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The article is concerned with the determination of physical plasticity δH (the ratio of the plastic strain to the total strain) and yield stress σS by indentation and the application of these characteristics for analysis of the wear rate W during the friction. The experimental part of the work is performed on the AISI O2 and AISI D2 steels, the surface layers of which were hardened by combined thermomechanical treatment consisted of sequential use of laser heat treatment and ultrasonic impact treatment. For the metals, W is shown to be proportional to δH and inversely proportional to σS. The general scheme for the dependence of W on δH is proposed and based on experimental results for tool steels and hard alloys. For the steels, whose wear is caused by the plastic deformation, W increases with increasing δH, and it decreases conversely for hard alloys worn predominantly by the fracture mechanism. The use of physical plasticity δH and yield stress σS, which are calculated using the hardness and Young’s modulus, characterizes both the hardening extent and the wear rate of the surface layers in more full measure and more accurately than the hardness magnitude itself.

A fragment of the Al corner in the ternary Al–Ge–Mg phase diagram has been constructed. Experimental methods have shown that the tie-line of the L ⇆ α-Al + Mg2Ge three-phase eutectic equilibrium (corresponding to the maximum temperature of eutectic transformation) does not match the stoichiometric Al–Mg2Ge section in the ternary Al–Ge–Mg phase diagram and is shifted toward its magnesium-rich side. The temperature–composition parameters of the univariant L ⇆ α-Al + Mg2Ge eutectic transformation and the boundaries of two-phase α-Al + Mg2Ge alloys after crystallization and annealing have been determined. The results will be used in the development of new aluminum casting alloys.

In this review, the development of techniques for determining the plasticity of materials by the indentation is considered. The development of methods for determining the plasticity of materials by the indentation is based on the use of fundamental ideas of the physics of strength and plasticity. Significant development of these methods became possible after the introduction of a new plasticity characteristic δ∗=ϵр/ϵt, where ϵр is the plastic deformation, and ϵt is the total deformation. This plasticity characteristic corresponds to the modern physical definitions of plasticity, in contrast to the widely used elongation to failure δ. The new plasticity characteristic is easily determined by standard determination of hardness by the diamond pyramidal indenters at constant load P (designated as δН) and by instrumental nanoindentation (designated as δА, and δН≈δА). A significant advantage of the new plasticity characteristic is the ability to determine it not only for metals, but for materials, which are brittle at the standard mechanical tests (ceramics, thin layers, coatings, etc.), as well. In the development of ideas about theoretical strength, concepts of theoretical plasticity under the dislocation-free and dislocation deformation mechanisms are introduced. A number of studies have established a correlation of δН with the electronic structure of the material and its physical properties. As shown, the Tabor parameter С (C=HM/σS, where HM is the Meyer hardness, and σS is the yield stress) is easily calculated by the δН value. Therefore, indentation allows currently determining simply not only the hardness, but also the plasticity and yielding stress of materials. Thus, indentation became a simple method for determination of the complex of mechanical properties of materials in a wide temperature range using a sample in the form of a metallographic specimen.

The surface layers of tool steel AISI D2 were modified by laser heat treatment (LHT) conducted using the solid state fiber-laser, by ultrasonic impact treatment (UIT) and by the combined LHT + UIT process. The paper is focused on the establishing the correlation between the microstructure, hardness and wear resistance of the modified layers. XRD analysis and TEM observations show that the LHT process results in the formation of microstructure comprised submicronic ferrite/austenite grains, martensitic needles and secondary carbides while the combined LHT + UIT process leads to the formation ultra-fine grained structure (~ 80–250 nm) with grain boundaries fixed with fine secondary carbides (~ 20 nm), and some areas of martensitic feathers. The observed microstructural features and phase compositions are shown to affect the wear resistance of the AISI D2 steel surface measured both in quasi-static and dynamic conditions. The modified layers demonstrate almost double, triple and four times decrease in the wear losses in dynamic conditions with regard to the initial surface after the LHT, UIT, and combined LHT + UIT processes, respectively. Theoretical evaluations of the wear resistance W− 1th using the Archard expression correlate well with the experimental data W− 1exp, especially when the local plasticity characteristics δН describing the retained plasticity was taken into account.

