Spatially resolved texture and microstructure evolution of additively manufactured and gas gun deformed 304L stainless steel investigated by neutron diffraction and electron backscatter diffraction

In this study, we report the characterization of a 304L stainless steel cylindrical projectile produced by additive manufacturing. The projectile was compressively deformed using a Taylor Anvil Gas Gun, leading to a huge strain gradient along the axis of the deformed cylinder. Spatially resolved neutron diffraction measurements on the High Pressure Preferred Orientation time-of-flight diffractometer (HIPPO) and Spectrometer for Materials Research at Temperature and Stress diffractometer (SMARTS) beamlines at the Los Alamos Neutron Science CEnter (LANSCE) with Rietveld and single-peak analysis were used to quantitatively evaluate the volume fractions of the alpha, gamma, and epsilon phases as well as residual strain and texture. The texture of the gamma phase is consistent with uniaxial compression, while the alpha texture can be explained by the Kurdjumov-Sachs relationship from the gamma texture after deformation. This indicates that the material first deformed in the gamma phase and subsequently transformed at larger strains. The epsilon phase was only found in volumes close to the undeformed material with a texture connected to the gamma texture by the Shoji-Nishiyama orientation relationship. This allows us to conclude that the epsilon phase occurs as an intermediate phase at lower strain, and is superseded by the alpha phase when strain increases further. We found a proportionality between the root-mean-squared microstrain of the gamma phase, dominated by the dislocation density, with the alpha volume fraction, consistent with strain-induced martensite alpha formation. Knowledge of the sample volume with the epsilon phase from the neutron diffraction analysis allowed us to identify the epsilon phase by electron back scatter diffraction analysis, complementing the neutron diffraction analysis with characterization on the grain level. (C) 2018 International Centre for Diffraction Data.