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Gary S. Was - One of the best experts on this subject based on the ideXlab platform.

  • Interpretation of Improved Creep Properties of a 9Cr-1Mo-Nb-V (T91) Steel by Grain Boundary Engineering
    2015
    Co-Authors: Gaurav Gupta, Gary S. Was
    Abstract:

    Ferritic-Martensitic alloys are expected to play a major role in supercritical water reactor internals. These steels offer better swelling resistance than austenitic alloys but may suffer from grain boundary or matrix creep and loss of strength at higher temperatures and unacceptably low toughness at lower temperatures. The focus of this investigation is to improve the creep resistance of T91 by grain boundary engineering. By increasing the fraction of Coincident Site Lattice (CSL), or special boundaries, the grain boundaries are strengthened against sliding and deformation, thus improving the creep resistance. Thermo-mechanical treatment for Coincident Site Lattice enhancement of T91 has already been developed. High temperature (500-550°C) creep experiments in argon are conducted to assess the effectiveness of the CSL enhanced microstructure on the creep rate. Experimental analysis shows that the CSL-enhanced condition results in a lower creep rate by a factor of 3-4 as-compared to A/R condition for in the stress range of 200–235 MPa

  • The role of stress in the efficacy of Coincident Site Lattice boundaries in improving creep and stress corrosion cracking
    Scripta Materialia, 2006
    Co-Authors: Bogdan Alexandreanu, Gary S. Was
    Abstract:

    Abstract While a consensus appears to exist on the improved resistance to intergranular stress corrosion cracking (SCC) initiation of coincidence Site Lattice boundaries (CSLBs) in austenitic alloys, the effect of such boundaries on SCC propagation is not well understood. Experimental results show a direct correlation between IGSCC and creep rate via the fraction of CSLBs, as well as a cause-and-effect relationship between grain boundary deformation and cracking. The objective of this paper is to highlight the importance of deformation in the SCC behavior.

  • The Role of Grain Boundary Engineering on the High Temperature Creep of Ferritic-Martensitic Alloy T91
    Journal of ASTM International, 2005
    Co-Authors: Gaurav Gupta, Gary S. Was
    Abstract:

    Ferritic-Martensitic alloys are expected to play a major role in supercritical water reactor internals. These steels offer better swelling resistance than austenitic alloys but may suffer from grain boundary or matrix creep and loss of strength at higher temperatures and unacceptably low toughness at lower temperatures. The focus of this investigation is to improve the creep resistance of T91 by grain boundary engineering. By increasing the fraction of Coincident Site Lattice (CSL), or special boundaries, the grain boundaries are strengthened against sliding and deformation, thus improving the creep resistance. Thermo-mechanical treatment for Coincident Site Lattice enhancement of T91 has already been developed. High temperature (500°C) creep experiments in argon are conducted to assess the effectiveness of the CSL enhanced microstructure on the creep rate. Experimental analysis shows that the CSL-enhanced condition results in a lower creep rate by a factor of 3-4 as-compared to A/R condition for T91 at a temperature of 500°C and in the stress range of 200–225 MPa by reducing the effective stress.

  • Role of Coincident Site Lattice boundaries in creep and stress corrosion cracking
    MRS Proceedings, 2004
    Co-Authors: Gary S. Was, B. Alexandreanu, Peter L. Andresen, Mukul Kumar
    Abstract:

    Interfaces control many properties in engineering materials, several of which are critical to the integrity of the engineering structure. In single phase, solid solution, austenitic alloys, grain boundaries are often the weak link, displaying susceptibility to creep, corrosion and stress corrosion cracking. As such, grain boundary structure control affords the opportunity to improve the overall performance of alloys in a variety of applications. The role of Coincident Site Lattice boundary (CSLB) enhancement and grain boundary connectivity is examined for how it affects the response of an alloy to stress and the environment. Specifically, the effect of grain boundary character on creep, grain boundary sliding, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking in austenitic nickel-base (high purity Ni-Cr-Fe and alloy 600) and iron-base (high purity Fe-Cr-Ni and 304 stainless steel) alloys and for ferritic- martensitic alloy T91 is discussed.

  • The effect of grain boundary character distribution on the high temperature deformation behavior of Ni–16Cr–9Fe alloys
    Acta Materialia, 2003
    Co-Authors: Bogdan Alexandreanu, Visit Thaveeprungsriporn, Bulent H Sencer, Gary S. Was
    Abstract:

    The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep rate on the Coincident Site Lattice (CSL) fraction. The model attributed the large reduction in creep rate in alloys with a high population of CSL boundaries to the greater difficulty of extrinsic grain boundary dislocation (EGBD) absorption at Coincident Site Lattice boundaries (CSLBs) vs. high angle boundaries (HABs). Ease of EGBD absorption was assessed by measuring the annihilation rates of EGBDs in both CSL-related and HABs following an anneal at 360 °C. Results showed that EGBDs are annihilated at HABs at a rate that is on average three times that at CSLBs, implying a grain boundary diffusion coefficient in CSLBs that is 12 times lower than that in HABs. The expectation that a reduction in EGBD absorption would lead to greater matrix hardening was investigated using nano-hardness measurements. Results showed that the hardness in the vicinity of CSLBs is greater than that near HABs, and the grain-averaged hardness increases with the fraction of contiguous CSLBs. Further, strain hardening is greater in CSL-enhanced samples than in reference, solution annealed samples. These results taken together substantiate the hypothesis that CSLBs impede dislocation absorption into the grain boundary, thereby increasing Lattice hardening and internal stress in the sample, resulting in a reduced creep rate.

