Nanomaterials on the basis of electroboosted rolling in grooves and calibres

The process of electroboosted rolling in grooves and calibres can be utilised as an effective way of obtaining of new materials with structure and properties, close to nanosizes. The features and technological capabilities of electroboosted rolling in grooves and calibres utilised for obtaining unique constructional(structural) and functional materials and hardware products from them. The cross-sectional(transversal) size of internal layers can be at the expense of repeated reduction of a package (packet) from the ordered threads or layers as metallic, and not of metallic materials.

Effect of multiaxial deformation on structure, mechanical properties, and corrosion resistance of a Mg-Ca alloy

This article provides a report on the effect of multiaxial deformation(MAD) on the structure, texture, mechanical characteristics, and corrosion resistance of the Mg-0.8(wt.)% Ca alloy. MAD was carried out on the alloy in the as-cast and the annealed states in multiple passes, with a stepwise decrease in the deformation temperature from 450 to 250 ℃ in 50 ℃ steps. The cumulative true strain at the end of the process was 22.5. In the case of the as-cast alloy, this resulted in a refined microstructure characterized by an average grain size of 2.7 μm and a fraction of high-angle boundaries(HABs) of 57.6%. The corresponding values for the annealed alloy were 2.1 μm and 68.2%. The predominant mechanism of structure formation was associated with discontinuous and continuous dynamic recrystallization acting in concert. MAD was also shown to lead to the formation of a rather sharp prismatic texture in the as-cast alloy, whilst in the case of the annealed one the texture was weakened. A displacement of the basal poles {00.4} from the periphery to the center of a pole figure was observed. These changes in the microstructure and texture gave rise to a significant improvement of the mechanical characteristics of the alloy. This included an increase of the ultimate tensile strength reaching 308 MPa for annealed material and 264 MPa for the as-cast one in conjunction with a twofold increase in ductility. A further important result of the MAD processing was a reduction of the rate of electrochemical corrosion, as indicated by a significant decrease in the corrosion current density in both microstructural states of the alloy studied.

Using new physics and technology to advance electrostimulated rolling of metals and alloys

Electrostimulated deformation of metals and alloys, using groove or smooth rolling, requires that several important conditions are satisfied. (1) The deformation site must geometrically overlap with the flow of electric current passing through a strip between the rolls; (2) The density of direct or alternating electric current supplied to deformation site must be sufficiently high (of an order of 104-106А/cm^2); (3) An efficient heat removal from the deformation site must be achieved. In general, the temperature of a strip must be within the range of 100-300℃. (4) The electric resistance at the roll-strip interface must be minimized. Our recent studies also indicate that the electrostimulated rolling in the shortcut regime is a further condition for obtaining high quality rolling of metals. In this regime, the rolls are placed in physical contact even in the absence of a strip that ensures an uninterrupted passage of electric current between the rolls.

Structure,mechanical characteristics,biodegradation,and in vitro cytotoxicity of magnesium alloy ZX11 processed by rotary swaging

Rotary swaging(RS)of alloy Mg-1.03Zn-0.66Ca(ZX11)was shown to refine the average grain size to 4.5±1.2μm in a longitudinal section and 4.8±0.9μm in a transverse section.In addition,a small amount of Mg2Ca particles about 300nm in size and Mg6Zn3Ca2 particles with a size of about lOOnm was detected.This resulted in pronounced strengthening:the yield strength and the ultimate tensile strength rose to 210±8 MPa and 276±6 MPa,respectively,while the elongation hardly decreased(22.0±1.8% and 18.3±2.9% before and after RS).Furthermore,RS led to an increase in the fatigue limit of the alloy from 120 MPa to 135 MPa and did not impair its resistance to chemical corrosion.The studies in vitro showed that ZX11 induces hemolysis without inhibiting the viability of peripheral blood mononuclear cells and has a more pronounced cytotoxic effect on tumor cells in comparison with non-transformed cells.No significant difference of the latter effect between the initial and the deformed states was observed.

