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Eduard Arzt - One of the best experts on this subject based on the ideXlab platform.
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Constrained Diffusional Creep in Thin Copper Films
MRS Online Proceedings Library, 2011Co-Authors: D. Weiss, Huajian Gao, Eduard ArztAbstract:The mechanical properties of thin metal films have been investigated for many years. How- ever, the underlying mechanisms are still not fully understood. In this paper we give an overview of our work on thermomechanical properties and microstructure evolution in pure Cu and dilute Cu-Al alloy films. Very clean films were produced by sputtering and annealing under ultra-high vacuum (UHV) conditions. We described stress-temperature curves of pure Cu films with a constrained Diffusional Creep model from the literature. In Cu-1at.%Al alloy films, Al surface segregation and oxidation led to a “self-passivating” effect. These films showed an increased high- temperature strength because of the suppression of constrained Diffusional Creep; however, under certain annealing conditions, these films deteriorated due to void growth at grain boundaries.
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constrained Diffusional Creep in uhv produced copper thin films
Acta Materialia, 2001Co-Authors: Dirk N Weiss, Huajian Gao, Eduard ArztAbstract:Abstract The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin-film devices, but its mechanisms are not fully understood. In this investigation, the mechanical properties of pure Cu and Cu–1 at.% Al films on diffusion-barrier coated Si substrates were studied with the wafer-curvature technique. In ultra-pure films, which were sputtered and annealed under ultra-high vacuum conditions, characteristic stress relaxation at high temperatures was measured, which could be clearly attributed to Diffusional Creep. Good quantitative agreement with a recent model of Diffusional Creep constrained by a substrate was obtained. These features were absent in the Cu–Al alloy films, in which Al surface segregation and oxidation had produced a “self-passivating” effect, and in films produced in less clean environments. Based on these results, we propose a model of thin-film deformation based on dislocation glide and constrained Diffusional Creep.
Huajian Gao - One of the best experts on this subject based on the ideXlab platform.
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CONSTRAINED Diffusional Creep IN ULTRA THIN COPPER FILMS DEPOSITED ON SUBSTRATES
2016Co-Authors: Markus J. Buehler, Er Hartmaier, Huajian GaoAbstract:In a recent study of Diffusional Creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into Diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begi
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3153 constrained Diffusional Creep in ultra thin copper films deposited on substrates
ICF11 Italy 2005, 2013Co-Authors: Markus J. Buehler, Alexander Hartmaier, Huajian GaoAbstract:In a recent study of Diffusional Creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into Diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in microand nanostructured materials.
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Constrained Diffusional Creep in Thin Copper Films
MRS Online Proceedings Library, 2011Co-Authors: D. Weiss, Huajian Gao, Eduard ArztAbstract:The mechanical properties of thin metal films have been investigated for many years. How- ever, the underlying mechanisms are still not fully understood. In this paper we give an overview of our work on thermomechanical properties and microstructure evolution in pure Cu and dilute Cu-Al alloy films. Very clean films were produced by sputtering and annealing under ultra-high vacuum (UHV) conditions. We described stress-temperature curves of pure Cu films with a constrained Diffusional Creep model from the literature. In Cu-1at.%Al alloy films, Al surface segregation and oxidation led to a “self-passivating” effect. These films showed an increased high- temperature strength because of the suppression of constrained Diffusional Creep; however, under certain annealing conditions, these films deteriorated due to void growth at grain boundaries.
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atomistic and continuum studies of Diffusional Creep and associated dislocation mechanisms in thin films on substrates
Multiscale Phenomena in Materials - Experiments and Modeling Related to Mechanical Behavior. Symposium held at the 2003 MRS Spring Meeting, 2003Co-Authors: Markus J. Buehler, Alexander Hartmaier, Huajian GaoAbstract:Motivated by recent theoretical and experimental progress, large-scale atomistic simulations are performed to study plastic deformation in sub-micron thin films. The studies reveal that stresses are relaxed by material transport from the surface into the grain boundary. This leads to the formation of a novel defect identified as diffusion wedge. Eventually, a crack-like stress field develops because the tractions along the grain boundary relax, but the adhesion of the film to the substrate prohibits strain relaxation close to the interface. This causes nucleation of unexpected parallel glide dislocations at the grain boundary-substrate interface, for which no driving force exists in the overall biaxial stress field. The observation of parallel glide dislocations in molecular dynamics studies closes the theory-experiment-simulation linkage. In this study, we also compare the nucleation of dislocations from a diffusion wedge with nucleation from a crack. Further, we present preliminary results of modeling constrained Diffusional Creep using discrete dislocation dynamics simulations.
