Surface nanocrystallization of body-centered cubic beta phase in Ti–6Al–4V alloy subjected to ultrasonic surface rolling process

• Published in: Surface & coatings technology Vol. 361; pp. 35 - 41
• Main Authors: Ao, Ni, Liu, Daoxin, Zhang, Xiaohua, Liu, Chengsong, Yang, Jing, Liu, Dan
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.03.2019; Elsevier BV
• Subjects: Beta phase; Deformation mechanisms; Dislocation; Dislocation density; Entanglement; Gradient nanostructure; Grains; Nanocrystallization mechanism; Nanocrystals; Nanostructure; Skin pass rolling; Surface layers; Thickness; Titanium alloy; Titanium base alloys; Twinning; Ultrasonic surface rolling process; β phase; β phase; Titanium alloy; Ultrasonic surface rolling process; Gradient nanostructure; Nanocrystallization mechanism; Dislocation
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.01.045

The nanocrystallization mechanism of a body-centered cubic β phase in Ti–6Al–4V alloy subjected to ultrasonic surface rolling process was investigated. A gradient nanostructure (thickness: ~400 μm) that the β grain size in thickness gradually changes from ~0.76 μm in the interior to ~36.5 nm at the topmost surface was formed in Ti–6Al–4V alloy surface layer. The gradient nanostructure of the β phase is formed primarily via dislocation activities without the occurrence of deformation twinning. Dislocations were first generated in β phase at the phase boundaries where a high density of dislocations occurred in α phase. The coarse β grains were then gradually transformed into equiaxed nano grains via longitudinal splitting and transverse breakdown, which are induced by dislocation glide, entanglement, accumulation, and rearrangement. Additionally, with increasing strain, the β nanograins will be further refined via dislocation activities. •The softer β phase deforms after α phase in USRP-treated Ti–6Al–4V alloy.•β phase deforms mainly via dislocation motion without twinning occurring.•Dislocations in β phase initiate at the α/β phase boundaries.•There is no shear band observed during deformation.