Effects of small additions of Zn on the microstructure, mechanical properties and corrosion resistance of WE43B Mg alloys

Zn is a commonly used alloying element for Mg alloys owing to its beneficial effects on mechanical properties. To improve the mechanical and corrosion properties of WE43B Mg alloys, the effects of 0–0.7wt% Zn addition on the microstructure and properties of sample alloys were investigated. Addition of Zn to as-cast WE43B alloy promoted the formation of the Mg12Nd phase;by contrast, after T6 heat treatment, the phase composition of WE43B alloys with and without Zn addition remained mostly the same. A long-period stacking ordered phase was predicted by CALPHAD calculation, but this phase was not observed in either the as-cast or heat-treated Zn-containing WE43B alloys. The optimum temperature and duration of T6 heat treatment were obtained using CALPHAD calculations and hardness measurements. Addition of Zn resulted in a slight reduction in the average grain size of the as-cast and T6 heat-treated WE43B alloys and endowed them with increased corrosion resistance with little effect on their mechanical properties.

Microstructure and mechanical and corrosion properties of hot-extruded Mg–Zn–Ca–(Mn)biodegradable alloys

Biodegradable Mg-based implants are widely used in clinical applications because they exhibit mechanical properties comparable to those of human bone and require no revision surgery for their removal.Among Mg-based alloys,Mg–Zn–Ca–(Mn)alloys have been extensively investigated for medical applications because the constituent elements of these alloys,Mg,Zn,Ca,and Mn,are present in human tissues as nutrient elements.In this study,we investigated the effect of the hot extrusion temperature on the microstructure,mechanical properties,and biodegradation rate of Mg–Zn–Ca–(Mn)alloys.The results showed that the addition of Mn and a decrease in the extrusion temperature resulted in grain refinement followed by an increase in the strength and a decrease in the elongation at fracture of the alloys.The alloys showed different mechanical properties along the directions parallel and perpendicular to the extrusion direction.The corrosion test of the alloys in the Hanks’solution revealed that the addition of Mn significantly reduced the corrosion rate of the alloys.The Mg–2 wt%Zn–0.7 wt%Ca–1 wt%Mn alloy hot-extruded at 300℃ with an ultimate tensile strength of 278MPa,an yield strength of 229MPa,an elongation at fracture of 10%,and a corrosion rate of 0.3 mm/year was found to be suitable for orthopedic implants.

Tribological behavior of A356-CNT nanocomposites fabricated by various casting techniques

Tribological behaviors of monolithic A356 aluminum alloy castings and A356.CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocasting, stir casting, and compocasting techniques. Effects of addition of carbon nanotubes (CNTs), casting process and the applied load on wear properties and mechanisms were investigated. It was found that wear loss, wear rate and friction coefficient of nanocomposite samples remarkably declined by the addition of CNTs. Moreover, changing the casting process from fully liquid to semisolid routes, plus increasing fractions of the primary phase were the two factors that improved the wear properties of the investigated samples, especially nanocomposite ones. In addition, it was revealed that adhesion and delamination were the dominant wear mechanism of the monolithic samples produced by fully liquid and semisolid routes, respectively. However, regardless of fabrication techniques, the abrasion was the main wear mechanism of nanocomposite samples.

Development of a magnesium alloy with good casting characteristics on the basis of Mg–Al–Ca–Mn system,having Mg–Al2Ca structure

Application of calcium as alloying element for magnesium alloys has been considered according to literature data.Mg–7%Al–4%Ca–0.5%Mn casting alloy was offered,which possesses the low propensity to the hot brittleness and good castability.The alloy has the moderate strength(σu=150 MPa)and the satisfactory percentage elongation(δ=3%).It is shown,that calcium-containing alloys smelting of Mg–Al–Ca–Mn system is preferable with the application of low-chloride flux FL10(20%MgCl_(2);29%KCl;12%BaCl_(2);23%CaF2;15%MgF2;1%B2O3).The alloy smelting in the atmosphere of argon and SF6 mixture results in the increased shelling and waste of calcium.The heat treatment is offered for the developed alloy,which is directed to the Al_(2)Ca phase spheroidizing.The developed magnesium alloy,alloyed with calcium,is perspective for the industry production of low-cost moulding.