Bogdan Alexandreanu - One of the best experts on this subject based on the ideXlab platform.

  • The role of stress in the efficacy of Coincident Site Lattice boundaries in improving creep and stress corrosion cracking
    Scripta Materialia, 2006
    Co-Authors: Bogdan Alexandreanu, Gary S. Was
    Abstract:

    Abstract While a consensus appears to exist on the improved resistance to intergranular stress corrosion cracking (SCC) initiation of coincidence Site Lattice boundaries (CSLBs) in austenitic alloys, the effect of such boundaries on SCC propagation is not well understood. Experimental results show a direct correlation between IGSCC and creep rate via the fraction of CSLBs, as well as a cause-and-effect relationship between grain boundary deformation and cracking. The objective of this paper is to highlight the importance of deformation in the SCC behavior.

  • the effect of grain boundary character distribution on the high temperature deformation behavior of ni 16cr 9fe alloys
    Acta Materialia, 2003
    Co-Authors: Bogdan Alexandreanu, Bulent H Sencer, Visit Thaveeprungsriporn
    Abstract:

    The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep rate on the Coincident Site Lattice (CSL) fraction. The model attributed the large reduction in creep rate in alloys with a high population of CSL boundaries to the greater difficulty of extrinsic grain boundary dislocation (EGBD) absorption at Coincident Site Lattice boundaries (CSLBs) vs. high angle boundaries (HABs). Ease of EGBD absorption was assessed by measuring the annihilation rates of EGBDs in both CSL-related and HABs following an anneal at 360 °C. Results showed that EGBDs are annihilated at HABs at a rate that is on average three times that at CSLBs, implying a grain boundary diffusion coefficient in CSLBs that is 12 times lower than that in HABs. The expectation that a reduction in EGBD absorption would lead to greater matrix hardening was investigated using nano-hardness measurements. Results showed that the hardness in the vicinity of CSLBs is greater than that near HABs, and the grain-averaged hardness increases with the fraction of contiguous CSLBs. Further, strain hardening is greater in CSL-enhanced samples than in reference, solution annealed samples. These results taken together substantiate the hypothesis that CSLBs impede dislocation absorption into the grain boundary, thereby increasing Lattice hardening and internal stress in the sample, resulting in a reduced creep rate.

  • The effect of grain boundary character distribution on the high temperature deformation behavior of Ni–16Cr–9Fe alloys
    Acta Materialia, 2003
    Co-Authors: Bogdan Alexandreanu, Visit Thaveeprungsriporn, Bulent H Sencer, Gary S. Was
    Abstract:

    The objective of this work was to test the Thaveeprungsriporn model for the dependence of creep rate on the Coincident Site Lattice (CSL) fraction. The model attributed the large reduction in creep rate in alloys with a high population of CSL boundaries to the greater difficulty of extrinsic grain boundary dislocation (EGBD) absorption at Coincident Site Lattice boundaries (CSLBs) vs. high angle boundaries (HABs). Ease of EGBD absorption was assessed by measuring the annihilation rates of EGBDs in both CSL-related and HABs following an anneal at 360 °C. Results showed that EGBDs are annihilated at HABs at a rate that is on average three times that at CSLBs, implying a grain boundary diffusion coefficient in CSLBs that is 12 times lower than that in HABs. The expectation that a reduction in EGBD absorption would lead to greater matrix hardening was investigated using nano-hardness measurements. Results showed that the hardness in the vicinity of CSLBs is greater than that near HABs, and the grain-averaged hardness increases with the fraction of contiguous CSLBs. Further, strain hardening is greater in CSL-enhanced samples than in reference, solution annealed samples. These results taken together substantiate the hypothesis that CSLBs impede dislocation absorption into the grain boundary, thereby increasing Lattice hardening and internal stress in the sample, resulting in a reduced creep rate.

Doh-yeon Kim - One of the best experts on this subject based on the ideXlab platform.

  • Temperature dependence of the coarsening behavior of (Ba, Sr)TiO3 grains dispersed in a SiO2-rich liquid matrix
    Journal of the European Ceramic Society, 2003
    Co-Authors: Ui-jin Chung, Nong-moon Hwang, Doh-yeon Kim
    Abstract:

    Abstract The shape of (Ba 0.35 Sr 0.65 )TiO 3 (BST) grains and their coarsening behavior were investigated as a function of temperature. The BST grains exhibit a morphological change at approximately 1410 °C; the grains were angular at 1390 °C and corner-rounded at 1420 °C. At 1390 °C, a few very large grains appear in the microstructure. Such abnormal grain growth is explained in terms of a coarsening advantage due to the Σ3 Coincident Site Lattice (CSL) boundaries. On the other hand, at 1420 °C, normal grain growth was observed to occur. The change in coarsening behavior with temperature is related to the structural transition of the interface.

