METHODS FOR HARDENING AND IMPROVEMENT OF FATIGUE CHARACTERISTICS OF TITANIUM AND IRON-CHROMIUM NICKEL ALLOY SAMPLES

This work describes the procedure for determining residual surface stresses using the mechanical method and four methods of hardening samples. The urgency of the problem stated in the article is due to the fact that surface tensile stresses arising in the manufacture of highly loaded parts can significantly reduce the mechanical, resource and fatigue characteristics of products. The aim of the study was to harden samples of titanium and iron-chromium-nickel alloys to improve their strength, fatigue and resource characteristics and determine residual stresses by layer-by-layer removal of the studied layers by electrochemical etching. The determination of surface residual stresses was carried out mechanically using a measuring and calculation complex during continuous etching of the metal from the test surface of the sample, which made it possible to measure the residual stresses at different depths and determine the energy of the surface stress state. Residual stresses were calculated from the deformation of the remaining part of the sample with a change in the depth of the studied layers. The hardening of the samples was carried out in four ways, namely: ultrasonic hardening; ultrasonic curing + Rosler (vibration processing); Rosler (vibration processing) + ultrasonic curing; Rosler (vibration processing) + ultrasonic hardening. The results of the study showed that the surface of the products is a weaker area than the inside. After quenching, surface compressive stresses arise for all samples of titanium and iron-chromium-nickel alloys. The preferred case of hardening is the second (ultrasonic hardening + centrifugal hardening). The presence of residual compressive stresses in the outer layers of the products increases their fatigue limit by ≈20%. The results of the work can be used to manufacture products with high mechanical, resource and fatigue characteristics.