Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

Schaefer, H.‐E.; Baier, F.; Müller, Markus; Reichle, K. J.; Reimann, K.; Rempel, А. А.; Sato, K.; Feng, Yujun; Zhang, Xiangyi; Sprengel, Wolfgang

doi:10.1002/pssb.201147103

Cited by 10 publications

(9 citation statements)

References 59 publications

(128 reference statements)

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“…Based on the positron lifetime calculations, the occurrences of mono-vacancies and dislocations were established. [17] The defects concentration in the T-type parts (A1 and A2 areas) indicates that the dominant type of defects in both areas is vacancies. However, it should be noted that the concentration of each defect type in the discussed areas is different.…”

Section: Resultsmentioning

confidence: 99%

“…The advantage of this method is the detection of small concentrations of defects that could not be detected by other methods. [17] Positron techniques have been used for studies of defect behavior in the Ni 3 Al system [18] and polycrystalline Ni-based superalloys, [19] but there are no results as yet for investigation of defects inhomogeneity in the single-crystalline turbine blades.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Krawczyk

Bogdanowicz

Hanc-Kuczkowska

et al. 2018

Metall Mater Trans A

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Single-crystalline superalloy CMSX-4 is studied in the as-cast state and after heat treatment, with material being taken from turbine blade castings. The effect of the heat treatment on the defect structure of the root area near the selector/root connection is emphasized. Multiscale analysis is performed to correlate results obtained by X-ray topography and positron annihilation lifetime spectroscopy (PALS). Electron microscopy observations were also carried out to characterize the inhomogeneity in dendritic structure. The X-ray topography was used to compare defects of the misorientation nature, occurring in as-cast and treated states. The type and concentration of defects before and after heat treatment in different root areas were determined using the PALS method, which enables voids, mono-vacancies, and dislocations to be taken into account. In this way, differences in the concentration of defects caused by heat treatment are rationalized.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Krawczyk

Bogdanowicz

Hanc-Kuczkowska

et al. 2018

Metall Mater Trans A

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“…Schematic illustration how lattice (left) and dislocation core (or pipe) diffusion (right) lead to dis-location climb according to Asby and Jones[24].…”

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confidence: 99%

Molybdenum Disilicide - Diffusion, Defects, Diffusion Correlation, and Creep

Mehrer

Schaefer

Belova³

et al. 2012

DDF

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Molybdenum disilicide (MoSi2) is an interesting material for high-temperature applications. It has a high melting temperature, good thermal and electrical conductivity and an excellent oxidation resistance. For many years the primary use of MoSi2has been in heating elements, which can be used for temperatures up to 1800°C. Since the 1990s the potential of MoSi2as a high-temperature structural material has been recognized as well. Its brittleness at lower temperatures and a poor creep resistance above 1200°C have hindered its use as in load-bearing parts. These disadvantages may be offset at least partly by using it together with a second material in a composite or an alloy. Projected applications of MoSi2-based materials include, e.g. stationary hot section components in gas turbine engines and glow plugs in diesel engines. For future research and development directions of MoSi2-based composites diffusion is a crucial property because creep is closely connected with diffusion. This paper is devoted to the basic diffusion and defect properties of MoSi2. Data of Si and Mo as well as Ge diffusion from the Münster laboratory for both principal directions are briefly summarized. For all three kinds of atoms diffusion perpendicular to the tetragonal axis is faster than parallel to it. The diffusivities of Mo in both directions are many orders of magnitude slower than those of Si and Ge. The huge asymmetry between Mo and Si (or Ge) diffusion suggests that atomic motion of each constituent is restricted to its own sublattice. Positron annihilation studies on MoSi2from the Stuttgart laboratory are reviewed as well. They show that formation of thermal vacancies occurs primarily on the Si sublattice but cannot exclude vacancy formation on the Mo sublattice at higher temperatures. Correlation factors for Si and Mo diffusion via sublattice vacancies in the respective sublattices of MoSi2have been calculated recently mainly by Monte Carlo simulation techniques and are also briefly described. Diffusion, in particular self-diffusion, is discussed in connection with literature data on high-temperature creep, which is diffusion-controlled. Grain-size effects of creep have been reported and can be attributed to Nabarro-Herring and Coble creep. Power-law creep is attributed to diffusion-controlled dislocation creep. Some details are, however, not completely understood, presumably due to a lack of theoretical concepts for creep in uniaxial, stochiometric compounds and due to missing information on grain-boundary diffusion.

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“…At the same time, there are very few data on vacancies that appear after SPD in intermetallic compounds. The vacancy defects in these compounds are more diverse than in pure metals and disordered solid solutions [44]. For example, in Fe 3 Si samples, which have a nanocrystalline structure after SPD in ball mills, vacancy-like defects were detected by the PAS method, which can be attributed to interface defects [45].…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure Defects in Titanium Nickelide after Abc Pressing at Lowered Temperature

et al. 2022

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The experimental results regarding the effect of warm (573 K) abc pressing with an increase in the specified true strain, e, up to 9.55, on the microstructure and crystal structure defects (dislocations, vacancies) of the Ti49.8Ni50.2 (at %) alloy are presented. It is shown that all samples (regardless of e) have a two-level microstructure. The grains–subgrains of the submicrocrystalline scale level are in the volumes of large grains. The average sizes of both large grains and subgrain grains decrease with increasing e to 9.55 (from 27 to 12 µm and from 0.36 to 0.13 µm, respectively). All samples had a two-phase state (rhombohedral R and monoclinic B19’ martensitic phases) at 295 K. The full-profile analysis of X-ray reflections of the B2 phase obtained at 393 K shows that the dislocation density increases from 1014 m−2 to 1015 m−2 after pressing with e = 1.84 and reaches 2·1015 m−2 when e increases to 9.55. It has been established by positron annihilation lifetime spectroscopy that dislocations are the main type of defects in initial samples and the only type of defects in samples after abc pressing. The lifetime of positrons trapped by dislocations is 166 ps, and the intensity of this component increases from 83% in the initial samples to 99.4% after pressing with e = 9.55. The initial samples contain a component with a positron lifetime of 192 ps (intensity 16.4%), which corresponds to the presence of monovacancies in the nickel sublattice of the B2 phase (concentration ≈10−5). This component is absent in the positron lifetime spectra in the samples after pressing. The results of the analysis of the Doppler broadening spectroscopy correlate with the data obtained by the positron annihilation lifetime spectroscopy.

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Vacancies and atomic processes in intermetallics – From crystals to quasicrystals and bulk metallic glasses

Cited by 10 publications

References 59 publications

Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Molybdenum Disilicide - Diffusion, Defects, Diffusion Correlation, and Creep

Crystal Structure Defects in Titanium Nickelide after Abc Pressing at Lowered Temperature

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