In situtransmission electron microscopy study of the thermally induced formation of δ′-ZrO in pure Zr and Zr-based alloy

Abstract

This study reports in situ observations of the formation of the δ′‐ZrO phase, occurring during the annealing of transmission electron microscopy (TEM) thin foils of both pure Zr and a Zr–Sn–Nb–Mo alloy at 973 K in a transmission electron microsope. The lattice parameters of δ′‐ZrO were measured and determined to be similar to those of the ω‐Zr phase. The orientation relationship between the δ′‐ZrO and α‐Zr phases has been identified as either and or and depending on the orientation of the α grain relative to the TEM thin‐foil normal. The nucleation and growth of δ′‐ZrO were dynamically observed. This study suggests a new and convenient way to study oxidation mechanisms in Zr alloys and provides a deeper understanding of the properties of the newly reported δ′‐ZrO. Since δ′‐ZrO has a Zr sublattice which is identical to that of ω‐Zr, the orientation relationships between the α and δ′‐ZrO phases may also shed light on the orientation relations existing between α‐ and ω‐Zr, and hence α‐ and ω‐Ti.

Mechanism of the α-Zr to hexagonal-ZrO transformation and its impact on the corrosion performance of nuclear Zr alloys

“…Extensive research has been undertaken to identify the mechanisms controlling the α to ω phase transformation in the transition metals Ti and Zr [26-28, 77, 79-84], and studying this transformation may also shed light on the formation mechanisms of h-ZrO during aqueous corrosion. [27,35]. Direct comparison of these secondary orientation relationships reported here and that in the literature can be reflected in the distribution of corresponding poles, Fig.…”

“…[27] that showed the energy barrier for the α to ω transformation with the relationship (0002) α-Ti ∥(112 ̅ 0) ω-Ti is much higher than that for (0002) α-Ti ∥(1 ̅ 011) ω-Ti , and requires significantly more atomic shuffles [26,27]. There is also a relatively large mismatch between the second relationship identified in the current study and (0002) α-Zr/α-Ti ∥(112 ̅ 0) ω-Zr/ω-Ti reported in the literature [26,35,79], probably a result of higher level of accumulated stress required to trigger this less favorable transformation at the metal/oxide interface. In region 12 in Fig.…”

“…To explore the nature of the transformation from α-Zr to h-ZrO, it is necessary to analyze the orientation relationship between the two phases. Yu et al [35] have reported that h-ZrO formed during the annealing of Zr TEM thin foils under high vacuum conditions at temperatures above 700°C has a specific crystallographic orientation relationship with the Zr matrix. Two orientation relationships were observed, (0002…”

Untangling competition between epitaxial strain and growth stress through examination of variations in local oxidation

“…The pole figures show that in subset A and B, the sub-oxide follows the main orientation relationship identified in 56 , with {0002} #$ ||+1011, #$% and <2110> #$ ||<1012> #$% . This is also in agreement with TEM observations of sub-oxide formation during in-situ annealing 57 . In subset C, the orientation relationship is less clear, as this region is composed of two distinct sub-oxide orientations, however both of them are also close to the major orientation relationship reported previously 56,57 .…”

“…6a, which cover the three main sub-oxide orientations observed in this region. Contoured 57 . In subset C, the orientation relationship is less clear, as this region is composed of two distinct sub-oxide orientations, however both of them are also close to the major orientation relationship reported previously 56,57 .…”