Selection of Nanostructured Zirconium Dioxide Crystals under Dry Friction against Molybdenum

The article considers the issues of contact interaction of nanostructured zirconium dioxide crystals with molybdenum coating on titanium-based alloy ВТ9. The following statement is substantiated: the best mechanical properties of crystals correspond to the total amount of 2.8% additives of stabilizing and doping rare earths elements. Antifriction properties of crystals under dry friction against molybdenum are investigated. Tribological testing was performed on a reciprocating friction gauge simulating the operation of a plunger in a cylinder. The high scoring resistance of the friction couple under study was experimentally proved; the friction coefficient did not exceed 0.07. On the basis of the study performed, the friction couple is defined as promising for increasing the lifetime and reliability of friction units for hydraulic equipment and fuel pumps.

Tribological Properties of Sapphire under Dry Friction against Chromium and Zirconium Ceramics

The issues of sapphire friction and wear in contact with chrome steel and zirconium ceramics are discussed in this article. The kinetic microindentation method is used to study the mechanical properties of sapphire in frictional contact in modelling experiments on the indentation of a Vickers indent. Taking into account the anisotropy of the mechanical properties of sapphire, the influence of the load and orientation of the indent on the modulus of elasticity and hardness is analyzed. It has been established that, under dry friction conditions it is promising the use of zirconium ceramics in the supports of devices operating under conditions in which the use of lubricants is impossible. The possibility of using a friction couple of sapphire-zirconium ceramics in friction units operating in open space is noted.

A DISCUSSION ON THE PHYSICAL INTERPRETATION OF MEASUREMENTS OF TRIBOLOGICAL WEAR

Physical sense and practical significance of major measurements of tribological wear are analysed here. Definitions and methods of assessing these measurements are proposed on the basis of the laws of energy and mass conservation. Contributions of energy and displacement of particular friction forces corresponding to each element of a friction couple are addressed. Energy expenditure that causes wear is introduced into the definition of wear resistance. Planning and thermodynamic analysis of a tribological experiment and the application of thermodynamic concepts and quantities to the description and the interpretation of results are recommended. The author believes application of wear measures that have an unequivocal physical interpretation will limit problems with the incomparability and the irreproducibility of tribological results and issues with transferring them to real objects.

Elaboration of a lubrication system for universal spindle hinges of rolling mills

The experience of running drives of most of heavy-duty rolling mills shows that the designs of universal spindles with blade hinges under conditions of increased alternating loads are most acceptable comparing with other spindles types. Open friction surfaces are the drawbacks of these types of spindles, which complicate the matter of continuous supply of lubrication. Perfected effective system of forced lubrication of rolling mill spindles hinges proposed. The facility for their lubrication has a bearing support of balancing design, spindle, in radial holes of which spring-loaded plungers are installed in a diametrically opposite order. Besides, the facility has suction valves and force valves installed in the spindle axial holes, connecting with the radial ones. A methodology proposed to select the eccentricity of the internal cylindrical surface of the bearing support of the spindle hinge, the axis of which is located eccentrically relative the spindle rotation axis. A calculating scheme and a mathematical model of the process of lubrication supply into joints of rolling mill spindle hinge elaborated. A differential equation of lubrication motion in the conical slot of the hinge between a blade and insertions drawn up. Parameters of hydrodynamic motion of lubrication in the conical slot established. Modes of the lubrication motion in the conical slot between roller blade and hinge insertion determined. Based on experience of operation of friction couple bronze-steel, a lubrication for rolling mills universal spindles proposed. To improve the operation characteristics of hinges based on the friction couple bronze-steel, a thick lubrication having antifriction properties namely based on oils with additives ИП-10, КП-10 and ДФ-11 proposed. Dependence of pressure distribution along the length of the hinge conical slot presented for various lubrications of low viscosity (ИП-10 + ДФ-11) and high viscosity (КП-10 + ДФ-11). The quality effect of the speed of roller blade movable wall on distribution of speeds of lubrication layer motion over the height of the hinge conical slot for comparatively low and comparatively high boundary speeds demonstrated.

Elaboration of methodological base of quality evaluation of nitrogenization of steels of tribotechnical application

