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B. Malaman - One of the best experts on this subject based on the ideXlab platform.

  • Unexpected Magnetic Ordering on the Cr Substructure in UCr2Si2C and Structural Relationships in Quaternary U-Cr-Si-C Compounds
    Inorganic Chemistry, 2018
    Co-Authors: P. Lemoine, A. Vernière, M. Pasturel, G. Venturini, B. Malaman
    Abstract:

    Previous experimental and theoretical studies revealed that carbon insertion into the RCrSi compounds drastically affects the magnetic behavior, since chromium does not carry any magnetic moment in RCrSiC (R = Y, La-Sm, Gd-Er) compounds in contrast to RCrSi (R = Y, Sm, Gd-Lu, Th) compounds. In this study, we report on the unexpected magnetic ordering of chromium atoms in the isotype quaternary UCrSiC compound. While specific heat and magnetic measurements suggest a Pauli paramagnetic behavior, neutron powder diffraction reveals an antiferromagnetic ordering of the chromium substructure at high temperature ( T > 300 K), while that of uranium remains nonmagnetically ordered down to 2 K. Its magnetic behavior, inverse in comparison to the RCrSiC carbides involving a magnetic lanthanide, is discussed in relation with the singularity of its crystal structure among the series. Moreover, the crystallographic structures and the structural stability of UCrSiC and of two other quaternary U-Cr-Si-C compounds (i.e., UCrSiC and UCrSiC), based on the full occupancy of interstitial sites by carbon atoms, are discussed and compared to those of the related ternary intermetallics. Finally, the low-temperature form of UCrSi, corresponding to a Displacive Transformation around 210 K of the ThCrSi-type structure, is reinvestigated by considering a higher symmetry monoclinic unit cell ( C2/ m) instead of the previously reported triclinic cell ( P1̅). The antiferromagnetic ordering at low temperature ( T = 30(2) K) of the uranium substructure is confirmed, and its magnetic structure is reanalyzed and discussed considering the monoclinic crystal structure.

  • Unexpected Magnetic Ordering on the Cr Substructure in UCr2Si2C and Structural Relationships in Quaternary U‑Cr-Si‑C Compounds
    2018
    Co-Authors: P. Lemoine, M. Pasturel, G. Venturini, Anne Vernière, B. Malaman
    Abstract:

    Previous experimental and theoretical studies revealed that carbon insertion into the RCr2Si2 compounds drastically affects the magnetic behavior, since chromium does not carry any magnetic moment in RCr2Si2C (R = Y, La–Sm, Gd–Er) compounds in contrast to RCr2Si2 (R = Y, Sm, Gd–Lu, Th) compounds. In this study, we report on the unexpected magnetic ordering of chromium atoms in the isotype quaternary UCr2Si2C compound. While specific heat and magnetic measurements suggest a Pauli paramagnetic behavior, neutron powder diffraction reveals an antiferromagnetic ordering of the chromium substructure at high temperature (TN > 300 K), while that of uranium remains nonmagnetically ordered down to 2 K. Its magnetic behavior, inverse in comparison to the RCr2Si2C carbides involving a magnetic lanthanide, is discussed in relation with the singularity of its crystal structure among the series. Moreover, the crystallographic structures and the structural stability of UCr2Si2C and of two other quaternary U-Cr-Si-C compounds (i.e., UCr3Si2C and U2Cr3Si2C3), based on the full occupancy of interstitial sites by carbon atoms, are discussed and compared to those of the related ternary intermetallics. Finally, the low-temperature form of UCr2Si2, corresponding to a Displacive Transformation around 210 K of the ThCr2Si2-type structure, is reinvestigated by considering a higher symmetry monoclinic unit cell (C2/m) instead of the previously reported triclinic cell (P1̅). The antiferromagnetic ordering at low temperature (TN = 30(2) K) of the uranium substructure is confirmed, and its magnetic structure is reanalyzed and discussed considering the monoclinic crystal structure

H. K. D. H. Bhadeshia - One of the best experts on this subject based on the ideXlab platform.

  • Further evidence of tetragonality in bainitic ferrite
    Materials Science and Technology, 2014
    Co-Authors: Christopher Hulme-smith, M. J. Peet, I. Lonardelli, Ann Christin Dippel, H. K. D. H. Bhadeshia
    Abstract:

    There is growing evidence that bainitic ferrite which retains a substantial amount of carbon in solid solution does not have cubic symmetry. We provide additional data on a different nanostructured bainitic steel to support this evidence, based on synchrotron X-ray diffraction experiments. The data are consistent only with a Displacive Transformation mechanism for bainite.