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constrained Diffusional Creep in uhv produced copper thin films
Acta Materialia, 2001Co-Authors: Dirk N Weiss, Huajian Gao, Eduard ArztAbstract:Abstract The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin-film devices, but its mechanisms are not fully understood. In this investigation, the mechanical properties of pure Cu and Cu–1 at.% Al films on diffusion-barrier coated Si substrates were studied with the wafer-curvature technique. In ultra-pure films, which were sputtered and annealed under ultra-high vacuum conditions, characteristic stress relaxation at high temperatures was measured, which could be clearly attributed to Diffusional Creep. Good quantitative agreement with a recent model of Diffusional Creep constrained by a substrate was obtained. These features were absent in the Cu–Al alloy films, in which Al surface segregation and oxidation had produced a “self-passivating” effect, and in films produced in less clean environments. Based on these results, we propose a model of thin-film deformation based on dislocation glide and constrained Diffusional Creep.
J. Wolfenstine - One of the best experts on this subject based on the ideXlab platform.
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Original ArticlesDiffusional Creep and Diffusion-Controlled Dislocation Creep and Their Relation to Denuded Zones in Mg-ZrH2 Materials
Scripta Materialia, 1998Co-Authors: Oscar Antonio Ruano, O. D. Sherby, Jeffrey Wadsworth, J. WolfenstineAbstract:Langdon`s contention that Creep of Mg-0.5 wt% Zr is well characterized by Diffusional Creep at 400 C is in error. It is shown that Langdon and Gifkins` single analysis of denuded zones formed during Creep at 2 MPa, purporting to occur as a result of Diffusional Creep, in fact, took place in the power-law dislocation Creep range where solute atoms are interacting with moving dislocations. This observation supports the earlier conclusions made for Creep and denuded zones observed in the hydrided Mg-Zr alloy at 500 C. Furthermore, it is shown that Pickles` data at stresses below 2 MPa at 400 C are not related to Diffusional Creep as considered by Langdon. In this region, denuded zones appear in both longitudinal and transverse boundaries indicating that grain boundary sliding, accompanied by grain boundary migration, is the principal deformation process. It is proposed that denuded zones are caused by dissolution of precipitates at moving grain boundaries.
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use of Diffusional Creep to investigate mass transport in la sr mno3
Solid State Ionics, 1996Co-Authors: J. Wolfenstine, K C Goretta, R E Cook, J L RoutbortAbstract:Abstract The steady-state Creep rate of La1 − xSrxMnO3 (x = 0.10, 0.15 and 0.25) decreased with increasing Sr content in a regime where Diffusional Creep is the dominant deformation mechanism. This composition effect when compared to existing point defect models suggested that the rate-controlling species for mass transport in (La, Sr)MnO3 is lattice diffusion of the cations, either lanthanum or manganese. This is in agreement with previous Creep (based on an activation energy comparison) and sintering results. Diffusional Creep can be used effectively to investigate mass transport in (La, Sr)MnO3.
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rebuttal to in defense of Diffusional Creep
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1996Co-Authors: Oscar Antonio Ruano, Oleg D Sherby, J Wadsworth, J. WolfenstineAbstract:Abstract Rebuttals to the recent criticisms of Burton and Reynolds and of Greenwood to our papers challenging the existence of Diffusional Creep are presented and responses by us to the following specific areas are discussed. (1) Denuded zones, universally to be considered direct evidence for Diffusional Creep, are seen only under conditions where a high stress exponent (as opposed to a value of unity) is observed, indicating that diffusion-controlled dislocation Creep is the operative deformation process. (2) The Creep rate of fine-grained superplastic materials is invariably orders of magnitude greater than predicted by Diffusional Creep; in these cases, the deformation process has been established to be grain-boundary sliding accommodated by slip (GBS) rather than Diffusional Creep. (3) The Creep behavior of fine-grained copper measured by Burton and Greenwood can be described by a diffusion-controlled dislocation Creep mechanism at high stresses, by GBS at intermediate stresses, and by Harper-Dorn Creep at low stresses, with no clear evidence for Diffusional Creep.