Nitrogenization is one of most spread methods of surface hardening of critical parts of machines. To elaborate methodological base of structural evaluation of quality parameters of nitrogenized surface layers of sliding friction couple by methods of X-ray structural analysis and tribotechnical tests, structure and performance properties of nitrogenized structural steels and alloys were studied. Namely pearlitic and martensitic steels (40Х, 38Х2МЮА, ВКС-7), model iron-based alloys with a BCC lattice, steels alloyed by Cr, Mo, Al in amount of up to 4 % (at.), iron-based alloys with FCC lattice, alloyed by Ni (29 % (at.)), Cr, Al, Ti in the amount of up to 4 % (at.), as well as austenitic high-chromium steels 12Х18Н10Т, 08Х16Г15Н5МАФ, steel 16Х3НВФМБ-Ш and high manganese steel 40Г14Н8Х3Б1. The surface saturation of the samples was made by gas, ion, gas-baric nitrogenizing and by ion implantation of nitrogen. The sum of macroscopic (tribotechnical) and microscopic (structural) indicators was evaluated, which characterize the physics and mechanics of friction process at various hierarchical levels. This sum of indicators also provides information on properties of antifriction coatings, modified layers and performance ability of the friction couple under conditions of contact deformation. It was established, that increasing of the nitrogenizing temperature from 540 up to 700 °C for alloys with a ferrite matrix results in a decrease of the hardness of the surface layer and physical broadening of X-ray lines. In this case, the relative wear resistance reaches maximum at 620 °C. For alloys with an austenitic matrix, an increase of hardness, broadening of X-ray lines and relative wear resistance occurs with increasing of temperature. These parameters grow in the sequence Fe−Ni, Fe−Ni−Al, Fe−Ni−Cr, Fe−Ni−Ti. Gas-baric nitrogenizing enables to obtain higher performance characteristics of parts (wear resistance and contact strength). Based on the generalization of the results of experimental studies of nitrogenized steels and alloys with various compositions and various crystal lattices, the most significant characteristics of the structural state and properties of near-surface microvolumes were established, that affect the level of surface destruction during friction, as follows: the size of the alloying element nitrides particles, the distance between them, the micro-deformation of the crystal lattice of the solid solution, the values of the physical broadening of the X-ray lines of the solid solution, its hardness and the change in hardness during friction, the plasticity reserve. Generalized criteria for the properties of the surface layer, taking into account the characteristics of the structure and properties of the nitrogenized layer and the zone of surface contact plastic deformation elaborated. Also methodological foundations for the structural assessment of the quality parameters of the surface layers of sliding friction couples elaborated. Bench tests have confirmed the effectiveness of the application of the generalized structure parameter and properties of surface layers for the selection of materials for the friction unit. The formulated conditions are recommended for optimizing the nitrogenizing technological process from the standpoint of tribology and choice of materials for friction couple.

IMPROVED DESIGN OF A HEAD OF A TOTAL HIP REPLACEMENT

For the first time, the design of a modular ceramic head of a total hip replacement (THR) has been developed, which has the properties of a metal in join with the stem neck and the properties of a ceramic on the bearing surface of a friction couple. This is achieved by creating a low-cost, low-toxic, strong connection of alumina or zirconium ceramics and a titanium alloy to obtain a soldered joint that is efficient in human synovial fluid. With the help of finite element analysis, a qualitative and quantitative assessment of the strength and rigidity of the proposed head design has been made. Also shown is an image of a finished soldered head made of alumina ceramic with a sleeve made of titanium alloy VT1-0.

Frictional effect of spherical convex textured rigid bodies sliding on smooth PDMS

Surface texturing was applied to flexible friction couples to improve their tribological behavior. Spherical convex texture was fabricated on the surface of photosensitive resin by stereolithography (SLA), the friction coefficient between the textured resin sample and smooth polydimethylsiloxane (PDMS) under the conditions of low sliding speed and dry friction was measured using a self-made frictional test bench. It was found that surface texture is capable of reducing friction at low applied normal load compared with the non textured friction couple, as well as increasing friction at high load, in addition, smaller texture radii tend to increase friction. At last, the friction mechanism of the textured flexible friction couple was discussed by establishing a mechanical model.

Effect of organic acid concentration in lubricant on tribological characteristics of friction couple

Introduction.The possibility of using monocarboxylic acids as a lubricant composition additive, and the effect of their concentration in lubricant on the evolution of the friction factor of a brass-steel couple, as well as the morphology of the film surface under friction is considered. The work objective is to study the effect of the concentration of carboxylic acids in the lubricant composition on the evolution of the friction factor of copper – steel alloy.Materials and Methods.Tribological studies of a brass-steel friction couple in aqueous solutions of monocarboxylic acids with the concentrations of 0.025; 0.05; 0.1; 0.2; 0.5 mol/l are carried out. Using scanning electron microscopy, we have studied the morphology of the servovite film surface that is formed on a steel disk after frictional interaction of a brasssteel couple in aqueous solutions of acids with the concentration of 0.1 mol/l.Research Results.Tribological characteristics of the brasssteel tribocoupling in aqueous solutions of carboxylic acids of various concentrations are studied. The optimum acid concentration in the lubricant composition is specified. Herewith, a selective transfer and a wearless friction regime are implemented under friction of the brass 59–steel 40X couple. A decrease in the friction ratio to 0.009 and 0.007 is found out under friction in aqueous solutions of valeric and caproic acids, respectively. The formation of an anti-friction film on the steel surface is identified through the scanning electron microscopy. It is established that the film formed in an aqueous solution of caproic acid has a denser structure in comparison with the film formed under friction in aqueous solutions of butyric and caproic acids.Discussion and Conclusions.Thus, the tribological studies of a brass-steel friction couple in aqueous acid solutions show that the optimum molar acid concentration in the lubricant composition is 0.1 mol/l. At this acid concentration, the values of the friction factor characteristic of the wearless mode are attained.

A wear model for subrough surface contacts of martensitic steels

This article includes an analysis of techniques for determining wear of contact areas to show two lines of wear research – due to deformations and adhesion forces. It has been established that surface subroughness is not presently taken into account in calculations of wear despite the fact that this surface property is of increasing research interest. The paper aims to develop a mathematical model of wear for subrough surface contacts in the context of deformation and theories of adhesion. Mathematical wear modelling for subrough surfaces is based on studies on causes of their formation due to phase and structural heterogeneity of the material. The article considers contact interaction at the level of surface subroughness; physics of interaction of contact areas at the level of surface subroughness; a mathematical model of deformation and adhesive wear for subrough surface contacts of martensitic steels; some analytical dependences of the theoretical model for a body-centred tetragonal lattice. Analysis of the theoretical concepts shows that wear of subrough surface contacts depends largely on the deformation component, while the adhesive component is significant only during the ‘bedding-in’ period for a friction couple. The materials of the article can be used to calculate the wear for contact areas at the level of surface subroughness.