  • mechanism and kinetics of solid state Transformation in high temperature processed linepipe steel
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2013
    Co-Authors: H. K. D. H. Bhadeshia
    Abstract:

    A relatively new class of linepipe steels with yield strength greater than 500 MPa created for thermomechanical processing at temperatures in excess of 1473 K (1200 °C) has established a firm foothold in the market for modern, large diameter, and high-pressure gas transmission systems. The design concept for the steels takes advantage of the enhanced role which higher levels of niobium can play in very low carbon steels, during the plate manufacturing process. The Transformation products observed after cooling have been interpreted in conflicting ways in the literature, using ambiguous terms which are not established rigorously. Revealing characterization experiments have therefore been conducted to establish that the principal Transformation product grows by a Displacive Transformation mechanism, and that it is properly identified as bainite. The implications of this, on both the interpretation of microstructure and on the processing of the steel, are discussed.

  • Mathematics of Crystallographic Texture in Martensitic and Related Transformations
    Microstructure and Texture in Steels, 2009
    Co-Authors: H. K. D. H. Bhadeshia, Saurabh Kundu, H. Abreu
    Abstract:

    This paper is an introduction to the mathematical estimation of the crystallographic texture and microstructure resulting from the Displacive Transformation of austenite in steels, under the influence of an externally applied system of stresses. It begins with an introduction to the problem, a description of the phenomenological theory of martensite crystallography, and the application of this theory along with a variant selection criterion to determine the texture due to solid-state, Displacive Transformation. It is demonstrated that there remain difficulties which make a complete closure between theory and experiment unlikely. Progress is needed in relating the chemical and mechanical driving forces for phase Transformation to the evolution of overall volume fractions of different crystallographic variants.

  • Properties of Fine-Grained Steels Generated by Displacive Transformation
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008
    Co-Authors: H. K. D. H. Bhadeshia
    Abstract:

    It has been possible in recent times to make large quantities of steels in which the controlling scale is 20 nm or less, i.e., comparable to that of carbon nanotubes. The mechanical properties of such steels are abnormal. For example, in some cases the ductility vanishes as the strength increases, whereas in others the ductility almost entirely consists of uniform plastic strain. Some of the steels also can tolerate large fractions of brittle phases before fracture. These and other aspects of strong, nanostructured steels are critically assessed to arrive at a hypothesis which rationalises the odd observations.

  • Calculation of crystallographic texture due to Displacive Transformations
    International Journal of Materials Research, 2008
    Co-Authors: H. K. D. H. Bhadeshia, H. Abreu, Saurabh Kundu
    Abstract:

    Abstract Displacive Transformations involve the disciplined motion of atoms. As a result, there are clearly defined relationships between all aspects of the parent and product lattices. The theory for this is well established but has not been exploited in the calculation of Transformation textures. This paper is a critical assessment of the methods for the estimation of crystallographic textures during the Displacive Transformation of austenite into martensite, bainite or Widmanstatten ferrite in steels. The discussion is limited to the case where austenite is not in a plastically deformed state prior to its Transformation.

Chunjin Chen - One of the best experts on this subject based on the ideXlab platform.

  • diffusional Displacive Transformation in a metastable β titanium alloy and its strengthening effect
    Acta Materialia, 2020
    Co-Authors: Chunjin Chen, Binbin Jiang, Yulin Hao, Rui Yang
    Abstract:

    Abstract Diffusional-Displacive Transformations are generally associated with mechanical properties of materials such as high strength. Understanding structure evolution of these Transformations is of great interests from both physics and application perspectives. By combining atomic resolution electron microscopy, energy dispersive spectroscopy and first principles calculations, a continuous β→αʺ→α Transformation process has been quantitatively characterized at the atomic level in a metastable β-Ti alloy during aging treatment. The Transformation is revealed to develop by a novel mechanism involving continuous structural and compositional changes towards the equilibrium assisted by compositional fluctuation in the β matrix. Moreover, the product phase induces a precipitate-matrix lattice mismatch, thus produces a coherency strain field surrounding the precipitates. The coherent strain field contributes significantly to the increasing hardness of the alloy after aging. These results have great potential for tailoring thermomechanical treatment routes and improving mechanical properties of materials.

  • Reversible Displacive Transformation with continuous transition interface in a metastable β titanium alloy
    Acta Materialia, 2019
    Co-Authors: Chunjin Chen, Yulin Hao, Huichao Duan, Rui Yang
    Abstract:

    Abstract Super-elasticity and shape memory of materials are typically associated with reversible phase Transformations. The reversible phase Transformations and their governing factors thus have long been research interests of materials scientists and physicists. Here, a novel reversible ω Transformation has been observed in a metastable β-Ti alloy during tensile deformation with in situ aberration corrected transmission electron microscopy. We reveal that the reversible Transformation is attributed to a trigonal crystal structure of the ω phase. Moreover, continuous transition interfaces with no interfacial defects are formed between the ω and β phases, and they contribute essentially to the occurrence of the reverse Transformation. This reversible Transformation has great potential for developing super-elasticity and shape memory in materials.

