In situ phase transformation and deformation of iron at high pressure and temperature

Abstract

With a membrane based mechanism to allow for pressure change of a sample in a radial diffraction diamond anvil cell (rDAC) and simultaneous infra-red laser heating, it is now possible to investigate texture changes during deformation and phase transformations over a wide range of temperature-pressure conditions. The device is used to study bcc (α), fcc (γ) and hcp (ε) iron. In bcc iron, room temperature compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the deformation induced phase transformation to hcp iron, a subset of orientations are favored to transform to the hcp structure first and generate a texture of (01-10) at high angles to the compression direction. Upon further deformation, the remaining grains transform, resulting in a texture that obeys the Burgers relationship of (110) bcc // (0001) hcp . This is in contrast to high temperature results that indicate that texture is developed through dominant pyramidal 〈a+c〉 {2-1-12}〈2-1-13〉 and basal (0001)〈2-1-10〉 slip based on polycrystal plasticity modeling. We also observe that the high temperature fcc phase develops a 110 texture typical for fcc metals deformed in compression.

In situx-ray diffraction of fast compressed iron: Analysis of strains and stress under non-hydrostatic pressure

“…This peak is not observed in hydrostatic runs with neon. Both observations confirm the complexity of the phase transition from α to iron and its sensitivity to stress conditions and pressurization rate [40,41]. Previous studies on the deformation of polycrystalline iron analyzed latticepreferred orientations of α-and -Fe using radial diffraction experiments and variation of the diffraction intensities [12,41].…”

“…7(b)]. The mechanism of bcc-hcp transformation has been extensively discussed in Miyagi et al [41]. It is generally accepted that the transformation is sluggish and completed only at about 22 GPa.…”

Experimental method for in situ determination of material textures at simultaneous high pressure and high temperature by means of radial diffraction in the diamond anvil cell

“…Figure 7, for instance, presents inverse pole figures of the compression direction obtained for bcc and fcc iron at 12.5 GPa and 976 K and fcc and hcp iron at 33.2 GPa and 899 K. ODFs were obtained directly in MAUD and further smoothed with a 10°gauss filter in BEARTEX. 42 Upon compression, bcc iron develops a mixed ͕100͖ and ͕111͖ texture that is compatible with previous observations on bcc iron 16,43 and interpreted as slip along ͕110͖͗111͘. When bcc iron is heated between 295 and 976 K, we observe a recrystallization of the sample, as evident by the spotty pattern in Fig.…”

“…44 Textures obtained in hcp iron seem different from those reported before. 5, 16,34 Further study and modeling will be re- quired for full interpretation, which goes beyond the scope of this paper.…”

“…Recently, radial diffraction experiments in the DAC using in situ laser heating have made significant progress. 15,16 They are, however, complicated by the presence of large temperature gradients that develop during heating. So far externally heated DACs have not been used for stress and texture analyses because the resistive heater would lie in the x-ray path.…”