Initial Hardness Research Articles

Precipitation phenomena in a powder-processed quasicrystal-reinforced Al-Cr-Mn-Co-Zr alloy

The thermal behavior of a powder-processed Al-2.5Cr-1.35Mn-0.25Co-0.31Zr alloy (in at.%) has been studied by comparing hardness and SEM data from as-consolidated and heat-treated samples of the bulk alloy with data from in situ TEM heating experiments on sections through individual particles of the as-atomized powder. The starting microstructure consisted of an Al matrix with I-phase quasicrystalline dispersoids, and the distribution of the I-phase depended on the powder particle size. Most of the powder (≈ 70% by volume) exhibited a cellular dendritic Al microstructure with minority phases at the cell boundaries and I-phase at the powder particle surfaces. Upon heat treatment, the consolidated alloy retained the initial hardness and microstructure up to about 400 °C. At this point the alloy hardened by about 6%, and then softened significantly at higher temperatures. The main microstructural change was the precipitation of a plate-like ternary Al11(Cr,Mn)2 phase within the cellular Al matrix. In situ TEM observations on powder particles with the cellular dendritic microstructure at temperatures of 400–450 °C revealed the kinetics of the precipitation for this ternary phase. The kinetic data gave Avrami exponents of approximately 3 in the nucleation and growth regime. The temperature dependence of the rate constants gave an activation energy of 277 kJ/mol, which is consistent with Cr diffusion in the Al matrix being the rate-limiting process for the precipitation of Al11(Cr,Mn)2. The onset of the precipitation at 350–400 °C should not restrict the application of such alloys, but it may limit the processing if the decomposition of the supersaturated solid solution is to be avoided.

Coexistence of two distinct fatigue failure mechanisms in Super304H welded joint at elevated temperatures

Super304H steel is a promising candidate for boiler tube materials in thermal power plants operating under ultra-supercritical conditions, and the fatigue properties of its welded joint play a key role in the structural reliability of the thermal power plants. Herein, we report that there is a transition in the fatigue failure location (i.e., fatigue failure mechanism) from the base metal at a high strain amplitude (≥~0.4%) to the weld metal at a low strain amplitude (≤~0.3%) at a constant temperature in the operating range of 500–700 °C, and this leads to a significant reduction in the fatigue resistance of the welded joint as compared to that of the base metal. We found that a longer fatigue test time at a low strain amplitude induces a thermal aging effect that promotes different microstructural evolutions in the base metal and weld metal, deepening material inhomogeneity in the welded joint, and thereby triggering strain localization in the weld metal. With increasing fatigue test time (i.e., thermal aging time), Cr23C6 carbides precipitated in the interdendritic region of the weld metal and at the austenitic grain boundary of the base metal, and Nb (C, N) phases precipitated in the interior of austenitic grain in the base metal, which increased local hardness, whereas there was no significant microstructural change in the dendrite core of the weld metal, retaining its initial hardness. The intensified local hardness inhomogeneity caused the softest zone in the welded joint, wherein strain localization occurred, serving as a crack nucleation site and propagation path, to shift from the base metal to the weld metal (dendrite core). This induced a shift in the fatigue failure location from the base metal to the weld metal with decreasing strain amplitude.

Investigation on the Rolling Contact Fatigue Behaviors of Different Laser Cladding Materials on the Damaged Rail

Abstract Surface damages on rail became severe with the increase in the axle load and speed. Laser cladding was used to repair the local damages on rail surfaces to ensure the service performance and prolong the life of rails. In the present study, five types of cladding materials (304, 314, 2Cr13, 316L, and 434L) were clad at a small part (trapezoidal shape) of the rail disc to simulate the defected rail in the field. Vickers hardness tester, optical microscopy (OM), scanning electron microscopy (SEM), and electron-dispersive X-ray spectroscopy (EDS) were employed to investigate the service properties of the repaired rail discs. Results indicated that all these five clad rail discs had lower wear-rates than the unclad rail disc. The wear-rates decreased with the increase in the initial hardness of the clad layer. Cracks with large angles mainly propagated along the boundary at the front edge, while at the rear edge, the crack morphology was closely related to the hardness of clad layer. 434L would induce the minimum wear loss and the modest rolling contact fatigue (RCF) of the repaired rail disc, which could be the potential cladding material for repairing the damaged rail.

Adjunctive procedure with solvent mixtures in non-surgical endodontic retreatment: does it affect root dentin hardness?

