Materials Science. Non-Equilibrium Phase Transformations.
Vol. 5 (2019), Issue 3

Table of Contents

  • Effect of structure and texture on the mechanical characteristics of magnesium alloys processed by equal-channel angular pressing

    pg(s) 67-70

    ECAP was carried out with a gradual decrease in temperature and an increase in the number of passes on two medical magnesium alloys: WE43 (Mg-3.56%Y-2.20%Nd-0.47%Zr) and ZX10 (Mg-1.0%Zn-0.3%Ca). It was shown that ECAP leads to a significant refinement of the alloys structure. For ZX10 alloy, the average grain size after ECAP decreased from ~ 105 μm in the initial state to 8 ± 0.18 μm in the longitudinal section and to 4 ± 0.19 μm in the transverse one. For the WE43 alloy, the average grain size was changed from 70 μm to 0.69 ± 0.13 μm and the precipitation of particles of the Mg41Nd5 phase with an average size of 0.45 ± 0.18 μm was also discovered. At the same time, the grain refinement led to an increase in the strength characteristics of the both alloys (including fatigue strength), and increased prismatic slip activity (along with the formation of an inclined basal texture in ZX10 alloy) led to an increase in their ductility. The alloy structure formed during the ECAP process does not lead to a decreasing in resistance to chemical corrosion.

  • Functionally graded Al matrix materials containing 10, 20 and 30 % B4Cp stacks

    pg(s) 71-73

    As a relatively new class of materials that exhibits a gradual compositional or microstructural change along one axis, functionally graded materials (FGM) emerged. As a result of this change, properties of the material also vary. This property change can be controlled by tailoring the composition or microstructure of the individual stacks in the FGM.
    In the present study, aluminum matrix functionally graded composite materials with increasing amounts of B4C particles in an aluminum matrix were formed. The functionally graded materials were composed of 4 composite stacks with different compositions; namely, 0, 10, 20 and 30 volume % B4C particles. The matrix material was aluminum – 4 wt.% copper alloy. Preparation of the functionally graded materials was conducted through powder metallurgical methods including mixing, cold pressing and sintering without pressure. Samples were produced in dimensions according to 3-point bending standards.
    Microstructure of the functionally graded materials contained some porosity, amount of which was seen to increase with increasing B4C reinforcement amount. All the stacks were subjected to Vickers microhardness measurements and it was seen that the hardness of the layers increased significantly with increasing reinforcement amount. The unreinforced layer had a hardness of 55 HV0.1 and that of the layer containing 30 % B4C was 143 HV0.1. On the other hand, the bending strength of the functionally graded material was seen to be lower than that of the unreinforced sample.

  • The mode of hardening heat treatment for deformable piston hypereutectic silumins

    pg(s) 74-77

    A series of piston hypereutectic silumin based on Al – (15÷20) % Si, alloyed with copper, magnesium, nickel, chromium is investigated. The mechanical characteristics of ingots from experimental alloys were determined: temporary tensile strength, hardness, relative elongation depending on the composition of the alloys, and temperature coefficient of linear expansion (TCLE). It is shown that the tensile strength of forged blanks is 1.5-2.4 times higher than ingots of hypereutectic silumins. The resulting structure of forgings ensures their high plasticity (relative elongation δ = 5.7÷7.5%; relative narrowing Ψ = 10.3÷14.2%). The optimal mode of heat treatment of deformed silumin is determined: quenching from step heating and aging, which allows increasing the strength of forgings up to 370-470 MPa. Moreover, the plasticity indicators remain at a high level, and the average thermal expansion coefficient of the alloys is (18.0 ÷ 19.2) · 10-6 K-1 in the range of 50 ÷ 200 ° C.

  • Structure, phase composition and hydrogen sorption properties of eutectic alloy Ti47.5Zr30.2Mn22.5 obtained using titanium sponge

    pg(s) 78-80

    The microstructure and phase composition of the eutectic alloy Ti47.5Zr30.2Mn22.5 obtained using titanium sponge, as well as the phase composition of hydrogenation product were investigated by scanning electron microscopy and X-ray phase analysis. It was found that when iodide titanium was completely replaced by titanium sponge, the alloy structure remained eutectic and consisted of bcc solid solution and Laves phase. It was shown that after a sorption-desorption cycle the alloy was in activated state and was capable to absorb hydrogen at room temperature and low pressure (0.21 MPa) starting from the first seconds of contact with hydrogen atmosphere, with hydrogen capacity of 2.61 wt.%.

  • Computer modeling of influence of previous deformation degree and strain rate on carbonitrides precipitation kinetics in low-carbon micro-alloyed steel

    pg(s) 81-83

    Using computer modelling with originally developed semi empirical physical grounded models a study was carried out to investigate influence of previous hot deformation on carbonitrides formation from austenite in low-carbon micro-alloyed steel. Studied in the article is an influence of degree and rate of the deformation on processes of nucleation and growth of Nb and Ti carbonitride particles. The model helps to predict not only process of changing in number and average size of the particles but also to estimate their final size distribution. One of additional peculiarities of the developed model is its ability to predict composition of the cabinetries formed in certain conditions. The model takes into account process of recrystallization and returning, which affect carbonitrides precipitation and are influenced by it. Acceleration was shown of both nucleation and growth rates of the particles due to increasing of deformation degree and strain rate. Another result is that previous deformation significantly affects size distribution function of the particles precipitated with rather lesser effect on their average size. Kinetic curves and final size distribution plots are given.

