The influence of contact stresses on the phase and concentration composition of thin surface layers and wear products in the tribological contact zone of high-nitrogen FeMn22Cr18N0.83 steel was studied using Mössbauer spectroscopy, X-ray structural analysis, and electron microscopy. It was shown that contact compressive stresses developing under the conditions of dry sliding friction in the surface layers (20–25 microns) resulted in the strain-induced dissolution of cellular precipitation products (nitrides Cr2N) and increased the average content of nitrogen in austenite. Antiferromagnetic ordering in austenite caused by the precipitation of secondary nitrides with low chromium and nitrogen content was observed in tiny external layers (~0.1 microns) of the friction surface and products of steel adhesive wear. The effect of tension stresses in the friction contact zone on the formation of strain-induced martensite and nitrides with α″-Fe16N2 structures was established in the wear products.

Using the Mössbauer spectroscopy and transmission electron microscopy (TEM) methods, the temperature boundary of a strain-induced transformation with the inversion of the direction of nitrogen redistribution is determined in the structure of the FeMn 22 Cr 18 N 0.83 austenitic steel. Deformation by high pressure torsion in Bridgman anvils below the temperature limit (298 K) leads to an increase in the amount of nitrogen in the interstitial solid solution and deformation above the limit (373 K) leads to a decrease in this value. An increase in the deformation temperature leads to the complete dissolution of the products of cellular decomposition and the formation of submicrocrystalline austenite with secondary nanocrystalline nitrides. Changes in the direction of nitrogen redistribution are explained by the competition between the mechanisms of relaxation of the structure along the paths of dispersion, dissolution of nitrides by dislocation, and decomposition of a solid solution supersaturated with nitrogen.

Metallography, electron microscopy, and X-ray diffraction are used to study the effect of preliminary plastic deformation in the friction-contact zone on the structural transformations and wear resistance of 12Cr19N9T austenitic stainless steel subjected to subsequent oxidation in air at temperatures of 300–800°C for 1 h. Severe deformation under dry sliding friction produces a two-phase (γ + α) nanocrystalline structure in a ~10-μm-thick surface layer of the steel. The microhardness is 5.2 GPa. Subsequent oxidation at 300–500°C causes an additional increase in the microhardness of the deformed surface layer of steel to the value of 7.0 GPa. This is due to the active saturation of austenite and deformation-induced α'-martensite with oxygen atoms, which rapidly diffuse deep into the metal along the grain boundaries. The oxygen concentration in the surface layer and steel wear products reaches 8.5 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ- and α' phases, increasing the strength and wear resistance of the surface of the 12Cr19N9T steel. Oxidation at 550–800°C results in the formation of a large number of Fe3O4 (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance.

The paper studies the effect of ε (hcp) martensite on the structure and tribological properties of chromium-manganese metastable austenitic steels.The effect of TiC carbide particles on the friction coefficient and wear resistance of Cr-Mn austenitic steels is considered.Structural transformations occurring in the surface layers of the steel in the course of frictional processing are studied via methods of metallography, X-ray diffraction and electron microscopy analysis.It has been found that the formation of nanocrystalline hcp martensite in the steels under study decreases considerably their friction coefficient and increases their resistance to adhesive wear in comparison with the cases of the 40Kh25N20 stable austenitic stainless steel and the 12Kh18N9 austenitic stainless steel, the latter being metastable to γ→α martensitic transformation.The presence of 1-4.5 wt % of TiC carbide particles in the structure of the steels increases the friction coefficient of the materials and decreased their wear resistance.The ε phase in chromium-manganese austenitic steels is more capable of strain-induced hardening under friction than the ε phase in iron-manganese alloys.Accumulation of fine TiC particles of in the surface layer of the titanium-alloyed chromiummanganese austenitic steels has been detected.

The following materials-science aspects of the frictional treatment (FT) of martensitic and austenitic steels with sliding indenters were considered in this study: mechanisms of nanostructuring of iron alloys upon FT under sliding-friction conditions; strengthening, resistance to thermal softening, wear resistance, and mechanical characteristics of steels subjected to frictional and combined thermomechanical treatments; application perspectives of the nanostructuring FT in innovative technologies.

The structural transitions and tribological properties of carbon-containing high-manganese aluminum-doped austenitic steels tested under different dry-conditions of sliding friction have been considered. The methods used for the structural study of steels are metallography, X-ray diffraction analysis, and transmission electron microscopy. It has been shown that the doping of the studied steels with aluminum taken in the amount of 1.2 wt % significantly increases their resistance to abrasive wear, and especially adhesive wear (up to 20 times). It has been hypothesized that the observed positive effect of aluminum on the wear resistance of austenitic steels is due to the activation of the planar dislocation sliding mechanism, which increases the dispersion of nanocrystals and, correspondingly, the hardness of the surface layer of steels under the conditions of nanostructuring rotational strain by means of friction.