A model of the indentation using conical and pyramidal indenters has been proposed, in which not only a sample but the indenter as well are elastoplastically deformed and their materials obey the Mises yield condition. These conditions are characteristic of the measuring of diamond hardness through a diamond indenter. The model that has been proposed generalizes and refines the known simplified Johnson’s model, which uses an elastically deformed indenter. The proposed model makes it possible to determine approximately the sizes of elastoplastic zones in the indenter and sample, the effective apex angle of the loaded indenter and effective angles of the indenter and imprint after unloading. Based on this model a procedure of the determination of the sample and indenter yield strengths (Y s and Y i , respectively) has been developed, in which the relations that use the experimental values of the effective angle of the sample imprint and measured values of the Meyer hardness, HM (mean contact pressure) are added to theoretical relations of the indentation model. The developed computational procedure was applied in indentation experiments on synthetic diamond at the temperature 900°C (at which diamond exhibits a noticeable plastic properties) using natural diamond pyramidal indenters having different apex angles. According to the proposed model, the stress-strain states of samples and indenters have been investigated and their yield strengths and plasticity characteristics were defined. The stress–strain curve of the diamond in the stress-total strain coordinates has been constructed. The strain hardening of diamond was also studied.

Ductile mode cutting has become an emerging technology of machining silicon, where the originally brittle material is removed by a plastic flow of the phase-transformed material, yielding ductile chips, thus leaving a crack-free smooth surface. However, the ductile mode cutting of silicon can be hardly realized by a careful selection of processing parameters only. It has been shown that the self-healing of microcracks, microfractures, and small spallings by filling the defect cavities with the ductile metallic silicon phase in reality can be easier achievable if the partial ductile mode takes place.

Aluminium alloys reinforced with ceramic, intermetallic or quasicrystalline particles can fill the needs of automotive and aerospace industries due to their superior properties. In this paper, near-surface layers in Al–6Mg alloy specimens were modified using an ultrasonic impact treatment (UIT) process, which induces mechanical mixing of matrix and reinforces quasicrystalline (QC) Al 63 Cu 25 Fe 12 particles to be introduced into a zone of severe plastic deformation. The wear and friction behaviours of the matrix alloy and QC reinforced layers were investigated in quasi-static and dynamic conditions with particular attention to the effects of QC particles size and test type on wear resistance and microhardness of sub-surface composite layers in Al–6Mg alloy. XRD and SEM analyses show that the layers of 40–50 μm thickness are fabricated by the UIT process which contain homogeneously dispersed fine QC F (0.5–3 μm) or coarse QC C (~15 μm) particles, with volume fractions V f of about 9% and 22%, respectively. In comparison to the annealed Al–6Mg alloy, noticeable increment in wear resistance was registered only for the composite layer reinforced with QC F particles. On the contrary, the QC C particles being fractured at the fabrication process and/or at the wear tests facilitate three-body abrasive wear conditions and deteriorate the wear resistance of the alloy. SEM and confocal laser microscopy show changes in wear mechanism from microcutting/ploughing in the QC F reinforced layer to microcracking/fracturing in the case of QC C reinforcement. Fine QC F particles are preferred for better wear resistance both at the quasi-static and dynamic conditions.

The deformation of metallic glasses (MG) may be considered on the basis of three models: the STZ (shear transformation zone) model; the free-volume model; and dislocation plastic flow. For the example of MG on the iron base, it is shown that dislocation plastic flow occurs at low temperatures; the activation energy is a few tens of eV. At higher temperatures, plastic deformation occurs with an activation energy of a few eV, which is close to the activation energy of self-diffusion. That corresponds to the first two models.

