L. G. Korshunov

Effect of severe plastic deformation on the microstructure and tribological properties of a babbit B83

The effect of severe plastic deformation carried out at room temperature by the methods of equal-channel angular (ECA) pressing and surface friction treatment (SFT) on the microstructure, rate of wear, and friction coefficient of a babbit B83 (11.5% Sb, 5.5% Cu, Sn for balance) has been investigated. It has been shown that severe plastic deformation that leads to a drop in the grain size of the babbit to 100–300 nm and to a strong refinement of particles of intermetallic phases (SnSb, Cu3Sn) causes a considerable (twofold-fourfold) reduction in the rate of wear and a decrease in the friction coefficient of a steel-babbit pair under test conditions with lubrication at small (0.07 m/s) and enhanced (4.5 m/s) sliding velocities. As was shown by structural investigations performed with the use of scanning electron microscopy, this positive influence of severe plastic deformation on the tribological properties of the babbit is connected with the formation on the deformed-babbit surface of a developed porosity, which improves conditions for lubrication of the babbit-steel friction pair due to the action of the self-lubrication effect and thereby favors the retention of a stable regime of boundary friction of this pair. The formation of porosity is a result of the accelerated spalling of hard brittle intermetallic particles of SnSb and Cu3Sn from the friction surface of the deformed babbit, which is caused by weakening and loss of the bonding of these particles with the plastic matrix (α solid solution based on tin) in the course of severe plastic deformation of the babbit. At the same time, under the conditions of dry sliding friction of the babbit-steel 45 pair, when a fatigue mechanism of wear of the alloy under consideration predominantly develops, this plastic deformation yields an approximately 1.6-fold increase in the rate of wear of the babbit. This increase is mainly due to numerous defects (microcracks) that are introduced into the babbit structure upon its severe plastic deformation and reduce the resistance of the surface layer of this material to the fatigue mechanism of wear.

Effect of strengthening friction treatment on the chemical composition, structure, and tribological properties of a high-carbon steel

The structure and chemical composition of nanocrystalline layers formed on the surface of a steel U8 with 0.83 wt % C (quenched, as well as quenched and tempered at 200°C) under the conditions of frictional loading by a hard-alloy indenter in different media (gaseous and liquid nitrogen, air) have been investigated by the methods of transmission electron microscopy, X-ray diffraction analysis, nuclear reactions, Rutherford back scattering, and wave- and energy-dispersive microanalyses. Maximum levels of defectiveness (high density of dislocations and point defects) and microhardness of the nanocrystalline structure have been attained upon friction treatment of the low-temperature tempered steel in a liquid-nitrogen medium because of deformation localization in a thin surface layer, intensification of deformation-induced dissolution of the ɛ carbide phase, and saturation of the layer with nitrogen and oxygen atoms, the latter dissolved in the liquid nitrogen as an impurity. A comparative analysis of the in-depth distribution of microhardness in frictionally strengthened surface layers has been performed for the steel with initial structures of tetragonal (untempered) and low-tempered (tempered at 200°C) martensite. A markedly larger depth of strain hardening has been attained upon friction treatment in the quenched untempered steel due to effective development of deformation-induced dynamic aging of high-carbon martensite even at small deformations. It has been established that the strengthening upon deformation of the surface by a sliding indenter exerts a positive influence on the tribological properties (wear rate and friction coefficient) of the steel under the conditions of frictional heating of different intensity.

Influence of the stressed state of the zone of friction contact on the formation of the structure of a surface layer and tribological properties of steels and alloys

An investigation has been performed of the influence of contact stresses, which appear in the zone of friction of iron-manganese alloys with 16.9–40.5 wt % Mn, wear-resistant high-manganese austenitic steels, and carbon steel U13, on the phase composition, structure, and strengthening of surface layers of these materials under conditions of dry friction at small (0.03 and 0.07 m/s) sliding velocities, when the frictional heating of the surface layer of the samples is virtually absent. A quantitative estimation of the arising compressive contact stresses (pressures) has been carried out. It is shown that the value of the compressive contact stresses approximately corresponds to the values of microhardness measured on the friction surface of the materials investigated. These compressive contact stresses initiate the occurrence a γ-ɛ martensitic transformation in the iron-manganese alloys with 16–40% Mn, which is characterized by a negative volume effect, but impedes the development of the ɛ-α and γ-α martensite transformations (in austenitic steels) which occur with an increase in the specific volume. The stresses in question favor the formation of nanocrystalline structures in a thin (≤10 μm thick) surface layer of friction steels and alloys. The contact tensile stresses following the contact compressive stresses initiate the formation and propagation of microscopic cracks in the surface layer of the friction materials, and activate the development of martensitic ɛ-α and γ-α transformations in this layer. It is shown that the structural and phase transformations initiated by contact stresses exert a substantial effect on the microhardness, friction coefficient, and resistance to adhesive wear of the steels and alloys under study.

