Hexagonal Close-packed Lattice Research Articles

Discovering Pyramidal Treasures: Multi-Scale Design of High Strength-Ductility Titanium Alloys.

Mechanical properties of titanium alloys, one of humankind's most essential structural materials, suffer from the lack of 〈c + a〉 dislocations on pyramidal slip planes, failing homogeneous plastic strain accommodation. This mechanical treasure is not easily accessible in titanium alloys because of the required excessively high stress levels. The present work demonstrates that such a dilemma may be overcome by meticulously tuning the c/a ratio, the simplest crystallographic parameter of the hexagonal close-packed lattice, through Sn alloying. Combining this lattice-scale design concept with a cross-rolling based polycrystal-scale design solution, this study showcases a facile route to bimodal (α + β) titanium alloys with exceptional strength-ductility synergy.

On a mathematical theory for the crystallography of shear transformations in metals: Unification of mechanisms

A theory for shear transformations in crystalline materials linking their Crystallography, atomic-scale mechanisms and Thermodynamics is introduced. The lattice and transformation function are treated as vector space and functions respectively to overcome shortcomings of classical matrix-based theories for martensite crystallography. The extremum principle is used to obtain the atomic paths minimising and maximising the energy from all possible solutions, therefore explaining which sequences are more Thermodynamically feasible. The face-centred cubic (FCC)→body-centred cubic (BCC) transformation in Fe is used as case study. The theory predicts that the average values of the extrema correspond to the crystallography, shear magnitude, interface defects and habit planes of main transformations in Fe, i.e. Widmanstätten Ferrite, Bainite, lath martensite, plate and lenticular martensite. Bainite represents the macroscopic average minimum energy configuration, whereas Widmanstätten Ferrite corresponds to a local and discrete minimum energy configuration. Lath martensite corresponds to the average shear configurations minimising atomic displacements when there is no other driving force, e.g. diffusion, whereas the maximum energy configurations correspond to plate and lenticular martensite forming twin pairs. Targeted results for the FCC→hexagonal close-packed lattice transformation are presented to demonstrate the robustness of the theory. The predictions are combined with elasticity theory to compute the Driving Force and predict the start temperatures – therefore connecting for the first time – local and macroscopic crystallographic features with the Thermodynamics of shear-controlled structures in Fe. This work presents new results towards addressing longstanding challenges in Materials Science such as theoretically demonstrating that Bainite is a shear transformation.

Investigating hexagonal closed packed crystal lattice through QSPR modeling via linear regression analysis and Topsis

sThis research work covers three highly dominating reverse degree-based topological descriptors evaluated for the three-dimensional hexagonal close-packed (HCP) crystal structure lattice. HCP crystal lattice has a highly symmetrical and elegant crystal structure, and we have observed that results obtained from symmetrical structures draw symmetry in the numerical formulation obtained from topological descriptors. For this purpose, we will investigate whether the HCP lattice formed by an odd pair of unit cells is the best or an even pair of unit cells forming the lattice and how they behave in a dominating sense when investigated through the conclusions obtained from QSPR modeling. The QSPR model has been proposed to check the efficiency of each specified topological descriptor for five highly commendable physio-chemical properties: melting or boiling point, density, molar heat capacity, and enthalpy. Further, we have discovered the ideology to obtain the best possible structure when investigated and established on a statistically and mathematically strong proving and to what extent we can extract from QSPR to implement MCDM techniques, here considering TOPSIS that provide the best HCP structure lattice rankings. The obtained results may be helpful for researchers to better understand the structure and studying different physical/chemical properties of HCP crystal lattice.

Mechanical, electronic and thermodynamic properties of crystalline molecular hydrogen at high pressure

Solid molecular hydrogen exhibits a rich variety of unique properties, including insulator-to-metal transition. However, the specific structure of phase III remains unclear. Experimental evidence suggests high-pressure hydrogen shows a hexagonal close-packed lattice. Therefore, as a potential candidate for phase III, the structure, energetic, mechanical, electronic, and thermodynamic properties of P6122 structure are systemically studied. It is found phase III with P6122 space group is both mechanically and thermodynamically stable within the pressure range of 120∼300 GPa. Besides, we observed significant enhancements in the bulk modulus, shear modulus, and Young's modulus. The band structures exhibit a transition from topological insulator to topological semiconductor and eventually to a Wely semimetal as the pressure increases. The electron density accumulates between pseudo “H2” molecules in the insulating phase but it partly channels into the interlayer space in the semimetallic phase. Phase III with P6122 structure is barely explored previously in solid hydrogen, therefore, we believe our present investigation contributes valuable insights towards understanding the behavior of metallic hydrogen.

