Variation of the creep limit and structure of a welded joint in pT-3V titanium alloy under cyclic loading. Report 3

Abstract

The metallographic methods and microanalysis were used for investigation of the welded butt-joint specimens from PT-3V titanium alloys. The specimens were in initial state and after cyclic loading. Duration of loading was 5·104 and 1·107 cycles on a frequency of 35 Hz. The stress amplitude was 150 MPa; this value is below the endurance limit of weld material. The polished sections for investigations were cut out from a working part of specimens, which contains all zones of weld including the base metal. The plane of the polished section was disposed parallel to the surface of the weld and the axis of the polished section was located perpendicularly to the axis of the weld. The results show that migration of interstitial impurities takes place to boundaries of weld zones and regions of primary segregation of substitution elements. This process occurs under the action of cyclic loading that is followed by reduction of relative density of movable dislocations and length of dislocation segments, which are described in Communication 2. The mentioned causes lead to stabilization of weld material structure and enable an increase in the cyclic and static creep limits as is described in Communication 1. The physical processes, responsible for stabilization of dislocation structure and growth of creep stresses, are mainly completed after 5·104 cycles of loading.