O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

The main applied areas of tribology are:
- ensuring the required values of contact stiffness, wear resistance, durability of tribocouples (bearings, sealing devices, etc.) under specified operating conditions;
- reduction of energy losses due to friction (supports), ensuring high energy intensity (brakes, friction gears);
- saving materials by reducing their wear;
- Solving environmental problems.
Based on the results of fundamental research, new plastic and solid lubricants and oils, oil additives, tribotechnical materials, as well as surface modification methods are being developed. These include the application of various types of coatings, modification of the structure of the surface layer by deformation or transformation hardening, modification of the composition of the surface layer by thermochemical treatment in solid, liquid and gaseous media. In modern technology, combined methods of surface treatment are often used, in which both the chemical composition and structure of the surface layer change. Ion implantation is one of such methods.


LECTURE №3.
Working and contact surfaces of parts
3.1 Surface properties of parts
Surface - the interface between a solid and a liquid or gas, or two solids that differ in chemical composition or physical structure. The surface is an integral part of solids and often determines the performance properties of materials and structures. Surface concepts are found in many scientific disciplines and underlie friction-related technological processes and other technical applications of tribology.
Basic concepts
The surface of a part is a conventional name for the surface layer of a part, which differs in structure and physico-chemical characteristics from the material of the inner part of the part.
Friction is often a consequence of the action of adhesion forces. Adhesion is a surface phenomenon associated with the occurrence of adhesion between atoms and molecules of the surface layers of contacting bodies. Overcoming the forces of adhesion of the surfaces of two contacting surfaces of bodies occurs at the moment of the beginning of their mutual movement.
Adsorption is a change in the concentration of a substance at the interface. There are two types of adsorption: physical adsorption and activated or chemisorption.
In the crystal lattice of most metals, each atom is in coordination with 12 neighboring atoms, and on the surface - only with 6. Unsaturated bonds of the atoms of the surface layer determine the surface energy - an excess of the potential energy of a substance at the surface of a body compared to the energy in the bulk of the substance. The surface energy characterizes the activity of the atoms of the surface layer, its value is proportional to the size of the interface.
Excess surface energy also predetermines the chemical activity of the solid surface. Therefore, the surface of solids under normal conditions is never “clean”, but is always covered with corrosion products, adsorbed films, and other contaminants. It is very difficult to obtain a clean surface of a solid body. In the atmosphere, a freshly formed solid surface is covered with a monolayer of adsorbed gas in about hundredths of a second. In a vacuum at a pressure of p = 10 ^-4 Pa, this time is extended to 1 s. Further pumping ( p = 10 ^-8 Pa) only increases this time to several hours.
The surface of the part is characterized by geometric and physico-chemical parameters. They are mainly determined by the nature of the material from which the part is made, and the technological process of its processing. The surface condition affects the operational properties of the part: fatigue resistance, wear resistance, corrosion resistance, strength, etc.