INCREASE OF WEAR RESISTANCE OF Сr18Ni10Ti STAINLESS STEEL BY METHOD OF ELECTRIC-SPARK ALLOYING WITH ELECTRODES OF REFRACTORY METALS AND GRAPHITE

The article presents the results of wear testing of stainless steel Cr18Ni10Тi treated with electrodes made of refractory metals and graphite by the method of electric-spark alloying. It was established that all electrospark coatings had a higher wear resistance than the Cr18Ni10Ti uncoated steel. Wear resistance of coatings was increased in the direction Mo + GraphiteTi + Ni W + Graphite Ti + Al + Graphite. X-ray diffraction analysis showed that molybdenum, tungsten, titanium carbides and other solid materials such as titanium nitride and nickel-titanium intermetallide are formed on the doped steel surfaces, which increased microhardness from 4.9 to 8 times and wear resistance from 1.63 to 29 times.

TRIBOTECHNICAL CHARACTERISTICS OF CARBON-BEARING LUBRICANTS

The development of technology for manufacturing nanostructured substances in amounts that could suffice an interlaboratory research is a high priority task for the implementation of nanoproducts. The ultra dispersiblis clusters of synthetic carbon are used as on extra component in polymeric materials. The substances have a high dispersibility and activity of the surface. To study properties of mineral oils, modified ultra dispersiblis clusters of synthetic carbon is of interest. The present activity is devoted to the research of the modifying influence of ultra dispersiblis clusters of synthetic carbon on viscosity of the characteristic of mineral oils and their stability at various temperatures. In the preparation of diamond secondary suspensions not only statistic average sizes of particles should be taken into consideration, but also polydispersity parameters of nanodiamond particle population too.

EXPERIMENTAL STUDY OF THE INFLUENCE OF RUBBER PROPERTIES ON SLIDING FRICTION IN DRY CONTACT

This study is devoted to experimental research of rubber friction in sliding contact with rough surface. Influence of pressure, bulk temperature and sliding velocity on friction coefficient in dry conditions is analysed for two rubber compounds with different viscoelastic properties. Grosch method of master curves construction is used for analysing of friction measurements. Such analysis is performed for different temperatures and velocities at constant normal load. The obtained friction master curves are combined into a single friction map. The friction maps demonstrate the influence of viscoelastic properties of rubber on friction coefficient in dry rough contact. Also friction maps show the influence of adhesion and hysteresis contributions into friction coefficient for different rubber compounds.

PROBING ATOMIC LEVEL INTERACTIONS IN NI NANORODS AND AFM CANTILEVER USING ATOMIC FORCE MICROSCOPY BASED F–D SPECTROSCOPY

Atomic force microscopy based force-displacement spectroscopy is used to quantify magnetic interaction force between sample and magnetic cantilever. AFM based F–D spectroscopy is used widely to understand various surface-surface interaction at small scale. Here we have studied the interaction between a magnetic nanocomposite and AFM cantilevers. Two different AFM cantilever with same stiffness but with and without magnetic coating is used to obtain F–D spectra in AFM. The composite used has magnetic Ni nanophase distributed uniformly in an Alumina matrix. Retrace curves obtained using both the cantilevers on magnetic composite and sapphire substrate are compared. It is found for magnetic sample cantilever comes out of contact after traveling 100 nm distance from the actual point of contact. We have also used MFM imaging at various lift height and found that beyond 100nm lift height magnetic contrast is lost for our composite sample, which further confirms our F–D observation.

STUDY OF THE EFFECT OF H2O2 USED IN WHITENING TREATMENTS ON HUMAN ENAMEL WEAR RESISTANCE

Tooth whitening treatments are based on the application of bleaching agents on the teeth surface, which can impair teeth health, due to its effect on enamel properties. The present work has the purpose of studying the effect of pH of H2O2 solutions on wear resistance of teeth. Friction coefficient, enamel microhardness, morphology and topography were also evaluated to better understand the induced changes. Three pH values (2, 4 and 6) of H2O2 solution were tested. First, human molars and premolars were disinfected, polished, cut in four equal pieces and darkened in a black tea solution. After, the teeth samples were bleached in 30% H2O2 solution with the different pH values. Vickers microhardness, surface roughness and wear measurements were performed before and after bleaching. The results showed that the enamel wear resistance depends on the solution pH: the lowest wear resistance was obtained for the sample bleached with H2O2 at pH 2.

FRICTION AND ADHESION OF MONOMOLECULAR COATINGS

The paper presents data on measurements of friction and adhesion forces of silicon ball and silicon plate covered by DDPO4 (dodecylphosphoric acid ester), ODPO4 (octadecylphosphoric acid ester), SEBS (poly[styrene-b-(ethylene-co-butylene)-b-styrene]) and OTS (octadecyltrichlorsilane) and others. Tests were performed with reciprocating microtribometer and contact adhesion meter. The experimental results have shown, that coefficient of friction, between a silicon ball and silicon substrates modified by the monomolecular films, are varied in the range 0.05…0.25, with wear-resistance from 20 to 2000 cycles. An ambiguous correlation was found between friction and contact adhesion forces of investigated surfaces.

EFFECT OF THE TEMPORAL PROFILE OF THE FRICTION POWER ON THERMAL STRESSES DURING BRAKING

In this paper influence of the temporal profile of frictional heat flow density on the distributions of temperature and thermal stresses in a friction element during single braking was investigated. For this purpose a one-dimensional boundary-value heat conduction problem for a half-space body (which simulates a brake rotor) heated on the outer surface by the heat flux with different intensities was formulated and solved by means of Duhamel’s theorem. Solutions were obtained for ten temporal profiles of specific friction power, which are proportional to the intensity of frictional heat flow. Based on received transient temperature fields and Timoshenko’s model of thermal bending of a thick plate with unfixed edges, the analytical distributions of quasi-static thermal stresses in a friction element were found. Achieved solutions allow conducting numerical analysis of the distributions of temperature and thermal stresses in a brake rotor with different time profiles of the specific friction power.

CRITERIA OF PLASTICITY IN CONTACT OF THE SPHERICAL ASPERITIES OF THE ROUGH SURFACE

It is assumed that the influence of the remaining contacting asperities is equal to the action of the uniform loading qc outside the asperity contour. Three parameters are suggested as possible criteria of occurrence of plastic deformation in the subsurface layer of contact of a single asperity: critical value εc in which the equivalent stress is equal to the yield point σy; the relative contact area ηip at which plastic deformations occur; the ratio of the maximum pressure at the contact area to the yield point σy. For single asperities, the stability of the relative contact area at which plastic deformation begins is indicated. The criteria for plasticity characterizing respectively the onset of plastic deformation in the near-surface layer ηp ∗ and on the contact surface η̅p ∗ are proposed. The values of the criteria do not depend on the loading conditions and are determined by the complex parameter fy characterizing the microgeometry of the asperities and the mechanical properties of the material.

ENGINEERING AND RESEARCH OF WEARABILITY COATING ON THE BASIS OF HIGH-STRENGTH STEEL

Methods of the optical metallography, TEM, SEM- technique, X-ray analysis, tests for hardness and wear resistance, are resulted results of research and optimization of structure and properties facing materials with austenite-martensite structure and with various quantity of strengthening phases. The maintenance in facing material austenite 38% is shown, that, martensite 32% and strengthening phases of 30% provide the highest relative wear resistance  = 5.89 and hardness HRC 61.