Microstructural Mechanisms during Dynamic Globularization of Ti-6Al-4V Alloy

抄録

The microstructural mechanisms during dynamic globularization were investigated for ELI grade Ti-6Al-4V alloy with initial martensite microstructure. For this purpose, compression tests were carried out isothermally at 1073 K up to the strains of 1.0 and 1.4 with the strain rates ranging from 10⁻³ s⁻¹ to 1 s⁻¹. Fully dynamically globularized specimen exhibited higher Vickers hardness values due to the finer grain size and higher dislocation density compared to the conventionally produced one, i.e., partial dynamic globularization by subsequent annealing. The strain rate sensitivity (m) values of the flow stresses at initial stage (ε≈0.05) and final stage (ε≈1.4) of deformation were ≈0.15 and ≈0.36, respectively, leading to the conclusion that deformation was controlled by dislocation glide/climb at low strains and grain boundary sliding at high strains. Also, microstructural evolution during dynamic globularization was rationalized by examining the microstructures associated with kinking and fragmentation of lamellar plates.