Fatigue and corrosion-fatigue tests were carried out on commercial aluminum alloys of the Al–Mg system: AMg2, AMg5, and 1570. These alloys have a coarse-grained deformed microstructure with two types of inclusions oriented along the rolling axis. Fatigue tests were carried out at room temperature, using a bending-rotation scheme in air and in a 3

The article presents the results of corrosion-fatigue tests of industrial Al-Mg alloys were conducted in air and in a 3%NaCl aqueous solution. Fatigue curves can be characterized using the Basquin equation and the plastic deformation model at the crack tip. It has been demonstrated that the primary contributions to corrosion-fatigue failure in the Al-Mg alloys at low stresses are made by the process of pitting and intergranular corrosion, and by the plastic deformation at high stresses.

The superplastic behavior of ultrafine-grained (UFG) alloys Al-6% Mg-0.12% Sc-0.10% Zr-0.1% X, where X = Yb (alloy 1 (Yb)), Er (alloy 2 (Er)), and Hf (alloy 3 (Hf)), was studied. The objects of comparison were alloys Al-6% Mg-0.12% Sc-0.20% Zr (alloy 4 (Zr)) and Al-6% Mg-0.22% Sc-0.10% Zr (alloy 5 (Sc)). The effect of a simultaneous increase in the flow stress and elongation to failure in the superplasticity mode has been found. The maximum elongation to fracture in UFG alloys 1 (Yb) and 2 (Er) is observed at lower deformation temperatures than in alloys 4 (Zr) and 5 (Sc). The superplastic characteristics of alloy 3 (Hf) exceed those of alloys 4 (Zr) and 5 (Sc) with an increased content of alloying elements (in at %). UFG alloy 1 (Yb) at low temperature (400 degrees C) has good ductility (delta = 910%). The effect of the type and concentration of alloying elements on the deformation behavior and grain growth in UFG alloys Al-6% Mg is analyzed. With the superplasticity of UFG alloys, there is competition between strain-induced grain growth and dynamic recrystallization. It is shown that the fracture of UFG alloys under superplasticity is caused by the formation of pores on large Al3X particles.

The effect of the initial size of alumina particles on the density, microstructure, hardness, and fracture toughness of ceramics obtained by conventional and spark plasma sintering (SPS) has been studied. We studied ceramics obtained from commercial Al2O3 powders with an initial particle size of 40 – 50 nm, 0.2 mm, and 1 mm, and domestic fine powders with an initial particle size of 0.2 – 3 mm, and Al2O3 + 0.25 vol. % MgO and Al2O3 + 10 vol. % ZrO2. It is shown that the density of alumina ceramics nonmonotonically depends on the initial size of Al2O3 powder particles. It has been established that an increase in the grain size leads to a nonmonotonic change in the hardness of alumina ceramics. It has been established that the addition of 0.25 vol. % MgO accelerates the sintering of alumina. The addition of 10 vol. % ZrO2 makes it possible to provide an optimal combination of hardness and fracture toughness. It is shown that fine-grained ceramics obtained by the SPS method have a higher hardness. It has been suggested that SPS of submicron alumina powders with an amorphous layer on the surface, additionally stabilized by zirconia particles, is promising for further increasing the hardness of alumina ceramics.

The paper demonstrates for the first time the possibility of using an unalloyed tungsten powder with a spherical particle shape from 5 to 45 μm with a grain size of 0.5 to 2 μm obtained using plasma chemical synthesis, granulation, and spheroidization technologies to create products using additive technologies. The influence of the technological parameters of the selective laser melting (SLM) process on the physicomechanical characteristics and microstructure of test samples made of unalloyed tungsten powder has been studied. It is shown that the SLM parameters have a significant effect on the formation of the microstructure of test samples. It has been experimentally proved that, at optimal parameters of the SLM process, a homogeneous equiaxed microstructure with an average grain size of about 10 μm is formed in the samples. It was found that the maximum value of the Vickers hardness of the studied SLM samples of unalloyed tungsten is 310 HV10; the maximum value of microhardness is 4.1 GPa. The maximum density value of the obtained samples is 19.1 g/cm3 (relative density is 99.2