Influence of inhomogeneity of grain-boundary region of nanocristalline materials on elastic properties

Experimental data indicate that Young’s modulus of materials decreases with the decreasing of the grain size. Obviously, the primary factor of this decrease is presence of grain-boundary region, which Young’s modulus other than in the bulk of crystallites. There is a set of various expressions for calculation of Young’s modulus of polycrystals, obtained under the assumption, that it is possible to consider a polycrystal as a composite consisting of a crystalline matrix and a intercrystalline layers (grain-boundary region). Calculations showed incorrectness of application of a majority of these expressions and a large error in the calculations for the nanocrystalline materials. By us, on the basis of the same assumptions, is also obtained analytical expression for calculating Young’s modulus of materials with grain size more than 30 nm, which is more exact, than all others.It is necessary to consider under the calculation of effective Young’s modulus nanocrystalline materials with grain size of less than 30nm, that grain-boundary region itself is not uniform. It is reliably established, that the triple joints of grain boundaries have a structure and properties, different from the structure and the properties of grain boundaries, which these joints connect. For nanocrystalline materials the volume fraction of the triple joints in the grain-boundary region can reach 50% and even more. Therefore assumption was made, that the nanocrystalline materials should be represented as consisting of three phases (triple joints, grain boundary between the triple joints and crystallite). On the basis of this idea is obtained analytical expression for calculating of Young’s modulus nanocrystalline materials. The analysis shows that Young’s modulus calculated by this analytical expression coordinated with the theory and the experiment.

Miniaturized disk bend test-a new techniquefor monitoring the changes of mechanicalproperties of structural materials operatingin extreme conditions

Method of Miniaturized Disk Bend Test (MDBT) originally designed for the tests of irradiated materials is a convenient technique for monitoring the degradation of mechanical properties of structural materials operating in extreme conditions. A small size of specimens (disks with 3 mm in diameter and 0.1-0.3 mm in thickness) as well as possibility to use the standard equipments for tension and/or pressure tests allow minimizing the financial charge for application of this method in practice and enable to keep up in the real time with (watch on) the changes of materials mechanical properties induced by the effect of unfavorable environment. Wide application of MDBT or other methods for miniaturized specimen tests does possible to inspect on the fly the changes of strength and ductility of the materials, and, of the expense of it, to prevent an alert conditions caused by the materials degradation, for instance, catastrophic embrittlement.In the paper, methodical aspects of MDBT technique application for estimation of structural materials mechanical properties have been considered. By the example of own results and literature data, the possibilities of MDBT method are demonstrated as well as the correlation of obtained from this technique parameters with the standard mechanical properties such as strength, yield stress and ductility of metals.

Application of cold plasma technology in fiber-reinforced composite materials

A study is presented concerning a cold plasma technique for improving the bondability of high-strength high-modulus multi-filament polyethylene fibers to polymer matrices and the fibers impregnation with the objective to fabricate composite materials (CMs). Strong bonding between the matrixes and reinforcing fibers during the production of composites appears in the case if interaction is chemical. The value of the activation energy of the chemical interaction for very high performance polyethylene fiber was estimated. It was 1.14 eV. This allows using the cold plasma technique for producing CMs. In order to understand the effect of cold plasma treatment treated and untreated fibers were used to fabricate CMs. The strong bond between the matrix and plasma-activated fibers affects both the properties and failure mode of composite. The properties and failure modes were compared to those of CMs reinforced with untreated fibers. After plasma treatment the properties of CMs are increased. CMs are broken as a unit whole under tension. The ideas of the activating the fibers by cold plasma treatment above the activation energy of the chemical interaction may be extended over other types of the fibers and matrices to produce new types of fiber-reinforced composite materials with high physicomechanical indices.

Al-Ca-Fe合金中Al_(10)CaFe_(2)化合物的形成与表征

采用热力学计算和实验技术研究铝角的Al-Ca-Fe体系相图,包括液相面投影图和凝固反应。结果表明,与铝固溶体(Al)平衡的不是Al_(3)Fe相,而是一种组成符合化学式Al_(10)CaFe_(2)的三元化合物。通过包晶转变L+Al_(3)Fe→(Al)+Al_(10)CaFe_(2)(638℃,3.3%Ca和0.5%Fe,摩尔分数)发生从二元化合物到三元化合物的转变。与针状Al_(3)Fe相夹杂物不同,三元化合物的初晶和共晶具有致密的形貌。使用第一性原理计算和X射线衍射分析确定三元化合物Al_(10)CaFe_(2)的晶格结构。此外,近共晶合金Al-6%Ca-1%Fe(质量分数)在500~600℃退火后具有细晶组织,过量相的总体积分数约为25%。因此,Al-Ca-Fe体系可用于制造新的铝基复合合金。