Development of Mg-Zn-Y-Zr casting magnesium alloy with high thermal conductivity

Magnesium alloys are used in aircraft because of their light weight.However,for these alloys to be applied in electronic devices,high thermal conductivities are required.Several high-potential compositions of Mg-Zn-Y-Zr alloys were selected by phase composition and their freezing ranges calculated using Thermo-Calc software.The alloys were prepared,and their fluidity,hot tearing susceptibility,mechanical properties,and thermal conductivity were obtained and compared.The alloy composed of Mg-4 wt%Zn-3 wt%Y-0.3 wt%Zr was selected for further investigation,because of its high thermal conductivity and satisfactory mechanical properties.The Mg-4 wt%Zn-3 wt%Y-0.3 wt%Zr alloy’s fluidity and hot tearing susceptibility were similar to those of the widespread AZ91 commercial casting magnesium alloy.The influence of a heat treatment regime on the microstructure,thermal conductivity,and mechanical properties of the developed alloy was also investigated.It was established that the room temperature thermal conductivity of the Mg-4 wt%Zn-3 wt%Y-0.3 wt%Zr alloy after aging at 300℃for 5 h was 105 W/m K^(-1).Additionally,the following tensile test results were obtained in aged condition:120 MPa yield strength,200 MPa ultimate tensile strength,and 4%elongation.The utilization of solid solution heat treatment at 520℃for 8 h prior to aging can promote up to 9%increase in elongation.The Mg-4 wt%Zn-3 wt%Y-0.3 wt%Zr casting alloy can be used as a high thermal conductivity material with industrial applications.

Influence of Al-5Ti-1B master alloy addition on the grain size of AZ91 alloy

The mechanical properties of castings depend on the grain size.There is evidence that titanium and boron(Al-5Ti-1B master alloy)affect the grain size of magnesium alloys.Here,the influence of the addition of 0-1 wt.%of Al-5Ti-1B master alloy on the grain size of AZ91 magnesium alloy was investigated.Melting of the alloy was performed in steel and corundum crucibles.To study the effect of cooling rate on grain size,cylindrical samples were cast in steel and fireclay molds.The Al-5Ti-1B master alloy addition did not change the phase composition of the AZ91 alloy.This study demonstrates that the addition of Al-5Ti-1B did not contribute to the grain refinement of the AZ91 alloy,but rather led to its coarsening for samples cast in both the steel and fireclay molds.Increasing the holding time after the addition of the Al-5Ti-1B master alloy from 15 to 110 minutes also did not lead to significant grain coarsening.The mechanical properties of the AZ91 alloy samples slightly improved after Al-5Ti-1B addition.

Design of Mg-Zn-Si-Ca casting magnesium alloy with high thermal conductivity

Magnesium alloys are commonly used to produce lightweight parts.While most magnesium alloys exhibit low thermal conductivities,high thermal conductivities are needed for electronic devices.In this study,we attempted to develop new magnesium casting alloys with high thermal conductivities.The Mg-Zn-Si-Ca alloy compositions were chosen using CALPHAD(CALculation of PHAse Diagrams)calculations,and alloy samples were prepared.The fluidity and hot-tearing resistance were measured.The results indicated that these properties were similar to those of AZ91 alloy.Tensile tests showed that high-pressure die casting could produce Mg-Zn-Si-Ca alloys possessing mechanical properties 1.5-3 times higher than those produced via sand casting.The alloy thermal conductivity was 126 W/mK at room temperature.The corrosion rates of the as-cast samples in NaCl/water solutions were two times higher than that of AZ91.

Non-isothermal oxidation of coal with Ce(NO3)3 and Cu(NO3)2 additives

Non-isothermal oxidation of brown coal with 5 wt% of Cu(NO3)2, 5 wt% of Ce(NO3)3 and {2.5 wt% Cu(NO3)2 + 2.5 wt% Ce(NO3)3} additives was studied. The introduction of additives was carried out by an incipient wet impregnation method to ensure uniform distribution of cerium and copper nitrates within the structure of coal powdery samples (according to SEM and EDX mapping). The samples reactivity was studied in an isothermal oxidation regime at 200 °C (1 h) and by DSC/TGA at 2.5 °C/min heating rate. The additives implementation was found to reduce significantly the oxidation onset temperature (△Ti = 20-55 °C), the samples oxidation delay time (△ti= 2-22 min) and overall duration of the oxidation process (△tc = 8-16 min). The additives efficiency could be graded in accordance with the activation on the coal oxidation in the following row: Cu(NO3)2 >{Cu(NO3)2 + Ce(NO3)3}> Ce(NO3)3. According to the mass spectroscopy, the obtained row of activation correlates well with the initial temperature of the studied nitrate's decomposition (from 190 to 223 °C). A presence of nitrates was found to change significantly the trend of heat release taking place during the oxidation of coal samples (according to DSC/TGA data). The influence of coal morphology and volatiles concern in initial sample on the parameters of the oxidation process was studied as well. Activation energy (Ea) of the coal oxidation was calculated using Coats-Redfern method. Maximum decrease in Ea from 69 to 58 kJ/mol was observed for the samples with Cu(NO3)2. Graphical abstract.