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refutation of the relationship between denuded zones and Diffusional Creep
Scripta Metallurgica Et Materialia, 1993Co-Authors: J. Wolfenstine, Oscar Antonio Ruano, J Wadsworth, O. D. SherbyAbstract:The first direct microstructural observation used as evidence for Diffusional Creep is from the work of Squires, Weiner, and Phillips (S-W-P). They observed denuded zones at grain boundaries after Creep in a Mg-0.5 wt.% Zr alloy that contained inert precipitates. It is the purpose of this paper to show that the reported Creep data for the Mg-0.5 wt.%Zr alloy was, in fact, obtained in a region where dislocation Creep, rather than Diffusional Creep, was the dominant deformation mechanism. Details of the denuded zone formation will also be presented which question the relation of denuded zones to Diffusional Creep. Therefore, it is contended that the microstructurally-observed denuded zones cannot be a result of Diffusional Creep. This contention supports previously-published views by the present authors that conclusive proof for Diffusional Creep in polycrystalline materials remains elusive.
Oscar Antonio Ruano - One of the best experts on this subject based on the ideXlab platform.
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denuded zones Diffusional Creep and grain boundary sliding
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2002Co-Authors: J Wadsworth, Oscar Antonio Ruano, Oleg D SherbyAbstract:The appearance of denuded zones following low stress Creep in particle-containing crystalline materials is both a microstructural prediction and observation often cited as irrefutable evidence for the Nabarro-Herring (N-H) mechanism of Diffusional Creep. The denuded zones are predicted to be at grain boundaries that are orthogonal to the direction of the applied stress. Furthermore, their dimensions should account for the accumulated plastic flow.
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deformation by grain boundary sliding and slip Creep versus Diffusional Creep
The Minerals Metals and Materials Society (TMS) 1999 Annual Meeting San Diego CA February 28-March 4 1999, 1998Co-Authors: Oscar Antonio Ruano, O. D. Sherby, J WadsworthAbstract:A review is presented of the debates between the present authors and other investigators regarding the possible role of Diffusional Creep in the plastic flow of polycrystalline metals at low stresses. These debates are recorded in eleven papers over the past seventeen years. ln these papers it has been shown that the Creep rates of materials in the so-called "Diffusional Creep region" are almost always higher than those predicted by the Diffusional Creep theory. Additionally, the predictions of grain size effects and stress exponents from Diffusional Creep theory are often not found in the experimental data. Finally, denuded zones have been universally considered to be direct evidence for Diffusional Creep; but, those reported in the literature are shown to be found only under conditions where a high stress exponent is observed. Also, the locations of the denuded zones do not match those predicted. Alternative mechanisms are described in which diffusion-controlled dislocation Creep and/or grain boundary sliding are the dominant deformation processes in low-stress Creep. It is proposed that denuded zones are formed by stress-directed grain boundary migration with the precipitates dissolving in the moving grain boundaries. The above observations have led us to the conclusion that grain boundary sliding andmore » slip Creep are in fact the principal mechanisms for observations of plastic flow in the so-called "Diffusional Creep regions".« less
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Original ArticlesDiffusional Creep and Diffusion-Controlled Dislocation Creep and Their Relation to Denuded Zones in Mg-ZrH2 Materials
Scripta Materialia, 1998Co-Authors: Oscar Antonio Ruano, O. D. Sherby, Jeffrey Wadsworth, J. WolfenstineAbstract:Langdon`s contention that Creep of Mg-0.5 wt% Zr is well characterized by Diffusional Creep at 400 C is in error. It is shown that Langdon and Gifkins` single analysis of denuded zones formed during Creep at 2 MPa, purporting to occur as a result of Diffusional Creep, in fact, took place in the power-law dislocation Creep range where solute atoms are interacting with moving dislocations. This observation supports the earlier conclusions made for Creep and denuded zones observed in the hydrided Mg-Zr alloy at 500 C. Furthermore, it is shown that Pickles` data at stresses below 2 MPa at 400 C are not related to Diffusional Creep as considered by Langdon. In this region, denuded zones appear in both longitudinal and transverse boundaries indicating that grain boundary sliding, accompanied by grain boundary migration, is the principal deformation process. It is proposed that denuded zones are caused by dissolution of precipitates at moving grain boundaries.
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rebuttal to in defense of Diffusional Creep
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1996Co-Authors: Oscar Antonio Ruano, Oleg D Sherby, J Wadsworth, J. WolfenstineAbstract:Abstract Rebuttals to the recent criticisms of Burton and Reynolds and of Greenwood to our papers challenging the existence of Diffusional Creep are presented and responses by us to the following specific areas are discussed. (1) Denuded zones, universally to be considered direct evidence for Diffusional Creep, are seen only under conditions where a high stress exponent (as opposed to a value of unity) is observed, indicating that diffusion-controlled dislocation Creep is the operative deformation process. (2) The Creep rate of fine-grained superplastic materials is invariably orders of magnitude greater than predicted by Diffusional Creep; in these cases, the deformation process has been established to be grain-boundary sliding accommodated by slip (GBS) rather than Diffusional Creep. (3) The Creep behavior of fine-grained copper measured by Burton and Greenwood can be described by a diffusion-controlled dislocation Creep mechanism at high stresses, by GBS at intermediate stresses, and by Harper-Dorn Creep at low stresses, with no clear evidence for Diffusional Creep.