Phase-Controlled Ruthenium Nanocrystals on Colloidal Polydopamine Supports and Their Catalytic Behaviors in Aerobic Oxidation Reactions.

The past decade has witnessed rapidly growing interest in noble metal nanostructures adopting unconventional metastable crystal phases. In the case of Ru, chemically synthesized nanocrystals typically form thermodynamically favored hexagonal close-packed (hcp) crystal lattices, whereas it remains significantly more challenging to synthesize Ru nanocrystals in the metastable face-centered cubic (fcc) phase. In this work, we have synthesized polydopamine (PDA)-supported hcp and fcc Ru nanocrystals in a phase-selective manner through one-pot thermal reduction of appropriate Ru(III) precursors in a polyol solvent. Benefiting from the unique surface-adhesion function of PDA, we have been able to grow phase-controlled sub-5 nm Ru nanocrystals directly on colloidal PDA supports without prefunctionalizing the particle surfaces with any molecular linkers or surface-capping ligands. Success in phase-controlled synthesis of capping ligand-free Ru nanocrystals dispersed on the same support material enables us to systematically compare the intrinsic mass-specific and surface-specific activities of fcc and hcp Ru nanocatalysts toward the aerobic oxidation of a chromogenic molecular substrate, 3,3',5,5'-tetramethylbenzidine (TMB), under a broad range of reaction conditions. We use UV-vis absorption spectroscopy to monitor the conversion of the reactant molecules into the one-electron and two-electron oxidation products in real time during Ru-catalyzed oxidation of TMB, which is found to be a mechanistically complex molecule-transforming process involving multiple elementary steps. The apparent reaction rates and detailed kinetic features are observed to be not only intimately related to the crystalline structures of the Ru nanocatalysts but also profoundly influenced by several other critical factors, such as the pH of the reaction medium, the initial concentration of TMB, Ru coverage on the PDA supports, and degree of nanoparticle aggregation.

Intermetallic bulk phase Nb5Al3Cx synthesized via wet ball milling

It’s known that the Nb–Al–C system may crystallize in ternary compounds, including well studied MAX phases (Nb2AlC, Nb4AlC3) and a stable Nb3Al2C phase. This study has shown a route of synthesizing novel bulk Nb5Al3Cx intermetallic phase via wet ball milling of niobium and aluminum powders in petroleum ether and subsequent thermal treatment. The synthesized intermetallic phase has a hexagonal close-packed (hcp) lattice of space group D88 . The phase is formed at 757 °C, keeping stable at least up to ∼1130 °C. The lattice parameters are a = 7.808–7.813 Å, c = 5.270–5.279 Å, c/a = 0.675–0.676 for this phase.

Hexagonal Close-Packed Polar-Skyrmion Lattice in Ultrathin Ferroelectric PbTiO_{3} Films.

Polar skyrmions are topologically stable, swirling polarization textures with particlelike characteristics, which hold promise for next-generation, nanoscale logic and memory. However, the understanding of how to create ordered polar skyrmion lattice structures and how such structures respond to applied electric fields, temperature, and film thickness remains elusive. Here, using phase-field simulations, the evolution of polar topology and the emergence of a phase transition to a hexagonal close-packed skyrmion lattice is explored through the construction of a temperature-electric field phase diagram for ultrathin ferroelectric PbTiO_{3} films. The hexagonal-lattice skyrmion crystal can be stabilized under application of an external, out-of-plane electric field which carefully adjusts the delicate interplay of elastic, electrostatic, and gradient energies. In addition, the lattice constants of the polar skyrmion crystals are found to increase with film thickness, consistent with expectation from Kittel's law. Our studies pave the way for the development of novel ordered condensed matter phases assembled from topological polar textures and related emergent properties in nanoscale ferroelectrics.

