Experimental Setup and Pressure Calculations

Microstructural fingerprints of phase transitions in shock-loaded iron

S.J. Wang1, M.L. Sui2,*, Y.T. Chen3, Q.H. Lu1, E. Ma4, X.Y. Pei3, Q.Z. Li3, and H.B. Hu3

1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

2 Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China

3 Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China

4Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA

Supplementary Materials Includes:

Figs. S1, S2, S3, S4, S5, S6.

Tables S1, S2, S3.

Fig. S1: Microstructure of the whole shocked α-Fe grain for Fig. 2a. Itincludes 58 bright-field TEM images. A number of needle-type colonies mainly along two directions are seen in the grain. The white line shows the grain boundary. Across the grain boundary, the needle-type colonies in the neighboring grains present different orientations.

Fig. S2 One of the original TEM images of Fig. 2a without the demarcation line on the needle-like regions. The enlarged detail shows the clear boundaries of the needle-like colony. The red arrow indicates a small-angle boundary. Its SADP is presentedin the inset.

Fig. S3: Microstructure of a shocked grain with the shock pressure direction deviating from [001]bcc by a large angle of 30°.PTZ stands for the phase transition zone. D112T and D332T stand for {112} and {332} deformation twins, respectively. The red arrow stands for the projection direction of shock pressure in the observed (110)bcc plane.

In this grain, both plastic deformation and phase transition occur. The deformation twins form along the (1-12)[-111]bcc system, for which the Schmid factor (0.39) is high, whereas phase transition with characteristic threefold symmetry occurs only along the (-112)bcc plane (Schmid factor is as low as 0.08 for (-112)[1-11]bcc ). For the deformation twins, the maximum tilt angleφ of (1-12)Tand (1-12)M planes is less than 2°, which is very different from those stemming from phase transitionwithφ≈5°.

With the shock pressure different in every single grain in polycrystalline iron, the morphology of the needle-like microstructure is different, but the phase transition characters and phase transition mechanism remain the same.

Fig. S4: Experimental setup.(a) A schematic of the iron hollow cylindrical sampleunder shock wave. (b) A top-viewschematic of the hollow cylinder under shock-loading. The shock wave proceeds in the radial direction of the cylinder, labeled by the purple arrows.A VISAR was used to record the inner free surface velocity. (c) A top-view image of the experiment setup before filling PETN.

Fig. S5: The inner free surface velocity recorded by VISAR equipment.

Fig. S6Pressure calculations.(a) The calculated pressure history of the points at 4.6, 1.9, 1.2 mm in the experiment. (b) The inner free surface velocity curve from the calculation, in comparison with the experiment.

The details of the statistical analysis on the angle φ and volume fraction transformed (F).The angle φ values in Table S1 are measured in twenty diffraction patterns which were obtained from boundaries of needle-like colonies. Statistical analysisgives the mean value and standard deviation value. Table S2 shows the F value measured from several different grains in the locations at radius ~1.2 mm. The corresponding peak pressure hereis ~14.2 GPa.Table S3 shows the measured F at ~1.9 mm, ~13.3GPa.

Table S1 The angle φ measured in twenty diffraction patterns.

Table S2 Measured F at ~1.2 mm (~14.2 GPa).

Table S3 Measured F at ~1.9 mm (~13.3GPa).