The aim of this study was to compare the effects of new irrigation solvent mixtures with Methyl ethyl ketone (MEK)/Tetrachloroethylene (TCE) and MEK/Orange oil (OOil), and different agitation techniques on dentin hardness. One hundred forty-four mandibular teeth were prepared and standardized, with each root's middle part transversely sectioned. Initial hardness was measured using a Vickers microhardness tester. Specimens were divided into four groups of agitation techniques (n = 36): no agitation; EndoActivator; IrriSafe; and XP-endo Finisher R. Each group was subdivided into six subgroups of irrigation protocols (n = 6): saline solution; NaOCl + EDTA; NaOCl + EDTA + MEK/TCE; MEK/TCE; NaOCl + EDTA + MEK/OOil; MEK/OOil. Final hardness was measured. The irrigation protocols NaOCl + EDTA, NaOCl + EDTA + MEK/TCE, and NaOCl + EDTA + MEK/OOil significantly decreased dentin hardness, while MEK/OOil increased it (p < 0.05). Comparing to NaOCl + EDTA sequence, dentin hardness increased significantly with the additional exposure to MEK/TCE (3%NaOCl + 17%EDTA + MEK/TCE) or MEK/OOil (3%NaOCl + 17%EDTA + MEK/OOil) (p < 0.05). There were no significant differences regarding agitation effects on dentin hardness decrease. The irrigation protocols affected dentin hardness significantly. However, the additional solvent proposals do not seem to address further concerns on dentin's mechanical properties. Agitation did not show any influence on dentin's hardness reduction.

PENENTUAN KONSTANTA FREUNDLICH PADA PENURUNAN KESADAHAN AIR DENGAN MENGGUNAKAN KARBON AKTIF

Water is important for human being. It's used for the daily living need and industries. The ground water is one of the important source for drinking water, usually contains Calsium (Ca) and Magnesium (Mg) that causing the hardness. There are two kind of hardness, temporary and primary hardness. It can caused some bad layer in the bottom of kettle decrease the bubble of foam, and dangerous for the health. The purpose of this research with to find the Freundlich constant to decrease the hardness by active carbon, knowing the effect of using the active carbon in decreasing the hardness, and to know the optimal size of active carbon to decrease the hardness. The research was done experimentally to decrease the hardness by active carbon with flowing water in the 8,5 cm diameter and 5 cm high of pile - adsorber column, then analyzing the sample with EDT A. The fixed variable of this research were high of active carbons pile and debit. And the unfixed variable are size of carbon active, (-4+8), (-8+10), (-10) and the flowing direction, upstream and downstream, looked every 20 second with the range of 0-180 second. This research had the results of decreasing the hardness every second and every size of active carbon. The decreasing of hardness from the upstream, from the initial hardness 14, 2 mg/It become 5, 6 mg/It, and for the downstream from the initial hardness 16,48 mg/It become 6,4 mg/It. Freundlich constant for each variable were, for the upstream with carbon size (-4+8) mesh, kF = 1,6237 x 10-6,n = 0,999; (-8+10) mesh, kF = 1,8893 x 10-6,n = 1,000; (-10) mesh, kF = 2,0821 x 10-6,n =1,483. For the upstream with carbon size (-4+8) mesh, kF = 1,5603 x 10-6,n = 1,077; (-8+10) mesh, kF = 1,8587 x 10-6,n = 0,995; (-10) mesh, kF = 0,5998 x 10-6,n = 12,610. From this research can be concluded that active carbon as adsorben can be used to decrease the hardness of water. Th

Microstructural and mechanical characterization of self-passivating W-Eurofer joints processed by brazing technique

Self-passivating tungsten alloys have arisen as a potential candidate for the blanket first wall due to their high oxidation resistance and good thermal shock resistance. However, joining technologies have to provide a suitable process to conform the component. In this investigation, brazing technique was applied to join a self-passivating tungsten alloy to Eurofer using 50 μm thick Cu interlayer. In addition, the use of post-brazing thermal treatment (PBTT) was also investigated to recover the as-received hardness of steel after the brazing cycle. The results showed the achievement of high brazeability joints in terms of metallic continuity and strength. With the PBTT the initial hardness of Eurofer was recovered but it gave rise to lower shear strength of the joint due to the softening of copper. The high strength and the fracture mechanism observed in some joints, propagating the fracture through the base material instead of the joint interfaces, showed the high adhesion properties achieved in both studied conditions.