Multiscale Monte Carlo simulations of gold nanoparticle dose-enhanced radiotherapy I: Cellular dose enhancement in microscopic models.

The introduction of Gold NanoParticles (GNPs) in radiotherapy treatments necessitates considerations such as GNP size, location, and quantity, as well as patient geometry and beam quality. Physics considerations span length scales across many orders of magnitude (nanometer-to-centimeter), presenting challenges that often limit the scope of dosimetric studies to either micro- or macroscopic scales. To investigate GNP dose-enhanced radiation Therapy (GNPT) through Monte Carlo (MC) simulations that bridge micro-to-macroscopic scales. The work is presented in two parts, with Part I (this work) investigating accurate and efficient MC modeling at the single cell level to calculate nucleus and cytoplasm Dose Enhancement Factors (n,cDEFs), considering a broad parameter space including GNP concentration, GNP intracellular distribution, cell size, and incident photon energy. Part II then evaluates cell dose enhancement factors across macroscopic (tumor) lengthscales. Different methods of modeling gold within cells are compared, from a contiguous volume of either pure gold or gold-tissue mixture to discrete GNPs in a hexagonal close-packed lattice. MC simulations with EGSnrc are performed to calculate n,cDEF for a cell with radius µm and nucleus µm considering 10to 370keV incident photons, gold concentrations from 4 to 24mgAu /gtissue , and three different GNP configurations within the cell: GNPs distributed around the surface of the nucleus (perinuclear) or GNPs packed into one (or four) endosome(s). Select simulations are extended to cells with different cell (and nucleus) sizes: 5µm (2, 3, and 4µm), 7.35µm (4 and 6µm), and 10µm (7, 8, and 9µm). n,cDEFs are sensitive to the method of modeling gold in the cell, with differences of up to 17% observed; the hexagonal lattice of GNPs is chosen (as the most realistic model) for all subsequent simulations. Across cell/nucleus radii, source energies, and gold concentrations, both nDEF and cDEF are highest for GNPs in the perinuclear configuration, compared with GNPs in one (or four) endosome(s). Across all simulations of the (rcell , rnuc ) = (7.35, 5)µm cell, nDEFs and cDEFs range from unity to 6.83 and 3.87, respectively. Including different cell sizes, nDEFs and cDEFs as high as 21.5 and 5.5, respectively, are observed. Both nDEF and cDEF are maximized at photon energies above the K- or L-edges ofgold by 10 to 20 keV. Considering 5000 unique simulation scenarios, this work comprehensively investigates many physics trends on DEFs at the cellular level, including demonstrating that cellular DEFs are sensitive to gold modeling approach, intracellular GNP configuration, cell/nucleus size, gold concentration, and incident source energy. These data should prove especially useful in research as well as treatment planning, allowing one to optimize or estimate DEF using not only GNP uptake, but also account for average tumor cell size, incident photon energy, and intracellular configuration of GNPs. PartII will expand the investigation, taking the PartI cell model and applying it in cm-scalephantoms.

Multiscale thermo-kinetic characterization for β′ and β1 precipitation in Mg-Sm alloys

Two types of metastable β-series phases have been reported to exist in aged Mg-Sm alloys. The first type refers to preferentially precipitated β′-series phases (including β′s, β′l and β′h), which are intrinsically different Sm orderings on the hexagonal close-packed (HCP) lattice of α-Mg, while the second type refers to subsequently precipitated β1 phase having a face-centered cubic (FCC) lattice. Up to now, whether β1 forms from the α-Mg matrix or the pre-existing βʹ is still on debate, due to unavailable convincing experimental evidence. Employing the first-principles calculations and a statistical mechanics approach consisting of the cluster expansion (CLEX) model and the Monte Carlo simulation, a multiscale phase-field model is herein constructed to thermo-kinetically characterize the precipitations of β′s, β′l, β′h and β1 in Mg-Sm alloys. Equipped with a newly revised explicit nucleation algorithm developed from so-called thermo-kinetic correlation, the present phase-field model can reproduce multi-particle morphologies upon independent precipitations of β′s, β′l, β′h and β1. And then, correlative precipitations of β′ (referring to β′s, β′l or β′h) and β1 are focused on, where, it has been proved that, any pre-existing βʹ variant can transform to a specific single variant or multi-variant configurations of β1. Notably, the precipitations above should follow a rule determined by so-called strain energy dominated thermo-kinetic connectivity. The newly proposed nucleation algorithm is widely applicable for precipitation modeling, and the revealed thermo-kinetic mechanism for precipitations of β-series phases should be enlightening for the rational design of Mg-rare earth (RE) alloys.

