Combined Effects of Texture and Grain Size Distribution on the Tensile Behavior of α-Titanium

Abstract

This work analyzes the role of both the grain size distribution and the crystallographic texture on the tensile behavior of commercially pure titanium. Specimens with different microstructures, especially with several mean grain sizes, were specifically prepared for that purpose. It is observed that the yield stress depends on the grain size following a Hall–Petch relationship, that the stress–strain curves have a tendency to form a plateau that becomes more and more pronounced with decreasing mean grain size and that the hardening capacity increases with the grain size. All these observations are well reproduced by an elasto-visco-plastic self-consistent model that incorporates grain size effects within a crystal plasticity framework where dislocations’ densities are the state variables. First, the critical resolved shear stresses are made dependent on the individual grain size through the addition of a Hall–Petch type term. Then, the main originality of the model comes from the fact that the multiplication of mobile dislocation densities is also made grain size dependent. The underlying assumption is that grain boundaries act mainly as barriers or sinks for dislocations. Hence, the smaller the grain size, the smaller the expansion of dislocation loops and thus the smaller the increase rate of mobile dislocation density is. As a consequence of this hypothesis, both mobile and forest dislocation densities increase with the grain size and provide an explanation for the grain size dependence of the transient low work hardening rate and hardening capacity.

Promising Tensile and Fatigue Properties of Commercially Pure Titanium Processed by Rotary Swaging and Annealing Treatment

“…This preferred orientation feature is typical for HCP-Ti produced by swaging and/or drawing [41], suggesting that annealing treatment for a short time does not change the texture formed during RS. It has been revealed that texture plays an important role in the overall mechanical behavior of hexagonal close-packed (HCP) metals [42,43,44,45]. Thus the strong texture would influence the mechanical properties of RSA450 sample and play a different role compared with the ultrafine-grained structure.…”

“…This is why dislocation recovery after a short annealing can make the RS-processed Ti sufficiently tough, because of the remarkable decrease in dislocation density, as seen in Figure 3. It should be noted that, in contrast to the fine grain size that sharply enhances yield strength, the soft model for dislocation slip would result in a decrease of yield strength due to the relatively low critical resolved shear stress [44,47]. Therefore, there is an equilibrium of strength between the improvement from fine grain size and the drop due to the soft mode of dislocation slip.…”

Fatigue Crack Growth Characteristics of 34CrMo4 Steel for Gas Cylinders by Cold Flow Forming after Hot Drawing

“…It can be found that the yield stress of BM was obviously lower than those of HD and CF materials by 30.9-42.1% approximately. The yield stress was considered to be associated with the grain size, grain boundaries, and so on [27]. Compared with the HD and CF materials, the grain size of BM was sharply large, leading to a reduction in the yield stress of BM.…”

Grain-Size Distribution Effects on the Attenuation of Laser-Generated Ultrasound in α-Titanium Alloy

“…Average grain size (diameter) is usually used to describe a polycrystalline medium; however, many investigations demonstrate the grain-size distribution actually has a measurable effect on most mechanical properties, such as tensile strength [1], yield stress [2], flow stress [3,4], hardness [5], etc. For example, good ductility and high strength can be achieved for fine grains with a small distribution width after recrystallization for commercial pure titanium alloy [6], while exceptionally large grains can result in unacceptably low mechanical strength for a pure niobium sample [7].…”