogen capacity.

Effects of order-disorder transition on phase relationship, elastic strength, and mechanical anisotropy of Al-Li alloys

In this work, the effects of order-disorder transition on phase relationship, elastic strength, and mechanical anisotropy of Al-Li system are investigated by first-principles calculations with the help of cluster expansion, Monte Carlo simulation and quasi-harmonic Debye model. The results show that at higher temperature disordered FCC is energetical favorable at xLi < 0.59, while BCC becomes stable at xLi ≥ 0.59. The order-disorder transition at low temperature, deduced from metastable phase diagram at Al-rich side (0.00 ≤ xLi ≤ 0.54), promotes the transformation of disordered α FCC to ordered δ’ L12 Al3Li and δ B32 AlLi structures. The elastic strength indicates the precipitate hardening of Li addition originates from the α – δ’ ordering, while softening is found after the α – δ ordering or δ’ – δ phase transition. The change of FCC, either ordered or disordered, to BCC structures incurs strong mechanical anisotropy, as a result of centrosymmetry breaking and angular electronic bonding. The newly identified long-range ordering of AlLi4 tetrahedron pairs and corresponding bonding electron morphology play the key role in the order-disorder transition and mechanical anisotropy. Our findings not only provide clues for the rational design of Al-Li alloys with higher Li concentration, but also shed lights on the complex experimental phenomena of Al-Li alloys.

TOWARD QUALITY IMPROVEMENT OF ELECTRODEPOSITED HARD METAL Mo/Cu COATINGS: SUITABILITY FOR CIGS SOLAR CELL APPLICATIONS

Bright and thick molybdenum (Mo) coatings with good purity and adhesion were electrodeposited on Copper (Cu)-supported Mo/Cu, which is based on aqueous bath containing molybdate ions. All the electrodeposition process was carried out at a fixed duration of 1200[Formula: see text]s, according to five different current densities 400, 450, 500, 550, and 600[Formula: see text]mA/cm2 at room temperature [Formula: see text]C. Metallic Mo deposits structure may correspond to that of body-centered cubic (bcc) structure. The lattice parameter, residual stress, crystallites size, micro-strain, and dislocation densities were inferred from Mo (110) texture. Synthetized Mo coatings have relatively same rough surface morphology (50–60[Formula: see text]nm) characterized by some superficial cracks, small uniform grain size having change less than 14%, low residual stress and a good adhesion, a good conductivity, and an appropriate purity that has reached 94 (Mo %wt.). We have deduced that structural and electrical properties of Mo deposits did not obey the existing cracks at surfaces. One important result was that the most cracked and unstressed coating obtained at 450[Formula: see text]mA/cm2 was the same coating having the best purity (Mo %wt.), the best conductivity, and highest free electrons mobility. We suggest that appearance of cracks is closely related to electrochemical facts such as the deposition rate and hydrogen evolution reaction process since cracks decrease beyond 450[Formula: see text]mA/cm2. A good correlation between each investigated property was, also, established and discussed.

Ultra-High Mixing Entropy Alloys with Single bcc, hcp, or fcc Structure in Co–Cr–V–Fe–X (X = Al, Ru, or Ni) Systems Designed with Structure-Dependent Mixing Entropy and Mixing Enthalpy of Constituent Binary Equiatomic Alloys

