February 2022 Volume 4

FORGING RESEARCH

Prediction of Relative Globularization Rates in + β Titanium Alloys as a Function of Initial Crystal Orientation Final Report Benjamin A. Begley and Victoria M. Miller Project Dates: 1 June 2020 - 23 August 2021 Industry Partner: ATI Specialty Metals

The thermomechanical processing of two-phase Ti alloys is both energy- and cost-intensive; the goal of this project was to enable development of tailored forging pathways for Ti alloys which require less energy input during conversion from billet to semi- nished mill product. Substantial progress was made toward this goal, and further evidence supporting the core modeling approach was obtained. The FIERF microgrant has served as a spring-board, enabling PI Miller and her team to generate preliminary results, engage additional potential industry partners, and write full length proposals to federal funding bodies. The fundamental hypothesis of this work is that the layer breakdown kinetics of lamellar — β Ti alloys can be primarily explained by simple arguments about crystallographic rotation during plastic deformation; prediction of layer breakdown will not require detailed modeling of the atomistic processes occurring at the nanoscale. Toward this goal, two original tasks were proposed: 1. Simulation of plastic rotation for many starting colony orientations under numerous loading scenarios; and 2. Experimental validation that predicted plastic rotation metrics from simulation correlate with experimental observations of spheroidization and microtexture persistence.

Due to the effects of the COVID-19 pandemic and restrictions in on-campus activities for undergraduate students, the emphasis on Task 1 was increased relative to Task 2. However, substantial progress was made on both tasks. 1. Simulation of plastic rotation for varied loading scenarios 1.1 Core simulation methodology and prior results The primary simulation method employed in this award is using the viscoplastic polycrystal plasticity model (VPSC) to simulate deformation and predict plastic rotations for the and β phases. It was hypothesized that the VPSC-predicted plastic rotation amounts would correlate with lamellar breakdown and retained strength of microtexture during deformation, as summarized in Figure 1. In —β colonies where little plastic rotation of either phase is expected, neither microtextured region (MTR) evolution nor spheroidization would be predicted. In colonies where plastic rotation of the and β phases is predicted to occur in opposite directions, both MTR evolution and breakdown is predicted. Finally, in colony orientations where signicant plastic rotation in similar directions is predicted for both the and β phases, MTR evolution will occur but little globularization would be expected.

Figure 1: Hypothesized relationship between plastic rotation of the and β phases and the spheroidization behavior during hot deformation. Figure 1: Hypothesized relationship between plastic rotation of that α and β phases and the spheroidization behavior during hot deformation.

FIA MAGAZINE | FEBRUARY 2022 78