The internal structure of explosively shocked zirconia powders was examined using transmission el... more The internal structure of explosively shocked zirconia powders was examined using transmission electron microscopy. Lower-pressure (20 GPa) shocked powders exhibit crystallite size reduction accompanied by extensive deformation. High-pressure (27 GPa) shocked specimens exhibit a high degree of deformation as well as localized particle-size reduction accompanied by recrystallization to the high-temperature tetragonal zirconia polymorph. Recrystallization of heavily deformed monoclinic zirconia particles in both low- and high-pressure shocked powders could be induced by electron-beam heating. Ultra-fine (< 30 nm) tetragonal particles in the high-pressure shocked powders were resistant to recrystallization during electron-beam heating.
is correct in asserting that the role of plastic deformation in room temperature fracture of sapp... more is correct in asserting that the role of plastic deformation in room temperature fracture of sapphire is controversiat. Unfortunately, the experiments he described a r e neither new nor novel, nor do they shed light on the controversy. In particular, they do not allow the conclusion that. .. "direct and indirect evidence support the view that plastic deformation accompanies fracture in sapphire and ruby at room temp e r a t u r e " , o r that. .. "microslip can occur and can therefore be treated by itself to understand the mechanical properties of sapphire and ruby". Numerous investigators have previously reported obtaining crack-free microhardness indentations in sapphire, e.g., Refs. 17 to 19. In addition, it has been demonstrated that permanent deformation accompanies s c r a t c h i n g and a b r a s i o n of sapphire s u r f a c e s. ~9-2s T h e s e e x p e r i m e n t s have been given as evidence for plastic d e f o r m a t i o n by both slip and deformation twh~ning in sapphire. The exact nature of the plastic deformation a s s o c i a t e d with g i c k e r s hardness indentations in sapphire has r e c e n t l y been d e m o n s t r a t e d by Hockey a4-~6 using t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y , s e e Fig. 1. Hockey "~a has concluded that, " H i g h densit i e s of dislocations a r e produced within the n e a r s u rface regions by m e c h a n i c a l polishing with a fine diamond compound (0.25/~) and that plastic deformation by both slip and m e c h a n i c a l twinning o c c u r s during the placement of g i c k e r s m t c r o h a r d n e s s i n d e n t a t i o n s. " The fact that plastic deformation
Proceedings of International Solid State Sensors and Actuators Conference (Transducers '97)
... martensite. The bias force has to exceed the elastic limit of the martensite (approximately 1... more ... martensite. The bias force has to exceed the elastic limit of the martensite (approximately 1%[12]), as else there is no accommodation of strain by the SME mechanism. We report on a new design to achieve a greater stroke. ...
: This program supported the early phases of a Future Naval Capabilities (FNC) program at the Nav... more : This program supported the early phases of a Future Naval Capabilities (FNC) program at the Naval Research Laboratory (NRL), devoted to transitioning a novel low temperature (500 Celsius) interstitial hardening process for stainless steels for impellers, fasteners and other marine items. Although the FNC program is a five (5) year program, CWRU support under this program was available only for the first two (2) years of the FNC program. The objectives of the CWRU effort were to increase the understanding and applications of this exciting technology, focusing on four areas: 1) acetylene-based carburizing, 2) gas phase nitriding, 3) gas phase nitrocarburizing, and 4) carburizing machined fasteners.
The cut-then-stack paradigm of computer-aided manufacturing of laminated engineering materials (C... more The cut-then-stack paradigm of computer-aided manufacturing of laminated engineering materials (CAM-LEM) offers choice of feedstock material, ease of handling finely divided (and therefore sinterable) powders, and the ability to mix materials. This combination of features was exploited to process fluidic devices. CAM-LEM processing was used to render the Part in aluminum oxide, silicon nitride, and stainless steel.
For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we i... more For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we introduce a process based on pyrolysis of solid reagents, e.g., urea, performed in an evacuated closed vessel. Upon heating to temperatures high enough for rapid diffusion of interstitial solute, but low enough to avoid second-phase precipitation, the reagent is pyrolyzed to a gas atmosphere containing molecules that (i) activate the alloy surface by stripping away the passivating Cr2O3-rich surface film (diffusion barrier) and (ii) rapidly infuse carbon and nitrogen into the alloy. We demonstrate quantitatively that this method can generate a subsurface zone with concentrated carbon and nitrogen comparable to what can be accomplished by established (e.g., gas-phase- or plasma-based) methods, but with significantly reduced processing time. As another important difference to established gas-phase processing, the interaction of gas molecules with the alloy surface can have auto-catalytic ef...