Characterization of a novel AlLiMgTiZr-type light high entropy alloy

Al11Li10Mg23Ti21Zr35 was designed as a novel Light High Entropy Alloy (LHEA) considering terms and parameters of respective phase formation rules. The alloy was vacuum melted utilizing high-purity elements, then suction cast and homogenized. The experimentally measured density of the ingot was 4.43 g/cm3 compared to the theoretical density of 4.02 g/cm3. Chemical composition, microstructural properties, phase structure, compressive mechanical properties, and microhardness were characterized. Approximate chemical homogeneity was observed in the microstructure and the Hexagonal Close-Packed (HCP) solid solution phase with c/a = 1.544 and AlZr2 intermetallic compounds were identified. High specific hardness (230 Vickers. cm3/g) was achieved satisfying among all LHEAs introduced up to now. Different hardness values were measured at various points of the microstructure connected to the presence of AlZr2 intermetallic. The lattice distortion of alloys' crystal structures was analyzed accurately, and the distorted solid solution structure consists of elements with different atomic radii, proposed as the dominant mechanism (contributed more than 80%) among grain boundary, dislocation strengthening and solid solution strengthening mechanisms. The alloy's ductility was fair due to the HCP lattice and intermetallic compounds.

Fracture Kinetics and Mechanisms of Ultrafine-Grained Materials during Fatigue Tests in the Low-Cycle Fatigue Region

In this paper, the fracture kinetics and mechanisms in the low-cycle fatigue region were analyzed for different ultrafine-grained (UFG) materials with body-centered cubic (bcc), hexagonal close-packed (hcp) and face-centered cubic (fcc) lattices. Three-point bending principle fatigue tests were performed. The tests show that the UFG structure formation in the investigated materials has an ambiguous effect on the total number of cycles to failure (life) of the samples. The number of cycles to fatigue crack initiation (Nin) is about 20% of the total life of the samples, irrespective of the material state and the crystal lattice type. At the same value of the stress intensity coefficient range (∆K), for the majority of the investigated UFG materials, the fatigue crack propagation rate (dl/dN) is close to or lower than that of the initial coarse-grained (CG) materials. For the UFG materials, the coefficient n in the Paris equation is, in most cases, lower than that for the CG materials, which indicates that the UFG materials are less sensitive to cyclic overload. The fatigue fracture mechanisms of the investigated CG and UFG materials are rather similar, although the fracture of the UFG materials is accompanied by the formation of many secondary cracks, irrespective of the crystal lattice type.

Green synthesised ZnO nanoparticles from Plectranthus amboinicus plant extract: removal of Safranin- O and Malachite green dyes & anti-bacterial activity

ABSTRACT The synthesis of Zinc oxide nanoparticles using a plant-mediated approach is presented in this paper. The nanoparticles were successfully synthesised using the sulphate derivative of Zinc and plant extract of the indigenous medicinal plant Plectranthus amboinicus. The XRD analysis confirms the hexagonal close-Packed lattice of the synthesised ZnO nanoparticle. In the UV visible spectrometer (UV – Vis) absorption peak was observed at 314 nm, which is specific for Zinc oxide nanoparticles. Field Emission Scanning Electron Microscope (FESEM) reveals the presence of Zinc oxide nanoparticles in its nanoflakes form. Energy Dispersive Spectrum (EDX) results show strong energy signals of 71.60% and 18.40% for Zinc and Oxygen, respectively. The absorption peak of Zn – O bonding between 404 cm−1 is confirmed by FT- IR spectra. The ZnO nanoparticles degrade 85.29% of Safranin-O dye and 81.57% of Malachite green dye within 90 minutes of time. Antibacterial studies with Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria have given more than 90% results.

