A brief analysis of studies in field of metal-matrix composite (MMC) materials production with use of pulsed-discharge technology (PDT) is performed in present paper. It is shown that high voltage electric discharge (HVED) in liquid allows obtaining homogeneous highly disperse blend of complex chemical composition. Consolidation of blend by method of spark-plasma sintering (SPS) ensures preservation of grain size, which allows achieving high strength characteristics of MMC.
Materials Science. Non-Equilibrium Phase Transformations.
Vol. 1 (2015), Issue 1
Table of Contents
NONEQUILIBRIUM PHASE TRANSFORMATIONS DURING SOLID SOLUTION DECOMPOSITION IN MAGNESIUM ALLOYS CONTAINING THE RARE-EARTH METALS OF DIFFERENT SUBGROUPSpg(s) 19-21
The nonequilibrium phase transformation during decomposition of Mg supersaturated solid solutions, containing two rare-earth metals of the different subgroups (cerium and yttrium) are presented and generalized. These processes in the alloys of ternary systems differ from those in the alloys of the adjoining binary systems. They reveal also the similar features in kinetics and the nonequilibrium phase formed during solid solution decomposition
It is known, nanocrystalline metals are characterized by high strength and hardness, but low ductility. One way to increase the ductility is based on the creation materials with bimodal grain structure. General principle of this method is the nano- or ultrafine matrix provides a high strength, and evenly dispersed therein coarse grains contribute acceptable ductility. An important condition for preparing the bimodal material is to control and retention of the bimodal structure during processing. SPS method is promising for the development of materials, where need the collaborative and rapid consolidation of micro and nanosized powders. In this paper as the initial materials used copper powder of different fractional composition – a particle size of 40-90 μm and 50-70 nm. Nanopowder has consisted of micro agglomerates which have been divided during the preparation of the powder mixture. Initial powders were mixed in the mechanical mixer. Experiments were conducted a spark-plasma sintering system model Labox-625. The increasing of sintering temperature results in the density increasing. The pressure and the sintering time can also cause density increasing, but not as much as the temperature. The density of the sintered sample was measured by the Archimedes method. The mechanical property was tested using the hardness testing instrument (FM-800). In order to compare the mechanical properties of mono- and bimodal copper prepared by SPS, samples with a diameter of 10 mm were prepared. As a result, the microhardness of bimodal sample (180 HV) is higher than that of the micro- (63 HV) and nanosamples (159 HV) obtained by SPS. Fabricated by SPS the bimodal copper has a higher microhardness, compared with micro- and nanocrystalline samples. The microstructure of the bulk compact was observed by JEOL 6610LV scanning electron microscopy. The final grain size of the sintered nanomaterial varies depending on the sintering temperature ranging from 200 to 500 nm.
STRUCTURAL PRINCIPLES OF FORMATION HIGHLY DURABLE TRIBOTECHNICAL MATERIALS BASED ON POLYTETRAFLUOROETHYLENEpg(s) 25-31
The preconditions of forming a structural paradox within the existing technological paradigm, which manifests itself in reducing the parameters of strength and tribological characteristics of composite materials based on polytetrafluoroethylene when administered in their composition of fillers and modifiers of different composition and geometry when the content of 15-20 wt. % Established effects of forming the structural conditions derating improved performance due to the formation of cluster structure of the binder particles (PTFE) and the modifier. The effective technological methods to ensure reducing the likelihood of cluster components in the manufacturing process of highly composites with a filler content of 20-35 wt. %. The technology of producing high-strength wear-resistant fluorine composites, 1.5-20 times superior to common parameters analogues produced under the trademarks "Flubon", "Fluvis", "Superfluvis.". We consider the effective use of highly fluorine composites in mechanical engineering, chemical industry and energy.
The paper studies the mechanism, kinetics and morphology of phase changes primarily at heating by concentrated energy flows (CEF). The objects of study have been a medium carbon low-alloy steel 37Cr4 (DIN), a high-carbon tool steel X210Cr12 (DIN) and grey cast irons with flake and spheroidal graphite (GG 15, GG 30, GGG 50 – DIN) treated by plasma and electron beam heating.
It has been established that the mechanisms of phase changes at heating with CEF differ considerably from the familiar ones and can be classified as mechanisms of the following type: of migration by plastic deformation; of migration with a wave effect; of baric migration; of thermokinetic migration and of accelerated migration under the impact of electrodynamic fields and radiation. These mechanisms have been tested and proven by the fixed imbalance conditions of the structures obtained in the experiments.
STRUCTURAL EVOLUTION DURING MECHANICAL MILLING AND SUBSEQUENT ANNEALING OF HIGH-ENTROPY AlCuNiFeTi ALLOYpg(s) 32-35
This study reports the structural evolution of equiatomic AlCuNiFeTi high-entropy alloy (HEA) from elemental materials to solid solution during mechanical alloying (MA), and further, to equilibrium phases during subsequent thermal annealing. It was justified experimentally that MA of Al-Cu-Ni-Fe-Ti powder mixture during 15 hours resulted in a single-phase nanocrystalline HEA with a structure of ВCC solid solution. During thermal annealing recovery and recrystallization of the BCC solid solution take place at temperatures ranging from 130 to 650 °C, and phase transformation, and grain growth of equilibrium phases occur at higher temperatures. The phase composition transforms to BCC and FCC solid solutions when the MA powder was annealed at 700 °C for 1 h. The BCC and FCC solid solution structure can be maintained even after the alloy was annealed at 1000 °C. The alloy powder was consolidated by pressure sintering at 800 °C with 5 GPa pressure for half an hour. The sintered sample exhibits 10.7±0.3 GPa in Vickers hardness.