... For example, Jolles and Monty [34] studied wtistite (Fel-xO) at temperatures between 850 and ... more ... For example, Jolles and Monty [34] studied wtistite (Fel-xO) at temperatures between 850 and 1150~ and determined that Q ,-~ 3 eV, independent of temperature; they interpreted this as the activation energy for oxygen self-diffusion (the slowest moving species). ...
In the absence of a corrosive environment, brittle materials such as silicon should be immune to ... more In the absence of a corrosive environment, brittle materials such as silicon should be immune to cyclic fatigue. However, fatigue effects are well known in micrometer-sized polycrystalline silicon (polysilicon) samples tested in air. To investigate the origins of this phenomenon in polysilicon, we developed a fixed-grip fracture mechanics microspecimen but could find no evidence of static stress corrosion cracking. The environmental sensitivity of the fatigue resistance was also investigated under cyclic loading. For low-cycle fatigue, the behavior is independent of the ambient conditions, whether air or vacuum, but is strongly influenced by the ratio of compressive to tensile stresses experienced during each cycle. The fatigue damage most likely originates from contact stresses at processing-related surface asperities; subcritical crack growth then ensues during further cyclic loading. The lower far-field stresses involved in high-cycle fatigue induce reduced levels of fatigue dama...
2000 Solid-State, Actuators, and Microsystems Workshop Technical Digest, 2000
A microfabricated normally-closed microvalve consisting of a flat silicon spring, a co-sputtered ... more A microfabricated normally-closed microvalve consisting of a flat silicon spring, a co-sputtered and patterned Titanium-Nickel (TiNi) shape memory alloy (SMA) actuator, and an orifice die, is presented. All three components are batch microfabricated using silicon substrates. This microvalve is designed for an actuation mechanism for a pneumatically controlled, biologically inspired six-legged microrobot. We have used a TiNi SMA thin film as an actuator since it is capable of both high strains (3%) and high forces (work density of 5 x lo7 Urn"). Flow rates of up to 0.17 lpm are achieved when the input air pressure is 34.5 kPa (5.0 psi). A CNC-machined plastic package accommodates the electrical and fluidic interconnects.
Proceedings, annual meeting, Electron Microscopy Society of America, 1982
Introduction. There is considerable interest in the effect of oxidation on the microstructure of ... more Introduction. There is considerable interest in the effect of oxidation on the microstructure of yttria-doped silicon nitride, since some compositions are unstable at low temperatures (=1000°C) despite their apparent stability at 1400°C (1). The material used in this study was the same commercial hotpressed Si3N4-8%Y2O3 (NCX-34) as one investigated previously, which had exhibited only passive oxidation during heating in air from 600° to 1400°C. Some thin (=100μm) specimens were oxidized at 800°, 1000° and 1450°C in ambient air and then ion-thinned from one side; others were ion-milled and oxidized. Specimens were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along with energy dispersive x-ray (EDX) analysis.
Two distinctly different morphologies of Mo5Si3 precipitates have been observed in a single cryst... more Two distinctly different morphologies of Mo5Si3 precipitates have been observed in a single crystal MoSi2. Both precipitates are laths elongated along the (110) direction common to the matrix and the precipitate but differ in their cross-sectional shape and lattice orientation. Type I precipitates exhibit a rectangular cross-section, with interfaces parallel to low-index planes (110)m∥(002)p and (002)m∥(220)p, while type II precipitates are parallelograms, with their major interface at 13° to the low-index planes (002)m∥(220)p (the subscripts m and p denote the MoSi2 matrix and Mo5Si3 precipitate, respectively). The orientation relation-ships corresponding to the two characteristic morphologies differ by a 1 8° rotation around the lath axis. A periodic array of dislocation loops and associated ledges enveloping the precipitates were revealed by high-resolution electron microscopy and selected area electron diffraction. The Burgers vector of these dislocations was determined unambiguously from high-resolution images in orthogonal viewing directions. The differences between the two characteristic morphologies and their orientation relationships are due to a difference in the stacking sequence of ledges.