Synthesis of superconducting hcp- ZrH3 under high hydrogen pressure

Zirconium trihydride and, for comparison, trideuteride with hexagonal close-packed (hcp) metal lattices were synthesized at a hydrogen/deuterium pressure of 9 GPa and a temperature of 873 K using toroid-type high-pressure chambers. After a rapid cooling (quenching) to 100 K and lowering the pressure to atmospheric, the quenched sample was removed from the chamber and studied by hot extraction analysis, powder x-ray diffraction, and ac magnetic susceptometry. The hot extraction showed that thermal decomposition of both hcp-${\mathrm{ZrH}}_{3}$ and hcp-${\mathrm{ZrD}}_{3}$ in vacuum begins after heating at a rate of 10 K/min to \ensuremath{\sim}200 K and almost ceases at 270 K, leaving tetragonal $\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{ZrH}}_{2}/\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{ZrD}}_{2}$ as a result. The x-ray diffraction study at 85 K gave lattice parameters $a=3.443(2)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=5.964(4)\phantom{\rule{0.16em}{0ex}}\AA{}$ for hcp-${\mathrm{ZrH}}_{3}$ and somewhat smaller values of $a=3.430(5)\phantom{\rule{0.16em}{0ex}}\AA{}$ and $c=5.947(5)\phantom{\rule{0.16em}{0ex}}\AA{}$ for hcp-${\mathrm{ZrD}}_{3}$. The measurements of magnetic susceptibility revealed superconductivity with an onset at 11.6(1) K for hcp-${\mathrm{ZrH}}_{3}$ and 9.5(2) K for hcp-${\mathrm{ZrD}}_{3}$.

Dumbbell Defect Containing Chromium-Rich Lithium-Vacant Layered LiyCr1–xFexO2(y≤ 1, 0 ≤x≤ 0.2): An Unexplored and Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

Oxygen electrochemistry plays a critical role in water electrolysis, fuel cells, and metal–air batteries as efficient energy storage and conversion technology to harness renewable energies. Dumbbell defects containing chromium-rich lithium-vacant layered structure LiCrO2 are envisaged here as an efficient oxygen evolution reaction (OER) electrocatalyst due to the presence of Cr6+ ions at interstitial sites that facilitates −Cr–O–OH formation in basic media. The presence of Cr6+ ions at the dumbbell interstitial sites of the hexagonal close-packed LiCrO2 lattice was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy studies. The crystal structure, morphology, and composition of the materials were confirmed by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and inductively coupled plasma–mass spectrometry analysis. Rhombohedral structure formation and formation of Cr6+ ion interstitials in the Li layer increase that varies with Fe doping in LiyCr1–xFexO2 (y ≤ 1, 0 ≤ x ≤ 0.2), and the best OER activity is achieved for Li0.6Cr0.9Fe0.1O2 (LCFO-10) with a Tafel slope of 50 mV dec–1 and an overpotential of 311 mV at a current density of 10 mA cm–2, better than that of the RuO2 (overpotential ∼336 mV) benchmark catalyst. At an overpotential of 350 mV, the OER current density of LCFO-10 is 28.07 mA cm–2, which is ∼2 times higher than the OER current density observed with commercial RuO2 (13.22 mA cm–2), indicating its superior electrocatalytic performances. The remarkable enhancement of OER performance may be attributed to the synergistic interaction of Cr6+ and Fe3+ ions present in the lattice.

The influence of structure and local structural defects on the magnetic properties of cobalt nanofilms.

The present paper considers a mathematical model describing the time evolution of spin states and magnetic properties of a nanomaterial. We present the results of two variants of nanosystem simulations. In the first variant, cobalt with a structure close to the hexagonal close-packed crystal lattice was considered. In the second case, a cobalt nanofilm formed in the previously obtained numerical experiment of multilayer niobium-cobalt nanocomposite deposition was investigated. The sizes of the systems were the same in both cases. For both simulations, after pre-correction in the initial time stages, the value of spin temperature stabilized and tended to the average value. Also, the change in spin temperature occurred near the average value. The system with a real structure had a variable spin temperature compared to that of a system with an ideal structure. In all cases of calculations for cobalt, the ferromagnetic behavior was preserved. Defects in the structure and local arrangement of the atoms cause a deterioration in the magnetic macroscopic parameters, such as a decrease in the magnetization modulus.