Mukul Kumar - One of the best experts on this subject based on the ideXlab platform.

  • The structure of the cubic Coincident Site Lattice rotation group.
    Acta crystallographica. Section A Foundations of crystallography, 2004
    Co-Authors: Bryan W Reed, Roger W Minich, Robert E Rudd, Mukul Kumar
    Abstract:

    This work is intended to be a mathematical underpinning for the field of grain-boundary engineering and its relatives. The inter-relationships within the set of rotations producing Coincident Site Lattices in cubic crystals are examined in detail. Besides combining previously established but widely scattered results into a unified context, the present work details newly developed representations of the group structure in terms of strings of generators (based on quaternionic number theory, and including uniqueness proofs and rules for algebraic manipulation) as well as an easily visualized topological network model. Important results that were previously obscure or not universally understood (e.g. the Sigma combination rule governing triple junctions) are clarified in these frameworks. The methods also facilitate several general observations, including the very different natures of twin-limited structures in two and three dimensions, the inadequacy of the Sigma combination rule to determine valid quadruple nodes, and a curious link between allowable grain-boundary assignments and the four-color map theorem. This kind of understanding is essential to the generation of realistic statistical models of grain-boundary networks (particularly in twin-dominated systems) and is especially applicable to the field of grain-boundary engineering.

  • Role of Coincident Site Lattice boundaries in creep and stress corrosion cracking
    MRS Proceedings, 2004
    Co-Authors: Gary S. Was, B. Alexandreanu, Peter L. Andresen, Mukul Kumar
    Abstract:

    Interfaces control many properties in engineering materials, several of which are critical to the integrity of the engineering structure. In single phase, solid solution, austenitic alloys, grain boundaries are often the weak link, displaying susceptibility to creep, corrosion and stress corrosion cracking. As such, grain boundary structure control affords the opportunity to improve the overall performance of alloys in a variety of applications. The role of Coincident Site Lattice boundary (CSLB) enhancement and grain boundary connectivity is examined for how it affects the response of an alloy to stress and the environment. Specifically, the effect of grain boundary character on creep, grain boundary sliding, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking in austenitic nickel-base (high purity Ni-Cr-Fe and alloy 600) and iron-base (high purity Fe-Cr-Ni and 304 stainless steel) alloys and for ferritic- martensitic alloy T91 is discussed.

J.th.m. De Hosson - One of the best experts on this subject based on the ideXlab platform.

  • Determination of near Coincident Site Lattice orientations in MgO/Cu compoSite
    Journal of Materials Science, 2002
    Co-Authors: Yong-ling Wang, Ze Zhang, G. H. Yan, J.th.m. De Hosson
    Abstract:

    Orientation relations between MgO precipitates and Cu matrix have been characterized by electron diffraction. Four orientation relations were newly found to be Coincident with Σ41 [110], Σ13 [111], Σ29 [100] and Σ35 [112] near coincidence-Site orientations. The possible dislocation network for these orientation relations was analyzed using O-Lattice theory. The size of MgO precipitates with these orientations are in a range of 0.5–1 micron. Frequently appearance of these special orientation relations implies that they may be the favorable orientations for precipitation and coarsening of MgO particles to some extent.

  • Determination of the Σ 21 [211] orientational relationship in a MgO/Cu compoSite
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001
    Co-Authors: Yong-ling Wang, G. H. Yan, J.th.m. De Hosson
    Abstract:

    Abstract The microstructure of an internally oxidized CuMg alloy has been examined by means of high-resolution transmission electron microscopy. A new orientational relationship, Σ 21 [211], has been determined by selected-area electron diffraction. The dislocation network for such an orientational relationship, calculated using the near Coincident Site Lattice theory, is a parallel array of edge dislocations with Burgers vectors of the type 1/21[1 0 2 1 ] , 1/21[1 4 2] , and 1/21[ 4 5 8 ] .

  • Determination of the Σ21 [211] orientational relationship in a MgO/Cu compoSite
    Materials Science and Engineering: A, 2001
    Co-Authors: Y. G. Wang, G. H. Yan, J.th.m. De Hosson
    Abstract:

    The microstructure of an internally oxidized CuMg alloy has been examined by means of high-resolution transmission electron microscopy. A new orientational relationship, Σ 21 [211], has been determined by selected-area electron diffraction. The dislocation network for such an orientational relationship, calculated using the near Coincident Site Lattice theory, is a parallel array of edge dislocations with Burgers vectors of the type 1/21[1 0 2 1¯], 1/21[1 4¯ 2], and 1/21[4¯5¯8¯]