The superplastic behavior of ultrafine-grained (UFG) alloys Al–6

The abnormal low-temperature ductility mechanism in the compression creep testing of the ceramic samples of binderless tungsten carbide with different grain sizes has been studied. The samples with high relative density (96.1-99.2%) were obtained by Spark Plasma Sintering (SPS) from nano-, submicron, and micron-grade alpha-WC powders. In addition, ceramics SPSed from submicron-grade powders with increased oxygen and graphite contents were studied. The ceramics had a nonuniform macrostructure with coarse-grained surface layers of similar to 300 mu m in thickness and fine-grained central parts consisting of tungsten monocarbide alpha-WC with a small fraction of W2C particles. The creep tests were conducted in two regimes: isothermal holding at different temperatures (1300-1375(& ocy;)C) at 70 MPa (Mode #1); tests at different stresses (50, 70, 90 MPa) at 1325(& ocy;)C (Mode #2). Tests in Mode #1 were done to determine the creep activation energy Q(cr) while tests in Mode #2 - to determine the magnitude of coefficient n in the power law creep equation. The magnitude of coefficient n in the power law creep equation equals to 3.1-3.7. The creep activation energy in the ultrafine-grained (UFG) tungsten carbide with the grain sizes similar to 0.15 mu m SPSed from nanopowders was shown to be similar to 31 kT(m) (786 kJ/mol). This value is 1.5-2 times greater than the creep activation energy in the fine-grained samples obtained by SPS from commercial powders. The mechanical removing of the coarse-grained layers from the surfaces of the tungsten carbide sample was shown to result in an accelerated creep, slight decrease in the activation energy and coefficient n to 2.5-2.6. The creep rate of the tungsten carbide samples obtained by SPS (epsilon= epsilon v+ epsilon b) was suggested to be determined simultaneously by the creep process in the coarse-grained surface layers (epsilon(v)) and the creep process in the fine-grained central parts of the samples (epsilon(b)). The creep rate in the surface coarse-grained layers (epsilon(v)) is determined by intensity of carbon diffusion in the alpha-WC crystal lattice while the creep rate in the fine-grained central parts ( epsilon(b)) - by the intensity of grain boundary diffusion. The increased volume fraction of the W2C particles formed when sintering the alpha-WC powders with increased adsorbed oxygen concentration was suggested to be one of the origins of the decrease in the creep activation energy Q(cr) when testing the UFG tungsten carbide samples. The decrease in the activation energy of Q(cr) is attributed to the formation of an excessive concentration of nonequilibrium vacancies during the phase transition of W2C <-> alpha-WC.

A hot salt corrosion (HSC) test was performed on the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed via cold Rotary Swaging. The grain size and volume fraction of the recrystallized microstructure in the alloy were varied by choosing appropriate annealing temperatures and times. The microstructure and corrosion resistance of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000 h of annealing at 250C. Metallographic studies were carried out to investigate the effects of annealing on the nature and extent of corrosive damage in the titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the titanium alpha-alloy samples were conducted using X-ray diffraction and electron microscopy. During the HSC testing of the titanium alpha-alloy Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC) and pitting corrosion was observed. To the best of our knowledge, it was shown for the first time that annealing affects the relationship among the IGC, pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged low-temperature annealing at 250C resulted in a more pronounced increase in the uniform corrosion rate than short-term high-temperature annealing for 30 min at 500-700C. An in-depth analysis of the effect of the structure and phase composition of the grain boundaries on the susceptibility of the alpha-alloy Ti-2.5Al-2.6Zr to HSC was conducted.

The effect of sintering regimes on the density, microstructure parameters, and mechanical properties of Al2O3 and Al2O3 + 0.25 % MgO ceramics has been investigated. The ceramics were sintered in three regimes: Regime I-heating at a constant rate (2.5, 5, 10, 20 degrees C.min-1) up to the temperature T =1650 degrees C; Regime II-heating with a varied heating rate up to 1565 degrees C with the duration corresponding to sintering at the heating rate of 10 degrees C.min-1 in Regime I followed by a three-fold decrease in the shrinkage rate; Regime III-two-stage sintering: heating according to Regime II up to the temperature T1 = 1550 degrees C, then lowering the temperature down to T2 = 1300-1500 degrees C and holding for 3 h at the T2. The sintering regimes were chosen so that the ceramics had the relative density of 97-99 % and a bimodal distribution of the microstructure parameters. The Al2O3 and Al2O3 + 0.25 % MgO ceramics obtained in Regimes I-III had a microstructure with abnormally large grains in a finegrained matrix. The sizes and volume fractions of the large grains depended on the sintering regime. Most abnormally large grains had elongated shapes that leads to deviations in the crack propagation trajectories from the straight line. The optimal parameters of the bimodal microstructure parameters distribution providing enhanced mechanical properties of the ceramics (hardness, indentation fracture toughness, ultimate strength) have been determined.