The theoretical and experimental problems of determining Martell hardness are considered, and the use of an energy approach to the problem of hardness determination is analyzed. The development of instrumented indentation makes it possible to determine the total indentation energy and the energy consumed for plastic deformation.

The publications reporting systematic investigations of the effect of structural state of WC-Co hard alloys (the cobalt binder content, WC grains size and contiguity) and temperature on mechanical properties and deformation mechanisms have been reviewed and generalized. The ductile-brittle transition, strain hardening, special features of WC-Co alloys deformations in various temperature ranges, and specificity of mechanical properties of the alloys with submicron WC grains have been discussed.

The effect of doping with transition refractory metals on the structure and properties of Al–Zn–Mg alloys produced by different methods is studied. It is ascertained that the strength of cast alloys is increased by scandium and zirconium doping due to the modifying action of scandium that arrests recrystallization and precipitation of the fine-grained phase matrix-coherent Al3(Sc1–x Zr x ) phase; the strength of alloys obtained by powder metallurgy (P/M) methods increases to a smaller extent, in which the ultrahigh cooling rate of melt atomized by high-pressure water plays the basic role in forming the fine-grained structure. The strength of powder metallurgy alloys based on wateratomized powders is substantially higher than that of similar alloys produced by the conventional casting method (standard commercial cast alloys and alloys produced by granular technology). The advantages of P/M alloys over cast alloys are especially prominent in the absence of scandium doping. The highest strength of the P/M alloys with scandium (σb = 651 MPa and σ0.2 = 596 MPa) is shown by Al–5Zn–3Mg–0.5Mn–0.7Zr–0.3Sc. Among the P/M alloys without scandium, the highest strength is shown by Al–5Zn–3Mg–0.85Zr–0.22Cr–0.17Ni–0.15Ti alloy (σb = 618 MPa and σ0.2 = = 553 MPa).

Composite layer reinforced with quasicrystalline (QC) Al63Cu25Fe12 particles was fabricated on the surface of Al–6 Mg alloy specimens by ultrasonic impact peening (UIP). Stress-controlled fatigue response of the specimens was studied and compared with those for the annealed and UIP-treated specimens. The notch effect of the UIP induced surface roughness calculated in terms of the stress concentration factor does not exceed∼10%. XRD, OM and SEM analyses were used to characterize formed surface layers and fatigue fracture surfaces. Surface composite layer of 40–50 μm thick contains the homogeneously dispersed QC particles (the volume fraction Vf∼0.15) trapped by high compressive residual stresses. The layer demonstrates almost triple increase in microhardness comparing to that for the annealed alloy and twice exceeding of that for the UIP-treated specimen. Superior fatigue endurance of Al–6 Mg alloy after the UIP process and the UIP-induced formation of the composite layer is explained by sub-surface fatigue cracks’ initiation promoted with high compressive residual stresses and tight interfacial bonding of QC reinforcement and the matrix alloy. The improved fatigue behavior of the UIP-treated specimens in both the low cycle and high cycle regimes can be ensured by combination of the following favorable characteristics: (i) sufficiently high ductility and resistance to fatigue damage and crack growth in the core parent material along with (ii) superior fatigue strength supported by high microhardness and compressive stresses in the surface layer, which contains fine grained matrix and/or uniformly distributed and tightly bonded QC reinforcements.

Mechanical properties of a type IIb synthetic diamond produced by the temperature gradient method have been studied at 900°C using indenters having different angles between the pyramid axis and face. The strain-strain curve has been constructed in the stress-total strain coordinates. It has been shown that in the diamond deformation the strain hardening with a linear dependence of flow stress on the plastic strain degree occurs. It has been found that the microhardness and fracture toughness of the tested synthetic diamond and natural diamond and the mechanism of their deformation do not differ essentially.