Non-equiatomic high-entropy alloys (HEAs) for which the mixing (Smix), configuration (Sconfig), and equivalent ideal (Sideal) entropies satisfy Smix > Sconfig = Sideal were reported for Co–Cr–V–Fe–(Al, Ru, or Ni) systems. Three Co20Cr20Fe20V10X30 (X = Al, Ru, or Ni) alloys (referred to as Al30, Ru30, and Ni30 alloys) were studied here using conventional arc melting and subsequent annealing. The X-ray diffraction profiles revealed that the Al30, Ru30, and Ni30 alloys annealed at 1600 K for 1 h exhibited B2 ordered, hcp, and fcc structures, respectively. A single structure was verified by scanning electron microscopy observations combined with elemental mapping via energy-dispersive X-ray spectroscopy. Thermodynamic calculations of Smix normalized by the gas constant (Smix/R) revealed that Al30, Ru30, and Ni30 alloys at 1600 K had Smix/R = 0.833, 1.640, and 1.618, respectively, where the latter two alloys exceeded Sconfig/R = 1.557. A compositionally optimized Al-containing HEA for Smix with a single bcc structure was computationally predicted and verified experimentally for the Al6Co27Cr34Fe19V14 alloy (Al6 alloy). The non-equiatomic Al6 alloy with Sconfig/R = 1.480 exhibited Smix/R of 1.703 at 1600 K, surpassing Sconfig/R = ln 5 = 1.609 for the exact equiatomic (EE) quinary alloy. The bcc Al6, hcp Ru30, and fcc Ni30 alloys were regarded as ultra-high mixing entropy alloys (UMHEAs) according to Smix > Sconfig. Structure-dependent Smix and the mixing enthalpy of constituent binary EE alloys are useful for future UHMEAs as a subset of HEAs.

First principles calculation on electronic structures and mechanical properties of TiCrTaV high–entropy alloy

The formability, electronic structures, Debye temperatures and mechanical properties of TiVCrTa multi-component alloys with different crystal structures are investigated with first principles methods based on plane-wave pseudopotential theory. Results show that the three structures exhibit ductility. The C15 structure (Ti41Cr25Ta12V22) is highly stable and has strong compressibility resistance along the X-axis. And the generation of the C15 structure increase the B value, and thus improves the deformation resistance of the material. The BCC2 structure (Ti27Cr27Ta18V28) partially improves the wear resistance of the material. The BCC1 structure (Ti23Cr25Ta23V29) has strong elastic anisotropy. The largest E value of the two BCC structures is observed in the [111] direction, and the lowest in the [100] direction. The opposite is observed in the C15 structure. The BCC2 structure has a strong covalent bond and thermodynamic stability. The C15 structure has the strongest electron interaction and best atomic bonding and most obvious metallic bonding characteristics.

An Nylon lattice structure with improved mechanical property and energy absorption capability

To study the mechanical behavior and energy-absorption capability, different lattices structures were designed and fabricated by using SLS technology with a raw material of Nylon. The quasi-static compression experiment and finite element simulation revealed the mechanical response and deformation mechanism of these structures. Meanwhile, the energy absorption capacity of the lattices structure was assessed by the impact resistance and corresponding calculations of specific energy absorption. The different design schemes were compared and analyzed under the same conditions. The results show that a minimal surface structure (MSS) has the best performance of compression properties. The designed composite scheme composed of the MSS and the BCC structures effectively enhances the impacting-bearing capability and improves the energy absorption performances.

Thermal, electrical, and mechanical properties of hard nitrogen-alloyed Cr thin films deposited by magnetron sputtering

CrN based materials, including stoichiometric CrN and Cr:N with a wide range of nitrogen contents, are commonly used as hard and corrosion-resistant coatings. Cr-rich films in this materials system can retain the bcc structure of metallic Cr with few percent of dissolved nitrogen, which can be used for tailoring the mechanical, thermal, and electrical properties. Here, we investigated low nitrogen containing Cr thin films deposited by high ion assisted magnetron sputtering with a substrate temperature of 200 °C. With the gas flow ratio maintained at fN2/Ar = 0.02, the substrate bias and the target power allows for control of the film composition (0.03 < N/Cr < 0.34). The films comprise a mixture of bcc-Cr and hexagonal Cr2N1-δ phases. The mechanical properties studied by nanoindentation and Brillouin inelastic light scattering revealed a hardening effect due to the multiphase nanostructure. The mechanical properties of the Cr:N films depend on the residual stress, on the amount of h- Cr2N1-δ phase and on the nanostructuring nature of the coatings. A maximum hardness of 37 GPa was achieved for a dense film with a Young's modulus of 340 GPa, a shear modulus of 118 GPa, and a relatively low thermal conductivity of 7 W/mK.