Cyclic Deformation Response of β-Annealed Ti-5Al-5V-5Mo-3Cr Alloy Under Compressive Loading Conditions

Abstract

This article reports the cyclic deformation behavior of the b-annealed metastable Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy under the condition of pure compressive fatigue stress. The following three aspects, namely, the mechanical response, the surface morphology evolution, and the dislocation structures, were systematically investigated. Under all testing conditions, the material demonstrated cyclic softening in the initial cycles followed by saturation. The progressive observation of surface morphology at fixed locations, but after different numbers of cycles, elucidated typical planar slip behavior and the early appearance of fatigue microcracks, which were found often to be induced by the highly localized planar slip bands. The transmission electron microscopy (TEM) study revealed dislocation annihilation upon cycling, i.e., the reduction of dislocation density as well as the simplification of dislocation configurations. In addition, detwinning and changed twin boundary structures upon cycling were also detected. Such activities, together with the intersection of coherent x precipitates by moving dislocations, are considered to be responsible for the initial softening, whereas the dislocation dipole flip-flop mechanism is presumably responsible for the cyclic saturation behavior. An attempt was made to explain the strain-localized planar slip behavior by considering the stacking fault energy (SFE) as well as the free-electron-to-atom (e/a) ratio. The nanoscaled x and a precipitation in the b matrix may also contribute to the planar slip behavior. The effect of the microstructure in the as-received material was also analyzed for the strain localization and planar-slip mode.

Effect of α-phase morphology on low-cycle fatigue behavior of TC21 alloy

“…Dislocation configurations indicate the planar slip in cyclic deformation of a phase, which is also reported in other titanium alloys [11,12]. The researchers suggest that the lower SFE, appropriate SRDs and the higher e/a ratio may cause planar slip in deformation of Ti-5553 alloy [12].…”

“…It is well known that microstructure has a significant effect on fatigue behavior of titanium alloys [8][9][10][11][12][13][14][15][16]. The fatigue strength decreases in the order of bimodal, lamellar (Widmannstatten) and equiaxed microstructure in Ti-6Al-4V alloy.…”

Effect of size of alpha phases on cyclic deformation and fatigue crack initiation during fatigue of an alpha-beta titanium alloy

“…10d displays that lots of deformation twins with size of about 50nm in widths are produced in α phase. It has been reported that deformation twins will be induced in many metals when the dislocation slip is not sufficient to accommodate the cyclic plastic deformation [6,[9][10][33][34]. In general, assuming everything else is equal, fatigue crack tends to nucleate in coarse grained material than the fine grained materials [6].…”

Microstructure and Mechanical Properties of Ti5553 Butt Welds Performed by LBW under Conduction Regime

“…The advantage of this alloy as compared to other β titanium alloys is the sluggish precipitation kinetics of the α phase [5,6]. Ti5553 offers high strength, excellent hardenability, fracture toughness as well as high fatigue resistance [7]. The potential applications of this alloy are in the high-strength related areas such as landing gear and pylon/nacelle areas.…”