Rui Yang - One of the best experts on this subject based on the ideXlab platform.

  • diffusional Displacive Transformation in a metastable β titanium alloy and its strengthening effect
    Acta Materialia, 2020
    Co-Authors: Chunjin Chen, Binbin Jiang, Yulin Hao, Rui Yang
    Abstract:

    Abstract Diffusional-Displacive Transformations are generally associated with mechanical properties of materials such as high strength. Understanding structure evolution of these Transformations is of great interests from both physics and application perspectives. By combining atomic resolution electron microscopy, energy dispersive spectroscopy and first principles calculations, a continuous β→αʺ→α Transformation process has been quantitatively characterized at the atomic level in a metastable β-Ti alloy during aging treatment. The Transformation is revealed to develop by a novel mechanism involving continuous structural and compositional changes towards the equilibrium assisted by compositional fluctuation in the β matrix. Moreover, the product phase induces a precipitate-matrix lattice mismatch, thus produces a coherency strain field surrounding the precipitates. The coherent strain field contributes significantly to the increasing hardness of the alloy after aging. These results have great potential for tailoring thermomechanical treatment routes and improving mechanical properties of materials.

  • Reversible Displacive Transformation with continuous transition interface in a metastable β titanium alloy
    Acta Materialia, 2019
    Co-Authors: Chunjin Chen, Yulin Hao, Huichao Duan, Rui Yang
    Abstract:

    Abstract Super-elasticity and shape memory of materials are typically associated with reversible phase Transformations. The reversible phase Transformations and their governing factors thus have long been research interests of materials scientists and physicists. Here, a novel reversible ω Transformation has been observed in a metastable β-Ti alloy during tensile deformation with in situ aberration corrected transmission electron microscopy. We reveal that the reversible Transformation is attributed to a trigonal crystal structure of the ω phase. Moreover, continuous transition interfaces with no interfacial defects are formed between the ω and β phases, and they contribute essentially to the occurrence of the reverse Transformation. This reversible Transformation has great potential for developing super-elasticity and shape memory in materials.

Andrei Artemev - One of the best experts on this subject based on the ideXlab platform.

  • Interaction between carbon partitioning and carbide nucleation inside austenite during a bainitic type Transformation
    Computational Materials Science, 2020
    Co-Authors: F. Elhigazi, Andrei Artemev
    Abstract:

    Abstract The interaction between the Displacive Transformation, carbon partitioning and carbide nucleation inside austenite during a bainitic type Transformation was studied using a phase field model incorporating the Displacive Transformation and diffusion processes. The carbide nucleation was modeled as a formation of carbon sinks inside austenite with different nucleation sequences. The results obtained with different nucleation sequences demonstrate that carbide nucleation may play a secondary role controlling the Transformation kinetics and microstructure evolution after the fast Transformation stage completion; however, elastic interactions can control the ferrite morphology even at a later stage, thus leading to the change of the ferrite grain shape from a rod-like to plate-like. A rate of the carbide nucleation and the number of nucleated carbides controlled the extension of the stasis period separating the fast and slow Transformation stages and the rate of the Transformation after the stasis or during a temporary slowdown period. Results show that the Transformation can proceed through several slowdown - acceleration periods.

  • The interaction between the Displacive Transformation and the diffusion process in the bainitic type Transformation
    Computational Materials Science, 2019
    Co-Authors: F. Elhigazi, Andrei Artemev
    Abstract:

    Abstract The interaction between the Displacive Transformation and the diffusion process during the bainitic type Transformation was studied using a phase field model incorporating both processes. A chemical free energy density function was derived to represent thermodynamic properties of low-alloy steels at high supercooling conditions at which the direct Transformation from austenite to ferrite at a constant carbon concentration is possible. The results demonstrate that in such conditions both the Displacive Transformation and diffusional decomposition process may play important roles controlling the Transformation kinetics and microstructure. A fast Displacive Transformation is dominant at the onset of the Transformation; however, the diffusion-controlled decomposition can take control over the Transformation kinetics and even the ferrite morphology at later stages as a result of the formation of a carbon enriched layer around ferrite grains. Both plate-like and rod-like shapes of ferrite grains can be obtained depending on the thermodynamic conditions and diffusion mobility.