This paper presents the results of a study of structural transformations and the main tribological properties (coefficient of friction and wear rate) of Al–2.2 Li and Аl–3.1 Сu–2.0 Li–0.1 Zr (wt %) alloys. Optical metallography and transmission electron microscopy have been used to examine the alloy structure after heating and friction. Tribological tests of the alloys in pair with steel are carried out by sliding friction using a pin-on-plate scheme during reciprocating motion of a sample. The sliding velocity is 0.07 m/s and the load is 294 N. Friction is carried out in air and in a nitrogen gas at room temperature. Alloying of the Al–Li alloy with copper (3.1 wt %) and zirconium (0.1 wt %) is shown to significantly increase the wear resistance, enhance the frictional hardening, and reduce the friction coefficient of the alloys. The positive effect of this alloying on the tribological properties of the Al–Li alloy is caused by friction-induced severe strain hardening. A high-strength nanocrystalline structure consisting of a mixture of matrix crystals and a metastable δ' (Al3Li) phase is formed in a surface layer to 10 μm thick. Planar dislocation slip is observed in both alloys. This sliding mechanism is assumed to be related to the low (f ~ 0.25) coefficient of friction of both alloys. Artificial aging carried out under different four regimes increases the hardness of alloys, but significantly reduces their resistance to wear. This paper offers an explanation for the effects obtained.

The effect of the preliminary high strain-rate deformation, performed via the method of dynamic channel-angular pressing (DCAP), and subsequent annealings on the tribological properties of a dispersionhardened Cu–0.092 wt % Cr–0.086 wt % Zr alloy has been investigated. It has been shown that the surfacelayer material of the alloy with a submicrocrystalline (SMC) structure obtained by the DCAP method can be strengthened using severe plastic deformation by sliding friction at the expense of creating a nanocrystalline structure with crystallites of 15–60 nm in size. It has been shown that the SMC structure obtained by the high strain-rate DCAP deformation decreases the wear rate of the samples upon sliding friction by a factor of 1.4 compared to the initial coarse-grained state. The maximum values of the microhardness and minimum values of the coefficient of friction and shear strength have been obtained in the samples preliminarily subjected to DCAP and aging at 400°С. The attained level of microhardness is 3350 MPa, which exceeds the microhardness of the alloy in the initial coarse-grained state by five times.

The paper studies the effect of high strain rate (105 s−1) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) under sliding friction on the evolution of the structure and properties of low-alloyed dispersion-hardened Cu–Cr–Zr alloys. It is shown that alloying of copper with chromium (0.09 – 0.14 %) and zirconium (0.04 – 0.08 %) microadditives changes mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: the cyclic character of structure formation associated with alternating of high-rate processes of fragmentation and dynamic recrystallization is changed to processes of fragmentation and partial strain aging resulting in precipitation of nanosized particles of the second-phase. The temperature-time regime of annealing (aging) of Cu–Cr–Zr SMC alloys processed by DCAP was established to improve the mechanical properties and electrical conductivity. In particular, for Cu–0.14 Cr–0.04 Zr SMC alloy it was shown that the optimal combination of microhardness (HV = 1880 MPa), electrical conductivity (80 % IACS), strength (σ0.2 = 464 MPa, σu = 542 MPa) and ductility (δ = 11 %) can be obtained by DCAP and aging at 400°C for 1 h. The improved mechanical properties of the alloys as compared to copper are associated with extra hardening caused by precipitation of Cu5Zr and Cr nanoparticles (5 – 10 nm) in the process of DCAP and aging. It was shown that low-alloyed Cu–Cr–Zr alloys possessed a high work-hardenability due to the methods of DCAP and SPD under sliding friction. By the example of Cu–0.09 Cr–0.08 Zr alloy it was established that the wear rate of samples with SMC structure obtained by the DCAP method decreased by a factor of 1.4 as compared to the coarse-grained state. It was also established that the combination of the treatment by DCAP, aging at 400°С, and SPD under friction of the alloy resulted in the formation of the friction-induced nanocrystalline structure with the grain size of 15 – 60 nm in the surface-layer material, which provided a high level of microhardness (3350 MPa) and low values of the friction coefficient (0.35).

Metallography, electron microscopy, and X-ray diffraction have been used to investigate structural transformations that take place in a 10-μm-thick surface layer in aluminum and Al–17% Si alloy under conditions of sliding friction and subsequent oxidation at 100 and 200°C for 1 h. Friction-induced deformation has been carried out at room temperature in air and at–196°C in liquid nitrogen by reciprocating sliding of a cylindrical indenter made of cubic boron nitride at a rate of 0.014 m/s and a load of 98 N. It is shown that deformation under these conditions forms nanocrystalline structures in the surface layer in aluminum and Al–17% Si alloy and increases their microhardness by a factor of 1.8–3.5. A high contact deformation and a high affinity of oxygen to aluminum and silicon cause the formation of anomalously supersaturated solid solutions of oxygen in aluminum and silicon in the surface layer of the alloy during friction. Oxidation at 100°C (1 h) of the deformed Al–17% Si alloy increases its microhardness due to the decomposition of anomalously supersaturated solid solutions of oxygen in aluminum and silicon and the formation of their oxides.