Wear-induced microstructural evolution of ultra-fine grained (UFGs) aluminum

We investigated hardness and tribological properties of ultra-fine grain (UFG) aluminum samples prepared by accumulative rolling bonding (ARB) and by physical vapor deposition (PVD). We have found wear-induced grain refinement in this material for the first time and we have identified a transition from grain growth to grain refinement as a function of the mean contact stress. This trend is the same for the PVD and ARB samples, which means it does not depend on the synthesis method. The hardness was found to increase with a decreasing grain size, but the results deviated from the Hall-Petch relation. Among ARB samples, UFG Al with the highest initial hardness was found to be the most wear-resistant. However, PVD-grown UFG Al was found to be most wear-resistant among all samples, even though it was not the hardest. The reason lies in the different dislocation contents of the samples prepared by different methods and in a subsequent wear-induced evolution of dislocation networks. The mechanisms of microstructural evolution in UFG Al were analyzed using transmission electron microscopy and the main mechanism identified is the dynamic recrystallization (DRX), including both continuous DRX and discontinuous DRX.

Influence of Ultrasonic Finishing on the Surface Roughness of Tool-Steel Components

The influence of plastic deformation by ultrasonic burnishing on the surface roughness of Р6М5 and 9ХС steel workpieces with initial surface hardness 57–60 HRC is investigated. A D-optimal Hartley–Kono experiment design is used. The four factors considered are the workpiece’s rotation frequency, the supply, the loading force, and the ultrasound power.

Thermal stability of aluminum–cerium binary alloys containing the Al–Al11Ce3 eutectic

Abstract The capability of Al–Ce binary alloys, containing from 5 to 20 wt% Ce and ranging from hypo-to hypereutectic compositions, to retain strength at high temperatures was assessed through the uniaxial compression up to 500 °C. As a reference the A380 (Al–8Si–3Cu, wt%) commercial alloy and pure Al were examined under identical conditions. The Al–Ce cast alloys, strengthened by the Al11Ce3 eutectic and proeutectic phases, reached at room temperature the yield stress of 60–100 MPa, being higher than 40 MPa measured for pure Al but well below 170 MPa achieved for A380. During high temperature compression, the yield stress of Al–Ce alloys reduced at a steady rate with temperature, retaining at 400 °C and 500 °C only 50% and 25%, respectively, of its initial room temperature level. This is in contrast to 80–90% of the initial hardness retained after 168 h heating at 500 °C. Although the high initial yield stress of the A380 alloy reduced sharply in the temperature range of 200–400 °C, its retained value after both the short and long term heat exposures was still above the level measured for Al–Ce alloys. It is concluded that the Al11Ce3 eutectic and proeutectic phases have a limited effectiveness in room temperature strengthening of Al–Ce binary alloys and in retaining their strength at increased temperatures. The high hardness retention ratio of Al–Ce alloys, accompanied by the low coarsening rate of the Al11Ce3 phase, do not correlate with the observed high yield stress reduction with testing temperatures.

Unraveling the significant role of retained austenite on the dry sliding wear behavior of medium manganese steel

For wear resistant steels, there is generally a linear relationship between the initial hardness and wear resistance, yet a high initial hardness limits the formability of components. The intrinsic ductility of austenite and strain hardening produced from the transformation-induced plasticity (TRIP) effect during service opens a new window for this contradiction. Herein, the wear resistance and the corresponding failure mechanisms of 5Mn steels after different heat treatment processes were evaluated using a ball-on-disk sliding test under dry conditions. The wear behaviors of the counterbodies were also studied to elucidate the wear mechanism of the tribo-system. The results show that the microstructures of the hot-rolled and air-cooled steel were mainly martensite. When the intercritical annealing temperature was relatively low (<695 °C), the microstructure primarily consisted of reversed austenite and ferrite. The samples annealed at 630 °C, 645 °C, 660 °C, and 675 °C had a similar initial hardness, while the sample annealed at 675 °C possessed a wear resistance that was 3.25 times that of the steel annealed at 630 °C. The large difference in the wear resistance was predominately due to the gradient of strain hardening provided by the varied amount and mechanical stability of the retained austenite. The transformation from austenite to martensite, which has an increased hardness, improves the work hardening. A strengthening layer formed with a certain thickness that provided stress support during the wear process and enhanced the wear resistance. When the annealing temperature reached 695 °C, a large amount of secondary martensite was generated from austenite that had a low thermal stability, which improved the initial hardness and wear resistance. The steels with a large amount of martensite had an enhanced wear resistance, but the elongation severely deteriorated, leading to unsatisfactory formability. The present work provides guidance for designing novel steels with an excellent balance of good formability and decent wear resistance by precisely adjusting the characteristics of the retained austenite.

