Mechanical Behavior of Ultrafine-Grained Ti-6Al-4V Alloy Produced by Severe Warm Rolling: The Influence of Starting Microstructure and Reduction Ratio

Abstract

To provide insight into the mechanical behavior and microstructural evolution of bulk ultrafinegrained (UFG) Ti-6Al-4V alloys, we produced Ti-6Al-4V alloy sheets with grain size smaller than 300 nm through severe warm rolling of three different starting microstructures (i.e., lamellar, equiaxed, and hybrid, that is half equiaxed plus half lamellar microstructures) with various reduction ratios (i.e., 60, 70, 80, and 90 pct) at 873 K (600°C). Accordingly, the tensile behavior, microhardness, grain size, and dislocation density of the UFG Ti-6Al-4V alloys with different starting microstructures and reduction ratios were comparatively analyzed. Our results show that, following the continuous enhancement of tensile strength and hardness as the rolling reduction ratio increased from 0 to 70 pct, there was a saturation state in which the values of strength and hardness remained constant as the reduction ratio further increased from 70 to 90 pct for all the alloy samples with different starting microstructures. In terms of microstructural evolution, although grain size decreased and dislocation density increased continuously as the rolling reduction ratio increased from 0 to 70 pct, grain size and dislocation density did not change significantly when the reduction ratio further increased from 70 to 90 pct. Our results suggest that, whereas the starting microstructure influences the early stages of grain refinement and mechanical performance, this influence diminishes as the rolling reduction ratio is increased beyond a critical value. This behavior was rationalized on the basis of the limits of grain boundary and dislocation strengthening during severe warm rolling.

Effect of Structure and Hydrogen on the Short-Term Creep of Titanium Ti-2.9Al-4.5V-4.8Mo Alloy

“…It follows from the slopes of the curves of the steady creep rate on the applied stress in the double-logarithmic coordinates ( Figure 7 ) that the stress sensitivity indices n were equal to 6.3 and 5.6 for the Ti-2.9Al-4.5V-4.8Mo alloys in the FG and UFG states, respectively. The high values of the n index for the Ti-2.9Al-4.5V-4.8Mo alloy are consistent with the data of creep investigation for other titanium alloys that were under conditions similar to the applied test conditions [ 43 , 44 , 45 , 46 , 47 ]. The obtained values of the stress sensitivity index n indicate that the creep of the titanium alloy in both states and under the studied conditions was realized by the movement (glide + climb) of dislocations [ 40 ].…”

An Overview of the Thermomechanical Processing of α/β Titanium Alloys: Current Status and Future Research Opportunities

“…The effect of a grain size on room-temperature strength has been determined for warm-rolled Ti64 samples having a partially-or fully-spheroidized starting microstructure. [235] In particular, it has been established that the yield-strength increment associated with grain size follows a Hall-Petch behavior (Figure 28).…”

“…In many cases, these have involved warm working in the temperature range between approximately 873 and 1073 K (600 and 800°C) via uniaxial or multiaxial ('abc') forging or plate/sheet rolling. [230][231][232][233][234][235][236] Methods such as equal-channel angular extrusion (ECAE) and high-pressure torsion (HPT) have also been utilized on a laboratory scale to establish the fundamental mechanisms of structure refinement and property enhancement. [237][238][239][240] When interpreting the mechanical behavior of SPD-processed a/b titanium alloys, it is important to differentiate the microstructural features of a particle size and a grain size.…”

“…28-Dependence of the yield strength (reduced by the contribution due to dislocations, Dr d ) on the inverse-square-root of the a grain size for Ti64 samples which were warm rolled by various means. [235] C. Solid-State Joining Processes Solid-state joining processes are typically broken into two broad categories-friction-stir welding (FSW) and rotary-/linear-friction welding (RFW/LFW).…”

Interfacial Mechanical Behavior and Electrochemical Corrosion Characteristics of Cold‐Sprayed and Hot‐Rolled Titanium/Stainless‐Steel Couples

“…Ti and its alloys are characterized by a unique combination of mechanical and chemical properties, e.g., high specific strength and excellent corrosion resistance . However, they are relatively expensive, and the cost‐effectiveness is essential to be taken into consideration when they are used in engineering structures .…”