Enhancement for phonon-mediated superconductivity up to 37 K in few-hydrogen metal-bonded layered magnesium hydride under atmospheric pressure.

The discovery of superconductivity in layered MgB2 has renewed interest in the search for high-temperature conventional superconductors, leading to the synthesis of numerous hydrogen-dominated materials with high critical temperatures (Tc) under high pressures. However, achieving a high-Tc superconductor under ambient pressure remains a challenging goal. In this study, we propose a novel approach to realize a high-temperature superconductor under ambient pressure by introducing a hexagonal H monolayer into the hexagonal close-packed magnesium lattice, resulting in a new and stable few-hydrogen metal-bonded layered magnesium hydride (Mg4)2H1. This compound exhibits superior ductility compared to multi-hydrogen, cuprate, and iron-based superconductors due to its metallic bonding. Our unconventional strategy diverges from the conventional design principles used in hydrogen-dominated covalent high-temperature superconductors. Using anisotropic Migdal-Eliashberg equations, we demonstrate that the stable (Mg4)2H1 compound is a typical phonon-mediated superconductor, characterized by strong electron-phonon coupling and an excellent Tc of 37 K under ambient conditions, comparable to that of MgB2. Our findings not only present a new pathway for exploring high-temperature superconductors but also provide valuable insights for future experimental synthesis endeavors.

Mathematical Models and Experiments on the Acoustic Properties of Granular Packing Structures (Measurement of Tortuosity in Hexagonal Close-Packed and Face-Centered Cubic Lattices).

In this study, the sound absorption characteristics of hexagonal close-packed and face-centered cubic lattices were estimated by theoretical analysis. Propagation constants and characteristic impedances were obtained by dividing each structure into elements perpendicular to the incident direction of sound waves and by approximating each element to a clearance between two parallel planes. Consequently, the propagation constant and the characteristic impedance were treated as a one-dimensional transfer matrix in the propagation of sound waves, and the normal incident sound absorption coefficient was calculated by the transfer matrix method. The theoretical value of the sound absorption coefficient was derived by using the effective density applied to the measured tortuosity. As a result, the theoretical value was becoming closer to the measured value. Therefore, the measured tortuosity is reasonable.

Effect of Coolant upon Hole Making Accuracy of Ti6Al4V by Drilling - Consideration of Hole Diameter in the Depth Direction -

Ti6Al4V, which is one of difficult-to-cut metals, is widely used in an aircraft structure, parts of a gas turbine and medical equipment so that a hole making operation of Ti6Al4V is indispensable to fasten the parts. When a highspeed drilling by a conventional twist drill is applied to hole making of Ti6Al4V, it is very difficult to obtain highly accurate hole in diameter, roundness and inlet-outlet edge quality due to a rise of cutting temperature caused by its small heat conductivity. Moreover, it is well-known that Ti6Al4V causes transiently phase transformation from α phase (close-packed hexagonal lattice) to β phase (body-centered cubic lattice) as soon as it reaches the phase transformation temperature of 883 ℃ (1621°F).When coolant is spouted from two coolant holes at the tip of twist drill to decrease a rise of cutting temperature, the temperature rise of twist drill and chip will be restrained thoroughly. However, it is thinkable that the temperature of Ti6Al4V neighboring the hole’s wall drilled would not be reduced so much since heat entering the workpiece is scarcely carried away by supplying coolant. In a machining site a deep hole shape of Ti6Al4V drilled often faces to be smaller in the depth direction although it is well-known that those of steel and aluminum alloy are smaller at the top than near the bottom such as a bell shape.To make clear the effect of coolant upon hole diameter in drilling of Ti6Al4V, a lot of holes having ϕ 8 mm × 24 mm depth for Ti6Al4V were machined by dry drilling and wet drilling on the condition that a feed rate is fixed at 0.05 mm/rev and a rotational speed is varied at 12 steps from 500 rpm to 2500 rpm. After hole diameter and roundness were measured in relation to depth of hole, effect of temperature heated and phase transformation of workpiece upon hole diameter is considered by using the temperature distribution in Ti6Al4V neighboring the hole’s wall drilled, which is estimated by referring the temperatures of workpiece, machined surface and drill during drilling verified by previous researchers, and metallurgy of phase transformation.Consequently, it was ascertained that the hole shape of Ti6Al4V, which is larger at the top than near the bottom, is caused by contraction and phase transformation of Ti6Al4V due to heat entering workpiece, and coolant is not effective to correct the hole shape in the depth direction although it decreases hole diameter uniformly from the top to the bottom due to reduction of drill’s heat expansion.