Effect of Cu addition on microstructural evolution and hardening of mechanically alloyed Al-Ti-O in-situ composite

The microstructure formation and strengthening of an Al-5 wt.%TiO2 composites with additions of 5 wt.%Cu and 2 wt.% stearic acid(as a process control agent, PCA) during mechanical alloying and subsequent thermal exposure were studied. The powder composites were prepared by high-energy ball milling for up to 10 h. Single line tracks of the powders were laser melted. Optical and scanning electron microscopy, XRD analysis and differential scanning calorimetry were used to study microstructural evolution. The results showed that the Cu addition promotes an effective mechanical alloying of aluminum with Ti O2 from the start of milling, resulting in higher microhardness(up to HV 290), while the PCA, on the contrary, postpones this process. In both cases, the composite granules with uniform distribution of Ti O2 particles were formed. Subsequent heating of mechanically alloyed materials causes the activation of an exothermic reaction of Ti O2 reduction with aluminum, the start temperature of which, in the case of Cu addition,shifts to lower values, that is, the transformation begins in the solid state. Besides, the Cu-added material after laser melting demonstrates a more dispersed and uniform structure which positively affects its microhardness.

High-pressure torsion deformation process of bronze/niobium composite

The deformation process in the material volume under high-pressure torsion(HPT)was studied.As a model object for the observation of deformation process,we used a composite comprising a bronze matrix and niobium filaments.The arrangements of the niobium filaments in the bronze matrix and their size have regular geometry.This allows us to monitor and measure the displacement of the niobium filaments in the sample volume,which results from HTP.The bronze/niobium composite samples were subjected to HPT at room temperature and 6 GPa,and the number of revolutions N=1/4,1/2,1,2,3 and 5.It was shown that HPT with revolution number of 1 leads to the 360° rotation of entire sample volume without sample slippage.Similar deformational behavior during HPT can be expected for high-ductility metallic materials.The increase in the number of revolutions more than 2 leads to twisting the niobium filaments in the sample volume and the formation of 'vortex' multilayer structure.The mechanisms for the formation of such structures were discussed.

Impact of In^(3+) cations on structure and electromagnetic state of M-type hexaferrites

The solid solutions of In^(3+) doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method,and Rietveld analysis of the neutron diffraction patterns was conducted.In^(3+) cations occupy octahedral (4f_(Ⅵ)and 12 k) and tetrahedral (4f_(Ⅳ)) positions (SG=P6_(3)/mmc(No.194)).The average particle size is 837–650 nm.Curie tempearature (T_(C)) of the compounds monotonically decreased down to~520 K with increasing x.A frustrated magnetic state was detected from ZFC and FC magnetizations.saturation magnetization (M_(s)) and effective magnetocrystalline anisotropy coefficient (k_(eff)) were determined using the law of approach to saturation.A real permittivity (ε″) maximum of~3.3 at~45.5 GHz and an imaginary permittivity (ε′) of~1.6 at~42.3 GHz were observed for x=0.1.A real permeability (μ′) maximum of~1.5 at~36.2 GHz was observed for x=0.Aμ″imaginary permeability maximum of~0.8 at~38.3 GHz was observed for x=0.1.The interpretation of the results is based on the type of dielectric polarization and the natural ferromagnetic resonance features.

