Diffraction artefacts from twins and stacking faults, and the mirage of hexagonal, polytypes or other superstructures

Cayron, Cyril

doi:10.1016/j.scriptamat.2020.11.014

Cited by 39 publications

(17 citation statements)

References 36 publications

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“…Nanotwins hosted in a matrix are commonly observed, in particular for materials such as diamond and SiC that contain abundant stacking faults [6,7,33,34]. In fact, the FFTs calculated from the thick region and the entire image show streaked reflections (white arrows in Figure 4d,e and Figure 5b), which can be associated with (1014) stacking faults that occur inside the 5-15 nm wide twin individuals.…”

Section: Hrtem Images Of the (1014) Calcite Twins And Doubled D 104 Spacingsmentioning

confidence: 99%

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Diffraction Features from (101¯4) Calcite Twins Mimicking Crystallographic Ordering

Németh

2021

Minerals

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During phase transitions the ordering of cations and/or anions along specific crystallographic directions can take place. As a result, extra reflections may occur in diffraction patterns, which can indicate cell doubling and the reduction of the crystallographic symmetry. However, similar features may also arise from twinning. Here the nanostructures of a glendonite, a calcite (CaCO3) pseudomorph after ikaite (CaCO3·6H2O), from Victoria Cave (Russia) were studied using transmission electron microscopy (TEM). This paper demonstrates the occurrence of extra reflections at positions halfway between the Bragg reflections of calcite in 0kl electron diffraction patterns and the doubling of d104 spacings (corresponding to 2∙3.03 Å) in high-resolution TEM images. Interestingly, these diffraction features match with the so-called carbonate c-type reflections, which are associated with Mg and Ca ordering, a phenomenon that cannot occur in pure calcite. TEM and crystallographic analysis suggests that, in fact, (101¯4) calcite twins and the orientation change of CO3 groups across the twin interface are responsible for the extra reflections.

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Section: Hrtem Images Of the (1014) Calcite Twins And Doubled D 104 Spacingsmentioning

confidence: 99%

“…However, the interpretation of TEM data can be challenging, and ambiguities can arise for cases that look simple [4]. In particular, the recognition of twins from TEM data can be difficult because their diffraction features can be confused with ordering and superstructures [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Diffraction Features from (101¯4) Calcite Twins Mimicking Crystallographic Ordering

Németh

2021

Minerals

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“…We further distinguished the MSRO-derived spot-like scattering from common TEM characterisation artefacts associated with the introduction of double diffraction and Moiré fringes from fcc-twinned structures 46 , 47 . The HRTEM–FFT pattern obtained from the overlapped zone of slip bands and mechanical twins shows replicated extra spots owing to double diffraction (outlined blue boxes in Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanically derived short-range order and its impact on the multi-principal-element alloys

Seol

Sohn

et al. 2022

Nat Commun

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Chemical short-range order in disordered solid solutions often emerges with specific heat treatments. Unlike thermally activated ordering, mechanically derived short-range order (MSRO) in a multi-principal-element Fe40Mn40Cr10Co10 (at%) alloy originates from tensile deformation at 77 K, and its degree/extent can be tailored by adjusting the loading rates under quasistatic conditions. The mechanical response and multi-length-scale characterisation pointed to the minor contribution of MSRO formation to yield strength, mechanical twinning, and deformation-induced displacive transformation. Scanning and high-resolution transmission electron microscopy and the anlaysis of electron diffraction patterns revealed the microstructural features responsible for MSRO and the dependence of the ordering degree/extent on the applied strain rates. Here, we show that underpinned by molecular dynamics, MSRO in the alloys with low stacking-fault energies forms when loaded at 77 K, and these systems that offer different perspectives on the process of strain-induced ordering transition are driven by crystalline lattice defects (dislocations and stacking faults).

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“…The SAED shows that there was typical Nishiyama–Wassermann (N-W) orientation relationship (OR) between SM and RA:

and

[ 24 ]. Moreover, the diffraction spots were elongated due to the presence of stacking faults [ 25 ]. The Mn content of was almost the same about that in dark gray area (SM), implying that SM and RA jointly belonged to PRA.…”

Section: Resultsmentioning

confidence: 99%

Effect of Intercritical Annealing Time on Microstructure Evolution and Mechanical Properties of Low Carbon Medium Manganese Steel Subjected to Multi-Step Heat Treatment Process

Wang

Ren

et al. 2022

Materials

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A novel multi-step heat treatment process was performed for 0.2C–5Mn steel, and the effect of intercritical annealing (IA) durations on the microstructure evolution and mechanical properties was studied. The results showed that the content of primary reversed austenite (PRA) hardly changed as the IA time increased from 6 h to 50 h, but only less than 10% of PRA remained after being tempered at 200 °C due to the appearance of secondary martensite (SM). The final microstructure contained SM, the primary martensite (PM), and RA, which was protected by the SM so that the transformation-induced plasticity (TRIP) effect was unlikely to occur. Meanwhile, the (Ti, V, Mo)C particle sizes were 14.27, 14.68 and 15.65 nm for the intermediate processes of IA-6 h, IA-12 h, and IA-50 h, respectively. As the IA time increased from 6 h to 50 h, both the dislocation and precipitation strengthening increment decreased. As a result, the best mechanical properties were obtained from the intermediate process of IA-12 h, with a yield strength of 1115.5 MPa, tensile strength of 1573.5 MPa, and −20 °C impact energy of 30.4 J.

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Diffraction artefacts from twins and stacking faults, and the mirage of hexagonal, polytypes or other superstructures

Cited by 39 publications

References 36 publications

Diffraction Features from (101¯4) Calcite Twins Mimicking Crystallographic Ordering

Diffraction Features from (101¯4) Calcite Twins Mimicking Crystallographic Ordering

Mechanically derived short-range order and its impact on the multi-principal-element alloys

Effect of Intercritical Annealing Time on Microstructure Evolution and Mechanical Properties of Low Carbon Medium Manganese Steel Subjected to Multi-Step Heat Treatment Process

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