The structure of armco iron after severe plastic deformation under friction with simultaneous nitrogen saturation has been studied by microstructure analysis, X ray diffraction, and transmission and scanning electron microscopy. A gradient surface layer, in which the grain size varies from micro to submi cro and nanometer scale values, is found to form. A mutual intensifying effect of the deformation induced refinement of a grain structure and the diffusion of nitrogen atoms in iron is shown. The formation of a nanocrystalline state is discussed as a result of dynamic recrystallization.

The effect of structure refinement of iron to submicro- and nanograins during intense plastic deformation under friction (SPDF) with simultaneous nitrogen saturation on the mechanical characteristics (hardness, plasticity, Young’s modulus) has been studied by nanoindentation. The nitrogen saturation of iron during SPDF is shown to increase the hardness of micro- and submicrocrystalline regions of the surface layer as compared to SPDF in argon as a result of solid-solution hardening. A high nitrogen concentration in an α-Fe[N] solid solution weakly affects the mechanical properties of nanocrystalline iron with grain sizes d < 50 nm, in which deformation is controlled by grain-boundary sliding.

We analyze the influence of the long-term operation of API X52 pipeline steel on the degradation of its mechanical properties. It is established that, after operation for 30 years, its strength and plasticity characteristics decrease substantially, and the fatigue toughness decreases particularly abruptly, which is connected with the development of the damageability. We use indentation methods for comparing the states of the operated and nonoperated material. It is shown that the indices of spread of the results of measurements (the coefficient of variance) of the mechanical properties (hardness, wear, etc.) are more sensitive to the damage of the material in the initial state and the damage after operation than their averaged values. Some correlations between the Vickers hardness, cyclic hardness, strength, and plasticity of the steel are established.

It was shown experimentally that changing the indenter load P and the indentation size does not change the total deformation during indentation ( e t ≈ const.), and that fracture does not influence the scale effect. For this reason the physical nature of the scale effect is revealed better by nanoindentation and under more “clean” conditions than in uniaxial deformation tests. The indentation size effect (ISE) is revealed as the change of mechanical properties determined by indentation. It was shown that reduction of the indent size leads to both increasing hardness and decreasing plasticity, determined by indentation. The phenomenological approach to the ISE (in which the power dependence of the indenter load P on the indenter displacement of h is used) made it possible to describe the dependence of nanohardness H ( P ) and H ( h ) by simple equations. Nanohardness was determined for 21 different crystals, and parameters that enabled the size dependence of H for these crystals to be calculated were determined. It is proposed to determine nanohardness at h = const. instead of P = const. and to recalculate H using our equations for fixed values of h f = 1000 nm for metals and h f = 100 nm for hard materials. The use of the developed technique makes it possible to compare results of nanohardness tests from different sources for different indenter loads.

Below is one of the most significant works by V. I. Trefilov and Yu. V. Mil’man. The idea that the temperature dependence of the yield stress is determined by the thermally activated escape of potential barriers by dislocations is used to derive an equation that includes, as a particular case, the Seeger equation that describes the linear dependence of the yield stress on low temperatures and the Haasen equation that represents the exponential temperature dependence of the yield stress. The equation derived was later used to describe brittle-ductile transition and introduce the so-called deformation temperature at which the yield stress begins to strongly depend on temperature and strain rate and the ductile and brittle ranges are separated. These ideas were widely used to examine the deformation and fracture mechanisms for a range of promising materials with contained plasticity (refractory metals, ceramic materials, covalent crystals, quasicrystals, sintered materials).

The paper examines how scandium and zirconium doping of Al–Mg alloys produced by conventional casting and powder metallurgy methods influences their structure and mechanical properties. It is shown that Al–Mg powder alloys are not recrystallized in the plastic deformation process and subsequent heating to 550°C. In cast alloys, recrystallization begins even in the extrusion process. Additions of scandium, zirconium, and chromium restrain the recrystallization of alloys when heated to 550°C. Doping of Al–Mg alloys with scandium and zirconium increases their strength by 80−120%. Doped powder alloys have much greater strength than cast alloys and quite high plasticity.