Mineral bio-accessibility and intrinsic saccharides in breakfast flakes manufactured from sprouted wheat

The objective was to produce breakfast flakes by extrusion using whole meal from sprouted wheat to increase mineral bio-accessibility and provide intrinsic sweetness without compromising their textural properties. Resting the ingredient mixture containing whole meal from (sprouted) wheat at 50 °C and pH 3.8 for 1 h prior to flake production allowed in situ endogenous phytase action. This resulted in end-products that had higher bio-accessibilities of Fe (29–38%) and of Zn (17–32%) than corresponding values for control flakes (8% and 8%, respectively). Further, the sweetness of breakfast flakes can be enhanced as sprouted grains are a source of intrinsic saccharides released by starch degrading enzymes. Substituting control wheat by sprouted wheat in the breakfast flake recipe led to darker flakes with increased density corrected hardness. The latter was due to lower bulk densities and higher starch crystallinity than observed for control flakes. Nevertheless, the flakes still had 70–80% of their initial hardness after soaking for 30 s in semi-skimmed milk. The here developed wheat flakes meet the growing consumer interest in healthy and tasty foods. Further, the presented technology lowers the need for extrinsic micronutrient fortification by making full use of the nutritional potential of wheat grains.

Hardness Prediction in Quenched and Tempered Nodular Cast Iron Using the Hollomon-Jaffe Parameter

The Hollomon-Jaffe parameter is usually used to stablish a equivalence between time and temperature in a tempering treatment, but not to predict the harness of the alloy after the treatment. In this paper this last possibility has been studied. A group of cast iron samples was annealed and cooled at different rates in order to obtain samples with three different hardness values. These samples were tempered using different times and temperatures. The Hollomon-Jaffe parameter was calculated for each case and a relationship based on a logistic function between that parameter and the final hardness was stablished. This relationship was found to depend on the initial hardness and the lowest hardness achievable.

ВЛИЯНИЕ МАТЕРИАЛА И РАЗМЕРОВ ИЗДЕЛИЯ НА ПАРАМЕТРЫ УПРОЧНЕНИЯ ВОЛНОЙ ДЕФОРМАЦИИ

Previously it was defined that geometrical dimensions of material worked have a significant impact upon the process of wave deformation strengthening, as at equal volumes of strengthened samples and processing modes there are observed different cards of micro-hardness in surface layers. &#x0D; In the paper there are shown investigations of the impact of dimensions of samples made of different material kinds (steel 45, titanium VT 1-0, bronze BRAZh 9-4, aluminum alloy B-95) upon wave deformation strengthening parameters). The investigations mentioned were carried out for the first time on a test desk specially developed. Strengthening effectiveness was estimated according to micro-hardness distribution in a surface layer. The analysis of the results obtained allowed defining that in chosen modes of WDS takes place strengthening not only a face surface but a back one of the sample at that in the core of the sample an initial hardness of material is kept. The investigations carried out allowed defining the fact that at the increase of material thickness from 10 to 20 mm resulted in the growth of degree (ΔHμ) and depth (hμ) of strengthening at WDS of samples of steel 45 - by 24 and 32%, samples of bronze BRAZh 9-4 – by 22 and 21%, samples of titanium VT 1-0 – by 24 and 32%, samples of aluminum alloy B-95 – by 40 and 62%. The samples length increase from 50 to 100 mm is accompanied by the decrease of ΔHμ and hμ at strengthening: steel 45 – by 36 and 70%, bronze BRAZh 9-4 – by 27 and 43%, titanium VT 1-0 – by 24 and 32%, aluminum alloy B-95 – by 40 and 62%.

Synthesis of a chitosan nanoparticle suspension and its protective effects against enamel demineralization after an in vitro cariogenic challenge.