Features of electromagnetic methods for testing the wear resistance of medium-carbon structural steel subjected to laser or bulk hardening and tempering

Features of applying attachable eddy-current transducers of two types (with a flat end surface and a protruding ferrite rod core with localities 5–6 and 3–4 mm in diameter, respectively) for testing the structural state, hardness, and abrasive wear resistance of structural steel 45X (0.45 mass % C and 0.85% Cr), which was hardened under the action of continuous laser radiation, have been studied. The feasibilities of the eddy-current and coercimetric techniques for evaluating the wear resistance of a medium-carbon steel subjected to laser or bulk hardening and tempering in the temperature range 75–600°C have been studied.

Structural transformations, strengthening, and wear resistance of titanium nickelide upon abrasive and adhesive wear

Wear resistance and structural transformations upon abrasive and adhesive wear of titanium nickelide Ti49.4Ni50.6 in microcrystalline (MC) and submicrocrystalline (SMC) states have been investigated. It has been shown that the abrasive wear resistance of this alloy exceeds that of the steel 12Kh18N9 by a factor of about 2, that of the steel 110G13 (Hadfield steel), by a factor of 1.3, and is close to that of the steel 95Kh18. Upon adhesive wear in a testing-temperature range from −50 to +300°C, the Ti49.4Ni50.6 alloy, as compared to the steel 12Kh18N9, is characterized by the wear rate that is tens of times smaller and by a reduced (1.5–2.0 times) friction coefficient. The enhanced wear resistance of the Ti49.4Ni50.6 alloy is due to the development of intense strain hardening in it and to a high fracture toughness, which is a consequence of effective relaxation of high contact stresses arising in the surface layer of the alloy. The SMC state produced in the alloy with the help of equal-channel angular pressing (ECAP) has no effect on the abrasive wear resistance of the alloy. The favorable effect of ECAP on the wear resistance of the Ti49.4Ni50.6 alloy takes place under conditions of its adhesive wear at temperatures from −25 to +70°C. The electron-microscopic investigation showed that under conditions of wear at negative and room temperatures in the surface layer (1–5 μm thick) of titanium nickelide there arises a mixed structure consisting of an amorphous phase and nanocrystals of supposedly austenite and martensite. Upon friction at 200–300°C, a nanocrystalline structure of the B2 phase arises near the alloy surface, which, as is the case with the amorphous-nanocrystalline structure, is characterized by significant effective strength and wear resistance.

Effect of frictional heating on the surface-layer structure and tribological properties of titanium nickelide

The effect of frictional heating (whose intensity was varied at the expense of changes in the sliding velocity from 0.35 to 9.00 m/s) on the rate of wear, friction coefficient, friction thermopower, structure, and microhardness of the Ti49.4Ni50.6 alloy in a microcrystalline (MC) state with grains 20–30 μm in size and in a submicrocrystalline (SMC) state with grains 300 nm in size has been investigated. The tribological tests were conducted under the conditions of dry sliding friction in air using the finger-disk (made of steel Kh12M, hardness HRC = 63) scheme at a normal load of 98 N. Due to the frictional heating, the temperature in the surface layer 0.5 mm thick of the samples changed from 150–200 (at a sliding velocity of 0.35 m/s) to 1100°C (at a velocity of 9 m/s). The alloy structure has been studied with the help of metallographic and electronmicroscopic (scanning and transmission microscopy) methods. It has been shown that the rate of wear of the titanium nickelide in the MC and SMC structural states is more than an order of magnitude lower than in the 12Kh18N9 steel and several times less than in the 40Kh13 steel. The fracture of the friction surface of the titanium nickelide occurs predominantly by the fatigue or oxidation-fatigue mechanisms, which are characterized by a relatively low wear rate, whereas the 40Kh13 and 12Kh18N9 steels show a tendency to intense thermal adhesive wear (seizure) at velocities higher than 0.35 m/s. It has been shown by the electron-microscopic investigation that nanocrystalline structures consisting of crystals of the B2 phase, oxides of the TiO2 type, and some amount of martensite B19′ are formed in the process of friction in the surface layer of the titanium nickelide. It has been concluded that an enhanced wear resistance of the titanium nickelide is caused by the high heat resistance (strength) and high fracture toughness of the nanocrystalline B2 phase and by the presence of high-strength thermostable oxides of the TiO2 type formed upon friction.

