Phase transition and twinning in polycrystals probed by in situ high temperature 3D reciprocal space mapping

Abstract

Polycrystalline materials exhibit physical properties that are driven by both the interatomic crystallographic structure as well as the nature and density of structural defects. Crystallographic evolutions driven by phase transitions and associated twinning process can be observed in situ in three-dimensional (3D) using monochromatic synchrotron radiation at very high temperatures (over 1000 °C). This paper focuses on continuous measurements of the 3D-reciprocal space maps by high-resolution x-ray diffraction as a function of temperature along a phase transition process occurring between 1200 °C and room temperature. These high precision measurements allow observing the reciprocal space node splitting and the evolution of the diffuse scattering signal around that node as a function of temperature. The capability of this experimental method is illustrated by direct in situ high temperature measurements of the 3D splitting of a reciprocal space node due to phase transition recorded on dense pure zirconia polycrystals.

Laue microdiffraction on polycrystalline samples above 1500 K achieved with the QMAX-µLaue furnace

“…As an illustrative example, we have shown the very first data obtained on a pure zirconia polycrystalline specimen undergoing a phase transition from monoclinic to tetragonal states upon heating. The acquired Laue patterns are fully consistent with previous analyses of the splitting of the 111 reciprocalspace node (Purushottam Raj Purohit et al, 2022b), where the specimen passes from a highly stressed microstructure comprising 24 variants to a simpler one with only three variants, although we show here that the distribution of the stress level in the tetragonal phase still lies in the gigapascal range (in agreement with forthcoming full-field computation results).…”

“…9(c) probably comprises many t crystals with almost identical crystallographic orientations. A similar feature has also been recently observed using high-temperature 3D reciprocal-space maps, recorded on much larger gauge volumes (sub-millimetre cubed), where the 24 111 or � 111 relatively spread RLNs of the monoclinic phase join together into three very well defined 111 RLNs of the tetragonal phase at 1423 K (Purushottam Raj Purohit et al, 2022b). To the best of our knowledge, Fig.…”

“…This can be explained by the combined effects of crystal size and internal stresses. Further evidence of huge elastic strain has been obtained recently using hightemperature 3D mapping of the reciprocal space close to the 111 tetragonal reciprocal lattice nodes (RLNs), around which diffuse scattering stems linked to the 111 and � 111 monoclinic RLNs have been observed (Purushottam Raj Purohit et al, 2022b). Therefore, it is expected that the huge internal stress field and the associated stress relaxation due to microcracking play an important role during t !…”