The structure and mechanical behavior of bulk Al–Cu–Fe materials sintered at high hydrostatic pressure are studied at room temperature. Quasicrystalline Al63Cu25Fe12 and Al62.7Cu25Fe12Sc0.3 powders and Al66Cu18Fe8Cr8, powder, which is the quasicrystal approximant, are sintered at high pressure. The powders are obtained by high-pressure water atomization. At an optimal hot compaction pressure of 4.5 GPa, the porosity of the compact materials is lower than 2%. Sintering is conducted at 700°C. The stress-strain curves of quasicrystals and their approximants that are brittle in standard test conditions are obtained using indentation method. It is shown that the crystalline approximants of quasicrystals are much closer in their mechanical behavior to quasicrystals than to crystalline solids.

The severe plastic deformation of armco iron by friction is experimentally studied, and the results obtained are used to show that efficient grain refinement is possible in the temperature ranges of warm and hot deformation. A nanocrystalline structure forms only under dynamic recrystallization conditions during hot deformation, which is ensured by deformation in different directions at a rate higher than 102 s−1.

Characterization of the plasticity of materials by the part of plastic strain in the total elastic-plastic strain and application of this characteristic at indentation is considered. The dependence of the new plasticity characteristic on the structure and temperature is discussed. The concept of theoretical plasticity is introduced and the theoretical plasticity is calculated for a number of materials.

The effects of ultrasonic impact peening (UIP) and laser-shock peening (LSP) without protective and confining media on microstructure, phase composition, microhardness and residual stresses in near-surface layers of an austenitic stainless steel AISI 321 are studied. An X-ray diffraction analysis shows both significant lines broadening and formation of strain-induced e- and α-martensite after UIP with additional peaks found near austenite ones in the low-angle part after LSP supposedly due to formation of a dislocation-cell structure in the surface layer. TEM studies demonstrate that a nano-grain structure containing either only austenitic grains with e-martensite (at strains up to 0.42) or both austenite and α-martensite grains (at higher strains) can form in the surface layer after UIP. Highly tangled and dense dislocation arrangements and even cell structures in fully austenitic grains are revealed both at the surface after LSP and in the layer at a depth of 80 μm after UIP. UIP is found to produce a sub-surface layer 10 times thicker and about 1.4 times harder than that formed by LSP. A mechanism of formation of the dislocation-cell structure in such steels (with a low stacking fault energy) is discussed. A nucleation process of α-martensite is discussed with respect to strain, strain rate, local heating and mechanical energy accumulated/applied to the surface layer under conditions of UIP and the LSP and compared to literature data for different loading schemes.

A new rapid solidification technology based on the use of modified water atomization followed by powder consolidation route has been developed recently and applied for manufacturing of a set of alloys for various applications. The paper analyses mechanical behavior in the range of 20–300 °C and microstructure of some elevated temperature Al–Fe–Ce base alloys produced by the above mentioned process in comparison with properties of similar alloys by other technologies. Mechanical properties were studied by tensile tests and Vickers hardness measurements. Microstructure and microchemistry of powders and powder metallurgy alloys were studied by electron microscopy, electron probe microanalysis and X-ray diffraction methods.

The microstructure and mechanical properties of Al-Fe-Ce alloys based on water-atomized powders between 20 and 300 °C are examined in comparison with the properties of similar alloys produced by other rapid crystallization techniques. Changes in atomization parameters vary both the cooling rate (from 104 to 106 K/sec) and powder size distribution (from 5 to 100 µm). The excellent compactability of water-atomized powders facilitates powder consolidation, which is based on hot extrusion and cold pressing of degassed powders. The mechanical properties are examined by tensile tests. The ultimate tensile strength is 500 to 550 MPa at 20 °C and 270 to 300 MPa at 300 °C at adequate plasticity. The properties achieved are comparable with those of similar alloys known from the literature.