Samples of ceramics based on Sr0.5Zr2(PO4)3 phosphate with the structure of the kosnarite mineral (NaZr2(PO4)3, NZP) were obtained by spark plasma sintering. Submicron phosphate powders with particle sizes less than 1 μm were produced by the sol–gel method. Powders and ceramics have a single-phase NZP structure. The relative density of the ceramics was 97.6

Abstract—The possibility of low-temperature in situ synthesis of (Ti, W)C using plasma-chemical WC nanopowders and industrial micron TiC powders is demonstrated. Sintering/synthesis of WC–(25, 50, and 75) wt

The chemical stability of Nd0.33Zr2(PO4)3 fine-grained ceramics, which can be used for immobilization of rare earth elements (REE) that are part of high-level waste was studied. Single-phase Nd0.33Zr2(PO4)3 submicron powders with the structure of the mineral kosnarite were prepared by colloid-chemical synthesis. Powders were prepared by successive annealing at 600, 800, and 900°C for 6 h at each stage. Nd0.33Zr2(PO4)3 ceramic was Nd0.33Zr2(PO4)3 ceramics was produced using spark plasma sintering method (SPS). The relative density of the ceramic was 89.9

The features of spark plasma sintering (SPS) of plasma-chemical nanopowders WC – (0.3, 0.6, 1) wt.% Co were studied. The SPS process of ultralow-cobalt hard alloys can be sequentially represented as a change of the following stages: rearrangement of particles at lower temperatures (Stage I) → sintering of WC – Co particles due to Coble diffusion creep of cobalt, the intensity of which is determined by the grain boundary diffusion rate (Stage II ) → sintering due to diffusion creep, the rate of which is limited by the bulk diffusion in cobalt (Stage III-1) → sintering of tungsten carbide particles along the intergranular boundaries of WC/WC under conditions of intensive grain growth (Stage III-2). Samples with a high density (96.4 – 98.4 %) and high mechanical properties were obtained (for the WC – 0.3 % Co hard alloy: Hv ~ 20.5 GPa, K1C = 7.1 MPa·m1/2).

The features of spark plasma sintering of submicron Al2O3 powders with different contents (0, 0.5, 1.5, 5 vol

The features of high-speed spark plasma sintering (SPS) of plasma-chemical nanopowders WC – (0.3, 0.6, 1) wt. % Co with the addition of 0.3 and 0.5 wt. % graphite were studied. The structural features of the ultralow-cobalt hard alloys with graphite addition during SPS are due to the simultaneous influence of an increased concentration of oxygen adsorbed on the surface of plasma-chemical WC – Co nanoparticles during mixing with graphite, and the effect of graphite, which leads to a decrease in activation energy of sintering due to a decrease in the intensity of formation of η-phase particles in “oxidized” WC – Co nanopowders, as well as the formation of a fairly uniform fine-grained structure. Samples of fine-grained ultralow-cobalt hard alloys with increased hardness and fracture toughness were obtained (for a WC – 0.6 wt. % Co – 0.3 wt. % C hard alloy with an average grain size of ~ (1 – 1.5) mm, the hardness is Hv = 20.2 – 20.5 GPa with a minimum crack resistance coefficient KIC = 9.2 – 10.4 MPa·m1/2).