  • Properties and performance of polyethersulfone membranes modified with halloysite and titanate nanotubes

    pg(s) 84-87

    Ultrafiltration polyethersulfone (PES) membranes were prepared by wet phase inversion method. Halloysite nanotubes (HNTs), hydrothermally synthesized titanate nanotubes (TNTs) or their mixture (HNTs/TNTs, weight ratio 50/50) were applied as nanofillers (NFs). N,N – dimethylformamide was used as a solvent, and deionized water was applied as a non-solvent. Some well dispersed aggregates as well as larger agglomerates of the NFs were observed on the surface of the membranes examined by atomic force microscopy. The retention of poly(ethylene glycol) (20 kDa) applied as a model organic compound, by the modified and unmodified membranes was similar and did not exceed 10%. The rejection of 500 kDa dextran ranged from 84 to 92%, and was the highest for the membrane modified with HNTs. A 71% improvement of pure water flux, compared to the neat membrane, was observed in the case of the membrane modified with the HNTs/TNTs. The best antifouling performance during bovine serum albumin filtration exhibited the HNTs-modified membrane.

  • The effect of phase transform on creep responces of fgm rotating disk

    pg(s) 88-92

    In many applications, FGM rotating discs are subjected to severe operating temperature and high rotational speeds. In such conditions the incidence of creep is inevitable. To study some aspects of this phenomenon, using the Sherby’s law the creep relaxation of a group of FGM rotating discs is modeled. Results show that even thought the temperature is uniform entirely, the stress variation leads to a phase transformation and so the creep mechanism is changed. In this paper the effect of this change of creep mechanism on the steady state creep behavior of FGM rotating discs made of Al-SiC is studied.

  • Iron powders with insulating layers: Structure and magnetic properties

    pg(s) 93-95

    The development and study of the composite magnetic soft material, the magnetic properties of which are close to the laminated metal magnets and the remagnetization losses is lower than that one of metal magnets is very relevant. The study of magnetic properties and magnitude of losses on the remagnetization of the developed low-frequency composite magnetically soft material, comprising separate iron 20 ÷ 100 mkm particles, covered by insulating layers (films) with thickness 3 ÷ 10 nm, in comparison with similar parameters of electrical steel 3412 (E320) was performed in this work.

  • Crystallization regularities of a high and low density polyethylene blend and composite materials on its basis

    pg(s) 96-98

    The results of studies of the regularities and mechanism of crystallization of polymer mixtures of high and low-density polyethylene in various proportions and composite materials based on blends of high and low density polyethylene taken in a 50/50 ratio are given. In filled composites, aluminum hydroxide was used in concentrations of 1, 3, 5, 10% wt. and bentonite in concentrations of 1, 3, 5, 10, 20, 30% wt. Dilatometric studies were carried out on an IIRT-1 device, in the process of stepwise cooling of samples with a load of 5.3 kg.

  • Phase transformations at heating of Sn–Ni–Zn powders obtained by cementation from solutions

    pg(s) 99-101

    The low-temperature method of Sn–Ni–Zn powders synthesis by cementation of tin and nickel with zinc powder from acidic solutions with the formation of “zinc core – porous nickel shell – external tin layer” structures has been proposed. The method provides metals ratio control in wide ranges (7–41 at. % of tin, 38–86 at. % of nickel and 7–24 at. % of zinc) by variation of the process duration. X-ray phase analysis data give evidence on the presence of β-Sn and Zn phases as well as NiZn3 and NiSn intermetallics in the powders obtained. Differential scanning calorimetry data show the availability of Sn–Zn eutectic with the melting point at 171.2 °C in the powders with high tin content (30–40 at. %). The formation of the ternary intermetallic τ1 phase (Ni3+xSn4Zn) has been established to occur as a result of the powders heating at 260 °C. The discovered low-temperature phase transformation in Sn–Ni–Zn system at 260 °C is of interest for electronic equipment assembly processes that include consecutive stages of soldering and resoldering.

  • Simulation phase-structure transformations in alloy steels for the piersing tools

    pg(s) 102-104

    In this work are presented the development of simulation metods of analysis the phase-structural transformations and properties in alloy steels. The analytical dependencies of this simulation were applied to the calculation of ferritic, pearlitic and bainitic transformations in carbon and alloy steels. To calculate the amount of martensite, the authors used a new equation that has been successfully used in others works too. Based on the developed regression model, isothermal and structural diagrams for 20CrNi4V and 25Cr2Mo1V steels have been constructed. The analysis is performed of the aerial quenching of tools from alloy steels 20CrNi4V and 25Cr2Mo1V, according to the recommended heat treatment schedules in the tools production. For steels 20CrNi4V and 25Cr2Mo1V, it is possible to obtain a bainitic structure in a wide range of cooling rate. Corrections of heat treatment schedule were proposed.