Modeling the evolution of microtextured regions during α/β processing using the crystal plasticity finite element method

Titanium alloy Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) is frequently used in the high-pressure compressor of aero engines. While exhibiting high strength at elevated temperatures, it is susceptible to dwell fatigue at temperatures below similar to 473 K due in part to the presence of microtextured regions (MTRs), also known as macrozones. This work investigates the role of forging direction on the mesoscale mechanical response of MTRs. The crystal plasticity finite element (CPFE) method was used to simulate large strain compression of MTRs with different initial crystallographic and morphological orientation with respect to the axial direction of the extruded billet. These simulations included cases where the c-axis of neighboring MTRs were (i) both perpendicular, (ii) one at 45 degrees and one perpendicular, and (iii) one parallel and one perpendicular, to the compression direction. The effectiveness of each processing direction on the breakdown of MTRs is inferred through the extent of lattice rotation and the development of internal misorientations within the MTRs. The calculations reveal that case (i) leads to the most effective MTR breakdown but the c-axis remains similarly aligned; the c-axis is more scattered in case (iii) but the extent is limited by the high critical resolved shear stress of the pyramidal slip systems. Under uniaxial compression, competitive slip system activity correlates with positive divergence of reorientation velocity field in Rodrigues' space as well as efficient breakdown of MTR.