Amit Bhattacharjee

Microstructure and texture of rolled and annealed β titanium alloy Ti-10V-4.5Fe-1.5Al

Abstract This work describes the evolution of texture during cold rolling and annealing of a hot rolled and solution treated sheet of a low cost β titanium alloy Ti–10V–4.5Fe–1.5Al. The alloy was cold rolled up to 60% reductions and then annealed in β phase field at different temperatures to study the re-crystallisation textures. The rolling and re-crystallisation textures obtained in this study are compared with those of other β titanium alloys and bcc metals and alloys such as tantalum and low carbon steel.

Flow behaviour of TiHy 600 alloy under hot deformation using gleeble 3800

Abstract To understand deformation behaviour of TiHy 600 alloy at higher temperatures, hot compression tests are performed in α region (1173 K), α + β regions (1223, 1248, and 1273 K) and β region (1323 K) at strain rates (0.001, 0.01, 0.1, 1 and 10/s) for up to 50% deformation in Gleeble 3800® thermo-mechanical simulator. Flow curve plots are drawn at each strain rates and temperatures and it is observed that dominant deformation mechanism at higher temperature 1323 K (β region) and strain rates (1 and 10/s) is dynamic recovery (DRV) whereas dynamic recrystallization (DRX) is mostly observed at lower strain rates (0.001, 0.01/s) in medium temperature range of 1223 K (α region) to 1248 K (α + β region). Hyperbolic sine law equation is used to calculate the activation energy (Q) and other material sensitive parameters (A, α and n1). The activation energies for DRX in α region and DRV in β region are obtained as 384 and 251 kJ/mol. Experimental peak stress values are compared with predicted peak stress values (R2 = 96.2%) and Zener-Hollomon parameter (R2 = 94.3%). The flow stress behavior up to the peak stress is verified with Cingara equation. Finally, calculated prediction results of DRX volume fraction obtained from Avrami equation is compared with experimental observed microstructure.

Texture studies of hot compressed near alpha titanium alloy (IMI 834) at 1000°C with different strain rates

IMI 834 Titanium alloy is a near alpha (hcp) titanium alloy used for high temperature applications with the service temperature up to 600°C. Generally, this alloy is widely used in gas turbine engine applications such as low pressure compressor discs. For these applications, good fatigue and creep properties are required, which have been noticed better in a bimodal microstructure, containing 15-20% volume fraction of primary alpha grains (αp) and remaining bcc beta (β) grains transformed secondary alpha laths (αs). The bimodal microstructure is achieved during processing of IMI 834 in the high temperature α+β region. The major issue of bimodal IMI 834 during utilization is its poor dwell fatigue life time caused by textured macrozones. Textured macrozone is the spatial accumulation of similar oriented grains in the microstructure generated during hot processing in the high temperature α+β region. Textured macrozone can be mitigated by controlling the hot deformation with certain strain rate under stable plastic conditions having β grains undergoing dynamic recrystallization. Hence, a comprehensive study is required to understand the deformation behavior of α and β grains at different strain rates in that region. Hot compression tests up to 5°% strain of the samples are performed with five different strain rates i.e. 10-3 s-1, 10-2 s-1, 10-1 s-1, 1 s-1 and 10 s-1 at 1000°C using Gleeble 3800. The resultant bimodal microstructure and the texture studies of primary alpha grains (αp) and secondary alpha laths (αs) are carried out using scanning electron microscopy (SEM)-electron back scattered diffraction (EBSD) method.

Effect of Modes of Rolling on Evolution of Texture and Yield Locus Anisotropy in a Multifunctional Ti-31Ta-12Nb-2V-8Zr-0.22O Alloy

Present work describes the evolution of texture during different modes of deformation by cold rolling of a Gum metal or multifunctional β titanium alloy. The starting and cold rolled materials exhibit the presence of β and β with small amount of stress induced martensitic (α˝) phases, respectively. The development of texture has been explained in terms of α and γ fibres. The bulk hardness appears to be independent of modes of deformation by cold rolling. The yield surfaces of as received and solution treated samples exhibit marked anisotropy which persists during different modes of deformation by rolling.