Table of contents

Preface

These proceedings are a collection of the selected articles presented at the 5th International Scientific Workshop «Advanced Technologies of Electromagnetic Field Assisted Consolidation of Materials», held in Moscow, Russian Federation on 29-31 August 2016. This workshop is regularly organized by Key Laboratory for Electromagnetic Field Assisted Materials Processing of National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Russian Federation.

The Scientific Workshop was sponsored by the Competitiveness Growth Program of MEPhI ("5–100" Russian Academic Excellence Project - http://5top100.ru).

One of the main goals of this Scientific Workshop was to train young scientists in matters of advanced technologies of electromagnetic field assisted consolidation of powder materials. Meetings were held in the form of review lectures of the leading scientists with free discussion and personal oral and poster presentations of the participants.

The general scope of the Scientific Workshop covered the advanced technologies of electromagnetic field assisted consolidation of materials.

The workshop was attended by 67 participants from 5 countries (Russia, Belarus, Ukraine, Latvia and USA). During the three days of the workshop 14 invited lectures, 35 oral presentations were delivered. However, only some papers were qualified for being published in the Open Access IOP Conference Series: Materials Science and Engineering (MSE).

Based on the peer-review of reports presented at the workshop 22 selected papers have been included in this volume. These papers present new research in the various fields of technology of electromagnetic field assisted consolidation of powder materials. We sincerely hope that the reports presented in this volume will contribute to the advancement of knowledge not only in these fields, but also others.

The organizing committee of the workshop thanks all the participants for their fruitful work and personal contribution to the development of these conference proceedings.

List of Figures, Editors and Committees are also availabe in this pdf

All papers published in this volume of IOP Conference Series: Materials Science and Engineering have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Samples of 3 % yttria-stabilized zirconia (3YSZ) ceramics have been sintered to near full density with no appreciable grain growth using an ultra-rapid microwave sintering process. The sintering experiments were carried out on a 24 GHz / 6 kW gyrotron system for microwave processing of materials with automatic process control. By varying the properties of the thermal insulation surrounding the samples it was possible to vary the microwave power required for heating. The final relative density of 3YSZ ceramic samples microwave heated at a rate of 50 °C/min to a temperature of 1400 °C without isothermal hold varied from 91.6 % when the specific absorbed microwave power was 4 W/cm³ to 99.4 % when the specific absorbed microwave power was 90 W/cm³. The specific absorbed power is therefore demonstrated to be the key parameter determining the achievable density in ultra-rapid field-assisted sintering processes.

This research paper provides an illustration of how to use the Spark Plasma Sintering technology (SPS) for powder materials in order to obtain lightweight ceramics Al₂O₃/ZrO₂ with enhanced strength properties. Optimization of SPS modes helps to produce ceramics with grain size of less than 400 nm, microhardness Hv = 24 GPa, and crack resistance K_IC = 4.2 MPa·m1/2.

We report one-step fast synthesis and consolidation of iron aluminide FeAl of high open porosity by pressureless reactive Spark Plasma Sintering (SPS). The starting material of the Fe-40at.%Al composition was a mixture of an iron powder with an average particle diameter of 4 μm and an aluminum powder with an average particle diameter of 6 μm. The rationale behind the choice of the SPS as a processing technique and fine and comparable sizes of the two reactants for the synthesis of high-open porosity FeAl was realization of fast full chemical conversion of Fe and Al into single-phase FeAl reducing the time available for the compact shrinkage. According to the XRD phase analysis, single-phase FeAl compacts formed after SPS at 800 and 900°C. These compacts had open porosities of 41 and 46%, respectively. The transverse rupture strength of the compacts sintered at 700-900°C was found to change little with the sintering temperature in the selected range.

The article presents a study of the effect of the high-voltage electric pulse modes of impact under pressure on the structural and mechanical properties of compacts of heavy tungsten alloy VNZh 7-3. Identified an increase in density of material, in microhardness and tensile strength with voltage increase in high-voltage discharge. The optimum exposure mode determinate, which provides the highest level of strength and ductility of the sintered material.

A new scheme of hybrid technology of compacting powders is proposed, which simultaneously use two sources of loading: static and dynamic. Compaction of «Al-B» powder compound is carried out in a metal casing by its longtitudal drawing and radial magnetic pulse crimping. The results of the search experiment are presented, confirming feasibility and efficiency of proposed technical solution. Developing technology of compacting powders will allow producing long-length products.

