Kenneth Vecchio | University of California, San Diego (original) (raw)

Papers by Kenneth Vecchio

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 6, 1989

In-situ experiments conducted within a transmission electron microscope provide the operator a un... more In-situ experiments conducted within a transmission electron microscope provide the operator a unique opportunity to directly observe microstructural phenomena, such as phase transformations and dislocation-precipitate interactions, “as they happen”. However, in-situ experiments usually require a tremendous amount of experimental preparation beforehand, as well as, during the actual experiment. In most cases the researcher must operate and control several pieces of equipment simultaneously. For example, in in-situ deformation experiments, the researcher may have to not only operate the TEM, but also control the straining holder and possibly some recording system such as a video tape machine. When it comes to in-situ fatigue deformation, the experiments became even more complicated with having to control numerous loading cycles while following the slow crack growth. In this paper we will describe a new method for conducting in-situ fatigue experiments using a camputer-controlled tensile straining holder.The tensile straining holder used with computer-control system was manufactured by Philips for the Philips 300 series microscopes. It was necessary to modify the specimen stage area of this holder to work in the Philips 400 series microscopes because the distance between the optic axis and holder airlock is different than in the Philips 300 series microscopes. However, the program and interfacing can easily be modified to work with any goniometer type straining holder which uses a penrmanent magnet motor.

arXiv (Cornell University), Dec 12, 2020

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1987

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symm... more Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

Materials & Design, Jun 1, 2021

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1993

Shock-induced reactions (or shock synthesis) have been studied since the 1960’s but are still poo... more Shock-induced reactions (or shock synthesis) have been studied since the 1960’s but are still poorly understood, partly due to the fact that the reaction kinetics are very fast making experimental analysis of the reaction difficult. Shock synthesis is closely related to combustion synthesis, and occurs in the same systems that undergo exothermic gasless combustion reactions. The thermite reaction (Fe2O3 + 2Al -> 2Fe + Al2O3) is prototypical of this class of reactions. The effects of shock-wave passage through porous (powder) materials are complex, because intense and non-uniform plastic deformation is coupled with the shock-wave effects. Thus, the particle interiors experience primarily the effects of shock waves, while the surfaces undergo intense plastic deformation which can often result in interfacial melting. Shock synthesis of compounds from powders is triggered by the extraordinarily high energy deposition rate at the surfaces of the powders, forcing them in close contact, activating them by introducing defects, and heating them close to or even above their melting temperatures.

International Journal of Solids and Structures, Apr 1, 2006

arXiv (Cornell University), Jul 25, 2020

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1990

Although it has been well established that microvoid coalescence occurs during static or quasi-st... more Although it has been well established that microvoid coalescence occurs during static or quasi-static fracture in ductile materials, the exact mechanism for microvoid formation is still unclear. It has been argued that microvoids initiate and grow from second phase particles. However this argument cannot be used to explain the existence of microvoids on the fracture surfaces of "pure" materials. An alternative mechanism for their formation in "pure" materials is that they initiate and grow along dislocation cell walls. If this premise is true; then the nature and extent of microvoid coalescence should be related to the stacking fault energy (SFE) of the material since the latter is a controlling parameter in the formation of dislocation cells. The relationship between microvoid coalescence and stacking fault energy may have some basis since absolute cell dimensions are of the same magnitude as the observed dimple sizes. The present study examines the effect of dislocation cell structures on the formation of microvoids as a function of the stacking fault energy of a given material through direct observation of the void formation and growth process within the TEM. The fundamental aspects of the work is to correlate the dislocation substructures, void initiation, growth, and coalescence to the resulting fracture surfaces.

Materials & Design, May 1, 2022

Optical pseudogap energy in multicomponent carbonitrides is shown to be tunable and predictable b... more Optical pseudogap energy in multicomponent carbonitrides is shown to be tunable and predictable based on composition. Carbonitride hue depends on pseudogap energy, and chroma can be predicted based on the electronic density of states of precursor materials. A model is developed for the prediction of color appearance of any combination of group 4/5 B1-carbides and nitrides. Novel hues previously inaccessible in mononitrides and monocarbides, such as pink and purple, are synthesized in multicomponent carbonitrides.

Materialia, Sep 1, 2020

Abstract FeAl/FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites were synthesized u... more Abstract FeAl/FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites were synthesized using a “multiple-thin-foil” configuration and a “two-stage reaction” strategy. Microstructure analysis via scanning electron microscope (SEM), energy-dispersive X-ray spectrometer (EDS) and electron backscatter diffraction (EBSD) confirms the formation of a two-intermetallic eutectoid structure, which decomposes from the high-temperature Fe5Al8 phase. The metal layers of eutectoid-MIL composites are fabricated with either pure iron or two different stainless steels without altering the intermetallic regions. The volume fraction of eutectoid layers is adjusted for optimizing the performance. The off-eutectoid phase is switched between FeAl and FeAl2 to investigate the effect on strength and ductility. The microstructure of the interfacial regions is fine-tuned, further demonstrating the ability to independently control the constituents of MIL composites. Additionally, a hybrid MIL composite of FeAl and the eutectoid structure are synthesized as a ‘proof-of-concept’. Finite element analysis (FEA) simulation is utilized to study the internal stress in the MIL composites from a macroscopic point of view. Incremental compression tests were conducted to track the fracture evolution from a microscopic point of view.