Quasicrystalline Al–Cu–Fe coatings with submicron-sized grains (∼ 400 nm) were produced by electron beam PVD. Mechanical properties of the Al–Cu–Fe quasicrystalline coating and a bulk Al–Cu–Fe quasicrystalline specimen with an average grain size of about 50 μm were examined using a set of micro- and nanoindentation techniques (with plotting stress–strain curves). It has been found that the length of the hardening stage in the stress–strain curve at room temperature for the coating is essentially greater, and the softening is weaker as compared with those for the bulk specimen. Possible reasons for such mechanical behavior of the coatings are discussed. Nanoindentation tests have shown that stepwise plastic flow is observed in both bulk sample and coating.

The corrosion behaviour of Al–5Zn–3Mg–0.6Cu–0.8Zr–0.25Cr–0.15Ni–0.15Ti alloys, produced by traditional and powder technologies, with similar thermo-mechanical treatments, in 3% sodium chloride solution, has been examined by electrochemical methods, scanning electron microscopy, transmission electron microscopy and X-ray microanalysis. The alloys reveal similar precipitation but of different shape, size and distribution; further, both alloys experience localized corrosion. Copper-rich precipitates initiate the dissolution of surrounding particles, enriched in Zn and Mg. As a result, the surface is enriched with other alloying elements after a full polarisation run. Cast material has lower corrosion properties because of the higher heterogeneity of the structure. The structure heterogeneity of the cast material involves a more non-uniform distribution of the precipitates, larger Zn- and Mg-rich particles, and depletion of the matrix and areas around the precipitates by alloying elements compared with the powder material.

A test method procedure for constructing stress-strain curves by indentation of brittle and low plastic materials under temperature ranging from 20 to 900?C was developed recently by Yu. Milman, B. Galanov et al. According to this test method procedure stress-strain curves ? - ? for Si, Ge, SiC, TiB2 and WC/Co hard alloy were constructed in the above temperature region and mechanical parameters such as elastic point, ?e, yield stress, ?s, etc. were extracted by using the measurement results obtained by a set of trihedral pyramid indenters with different angles at the tip, ?1, ranging from 45 to 85?C.

The structure, dislocation substructure, and mechanical properties of the targets made of four aluminum alloys after a impact loading by kinetic energy projectile have been investigated. The formula for approximation of the ballistic limit velocity by indentation technique is proposed. It has been shown that the maximum nonequiaxiality of the grain shape, increase of dislocation density, and decrease of dislocation cell size correspond to the 40–70% of plastic deformation at static compression for the investigated aluminum alloys.

The review of the works devoted to the influence of scandium on the structure, mechanical behavior and corrosion resistance of aluminum alloys is given. The wrought thermally non-hardenable alloys of Al- Mg system and thermally hardenable high-strength alloys of Al-Zn- Mg-Cu system are considered. The influence of Sc on the glass forming ability of amorphous alloys and on the superplastic behavior of aluminum alloys is discussed.

It is generally supposed that diffusion is the main factor controlling the process of powder sintering. In this work it is shown that plastic deformation achieved by means of dislocation movement is also an important constituent of the sintering process. Since temperature essentially affects dislocation mobility, the temperature ranges of cold, warm and hot deformation are discussed. The stresses occurring on powder sintering leading to plastic deformation of the material are estimated. On the base of results recommendations are made for selecting the optimal condition for the sintering of powders.

This is a preprint of an article published in Materials Science Forum, Vols. 503-504. The final authenticated version is available online at: http://doi.org/10.4028/www.scientific.net/MSF.503-504.645 Specific features of mechanical behaviour of ultra fine grained iron subjected to friction treatment with nitriding (FN) were clarified by comparison with that induced by friction treatment (FT) with air. Mechanical parameters such as Young’s modulus, nanohardness, and plasticity characteristic δA were found to be of high sensitive both to the scale of grain structure and to iron modification by nitrogen. Young’s modulus tends to decrease and Hall-Petch low fails to describe correlation between grain structure and hardness for submicro-grained and nanocrystalline iron. Hall-Petch coefficient, ky, decreases as grain size decreases within submicro-grained and, then, nano grained sections and it takes even negative value in nano grained section modified by nitrogen. Parameter δA is found to be dependent on combination of hardness and Young’s modulus, resulting in its variation with decreasing the grain size. The presence of secondary nanocrystalline Fe4N phase fundamentally changes mechanical behaviour of nanocrystalline iron, leading to strengthening the grain boundaries and triple junctions.