Oxide Y2.5Nd0.5Al5O12 with the structure of the garnet mineral has been obtained by coprecipitation after annealing at 1000°C. Fine-grained ceramics has been produced by spark plasma sintering based on synthesized powder. The relative density of the ceramics was 99.1

Al-6%Mg-Sc-Zr alloys with the total ratio of Sc + Zr = 0.32 wt.% make up the target of this research. The content of scandium and zirconium varied with an increment of 0.02%. The alloys were produced by induction casting. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Such cast alloys have a homogeneous macrostructure formed by small equiaxed grains in the central part of the ingot and columnar crystals along the edges of the cross section. After ECAP, the average grain size in the alloy specimens is 0.5–1 µm. The average grain size does not depend on the ratio of Sc and Zr in these alloys. Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10-3 and 3.3·10-1 s-1. UFG Al-6%Mg-0.20%Sc-0.12%Zr and Al-6%Mg-0.18%Sc-0.14%Zr alloys exhibit the highest superplasticity. It was suggested that changes in Sc:Zr ratio affect spatial distribution and composition of the following precipitating particles: Al3Sc, Al3Zr, Al3(ScxZr1-x). An increase in Zr concentration is shown to reduce the susceptibility of UFG alloys to cavitation fracture.

The temperature and heating rate affecting the shrinkage kinetics are studied for cylindrical workpieces obtained from submicron and fine aluminum oxide powder. The studies involve the powder from three batches: (1) submicron ( 0.15 µm) α-Al2O3 powder, (2) submicron ( 0.2 µm) α-Al2O3 powder having an amorphous layer deposited on the particle surface, and (3) fine ( 1 µm) α-Al2O3 powder. It is established that the powder particles in all batches has a monocrystalline structure. The powder workpieces are sintered using the electric pulse (spark) plasma sintering (SPS) technique. The shrinkage curves are analyzed using the Young–Cutler and the Coble models. The kinetics of sintering workpieces is shown to depend on diffusion developing between the powder particles. The sintering kinetics of workpieces made from submicron powder depends on intensity of the grain-boundary diffusion. In the sintering workpieces made of finely dispersed powder, the kinetics is additionally dependent on simultaneously developing volumetric and grain-boundary diffusion. It is established that the presence of an amorphous layer on the surface of particulate α-Al2O3 having submicron size affects the rate of migration of grain interfaces and the parameters of the Coble equation at the final SPS stage. It is assumed that the accelerated growth of grains and an increase in the microhardness of samples obtained through sintering workpieces made from submicron powder with an amorphous layer on the particle surface is caused by a higher density of defects at the grain interfaces. The elevated density of defects at grain interfaces can result from crystallization of the amorphous layer.

Extensive studies of the physical, mechanical and fatigue properties of Ti-6Al-4V titanium alloy samples produced selective laser melting and hot rolling technology have been carried out. For each type of samples the values of the yield strength, tensile strength, elongation to failure, yield strength under compression, microhardness, Young's modulus and density were obtained. In particular, it is shown that the strength limit of the samples produced by selective laser melting is 1300 MPa and exceeds by 30% the corresponding value for samples produced by hot rolling. The density of samples produced in optimal modes of selective laser melting reaches 99,3% of the density of samples produced by hot rolling. Low-cycle fatigue curves are got for Ti-6Al-4V titanium alloy samples produced by selective laser melting and hot rolling. A comparison of the nature of failure on samples produced by these technologies is carried out. It is shown that at high cycle stresses (more than 900 MPa), the fatigue life of samples produced by selective laser melting significantly exceeds the endurance of samples produced by hot rolling. A material with such properties can be used in products (parts) that work for a short time under extreme overload conditions. High values of strength characteristics are associated with a thin needle-like microstructure of the martensitic type with a high content of a'-phase, which is formed in the process of layered laser fusion due to the high crystallization rate, which can reach 105-107 K/s. The paper demonstrates the possibilities of the selective laser melting to creating a promising titanium alloy for the manufacture of Ti-6Al-4V osteointegrable medical devices with characteristics corresponding to or exceeding the characteristics of the material obtained by the traditional hot rolling method.

A novel experimental laboratory technique for the flow of miniature cumulative jet of copper and without using explosives, is described. To perform the microcumulative tests, miniature cylindrical specimens with conical pits were used. The dynamic loading of the specimens was performed using a gas gun with a striker accelerated up to speeds of 800 m/s. The optimal specimen geometry and testing regimes, including the focal distance during microcumulation testing, were then determined. The influence of the structural condition of the sample material on the parameters of the cumulative jet has been demonstrated A preliminary analysis of the effects of copper purity and processing regimes on the ultimate dynamic plasticity characteristics was performed Keywords: High-speed deformation, cumulative jet flow, copper, ultimate dynamic plasticity, light-gas gun.