Journal of the American Ceramic Society, May 23, 2018

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017

Scripta Materialia, Nov 1, 2020

Philosophical Magazine B-physics of Condensed Matter Statistical Mechanics Electronic Optical and Magnetic Properties, Apr 1, 1988

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Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016

Abstract Novel Ceramic-Fiber-Reinforced-Metal-Intermetallic-Laminate (CFR-MIL) composites, Ti–Al3... more Abstract Novel Ceramic-Fiber-Reinforced-Metal-Intermetallic-Laminate (CFR-MIL) composites, Ti–Al3Ti–Al2O3–Al, were synthesized by reactive foil sintering in air. Microstructure controlled material architectures were achieved with continuous Al2O3 fibers oriented in 0° and 90° layers to form fully dense composites in which the volume fractions of all four component phases can be tailored. Bend fracture specimens were cut from the laminate plates in divider orientation, and bend tests were performed to study the fracture behavior of CFR-MIL composites under three-point and four-point bending loading conditions. The microstructures and fractured surfaces of the CFR-MIL composites were examined using optical microscopy and scanning electron microscopy to establish a correlation between the fracture toughness, fracture surface morphology and microstructures of CFR-MIL composites. The fracture and toughening mechanisms of the CFR-MIL composites are also addressed. The present experimental results indicate that the fracture toughness of CFR-MIL composites determined by three- and four-point bend loading configurations are quite similar, and increased significantly compared to MIL composites without ceramic fiber reinforcement. The interface cracking behavior is related to the volume fraction of the brittle Al3Ti phase and residual ductile Al, but the fracture toughness values appear to be insensitive to the ratio of these two phases. The toughness appears to be dominated by the ductility/strength of the Ti layers and the strength and crack bridging effect of the ceramic fibers.

Acta Materialia, Feb 1, 2017

arXiv (Cornell University), Feb 22, 2020

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 6, 1989

In-situ experiments conducted within a transmission electron microscope provide the operator a un... more In-situ experiments conducted within a transmission electron microscope provide the operator a unique opportunity to directly observe microstructural phenomena, such as phase transformations and dislocation-precipitate interactions, “as they happen”. However, in-situ experiments usually require a tremendous amount of experimental preparation beforehand, as well as, during the actual experiment. In most cases the researcher must operate and control several pieces of equipment simultaneously. For example, in in-situ deformation experiments, the researcher may have to not only operate the TEM, but also control the straining holder and possibly some recording system such as a video tape machine. When it comes to in-situ fatigue deformation, the experiments became even more complicated with having to control numerous loading cycles while following the slow crack growth. In this paper we will describe a new method for conducting in-situ fatigue experiments using a camputer-controlled tensile straining holder.The tensile straining holder used with computer-control system was manufactured by Philips for the Philips 300 series microscopes. It was necessary to modify the specimen stage area of this holder to work in the Philips 400 series microscopes because the distance between the optic axis and holder airlock is different than in the Philips 300 series microscopes. However, the program and interfacing can easily be modified to work with any goniometer type straining holder which uses a penrmanent magnet motor.

arXiv (Cornell University), Dec 12, 2020

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1987

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symm... more Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

Materials & Design, Jun 1, 2021

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1993

Shock-induced reactions (or shock synthesis) have been studied since the 1960’s but are still poo... more Shock-induced reactions (or shock synthesis) have been studied since the 1960’s but are still poorly understood, partly due to the fact that the reaction kinetics are very fast making experimental analysis of the reaction difficult. Shock synthesis is closely related to combustion synthesis, and occurs in the same systems that undergo exothermic gasless combustion reactions. The thermite reaction (Fe2O3 + 2Al -> 2Fe + Al2O3) is prototypical of this class of reactions. The effects of shock-wave passage through porous (powder) materials are complex, because intense and non-uniform plastic deformation is coupled with the shock-wave effects. Thus, the particle interiors experience primarily the effects of shock waves, while the surfaces undergo intense plastic deformation which can often result in interfacial melting. Shock synthesis of compounds from powders is triggered by the extraordinarily high energy deposition rate at the surfaces of the powders, forcing them in close contact, activating them by introducing defects, and heating them close to or even above their melting temperatures.