Formation of a wear-resistant nanocrystalline layer strengthened by TiO2 (Rutile) particles on the surface of titanium

The effect of a thermomechanical treatment including severe plastic deformation under dry sliding friction conditions and subsequent heating in air to 350–650°C with further holding for 1 h on the structure and wear resistance of commercial titanium of grade VT1-0 has been studied. It has been shown that the deformation by friction leads to the formation of a nanocrystalline structure with α crystals 20–100 nm in size in a surface layer of titanium of about 10 μm thick. The heating of titanium deformed by friction at temperatures of 450–650°C for 1 h in air leads to the formation in the surface layer of this material ∼10 μm thick of nanocrystalline particles of the titanium oxide TiO2 (rutile), the volume fraction of which reaches tens of percents, while the dimensions are ∼10 nm. The presence in the surface layer of titanium of a nanocrystalline two-phase (α-Ti + rutile) structure leads to a significant increase in the wear resistance of the VT1-0 titanium in pair with steel 40Kh13. This is explained by the enhanced strength of the arising nanocrystalline layer and its positive influence (as of a transition layer) on the reduction of the level of internal stresses that exist at the interface between the titanium oxide TiO2 and the host metal.

Influence of prolonged heating on thermal softening, chemical composition, and evolution of the nanocrystalline structure formed in quenched high-carbon steel upon friction treatment

Methods of transmission and scanning electron microscopy, X-ray diffraction analysis, micro-hardness, and wavelength dispersive X-ray microanalysis have been used to investigate the changes (in the process of vacuum treatment for 10–1200 min at temperatures of 350–550°C) in the structure, microhardness, and chemical composition of the surface layers of steel U8 (0.83 wt % C) in the initial quenched state and after friction treatment in the argon medium under the conditions of sliding friction using a like spherical indenter-flat sample pair. It has been shown that the layer nanostuctured by friction treatment possesses an enhanced resistance to thermal softening compared with the undeformed quenched steel, not only upon relatively short heating (1–2 h), but also prolonged heating (to 20 h) at temperatures of 350, 450, and 550°C. This is due to the retention of predominantly nanocrystalline structure in the deformed layer upon the prolonged heating to a temperature of 350°C by retarding the processes of the formation of carbide particles and recovery in the α phase and by decelerating the development of recrystallization, including the absence of anomalous growth of separate recrystallized grains upon prolonged high-temperature holdings. After vacuum annealing for 10–1200 min at a temperature of 350°C, an increase was revealed in the carbon concentration by 0.2–0.4 wt % in a layer up to 1 μm thick on the surface of quenched eutectoid steel deformed by friction action.

Modification of the titanium nickelide surface using frictional treatment and subsequent heating in air

The effect of a combined treatment including severe plastic deformation under the conditions of dry sliding friction and heating in air to temperatures of 300–480°C (holding for 1 h) on the structure and wear resistance of the surface layer of the Ti49.4Ni50.6 alloy has been investigated. It has been shown that this frictional treatment results in an amorphous-nanocrystalline structure in the surface layer (of thickness to 10 μm) of the Ti49.4Ni50.6 alloy. Heating to 300°C brings about the complete crystallization of the amorphous phase; as a result, the structure of the deformed surface layer of the alloy becomes single-phase, consisting of nanocrystals of the B2 phase. At 400°C, in this deformed surface layer there arises a nanocrystalline oxide (TiO2) phase whose amount reaches tens of volume percent. The sizes of crystals of the B2 phase and oxide TiO2 are in the range of 1–50 nm. The arising two-phase (B2 + TiO2) nanocrystalline structure is located just below the oxide TiO2 film, which is less than 1 μm thick. With an increase in the heating temperature to 480°C, the deformed surface layer under consideration retains the nanocrystalline two-phase (B2 + TiO2) structure, but an increase in the amount of the oxide phase and a decrease in the microhardness of this structure are observed. In some cases (heating at temperatures of 430 and 450°C), the presence of the two-phase (B2 + TiO2) nanocrystalline surface layer leads to a noticeable (to ∼25%) enhancement in the adhesive wear resistance of the Ti49.4Ni50.6 alloy upon sliding friction in pair with steel 40Kh13.

Effect of laser quenching and subsequent heat treatment on the structure and wear resistance of a cemented steel 20KhN3A

The martensite-austenite structures that are formed under the action of continuous laser irradiation in the 20KhN3A steel subjected to various regimes of cementation have been studied by metallography, electron microscopy, and X-ray diffraction. It has been established that a decrease in the amount of retained austenite in the laser-quenched structures from 40–90 to 5–35 vol % resulted from cold treatment at −196°C exerts only a small (within 10%) effect on the abrasive wear resistance of the cemented steel; the effect is negative upon microcutting and positive upon microscratching. An increase in the carbon concentration from 0.8 to 1.2 wt % in the martensite-austenite structures that are formed in the cemented steel under the action of laser irradiation and upon cold treatment leads to changes in the abrasive wear resistance by no more than 10–13%. The presence of 20–40 vol % metastable retained austenite retards the decrease in the abrasive wear resistance of the quenched steel upon subsequent low-temperature tempering. It has been shown that the laser quenching and additional cold treatment positively affect the resistance of rolling bearing units of drill bits to contact-fatigue fracture.