Structure and Thermoelectric Properties of Nanostructured (Bi, Sb)₂Te₃(Review)

The investigation of the structure and thermoelectric properties of nanostructured solid solutions (Bi, Sb)2Te3 p-type has been carried out. The samples were obtained by grinding of original compositions in a planetary ball mill and by spark plasma sintering (SPS). Initial powder has an average particle size of 10 - 12 nm according to transmission electron microscopy, and the size of the coherent scattering region (CSR) obtained by X-ray line broadening. During sintering at Ts = 250°C - 400°C, the grain size and CSR increased, which was associated with the processes of recrystallization. The maximum of size distribution of CSR shifts to larger sizes when Ts increases so that no broadening of X-ray lines at Ts = 400°C can take place. At higher Ts, the emergence of new nanograins is observed. The formation of nanograins is conditioned by reducing of quantity of the intrinsic point defects produced in the grinding of the source materials. The study of the electrical conductivity and the Hall effect in a single crystal allows to estimate the mean free path of the holes-L in the single crystal Bi0.5Sb1.5Te3 which at room temperature is 2 - 5 nm (it is much smaller than the dimensions of CSR in the samples). The method for evaluation of L in polycrystalline samples is proposed. At room temperature, L is close to the mean free path in single crystals. Scattering parameter holes in SPS samples obtained from the temperature dependence of the Seebeck coefficient are within the measurement error equal to the parameter of the scattering of holes in a single crystal. The figure of merit ZT of SPS samples as a function of composition and sintering temperature has been investigated. Maximum ZT, equal to 1.05 at room temperature, is obtained for the composition Bi0.4Sb1.6Te3 at Ts = 500°C and a pressure of 50 MPa. The causes of an apparent increase in thermoelectric efficiency are discussed.

Multiscale wood micromechanics and size effects study via nanoindentation

Wood as a material is a natural composite with a complex hierarchically arranged structure.All scale levels of wood structure contribute to its macroscopic mechanical properties.The nature of such characteristics and deformation modes differs radically at different scale levels.Wood macroscopic properties are well studied,and the relevant information can be easily found in the literature.However,the knowledge of the deformation mechanisms at the mesoscopic level corresponding to the cellular structure of early and late wood layers of annual growth rings is insufficient.It hinders building the comprehensive multiscale model of how wood mechanical properties are formed.This paper described the results of scanning of mechanical properties of softwood and hardwood samples,such as common pine,small-leaf lime,and pedunculate oak,by means of nanoindentation(NI).The NI technique allows varying the size of deformed region within a wide range by altering maximal load(P max)applied to the indenter so that one can re-peatedly and non-destructively test wood structural components at different scale levels on the same sample without changing the technique or equipment.It was discovered that the effective microhardness(H eff)and Young’s modulus(E eff)decreased manifold with P max growing from 0.2 to 2000 mN.This drop in H effwas observed when the locally deformed region grew,and re-sulting from P max increase generally follows the rule similar to the Hall-Petch relation for yield stress,strength,and hardness initially established for metals and alloys,though obviously in those cases the underlying internal mechanisms are quite different.The nature and micromechanisms of such size effect(SE)in wood revealed using NI were discussed in this study.At P max<0.2 mN,the deformed area under the pyramidal Berckovich indenter was much smaller than the cell wall width.Hence,in this case,NI measured the internal mechanical properties of the cell wall material as long as free boundaries impact could be neglected.At P max>200 mN,the indentation encompassed several cells.The measured mechanical properties were significantly affected by bending deformation and buckling collapse of cell walls,reducing H effand E effsubstantially.At P max≈1-100 mN,an indenter interacted with different elements of the cell structure and capillary network,resulting in intermediate values of H effand E eff.Abrupt changes in H effand E effat annual growth ring boundaries allow accurate measuring of rings width,while smoother and less pronounced changes within the rings allow identification of earlywood and latewood layers as well as any finer changes during vegetation season.The values of ring width measured using NI and standard optical method coincide with 2%−3%accuracy.The approaches and results pre-sented in this study could improve the understanding of nature and mechanisms lying behind the micromechanical properties of wood,help to optimize the technologies of wood farming,subse-quent reinforcement,and utilization,as well as to develop new highly informative techniques in dendrochronology and dendroclimatology.

Application of artificial neural networks for stress state analysis based on the photoelastic method

The present article proposes an evolutionary development of the photoelasticity method for measuring stresses based on annular photoelastic sensors application along with stress pattern recording with the aid of a digital camera and its recognition using artificial neural networks.The analysis of the modern application of the photoelasticity method for various problems within the theory of strength is presented.The principle of operation of photoelastic sensors based on the photoelasticity effect is considered.Optical patterns in an annular photoelastic sensor are presented for various values of the horizontal stress.The calculation of the stress state of the sensor for the following full-scale experiment has been performed,the estimate of the threshold conditions under which the sensor can be applied has been performed.As a result of a laboratory experiment,a dataset of 1500 isochromatic images has been assembled.A subspecies of a neural network,namely a convolutional neural network,has been applied as a machine learning algorithm.Different combination of models and optimizers have been employed.The application of downhole sensors for continuous monitoring of alterations in the rock mass stress state and the integration of this data into a digital field model based on Internet of Things technologies has been proposed.