International Journal of Solids and Structures, Apr 1, 2006

arXiv (Cornell University), Jul 25, 2020

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1990

Although it has been well established that microvoid coalescence occurs during static or quasi-st... more Although it has been well established that microvoid coalescence occurs during static or quasi-static fracture in ductile materials, the exact mechanism for microvoid formation is still unclear. It has been argued that microvoids initiate and grow from second phase particles. However this argument cannot be used to explain the existence of microvoids on the fracture surfaces of "pure" materials. An alternative mechanism for their formation in "pure" materials is that they initiate and grow along dislocation cell walls. If this premise is true; then the nature and extent of microvoid coalescence should be related to the stacking fault energy (SFE) of the material since the latter is a controlling parameter in the formation of dislocation cells. The relationship between microvoid coalescence and stacking fault energy may have some basis since absolute cell dimensions are of the same magnitude as the observed dimple sizes. The present study examines the effect of dislocation cell structures on the formation of microvoids as a function of the stacking fault energy of a given material through direct observation of the void formation and growth process within the TEM. The fundamental aspects of the work is to correlate the dislocation substructures, void initiation, growth, and coalescence to the resulting fracture surfaces.

Materials & Design, May 1, 2022

Optical pseudogap energy in multicomponent carbonitrides is shown to be tunable and predictable b... more Optical pseudogap energy in multicomponent carbonitrides is shown to be tunable and predictable based on composition. Carbonitride hue depends on pseudogap energy, and chroma can be predicted based on the electronic density of states of precursor materials. A model is developed for the prediction of color appearance of any combination of group 4/5 B1-carbides and nitrides. Novel hues previously inaccessible in mononitrides and monocarbides, such as pink and purple, are synthesized in multicomponent carbonitrides.

Materialia, Sep 1, 2020

Abstract FeAl/FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites were synthesized u... more Abstract FeAl/FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites were synthesized using a “multiple-thin-foil” configuration and a “two-stage reaction” strategy. Microstructure analysis via scanning electron microscope (SEM), energy-dispersive X-ray spectrometer (EDS) and electron backscatter diffraction (EBSD) confirms the formation of a two-intermetallic eutectoid structure, which decomposes from the high-temperature Fe5Al8 phase. The metal layers of eutectoid-MIL composites are fabricated with either pure iron or two different stainless steels without altering the intermetallic regions. The volume fraction of eutectoid layers is adjusted for optimizing the performance. The off-eutectoid phase is switched between FeAl and FeAl2 to investigate the effect on strength and ductility. The microstructure of the interfacial regions is fine-tuned, further demonstrating the ability to independently control the constituents of MIL composites. Additionally, a hybrid MIL composite of FeAl and the eutectoid structure are synthesized as a ‘proof-of-concept’. Finite element analysis (FEA) simulation is utilized to study the internal stress in the MIL composites from a macroscopic point of view. Incremental compression tests were conducted to track the fracture evolution from a microscopic point of view.

Journal of the American Ceramic Society, May 23, 2018

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017

Scripta Materialia, Nov 1, 2020

Philosophical Magazine B-physics of Condensed Matter Statistical Mechanics Electronic Optical and Magnetic Properties, Apr 1, 1988

RefDoc Bienvenue - Welcome. Refdoc est un service / is powered by. ...

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016

Abstract Novel Ceramic-Fiber-Reinforced-Metal-Intermetallic-Laminate (CFR-MIL) composites, Ti–Al3... more Abstract Novel Ceramic-Fiber-Reinforced-Metal-Intermetallic-Laminate (CFR-MIL) composites, Ti–Al3Ti–Al2O3–Al, were synthesized by reactive foil sintering in air. Microstructure controlled material architectures were achieved with continuous Al2O3 fibers oriented in 0° and 90° layers to form fully dense composites in which the volume fractions of all four component phases can be tailored. Bend fracture specimens were cut from the laminate plates in divider orientation, and bend tests were performed to study the fracture behavior of CFR-MIL composites under three-point and four-point bending loading conditions. The microstructures and fractured surfaces of the CFR-MIL composites were examined using optical microscopy and scanning electron microscopy to establish a correlation between the fracture toughness, fracture surface morphology and microstructures of CFR-MIL composites. The fracture and toughening mechanisms of the CFR-MIL composites are also addressed. The present experimental results indicate that the fracture toughness of CFR-MIL composites determined by three- and four-point bend loading configurations are quite similar, and increased significantly compared to MIL composites without ceramic fiber reinforcement. The interface cracking behavior is related to the volume fraction of the brittle Al3Ti phase and residual ductile Al, but the fracture toughness values appear to be insensitive to the ratio of these two phases. The toughness appears to be dominated by the ductility/strength of the Ti layers and the strength and crack bridging effect of the ceramic fibers.

Acta Materialia, Feb 1, 2017

arXiv (Cornell University), Feb 22, 2020