The effect of reinforcement particle size (3 and 14 μm), matrix-to-reinforcement particle size ratio (PSR) ranging from 2.9 to 12.9 and volume fraction of the reinforcement (0–20 vol.%) on microstructure and mechanical properties (yield stress, tensile strength, elongation to fracture and Young’s modulus) is investigated for Al–6Cu–0.4Mn⧹SiC p composites manufactured by the powder metallurgy route. A model is proposed to determine the critical reinforcement content for the composite at known PSR and to calculate the porosity and Young’s modulus of the material containing an excessive amount of the reinforcement.

Nanoindentation testing was used to determine the hardness, elastic modulus and plasticity parameter of three newly developed ternary nitride coatings with nano-sized grains. With decreasing nitrogen deposition pressure, grain diameter of the coatings decreases that leads to both higher nanohardness and elastic modulus with conservation of satisfactory values of plasticity characteristic.

Aluminum-based alloys containing quasicrystalline particles of 50 – 600 nm in diameter as a reinforcing phase were produced in the form of powder or ribbons by water atomization or melt spinning techniques, respectively. Rods were compacted from powders and some ribbons by severe plastic deformation without sintering. Structure and mechanical behavior of alloys are discussed.

The tribological properties of the surface of railway tracks have been studied taking into account that the surface layer is composed of sublayers with different microstructures and mechanical properties. The tribological properties of the sublayers have been investigated both in the dynamic and static loading mode. The topmost sublayer is characterized by a very high hardness and the yield stress value of 3.2 GPa. It also has low plasticity. It was shown that as long as the layer is continuous it has high wear resistance in tribological tests. However, its fracture reduces the wear resistance considerably and increases the friction coefficient. Wear of the surface layer exposes subsequent sublayers to friction, so that the tribological properties of the rail track change during the wear process. The tribological properties of the top layer are similar for both the dynamical and static loading, while the tribological properties of the subsurface layers are sensitive to the loading mode.

Matrix to reinforcement particle size ratio (PSR) is the main factor governing the homogeneity of the reinforcement particle distribution in composites manufactured by the powder metallurgy route. To improve the homogeneity of the distribution, reinforcements with larger average particle size should be used. At the same time, increasing the reinforcement particle size leads to worsening of the mechanical properties due to lower work hardening and higher damage accumulation rates. It is therefore important to optimize the microstructure somewhere in between a smaller reinforcement particle size and a more homogeneous spatial distribution. The effect of PSR on the reinforcement spatial distribution, fabricability, and resulting mechanical properties of a P/M processed AlCuMn/SiC/15p composite was investigated. It was shown that increasing the PSR results in a less-uniform reinforcement distribution, which in turn leads to a decrease in the material fabricability and a general worsening of the mechanical properties. A close to linear dependence of the mechanical properties (yield stress, UTS, elongation before fracture, Young’s modulus) on PSR was found. Tensile elongation shows the highest sensitivity to the worsening of the homogeneity of the reinforcement spatial distribution caused by increasing the PSR. The effect of microstructural homogeneity on the relative change of mechanical properties does not seem to depend on matrix alloy plasticity.

The equilibrium between solid and 1iquid phases in sintered composite materials has been studied. It is shown that closed surfaces, which bound dispersed phases, influence the mechanical equilibrium between these phases. An expression is derived for a dihedral angle in composite materials, which includes values of surface tensions at the phase interfaces as well as parameters of a composite equilibrium structure (phase composition, particle contiguity and coefficients of a particle geometry). .