Structural changes occurring in the surface layer, up to 10 μm thick, of silumin (Al-17 % Si alloy) in the case of deformation under sliding friction and subsequent oxidation at 100 and 200 C for 1 hour are studied by metallographic analysis, X-ray diffraction analysis and electron microscopy.Frictional deformation was carried out in air at room temperature and in liquid nitrogen (at -196 C).Deformation under these conditions is shown to form a nanocrystalline structure in the surface layer of the Al-17 % Si alloy and to increase its microhardness by a factor of 1.8.In the alloy surface under friction, severe plastic deformation, as well as the high affinity of oxygen to aluminum and silicon, initiates the appearance of anomalously supersaturated solid solutions of oxygen in aluminum and silicon.Oxidation of the deformed Al-17 % Si alloy at 100 C for 1 hour increases its microhardness as a result of the decomposition of anomalously supersaturated solid solutions of oxygen in aluminum and silicon and the formation of their oxides.

Megaplastic deformation has been realized by sliding friction (or high-pressure torsion) on ion-plasma-nitrided surface of austenitic Fe-Cr-Ni steel. The deformation-induced dissolution of iron and chromium nitrides, the formation of secondary chromium nitride phases and the increase of depth of gradient-composition matrix pseudo-layer have been achieved under friction and subsequent annealing. A quasi-bimetallic foil with the largest dimension of deflection has been produced with the use of friction and subsequent annealing of the nitrided surface.

Structural transformations that occur in 110G13 steel (Hadfield) upon sliding friction in liquid nitrogen (–196°С) have been investigated by metallographic, electron-microscopic, and X-ray diffraction methods. The frictional action was performed through the reciprocating sliding of a cylindrical indenter of quenched 110G13 steel over a plate of the studied steel. A like friction pair was immersed into a bath with liquid nitrogen. It has been shown that the Hadfield steel quenched from 1100°С under the given temperature conditions of frictional loading retains the austenitic structure completely. The frictional action forms in a surface layer up to 10 μm thick the nanocrystalline structure with austenite grains 10–50 nm in size and a hardness 6 GPa. Upon subsequent low-temperature friction, the tempering of steel at 400°С (3 h) and at 600°С (5 min and 5 h) brings about the formation of a large amount (tens of vol %) of ε (hcp) martensite in steel. The formation of this phase under friction is supposedly a consequence of the reduction in the stacking fault energy of Hadfield steel, which is achieved due to the combined action of the following factors: low-temperature cooling, a decrease in the carbon content in the austenite upon tempering, and the presence of high compressive stresses in the friction-contact zone.

Purpose.Carburized chromium-nickel steels are widely used in the manufacture of drilling tools, gears, shafts, bushings and other parts which may be subjected to thermal effects and significant heating by friction at high speeds of sliding during operation.The aim of the paper is studying the possibilities of increasing the resistance of carburized chromium-nickel steel to thermal softening and heat seizure in the case of high-speed sliding friction by frictional treatment with sliding indenters.Methods.Steel 20KhN3A (wt.%: 0.20 C, 0.68 Cr, 2.90 Ni, 0.14 Mo) is subjected to carburizing, three heat treatments (quenching from 810 °C in oil; quenching and deep-freeze treatment at -196 °C; quenching and tempering at 180 °C) and frictional treatment using Al 2 O 3 or hard-alloy VK8 indenters.The structure and phase composition of the steel are studied by transmission electron microscopy and X-ray analysis.The effect of tempering temperature in a vacuum at 100 °C to 700 °C on the microhardness of the carburized steel surface and the tribological properties (wear rate and friction coefficient) during unlubricated friction on the steel disk with sliding speeds of 1.5 and 4.5 m/s is determined.Results: Friction treatment leads to the formation of a nanostructured surface layer and increases the hardness of the carburized surfaces from 7.3-9.5 to 10.1-11.6GPa.The presence of metastable retained austenite (25-30 vol.%) in low-tempered steel provides a significant increase in the depth of hardening during friction treatment as a result of the deformation decay of austenite and its transformation into high-strength strain-induced martensite.Nanostructuring frictional treatment improves the resistance to softening of carburized steel with different initial structures during heating to temperatures of 500-600 °C.Frictional treatment of quenched and lowtempered carburized steel enhances the heat wear resistance in tests with sliding friction at high speeds (over 2 m/s), when there is an intense in frictional heat, leading to the thermal softening of the surface.Nanostructuring frictional treatment provides not only a significant increase in wear resistance, but also a decrease in the friction coefficient at sliding speeds of 2.3-3.0 m/s.