Transient creep behavior and dislocation cell structure development during creep-fatigue deformation of fully annealed Cu–Cr–Zr alloy. (November 2018)

• Record Type: Journal Article
• Authors: Deguchi, Masaya; Yamamoto, Koji; Tobe, Hirobumi; Sato, Eiichi
• Is Part Of: International journal of fatigue. Volume 116(2018)
• Page Start: 156
• Page End: 162
• Publication Date: 2018-11
• Subjects: Copper alloys -- Creep-fatigue -- Microstructures -- Cyclic softening -- Dislocations; JAXA Japan Aerospace Exploration Agency; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2018.06.027
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: In each cycle during the creep-fatigue test, either normal-transient or inverse-transient creep appeared. Dislocation cell structure developed during tensile creep, and then part of the cell walls was broken by the subsequent severe compression. When a much larger compressive stress was applied and a relatively high dislocation density was introduced, recovery was predominant rather than work hardening, resulting in the appearance of inverse-transient creep. A new mechanism of inverse-transient creep through recovery of dislocations is proposed. Abstract: Creep-fatigue tests of Cu–0.7Cr–0.09Zr (mass%) alloy, which include stress-holding-type creep and strain-controlled fatigue, were conducted at elevated temperatures. A simple creep test was also carried out in order to compare the results with the results of the creep-fatigue test. The creep strains accumulated during creep deformation in creep-fatigue and simple creep tests were 310% and 12%, respectively. Such a large difference was due to the stacking of normal/inverse-transient creep in the creep-fatigue test. A dislocation cell structure smoothly developed in the simple creep test, whereas the cell intermittently developed in the creep-fatigue test because compressive plastic deformation immediately after creep partly broke apart the cell walls and prevented the cell structure from smoothly developing. Compressive stresses necessary for −1.5% strain were changed as cycling progressed in the creep-fatigue test. A much higher compressive stress would introduce a much higher dislocation density immediately before creep deformation. At the start of creep, these dislocations recovered and their number gradually decreased, which resulted in the appearance of inverse-transient creep.