Process Stability and Reproducibility of the Dieless Drawing Process for AZ31 Magnesium Wires

Magnesium (Mg)-based wires are in the focus of interest for numerous applications like micro-forming technologies or medical engineering. Manufacturing thin Mg-based wires is widely realized by applying a conventional multiple pass cold wire drawing process. This requires a complex manufacturing schedule of multiple passes with intermediate heat treatments to overcome work hardening, because of the cold forming process. Especially Mg and its alloys are known for their rather low formability at room temperature associated with the hexagonal close-packed lattice structure. The dieless drawing process uses local heating to initialize a localized plastic zone under an external tensile load to achieve higher reductions in diameter in a single wire drawing pass. It can therefore present a solution for a more efficient warm manufacturing process of Mg-based wires. In this study, the stability of the steady state material flow during a dieless wire drawing process and its reproducibility was investigated. For this purpose, a variation of process parameters was selected and wire manufacturing was carried out using magnesium alloy AZ31. A single and double dieless drawing process was applied. Additionally, a conventional cold wire drawing process including a die with the same forming schedule was executed as a benchmark experiment. The results of this study show, that the dieless drawing process is not only a stable process after reaching the steady state, but it is also a reproducible and accurately adjustable process. Moreover, the dieless drawing process maintains the property profile of the starting material to a large extend.

INFLUENCE OF HYDROGEN SATURATION ON CHARACTERISTICS OF ZIRCONIUM

The article presents a literature review on the effect of hydrogen saturation on the properties of zirconium alloys. Zirconium alloys are an indispensable structural material for the core of nuclear reactors. During operational loads, the interaction of zirconium materials with interstitial elements (oxygen, nitrogen, hydrogen) necessarily occurs. Zirconium shows the greatest affinity for hydrogen. One of the vulnerable zirconium elements is fuel rod tubes. The safe operation of a nuclear reactor depends on their integrity. In addition, it is fuel tubes that are most exposed to hydrogen. Therefore, the systematization of knowledge about the effect of hydrogen on the properties of zirconium tubes will make it possible to better predict their operational behavior. According to scientific literature data, depending on the volume of absorbed hydrogen, either a solid solution or zirconium hydrides can form. The dependence of the absorbed hydrogen zirconium on the dilution of the hydrogen medium and temperature is shown. The chemical composition of the zirconium alloy also affects the rate and amount of absorbed hydrogen. The effect of hydrogen on the mechanical properties of zirconium alloys is presented. The differences on the fracture surface after tensile tests at room temperature are shown depending on the amount of absorbed hydrogen. Data are presented that indicate that hydrogen atoms are located in octahedral or tetrahedral interstitial voids of a hexagonal close-packed zirconium lattice. It is shown that the thermal solubility of hydrogen in α-zirconium is extremely low, its value is ~6 at. % at the eutectoid transformation temperature, and at room temperature the solubility of α-Zr hydrogen does not exceed 1·10-5 wt. %. In high-temperature β-Zr, hydrogen dissolves up to ~50 at. %. It has been established that deterioration of the properties of zirconium elements of nuclear reactors during operation due to exposure to hydrogen is likely due to a number of factors: hydrogen embrittlement, the formation of large massive accumulations of hydrides and delayed hydride cracking. It is shown that the direction of arrangement of hydrides depends on the texture of the matrix and on the stresses present in the material that act during the formation of hydrides. It has been established that hydrogen can penetrate into a metal through an oxide film, diffusing, for example, along extended defects such as dislocations and grain boundaries. It is noted that the solubility of hydrogen in zirconium depends on other penetration elements already present in the metal, for example, the solubility of hydrogen in α-zirconium depends on the soluble oxygen in the metal matrix, which is confirmed by the reduced «Zr–O–H» ternary system.