Microstructural evolution in hot compressed TiHy 600 titanium alloy

TiHy 600 alloy is a near alpha titanium alloy, widely used for gas turbine engine applications such as disc and blades for high pressure compressors. One drawback of this alloy is that it is susceptible to cold dwell fatigue, which is due to the presence of micro-textured zones. Thus, appropriate processing parameters (i.e. temperature, strain and strain rate) are required to reduce the size of the micro-textured region. In order to find out the optimized processing parameters, hot compression tests were performed up to 50% engineering strain at temperatures range of 900oC-1050oC and strain rate range of 10-3 to 101 s-1 using thermo-mechanical simulator (Gleeble 3800®). Flow behavior characteristics were studied from the data obtained during hot compression and processing map was developed at true strain of 0.6 using Dynamic Materials Modeling (DMM) approach. Microstructural examination of deformed TiHy 600 titanium alloy were carried out at a particular strain rate of 10-3 s-1 and temperatures of 900oC, 950oC, 975oC, 1000oC and 1050oC. Microstructural examination consists of orientation image mapping along compression direction using electron backscatter diffraction. Hot compression mostly resulted into new dynamic recrystallized (DRX) alpha grains at 900oC, mixture of deformed large alpha grains containing subgrain boundaries and transformed beta phase consisting of secondary alpha laths at 950oC and 975oC and alpha laths transformed from deformed beta grains at 1000oC and 1050oC

Texture transition in friction stir processed Al powder compact

Green Al powder compacts of commercial purity with random orientation were subjected to single pass frictionstir processing (FSP) with different tool rotational and traverse speeds. The evolution of crystallographic textureobtained from large area electron back scattered diffraction were compared with the bulk texture of the nuggetzone characterized using synchrotron diffraction. Evolution of different deformation and recrystallization texturecomponents were discussed. While the grain size distributions were found to be independent of processparameters, the texture components and their strength of the FSPed samples were strongly influenced by theprocess parameters. Continuous dynamic recrystallization (CDRx) was found to be the primary restorationmechanism for most of the processing conditions leading to a bi-modal misorientation distribution. The possiblerelations between different texture components and the appearance or suppression of bimodal misorientationdistributions were discussed. Restoration mechanism changed to discontinuous dynamic recrystallization(DDRx) with the evolution of cube component at the stir zone along with random misorientation distribution.Dominance of a particular restoration mechanism depends on strain, strain rate and temperature attained duringthe processing

Peak stress studies of hot compressed TiHy 600 alloy

TiHy 600 is a near alpha titanium alloy similar to IMI 834 Ti alloy, widely used for gas turbine engine applications such as disc and blades for high pressure compressors. Flow behavior of TiHy 600 alloy is investigated by conducting hot compression tests at temperatures ranging from 900°C to 1050°C with in the strain rate range of (0.001/s) respectively up to 50% deformation. Constitute modeling of work hardening is established, using Cingara equation to verify the stress up to peak stress. It was found that experimental true stress-true strain curves are in good agreement with Cingara equation curves for all temperatures at strain rate of (0.001/s)up to their peak stress values. The average activation energy (Q) is calculated from the peak stress of the flow curves using the hyperbolic-sine law equation (Arrhenius equation) i.e. 851.506KJ/mol. The microstructures of 50% deformed samples are correlated with the post-peak stress flow curve, performed mainly to compare the various softening processes (DRV or DRX)

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

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