The article presents results of design analysis of stress and strain in the disk sample loaded by the Brazilian test (disk compression in the center plane). The research established correlations of the diameter and thickness of the sample acceptable to obtain reliable values of material strength in response to stress. Presented a strong relation of average tensile stresses in the central area of the disc to the stress parameter used to determine the strength of brittle rock materials

The article provides an experimental basis for application of the disk sample loaded by the Brazilian test method (disk compression in the diameter plane) for the brittle strength assessment of the metallic materials during testing of the small-sized samples. The research presents a strong correlation between strength of the cast iron, assessed by the testing of disk samples and the tensile strength. The method was used to study the mechanical properties of heavy tungsten pseudo-allows obtained by exposure to high-voltage electric pulse.

The main disadvantage of currently used endosteal implants is their unsatisfactory biostable performance. Under action of functional stress caused by flaws of the design or lower mechanical characteristics the areas of stresses extreme concentration exceeding strength limits of bone tissue appears in the bone surrounding the implant that leads to the tearing away the implant. The problem of specific pressure lowering on the bone and uniform distribution of stress is solved by two ways: the increase of the implant area and the search of implant materials with optimum biomechanical properties. Porous materials of spherical titanium powders have adjustable pore size and large unit surface area, as well as possess high biologic compatibility with living tissue. This allows reduction of the rejection reaction due to a more even stress distribution around the functioning implant. Clinical results show that such implants have more stable physical and chemical properties.

This paper considers peculiarities of the technology of production of structures from metallic hollow spheres (MHS) using magnetic fields and electric sintering. In these studies, the raw material was MHS obtained by burning of polystyrene balls coated by carbon steel. MHS had an outer diameter of 3-5 mm and a steel wall thickness of 70-120 microns. Pulsed current generators were used for electric sintering of MHS to obtain different spatial structures. Since MHS have small strength, the compressive pressure during sintering should be minimal. To improve the adhesion strength and reduce the required energy for sintering, hollow spheres were coated with copper by ion-plasma sputtering in vacuum. The coating thickness was 10-15 microns. The ferromagnetic properties of MHS allowed using of magnet fields for orientation of the spheres in the structures, as well as using of perforated tapes acting as orienting magnetic cores. Ultrasonic testing of MHS structures has been tried using through propagation of ultrasound in low kilohertz frequency range. Sensitivity of the propagation parameters to water filling of inter-spheres space and sintering temperature was demonstrated.

The study develops an original method of mechanical test of thin small-size disks for determining resistance of brittle materials to rupture. Based on this method a test of ultimate flexture strenght was conducted on Al₂O₃ ceramics and composites of β–Si₅AlON₇–BN, system obtained by the method of spark-plasma sintering. The obtained test results allowed determining the optimal process parameters for sintering this ceramic materials in terms of their strength level: composition and dispersion of the starting powder mixtures, the maximum sintering temperature, etc.

The paper dwells on the research conducted into sintering mechanisms, the structure and mechanical properties of ultrafine-grained heavy tungsten W-Ni-Fe alloys. The dependence of alloy density on temperature of sintering (T_sint) is found to be nonmonotonic with a maximum equivalent to the optimal sintering temperature. Studies also encompassed the impact that the size of tungsten particles may have on the optimal T_sint. An increase in time of mechanical activation (MA) and acceleration of grinding bodies accompanied by a decrease in alloy particle size and formation of non-equilibrium solid solutions is shown to reduce the optimal T_sint of alloys. High-energy MA and Spark Plasma Sintering methods were applied to obtain samples of tungsten alloys with high mechanical properties: macroelasticity limit of up to 2,250 MPa, yield strength of up to 2,500 MPa.

The paper dwells on the research conducted into high-rate consolidation of pure tungsten carbide nanopowders using the Spark Plasma Sintering. Studies included the effect that the original size of WC nanoparticles and their preparation modes have on density, structure parameters, and mechanical properties of tungsten carbide. It has been found that materials that show abnormal grain growth during sintering have lower values of sintering activation energy as compared to materials the structure of which is more stable during high-rate heating. A qualitative model is proposed that explains this effect through the dependence of the grain boundary diffusion coefficient on the grain boundary migration rate.

The article provides an example of applying the technology of spark plasma sintering (SPS) to ensure high-rate diffusion welding of high-strength ultra-fine-grained UFG titanium alloys. Weld seams produced from Ti-5Al-2V UFG titanium alloy and obtained through SPS are characterized by high density, hardness and corrosion resistance.