Specific features of the test method procedure capable for determining the plasticity characteristic dH by indentation of inhomogeneous coatings affected by residual stress was clarified. When the value of the plasticity characteristic for coating was found to be as great as dH > 0.5 a simplified model was found to be reasonably adequate, while a modified model assumed compressibility of the deformation core beneath indentation. The advantage of the modified approach compared to the simplified one was grounded experimentally only if the elastic deformation for coating becomes greater than ?e ? 3.5%, resulting in the decrease of plasticity characteristic dH < 0.5. To overcome non accuracy caused by the effect of the scale factor on measurement results a comparison of different coatings was suggested using stabilized values of the plasticity characteristic dH determined under loads higher than critical, P ? Pc, ensuring week dependence of micro hardness values on the indentation load.

The behaviour of Al–Zn–Mg base alloys produced by powder metallurgy and casting has been studied using potentiodynamic polarisation in 0.3% and 3% NaCl solutions. The influence of alloy production route on microstructure has been examined by scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectrometry. An improvement in performance of powder metallurgy (PM) materials, compared with the cast alloy, was evident in solutions of low chloride concentration; less striking differences were revealed in high chloride concentration. Both powder metallurgy and cast alloys show two main types of precipitates, which were identified as Zn–Mg and Zr–Sc base intermetallic phases. The microstructure of the PM alloys is refined compared with the cast material, which assists understanding of the corrosion performance. The corrosion process commences with dissolution of the Zn–Mg base phases, with the relatively coarse phases present in the cast alloy showing ready development of corrosion.

The temperature–concentration parameters defining the existence of the eutectic transformation L⇄L1 2 +β at the Al-rich corner of the Al–Ti–Cr phase diagram have been studied. The temperature of this transformation decreases from 1275 to 1250 °C with decreasing titanium content in the alloy, and its temperature interval is at most 10 °C. The univariant eutectic transformation line L⇄L1 2 +β was constructed, whose coordinates on the concentration triangle are defined by the equation (in at.%): C Al =95.48–3.45 C Ti + 0.068 ( C Ti ) 2 . As a result of this transformation, periodic microstructures consisting of lamellae and fibres of the cubic L1 2 and β phases are produced. Transformations in the solid state which occur during cooling lead to the precipitation of intermetallic compounds from the β-solid solution: TiAlCr (structural type C14) or AlCr 2 (structural type C11 b ). The position of the boundary at which the change of precipitating phases occurs was determined. The analysis of mechanical properties shows that the transition from single-phase L1 2 aloys to eutectic microstructures is accompanied by enhancement of both strength and plasticity, while retaining a high elastic modulus.

The phase stability and transformations in Al 3 (Ti 1- x Zr x ) intermetallic alloys ( x =0–1) produced by arc melting were studied in the temperature range of 20 to 1100°C by using an in situ X-ray diffraction (XRD) method. Two phases, D0 22 and D0 23 , both having ordered tetragonal structures, were present at room temperature at zirconium concentrations from 1 to 10 at.% ( x =0.04–0.4). At higher concentrations of Zr (0.4 x 23 phase was detected. For the alloy with x =0.32, the D0 23 transformed to D0 22 on heating at temperatures 1100 °C and above. On cooling, the D0 22 phase was stable to ∼650 °C, and the D0 23 phase was formed again in the temperature range of 600–650 °C. The positional parameters of the D0 23 atomic structure in the alloy Al 3 (Ti 0.68 Zr 0.32 ) were determined using a full-profile XRD analysis. It was shown that zirconium atoms substitute titanium atoms and increase the lattice parameters of the D0 23 structure. Zr fractions as small as x =0.1 are required to stabilize the D0 23 structure. A low temperature phase modification, Al 24 Ti 8 , was also detected in the surface layer in the temperature range below 650°C and it was found to be a result of surface grinding. Mechanical properties of the alloys studied are also discussed.