There were studied the mechanisms of interfacial processes when combining components of different composition, structure, and molecular weight in disintegrating type high-energy installations. The effects of formation of mechanochemical transformations products due to the flow of physical and chemical processes of interfacial interactions at the place of active centers of combined components were established. There were developed compositions and obtaining technology of composite materials and products containing mechanochemically combined components that cause the realization of synergies enhance the parameters of strength and tribological characteristics. The directions of the practical application of composites with mechanically activated components for the manufacture of tribological purpose products and coatings, which are used in metal-polymer constructions of vehicles and technological equipment.
Using methods of spectroscopy of thermally stimulated currents (TSC spectroscopy), atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis was done of the energy state of dispersed particles of different composition and structure – mineral (tripoli, shungit, clay, mica, silica) and synthetic (ultra dispersed polytetrafluoroethylene, nanodiamonds, silicate glass, metal oxides). There was established the effect of occurrence of the special energy state of dispersed particles, due to the presence of nanoscale components of the structure. There were studied parameters of the energy characteristics of the modifier (value and density of the residual charge, activation energy of the relaxation, time of charge relaxation et al.) depending on the action of technological factors – temperature, mechanical stress, energy flows. The optimal ranges of occurrence of effective modifying action in macromolecular matrices of various types – polymeric, oligomeric, combined. There were proposed technological principles formation of mechanical engineering nanocomposite materials with improved parameters of deformation and strength and tribological characteristics.
The paper shows the results of testing the obtaining process of filtering material based on metal powders and fibers by electrocution sintering. The equipment design and manufacturing techniques of test samples are presented; experimental samples of filtering materials based on powders of tin-phosphor bronze BrO10F1 and stainless steel 12X18H10T fibers have been manufactured. Method implementation requires no special equipment: a common spot welding machine has been used. Photographs of appearance and structure of the samples and the results of studying their properties have been presented: porosity, permeability coefficient, pore sizes. It has been shown that the materials manufactured by electrocution sintering possess a satisfactory complex of filtering properties and may be used for purification of liquids and gases.
The physicochemical and structural aspects of the modification of polymeric materials and fillers, laser exposure to a given intensity. Installed effects transform the morphology of the surface layers of dispersed, semi-finished fiber and membrane to form nano-sized components with increased vigour. Modification of certain process parameters laser that achieve predetermined functional characteristics. It sets the parameters of the effect of a significant increase of strength characteristics of film semi-finished products made of thermoplastic (HDPE, LDPE, PP, PA, PET, PTFE), due to the formation of spherulitic supramolecular structures. The energy parameters of the surface layers of composites, subjected to modification of a short-pulse laser exposure. Installed effect forming electrets structures and nano-relief, providing suppression of unfavorable biochemical processes in the application of products in practice. The results of the use of materials and products subjected to laser modification, engineering and medical practice.
The paper is devoted to studying the influence of technological process parameters of deposition on the composition, structure and strength characteristics of TiN coatings on titanium alloy OT4-1. The TiN coatings were deposited by a vacuum-arc evaporator. In addition, the influence of the type of layers formation on microhardness and wear resistance of TiN layers and a metal substrate is presented.
Investigation of low carbon microalloyed API 5L X80 steels for electric-welded pipes applied in building of metallic structures of different complexity. Problems of weldability of these steels and effect of technological and structural factors on mechanical properties of weld seams have been considered. Also mechanical characteristics at cyclic loading of the steels are considered.
EFFECT OF THERMOMECHANICAL TREATMENT WITH MULTIPLE PLASTIC DEFORMATION ON THE NANOPHASE HARDENING OF DIE STEEL WITH REGULATED AUSTENITIC TRANSFORMATIONpg(s) 9-14
A new class of die steels for hot deformation, namely, steels with regulated austenitic transformation realized during exploitation (RATE) have been developed in Russia. These steels are characterized by the technological advantages typical of traditional α-solid solution-based steels and, when working in the austenite state, assure the enhanced tool life. The structure, phase composition and hardening of RATE steel have been analyzed by an example of steel containing 0.41 % C, 1.04 % Si, 3.59 % Mn, 2.41 % Cr, 5.07 % Ni, 2.40 % Mo, 0.69 % V, 0.51 % Ti, 0.25 % Co subjected to thermomechanical treatment, which includes the austenization and multiple plastic deformation. The nanophase hardening occurs in RATE steels being in the austenitic state, during multiple plastic deformation at temperatures of 450-750 °C. The precipitation of nano-sized heat-resistant excess phases ensures the inhibition of recrystallization processes at operating temperatures, inhibits the grain growth, and increases the stability of the austenite.