Objective Our study aims to synthesize, characterize, and determine the effects of a ChNPs suspension on human enamel after cariogenic challenge via pH-cycling.Methodology ChNPs were synthesized by ion gelation and characterized by Transmission Electron Microscopy (TEM) and Dynamic Light Scattering. Forty enamel blocks were divided into four groups (n=10/group): (i) ChNPs suspension; (ii) chitosan solution; (iii) 0.05% sodium fluoride (NaF) solution; and (iv) distilled water. Specimens were exposed to cariogenic challenge by cycling in demineralization solution (3 h) and then remineralized (21h) for 7 days. Before each demineralization cycle, the corresponding solutions were passively applied for 90 s. After 7 days, specimens were examined for surface roughness (Ra) and Knoop hardness (KHN) before and after the cariogenic challenge; % KHN change (variation between initial and final hardness), and surface topography by an optical profilometer. The data were analyzed by repeated-measures ANOVA, One-way ANOVA, and Tukey tests (α=0.05).Results TEM images showed small spherical particles with diameter and zeta potential values of 79.3 nm and +47.9 mV, respectively. After the challenge, all groups showed an increase in Ra and a decrease in KHN values. Optical profilometry indicated that ChNPs- and NaF-treated specimens showed uneven roughness interspersed with smooth areas and the lowest %KHN values.Conclusion The ChNPs suspension was successfully synthesized and minimized human enamel demineralization after a cariogenic challenge, showing an interesting potential for use as an oral formulation for caries prevention.

Effect of S. mutans combinations with bifidobacteria/lactobacilli on biofilm and enamel demineralization.

The present study evaluated the ability of Bifidobacterium and Lactobacillus species associated with streptococci to increase insoluble extracellular polysaccharide (EPS) production and initial caries lesion progression. Bovine enamel blocks (n = 190; 4 mm x 4 mm) were prepared, selected according to initial surface hardness (SH), and divided into two groups: a) double combinations: S. mutans with Bifidobacterium or Lactobacillus, and b) triple combinations: S. mutans and S. sobrinus with Bifidobacterium or Lactobacillus species. The blocks were exposed to the bacterial associations for 7 days. Subsequently, quantity of EPS from biofilms and caries lesion depth were determined by means of colorimetric and cross-sectional enamel hardness (ΔKHN) analysis. The data were submitted to one-way analysis of variance, followed by the Bonferroni test (p < 0.05). S. mutans with B. animalis or B. dentium produced a higher quantity of EPS; S. mutans + B. animalis led to the highest ∆KHN. S. mutans + S. sobrinus + B. longum induced greater EPS and ∆KHN values. In conclusion, associations of B. animalis and B. longum with streptococci promoted EPS production and caries lesion progression.

Effect of High-Temperature Quenching on the Phase Composition, Structure, and Wear Resistance of Ni-Hard Chromium-Nickel Cast Iron

Metallographic, micro-X-ray spectral and X-ray structural analyses have been carried out. The quenching temperature increase from 900 to 1150 °C leads to high abrasive wear resistance in Ni-hard chromium-nickel cast iron. The initial hardness decreased before the test from 60 to 35 HRC due to the fact that the phase composition of the metal base before the wear test changes during quenching from medium-carbon martensite with secondary cementite to retained metastable austenite. It contributes to increase the crack resistance of cast iron. Austenite turns into dispersed friction martensite on the working surface in the process of wear testing or operation, as a result of the impact of abrasive particles. This martensite together with a part of cementite provides a high level of hardening and operability of the cast iron secondary microstructure.

МЕХАНИЧЕСКИЕ СВОЙСТВА ТЕРМОУПРОЧНЕННОЙ СТАЛИ 65Г, ПОВЕРХНОСТНО-АРМИРОВАННОЙ НАПЛАВКОЙ ТВЕРДЫМ СПЛАВОМ

Increasing the service life of soil-cultivating equipment parts by the use of surfacing reinforcement of working surfaces has found a fairly wide application. However, the studies carried out on this problem were focused on parts, the metal of which had not been subjected to preliminary heat hardening. Meanwhile, in recent years, the components of the working tools of agricultural implements are almost completely hardened by heat treatment. This is especially true for imported products. Information on the reinforcement of parts that have undergone this kind of processing is extremely scarce, and sometimes contradictory. Therefore, the research task was to study the properties of heat-strengthened steel 65G after its surface reinforcement. During the experiments, as the base metal, use was made of spring sheets made of 65G steel with a hardness of about 45 HRC. T-590 electrodes were used as the surfacing material, intended for surfacing of parts operated in an abrasive environment. The reliability of the results obtained was guaranteed by a large number of measurements. Mechanical properties were evaluated by HRC hardness. As a result of experiments, it was found that the hardness value of 44…47 HRC for leaf springs taken out of service makes them suitable for use as repair materials. When surfacing one roller, the initial hardness of the base metal remains at the same level; surfacing two rollers leads to a decrease in HRC by 9 units. Three zones are distinguished in the area between the rollers. The use of reinforcing rollers on the surface of heat-treated steel 65G increases its service properties due to their high hardness, a decreased contact path of the abrasive particle with the working surface and forms a “fl uidized” layer of a moving abrasive medium between the rollers.