Search for the doubly charmed baryon ■

A search for the doubly charmed baryon ■^+cc is performed through its decay to theΛ^+c K^-π^+ final state,using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7,8 and 13 TeV.The data correspond to a total integrated luminosity of 9 fb^-1.No significant signal is observed in the mass range from 3.4 to 3.8 GeV/c^2.Upper limits are set at 95%credibility level on the ratio of the ■^+cc production cross-section times the branching fraction to that ofΛ^+c and ■^++cc baryons.The limits are determined as functions of the ■^+cc mass for different lifetime hypotheses,in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c.

Processing and characterization of lead-free ceramics on the base of sodium-potassium niobate

Lead-free sodium-potassium niobate-based piezoelectric materials are most intensively studied in order to replace the widely used Pb-based ones.In this work,the effects of modification of compositions by donor and acceptor dopants in the A-and B-sites of perovskite lattice on structure,dielectric,ferroelectric,and piezoelectric properties of ceramics from Morphotropic Phase Boundary in the(1-x)(K_(0.5)Na_(0.5))NbO_(3)-xBaTiO_(3) system and in compositions with x=0.05 and 0.06 additionally doped by Ni^(3+) cations have been studied.

High yield production of ultrathin fibroid semiconducting nanowire of Ta2Pd3Se8

Immediately after the demonstration of the high-quality electronic properties in various two dimensional(2D)van der Waals(vdW)crystals fabricated with mechanical exfoliation,many methods have been reported to explore and control large scale fabrications.Comparing with recent advancements in fabricating 2D atomic layered crystals,large scale production of one dimensional(1D)nanowires with thickness approaching molecular or atomic level still remains stagnant.Here,we demonstrate the high yield production of a 1D vdW material,semiconducting Ta2Pd3Se8 nanowires,by means of liquid-phase exfoliation.The thinnest nanowire we have readily achieved is around 1 nm,corresponding to a bundle of one or two molecular ribbons.Transmission electron microscopy(TEM)and transport measurements reveal the as-fabricated Ta2Pd3Se8 nanowires exhibit unexpected high crystallinity and chemical stability.Our low-frequency Raman spectroscopy reveals clear evidence of the existing of weak inter-ribbon bindings.The fabricated nanowire transistors exhibit high switching performance and promising applications for photodetectors.

Melt-spun thin ribbons of shape memory TiNiCu alloy for micromechanical applications

The development of micromechanical devices(MEMS and NEMS)on the basis of nanostructured shape memory alloys is reported.A Ti_(50)Ni_(25)Cu_(25)(at.%)alloy fabricated by the melt spinning technique in the form of a ribbon with a thickness around 40µm and a width about 1.5 mm was chosen as a starting material.Technological parameters were optimized to produce the alloy in an amorphous state.The thickness of the ribbon was reduced to 5–14µm by means of electrochemical polishing.A nanostructural state of the thin ribbons was obtained via the dynamic crystallization of the amorphous alloy by application of a single electric pulse with duration in the range of 300–900µs.A microtweezers prototype with a composite cantilever of 0.8µm thick and 8µm long was developed and produced on the basis of the obtained nanostructured thin ribbons by means of the focused ion beam technique.Controlled deformation of the micromanipulator was achieved by heating using semiconductor laser radiation in a vacuum chamber of scanning ion-probe microscope.

Photovoltaic and photoelectric response of Sn_(2)P_(2)S_(6) ferroelectric films

In the present work,the comparative study of the electric response of Sn_(2)P_(2)S_(6) films to the visible light action was carried out without and under external electric field.The light flux modulated by a chopper induces the integral response comprising time-dependent photoelectric and photovoltaic components.It was shown that spontaneous polarization influences the electric response characteristics.

Search for the rare decay B^(0)→J/ψФ

A search for the rare decay B^(0)→J/ψФis performed using Pp collision data collected with the LHCb dete-ctor at centre-of-mass energies of 7,8 and 13 TeV,corresponding to an integrated luminosity of9 fb.No significant signal of the decay is observed and an upper limitof 1.1x 10^(-7)at 90%confidence level is set on the branching fraction.