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refutation of the relationship between denuded zones and Diffusional Creep
Scripta Metallurgica Et Materialia, 1993Co-Authors: J. Wolfenstine, Oscar Antonio Ruano, J Wadsworth, O. D. SherbyAbstract:The first direct microstructural observation used as evidence for Diffusional Creep is from the work of Squires, Weiner, and Phillips (S-W-P). They observed denuded zones at grain boundaries after Creep in a Mg-0.5 wt.% Zr alloy that contained inert precipitates. It is the purpose of this paper to show that the reported Creep data for the Mg-0.5 wt.%Zr alloy was, in fact, obtained in a region where dislocation Creep, rather than Diffusional Creep, was the dominant deformation mechanism. Details of the denuded zone formation will also be presented which question the relation of denuded zones to Diffusional Creep. Therefore, it is contended that the microstructurally-observed denuded zones cannot be a result of Diffusional Creep. This contention supports previously-published views by the present authors that conclusive proof for Diffusional Creep in polycrystalline materials remains elusive.
G W Greenwood - One of the best experts on this subject based on the ideXlab platform.
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grain shape effects on interface controlled Diffusional Creep under multiaxial stresses
Acta Metallurgica Et Materialia, 1995Co-Authors: G W GreenwoodAbstract:Abstract Interface control of the emission and absorption of vacancies reduces, but does not eliminate, the dependency of Diffusional Creep on grain size and shape and it increases the sensitivity to stress. Previous analyses of interfacially controlled Diffusional Creep of polycrystals with equiaxed grains under a uniaxial stress are extended and further developed to determine approximately the behaviour of material with anisotropic grain shapes under multiaxial stresses. Whilst all details of this Creep process are not fully understood, it is shown that, by noting a set of conditions to be fulfilled, the form of equation required to describe anisotropic Creep strength can be identified. Although interfacial control implies a power law dependance on stress, it is noted that the directionality in Creep deformation is governed by grain shape orientation and by linear functions of the applied stresses and so anisotropic aspects of Creep response under multiaxial stresses can be described by “Creep compliance coefficients” analogous to those representing anisotropic elastic behaviour. Since anisotropy is influenced by three parameters, representing the principal orthogonal grain dimensions, only three of these coefficients are independent. From this approach a Von Mises type function can be formulated through which anisotropic interface-controlled Diffusional Creep strength may be evaluated.
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denuded zones and Diffusional Creep
Scripta Metallurgica Et Materialia, 1994Co-Authors: G W GreenwoodAbstract:Numerous observations have followed the reporting of the absence of precipitates in zones adjacent to grain boundaries oriented approximately normal to the direction of elongation in materials subjected to low stresses at elevated temperatures. Such observations have usually been regarded as evidence that Diffusional Creep'' is then occurring by a process whereby atomic fluxes are created by the counter flow of vacancies between grain boundaries at different orientations. This view however has not gone unchallenged, and a recent publication has presented a detailed and critical review with the conclusion that any relationship between denuded zones and Diffusional Creep can be refuted. The present note puts forward some further points that are frequently overlooked in arguments of this kind and suggests some approaches that may be helpful in their resolution.
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a formulation for anisotropy in Diffusional Creep
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 1992Co-Authors: G W GreenwoodAbstract:Grain shape can introduce anisotropy in Creep which depends on the diffusion of vacancies between grain boundary sources and sinks. Such anisotropy is examined to determine the rate of Creep under multiaxial stresses both for lattice and grain boundary diffusion. Noting the role of grain boundary sliding in this form of Creep it is shown that, with some approximations that only become significant in an identified case, complete and fully self-consistent formulae can be derived for the rate of Creep in terms of grain dimensions. The results are presented in the form of compliance matrices which are analogous to those that have a well-established role in the characterization of elastic anisotropy. A comparable usefulness of these `Creep compliance coefficients' is envisaged in evaluating anisotropic Diffusional Creep behaviour and a similar approach can be extended to more general cases where Creep rates may be interface controlled.