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• A near-α TNW700 titanium alloy exhibtis excellent superplaticity with elongation above 400% at 925°C. • Flow stress curve behave as long period strain hardening and large strain softening. • Continuous dynamic recrystallization induced primary α phase refinement at the later deformation stage. • The strain hardening is attributed to β grain growth, silicide precipitates and α phase solid solution strengthening. • Dynamic dislocation recovery, α grain refinement and β phase volume fraction increase together cause flow softening. The new near-α TNW700 titanium alloy is a potential candidate material for high performance ultrasonic/hypersonic aircrafts, which is designed for short-term service at 700°C. This study systematically investigated the superplastic deformation microstructure evolution and mechanism of TNW700 alloy at different strain rates and true strains at 925°C. Results show that TNW700 alloy exhibits excellent superplastic behavior in a constant strain rate range of 0.0005–0.005 s−1 with elongation above 400%. The peak stress decreases with decreasing strain rate, which is related to the increase of β-phase volume fraction caused by the increase of thermal exposure time. In addition, significant strain hardening is observed in early-middle stage of superplastic deformation, and flow softening is followed in middle-late stage. To rationalize these complex flow behaviors, electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) were used to characterize the microstructure. Strain hardening is correlated to the synergistic effect of β grain growth, dislocation accumulation, silicide precipitate, and solid solution strengthening of α phase. Continuous dynamic recrystallization (CDRX) induced the fragmentation of primary α grains in middle-late stage of superplastic deformation, and the refinement of α grains, the increase of β phase volume fraction and dynamic dislocation recovery are main causes of high strain softening. In addition, EBSD and TEM observations confirmed texture randomization, fine equiaxed primary α grains and intragranular dislocation movement, indicating that grain boundary sliding (GBS) accommodated by dislocation sliding / climb is the dominant superplastic deformation mechanism of TNW700 alloy. [ABSTRACT FROM AUTHOR]

In this work, the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated. Based on the strain rate sensitivity m determined by flow data, superplastic region is estimated at relatively low temperature and strain rate domains, specifically around 1000 °C/10−3 s−1. Thereafter, the cylinder specimens are isothermally compressed at 1000 °C/10−3 s−1 and 1025 °C/10−3 s−1 with different strains, to exam the superplasticity and related mechanisms. The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization (DRX), and the grain boundary sliding (GBS) contributes to the total strain during superplastic compression as well. In addition, the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected, which is different from superplastic tensile deformation. [ABSTRACT FROM AUTHOR]

An ultrafine-grained (UFG) Mg-13Zn-1.55Y alloy (ZW132) with a high volume fraction (7.4%) of icosahedral phase ( I -phase, Mg 3 Zn 6 Y) particles was prepared by applying high-ratio differential speed rolling (HRDSR) on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures (tensile elongations of 455% and 1021% 473 K- 10 −3 s −1 and 523 K- 10 −3 s −1 , respectively). Compared with UFG Mg-9.25Zn-1.66Y alloy (ZW92) with a lower volume fraction of I -phase particles (4.1%), which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond 523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSR-processed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K. [ABSTRACT FROM AUTHOR]

The 7075 Al alloy was processed by accumulative roll bonding (ARB) at 350 °C using 2:1, 3:1 and 4:1 thickness reductions per pass ( R p ) up to 8, 6 and 3 passes, respectively. Microstructural examinations of the processed samples revealed that ARB leads to a microstructure composed of equiaxed crystallites with a mean size generally lower than 500 nm. It was found that, due to both the stored energy throughout the processing and the particle pinning effect, the alloy is affected by discontinuous recrystallisation during the inter-pass heating stages, the precise microstructural evolution being dependent on R p . Mechanical testing of the ARBed samples revealed that the main active deformation mechanism in the ARBed samples in the temperature range from 250 to 350 °C at intermediate and high strain rates is grain boundary sliding, the superplastic properties being determined by both the microstructure after ARB and its thermal stability. [ABSTRACT FROM AUTHOR]

The microstructure and texture in a commercially processed Al-6 wt% Cu-0.4 wt% Zr (Supral100) aluminium alloy have been investigated after annealing and hot tensile straining at 450 °C, using a field emission gun scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The microstructure of commercially processed alloy had a relatively large fraction of high angle grain boundaries (HAGBs) which were aligned parallel to the rolling direction, and a strong texture. Annealing at 450 °C led to an increase in the fraction of HAGBs and to an increase in HAGB spacing and these changes were progressively enhanced by subsequent tensile deformation. The increasing fraction of HAGBs was due to the annihilation of low angle grain boundaries (LAGBs). A sharpening of texture during annealing was attributed to preferential textural growth, and the reduction of texture at higher tensile strains led to the development of superplastic behaviour. The present work supports the view that the evolution of the fine grain microstructure during the high temperature straining of Supral100 is primarily due to the accumulation of a large area of grain boundary during the initial thermomechanical processing, and does not involve any unusual restoration processes. [Copyright &y& Elsevier]