The article describes the results of spark plasma sintering of ceramic materials based on titanium carbide, titanium carbosilicide, ceramic composite materials based on zirconium oxide, strengthened by carbon nanostructures and composite materials of electrotechnical purpose based on copper with addition of carbon structures and titanium carbosilicide. The research shows that the spark plasma sintering can achieve relative density of the material up to 98%. The effect of sintering temperature on the phase composition, density and porosity of the final product has been studied. It was found that with addition of carbon nanostructures the relative density and hardness decrease, but the fracture strength of ZrO₂ increases up to times 2. The relative erosion resistance of the electrodes made of composite copper-based powder materials, obtained by spark plasma sintering during electroerosion treatment of tool steel exceeds that parameter of pure copper up to times 15.

The paper studies the prospects of spark plasma sintering of aluminum oxynitride, determines the optimum modes and parameters of compacting. Optimum modes of preparing a powder mixture for sintering are determined. The structure and properties of sintered samples are studied. The factors affecting the transparency of the finished products are ascertained, and the ways that allow obtaining a high light transmittance are identified.

The research provides modeling of spark-plasma sintering process of aluminum oxide, specifically the distribution of temperature fields over the sample volume and mold at various stages of heating. Calculation was based on the experimental data on the measurement of temperature on the surface of the mold, inside the mold cavity and in its various internal parts including punches (diameter of 15 mm), in the absence of insulation felt. Experiments established that the main source of heat emission at temperatures less than 1300°C to 1400 °C is contact resistance at the borders of the punches and the matrix molds. Then heat emission zone moves towards the punches. Based on the received data, the temperature and electric parameters were selected for the materials used for the press mold, providing a good agreement between the observed and calculated distribution patterns at different temperatures. Obtained parameters were used in calculations of temperature fields in the press molds with insulation felt and for the press molds with diameter of 15 mm and 10 mm for the production of tablets as well as glazing beads.

The ultrasonic dispersion and spark plasma sintering technique have been used to process Al₂O₃/Graphene nanocomposite (Al₂O₃/G) with 0-2wt.% graphene. The topography of fracture, microstructure, density, microhardness, Young modulus, electrical and thermal conductivity of Al₂O₃/G nanocomposite are investigated.

The article presents the research and the analysis of the pulse-discharge processes of capacitor discharge sintering: CD Stud Welding, capacitor discharge percussion welding (CDPW), high-voltage capacitor welding with an inductive-dynamic drive (HVCW with IDD), pulse electric current sintering (PECS) of powders. The comparative analysis of the impact parameter is presented.

The work determines the influence of microwave radiation on the processes of active deformation and relaxation of mechanical stresses in loaded samples of stainless steel under the effect of current pulses and longitudinal and transverse orientation of the electric-field vector E of the microwave radiation to the axis of the deformated sample. With the longitudinal orientation of the vector E of the microwave radiation and under the action of the current the effect of metal softening increased from 22% to 30%. The analysis of the microstructure of the samples showed a significant influence of external energy impacts on the deformation of steel grains.

The article presents the recent research in electrodynamic processes for metal samples exposed to current pulses. The pinch effect and the skin effect cause the vibration of the metal rods. The results of these studies show how current and magnetic field interact with material samples of gold, silver and copper. The analysis allowed establishing the dependences of peak acceleration on current density and conductor diameter. The dependencies can be used in metal workings and for nondestructive testing.

This research analyses the influence of the parameters of high-voltage electric pulse welding on microstructure of weld seams and mechanical parameters of samples. Special tooling was developed for the process of high-voltage electric pulse welding, allowing welding of ring samples. The method of determination of mechanical characteristics of toroidal samples was developed. An influence is established of parameters of high-voltage electric pulse welding, such as current density and applied pressure, on microstructure of a weld seam and density of a weld joint. The study of magnetic parameters of samples is conducted.

In this work we consider obtaining high-density powder samples from austenitic stainless steel 316L, on the first national experimental layered build-up equipment by the method of selective laser melting (SLM) Melt Master3D - 550. The equipment description is given. Morphometric properties of the original powdered material is studied. Continuous unit vectors (tracks) and high-density samples with the relative density of 97% are obtained during the experiments. The laser radiation energy contribution is estimated to compare the conditions for obtaining samples with different technological parameters. In course of the study of the sample properties the dependence of density on the specific energy is revealed. Moreover, the influence of technological parameters on the microstructure and microhardness of the samples is established. The obtained data are compared with the results of other studies on similar foreign facilities.