Adhesive system with alpha-tricalcium phosphate addition for mineral deposition on caries-affected dentin

The aim of this study was to evaluate the influence of alpha-tricalcium phosphate (α-TCP) in the physical-chemical properties of an experimental adhesive resin and to analyze the immediate and long-term properties of caries-affected dentin (CAD) after selective removal to soft dentin restored with or without the α-TCP group. An experimental adhesive resin was formulated with BisGMA, HEMA (66.66:33.33 wt%), and a photoinitiator system. α-TCP was added at 2 wt% into this base resin, and one group remained without α-TCP as control. The adhesives were analyzed for softening in solvent, polymerization kinetics, and degree of conversion (DC). Human teeth naturally affected by caries were submitted to selective removal of carious dentin and were restored with the experimental adhesives. The teeth were evaluated by immediate and long-term (storage in simulated body fluid) tests: microtensile bond strength (μ-TBS), Knoop hardness of dentin, and mineral deposition by micro-Raman spectroscopy. The experimental adhesive resin with α-TCP showed higher initial Knoop hardness than the control group (p < 0.05). There was no difference regarding the softening in solvent (p > 0.05) and the DC (p > 0.05). The polymerization rate of α-TCP group was higher than the control. There was no difference for μ-TBS between groups (p > 0.05). The hardness of CAD increased in 100 and 200 μm from the adhesive interface after three months (p < 0.05), and both groups indicated higher mineral content on CAD by micro-Raman spectroscopy. The α-TCP addition did not affect the dental adhesives’ properties and did not change the mineral deposition and μ-TBS.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СХЕМЫ ВОЗДЕЙСТВИЯ СВЧ ЭЛЕКТРОМАГНИТНОГО ПОЛЯ НА ТВЕРДОСТЬ ОТВЕРЖДЕННОГО УГЛЕПЛАСТИКА С НАНЕСЕННОЙ НА ПОВЕРХНОСТЬ МОЛНИЕЗАЩИТНОЙ СЕТКОЙ

Currently, the use of fiber-reinforced polymer composite materials (PCM), in particular, carbon plastic and fiberglass, is much promising in manufacturing structural elements of aircrafts and wind turbines. In order to increase the resistance of these materials to static electricity and lightning strikes when passing storm fronts, the structure of the PCM includes various lightning protection coatings (LPC). The most common LPC are in the form of copper grids. The fin assembly and planes of aircrafts and also large-sized blades of wind turbines are exposed to cyclic high-amplitude and low-frequency bending loads as well as vibrations. Collisions with solid objects are quite possible. Thus, hardness is one of the key characteristics of PCM that determines their performance properties. Strength and endurance of PCM components can be increased by short-term exposure to a microwave electromagnetic field. The presence of a built-in metallic structure brings additional uncertainty in the tolerance to operating loads by anisotropic PCM, as well as in the process of their interaction with an ultrahigh frequency electromagnetic field. Research was performed on the hardness of carbon fiber-reinforced plastics with built-in LPC using various exposure schemes to a microwave electromagnetic field: from the side of the LPC, from the side opposite to the LPC and sequential processing from both sides. It was found that short-term processing in a microwave electromagnetic field with energy flux density of (17-18)×104mW/cm2 did not lead to any change in the initial hardness of the surface of the samples. However, the uniformity of hardness distribution on the surface of the samples in- creased by 35.8-70%, thus ensuring a more adequate tolerance to loads of different nature. The obtained results can be used in the development of finishing technologies to post-process PCM components and improve the latter’s stability to dynamic loading.

Gradient microstructure in tantalum formed under the wear track during dry sliding friction

The formation of a gradient microstructure in pure tantalum under the wear track of dry sliding wear test was investigated. Materials were exposed to different amounts of Severe Plastic Deformations, and the evolution of the microstructure and mechanical properties as well as the wear behavior were studied in this work. Results showed that the friction coefficient and the wear were independent of the initial microstructure and hardness of the material, but the depth of the gradient layer under the wear track depended on the history of the treatment which was previously applied to the material. Furthermore, it was revealed that imposing an excessive amount of deformation on the material caused the delamination and initiation of cracks in the sublayer of the wear track.