A high-throughput stress-state map of the bcc-to-hcp transformation in single-crystal iron from molecular dynamics

The α − Fe → ε − Fe transition in iron is commonly reported at 13 GPa , but the published onset stresses from experiments and simulations cover a much wider range when the stress profile and loading rate differ. We conducted a series of compressions of single-crystal iron at fixed volumetric strain ( ε v = 0.235 ), distributing that strain among the three Cartesian axes of the simulation cell through a θ φ grid for [100] and [110] orientations and thereby sampling hydrostatic, biaxial, uniaxial, and general triaxial paths. Each trajectory is reduced to a yield-like pressure P Y and a transformation pressure P T , together with V T , σ eq , and phase fractions. P Y stays in a narrow band ( 15.3 – 26.2 GPa ) while P T spans 23.8 – 106.9 GPa . Gradient-boosted regression on V T and σ eq T at the transformation instant recovers P T with cross-validated R 2 = 0.99 (RMSE 2.1 GPa ), and a Gaussian-process model on the same inputs gives ± 2 σ intervals whose held-out coverage stays within a few percent of the nominal 95%. The released dataset maps finite-rate transformation as a function of stress state and orientation in pure Fe, for comparison with static, shock, and ramp data.