Influence of ZrO_(2)/SiO_(2) nanomaterial incorporation on the properties of PEO layers on Mg-Mn-Ce alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2,4 and 6 g/l have been investigated.It has been established by SEM,EDS,and XPS that ZrO_(2)/SiO_(2)nanoparticles successfully were incorporated into the coatings.Micro-Raman spectroscopy showed the presence of ZrO_(2)in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg_(2)SiO_(4) in tetrahedral configuration uniformly distributed in the outer part of coatings.Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEOlayer(from 2.4×10^(–7)A/cm^(2) for base PEO layer to 0.7×10^(–7)A/cm^(2) for coatings with nanoparticles).It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness(this parameter was increased from 2.1±0.3 GPa to 3.1±0.4 GPa)and wearproof(the wear was reduced from(4.3±0.4)×10^(–5)mm^(3)/(N×m)to(3.5±0.2)×10^(–5)mm^(3)/(N×m)).

Amorphous-crystalline transition layers formation during quenching of Fe_(61)Co_7Zr_(10)Mo_5W_2B_(15) melt

New Fe-based multicomponent amorphous alloys have been developed recently based on empirical rules for large glass forming ability(GFA). In the present investigation, the master alloy ingot with the nominal composition of Fe 61Co 7Zr 10Mo 5W 2B 15(mole fraction, %) was prepared by arc-melting under Ti-gettered Ar atmosphere. The Fe-based buttons with different transverse cross sections were fabricated by arc-melting method, and the d 2.5 mm Fe-based rods were manufactured by injection technique. Characterization of the ingots and the parameters associated with the thermal stability were carried out by X-ray diffractometry(XRD) and high temperature differential scanning calorimeter(DSC), respectively. The interval of the supercooled liquid region is 39 K for the Fe-based alloy. The GFA of Fe-based alloys is relatively lower, to the buttons obtained are all crystallized. The Fe-based rod exhibites a high Vickers hardness up to HV 1 329. In addition, an amorphous-crystalline transition layers are observed in the rod. This transition zone is caused by unhomogeneous temperature distribution and relatively lower GFA for Fe-based alloys.

Single-crystal tungsten-based alloys with molybdenum and rhenium

Single crystals of ternary W-based alloys with 2% Re and less than 7% Mo have been grown for the first time at the Baikov Institute of Metallurgy and Materials Science RAS. Plasma arc melting allowed us to effectively purify the single crystals from a number of impurities. According to mass spectrometric analysis for 70 elements, the total content of impurities does not exceed 0.063%. It was found that, as the Mo content increases, the size of first-kind subgrains decreases and their mutual misorientation increases. In the W-based alloy with 2.3% Re and 6.7% Mo, no first-kind subgrains are observed, whereas second-kind subgrains are elongated along the growth direction. In this case, their total misorientation is well below that in the other low-alloy single crystals.Single-crystal of binary tungsten-based alloys with rhenium were prepared by electron-beam zone melting (1% Re, mass fraction) and plasma arc melting (2%Re,10%Re, 25%Re (mass fraction)). It was found that the low-alloyed (1%-2% Rh (mass fraction)) W-based alloys are characterized by a rather perfect single-crystal structure and misorientations of first- and second-kind subgrains of 20-50′ and 10-40′, respectively. Sections with the coarse-grained structure are observed in ingots of the alloy with 10% and 25% (mass fraction) Rh; in the alloy with 25% Rh, such structure is observed immediately from the seed.A device for measuring the liquidus and solidus temperatures of refractory metallic alloys has been designed. The liquidus temperatures of ternary single crystals (W-Mo-Re) have been measured.The studied single crystals, owing to their purity and high stability of the structure and properties, are widely used in electronics, electrical engineering, and analytical devices for various purposes.

Structure of low cobalt Fe-Cr-Co-based alloy for permanent magnets

Results of an experimental research into evolution of structure and micro hardness hard magnetic alloy Fe-30Cr-8Co-0.7Ti-0.5V-0.7Si at complex two-level in isothermal conditions on the circuit deposit - torsion at various temperatures in single-phase ( are given. It is revealed that deformation results in transformation of coarse-grained structure in fine-grained in all volume of the sample, however the generated structure is non-uniform on section of a sample. In an active zone of deformation near to mobile it is brisk the microcrystalline layer with the size of grains about 5 microns which thickness poorly depends on temperature is formed. In process of removal from an active zone of deformation the size of grains is increased, and micro hardness decreases.