ПІДВИЩЕННЯ АДГЕЗІЙНОЇ МІЦНОСТІ ПОКРИТТІВ ПРИ УЛЬТРАЗВУКОВОМУ ШЛІФУВАННІ

Abstract

Gas-thermal spraying of self-fluxing, ceramic and other powder materials is one of the effective methods of restoring and strengthening machine parts. The paper describes the gas-thermal spraying methods. The reason for the appearance of macrodefects during mechanical processing in the form of microcracks and burns, and during the operation of parts -in the form of delamination of coatings, is the instability of the structure and physical and mechanical properties of coatings, as well as insufficient adhesive strength and significant residual stresses. In turn, the adhesion strength of coatings depends on the level of surface activation of the base material. The analysis of methods of activation of the surface of the part was performed. Different methods are used: shot blasting or sandblasting, spraying the sublayer, forming a "torn" cut. They all have different performance. The main factors that affect the adhesive and cohesive strength are the incomplete connection of the particles forming the coating, the structure of the coating and the residual internal stresses of the coating. The interaction of adhesion strength and residual internal stresses determines the workability of the coating. As the residual internal stresses increase, the adhesive strength decreases. One of the effective methods of reducing residual internal stresses in coatings is the action of ultrasonic vibrations. The paper presents the results of experimental studies of the influence of the amplitude of ultrasonicvibrations on the adhesionstrength of coatings. Adhesive strength was determined by the method of breaking off a conical pin. The authors gave a formula for calculating the adhesion strength of coatings. The analysis of the results of the experiment showed that the replacement of static grinding with vibration significantly increases (by 15-20%) the adhesive strength. This phenomenon is determined by the action of two factors: a decrease in the level of damage to the coating; reducing the yield point of the coating material. It should be noted that the possibility of such a transition is due to the reduction of the fragility criterion to values less than 1. The paper provides a formula for calculating the value of the fragility criterion of coatings, as well as a formula for calculating the length of a critical microcrack. Knowing the length of the critical microcrack makes it possible to diagnose coatings for their performance.