922 SF3B1, a RNA splicing factor is frequently mutated in refractory anemia with ring sideroblast... more 922 SF3B1, a RNA splicing factor is frequently mutated in refractory anemia with ring sideroblasts (RARS) and RARS with thrombocytosis (RARS-T). Aside from its phenotypic importance, SF3B1 has been associated with good outcomes in MDS. Consistent with others, we found favorable survival outcomes in SF3B1 mutants. To explain the clinical phenotypes (good outcomes, anemia, and less progression to acute myeloid leukemia (AML)), we delved into the consequences of SF3B1 dysfunction in MDS. We hypothesized that SF3B1 mutations result in changes in RNA splicing of key genes in erythropoiesis resulting in anemia. Moreover, we postulated that SF3B1 is a founder mutation in RS formation but insufficient as a sole abnormality to induce a deleterious phenotype. The acquisition of genetic/ epigenetic aberrations may trigger the final phenotype. We reported abundant iron deposits in the mitochondria of SF3B1 mutants. We hypothesized that SF3B1 mutations change the composition/ chemical valence of...
The internal structure of explosively shocked zirconia powders was examined using transmission el... more The internal structure of explosively shocked zirconia powders was examined using transmission electron microscopy. Lower-pressure (20 GPa) shocked powders exhibit crystallite size reduction accompanied by extensive deformation. High-pressure (27 GPa) shocked specimens exhibit a high degree of deformation as well as localized particle-size reduction accompanied by recrystallization to the high-temperature tetragonal zirconia polymorph. Recrystallization of heavily deformed monoclinic zirconia particles in both low- and high-pressure shocked powders could be induced by electron-beam heating. Ultra-fine (< 30 nm) tetragonal particles in the high-pressure shocked powders were resistant to recrystallization during electron-beam heating.
is correct in asserting that the role of plastic deformation in room temperature fracture of sapp... more is correct in asserting that the role of plastic deformation in room temperature fracture of sapphire is controversiat. Unfortunately, the experiments he described a r e neither new nor novel, nor do they shed light on the controversy. In particular, they do not allow the conclusion that. .. "direct and indirect evidence support the view that plastic deformation accompanies fracture in sapphire and ruby at room temp e r a t u r e " , o r that. .. "microslip can occur and can therefore be treated by itself to understand the mechanical properties of sapphire and ruby". Numerous investigators have previously reported obtaining crack-free microhardness indentations in sapphire, e.g., Refs. 17 to 19. In addition, it has been demonstrated that permanent deformation accompanies s c r a t c h i n g and a b r a s i o n of sapphire s u r f a c e s. ~9-2s T h e s e e x p e r i m e n t s have been given as evidence for plastic d e f o r m a t i o n by both slip and deformation twh~ning in sapphire. The exact nature of the plastic deformation a s s o c i a t e d with g i c k e r s hardness indentations in sapphire has r e c e n t l y been d e m o n s t r a t e d by Hockey a4-~6 using t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y , s e e Fig. 1. Hockey "~a has concluded that, " H i g h densit i e s of dislocations a r e produced within the n e a r s u rface regions by m e c h a n i c a l polishing with a fine diamond compound (0.25/~) and that plastic deformation by both slip and m e c h a n i c a l twinning o c c u r s during the placement of g i c k e r s m t c r o h a r d n e s s i n d e n t a t i o n s. " The fact that plastic deformation
Proceedings of International Solid State Sensors and Actuators Conference (Transducers '97)
... martensite. The bias force has to exceed the elastic limit of the martensite (approximately 1... more ... martensite. The bias force has to exceed the elastic limit of the martensite (approximately 1%[12]), as else there is no accommodation of strain by the SME mechanism. We report on a new design to achieve a greater stroke. ...
: This program supported the early phases of a Future Naval Capabilities (FNC) program at the Nav... more : This program supported the early phases of a Future Naval Capabilities (FNC) program at the Naval Research Laboratory (NRL), devoted to transitioning a novel low temperature (500 Celsius) interstitial hardening process for stainless steels for impellers, fasteners and other marine items. Although the FNC program is a five (5) year program, CWRU support under this program was available only for the first two (2) years of the FNC program. The objectives of the CWRU effort were to increase the understanding and applications of this exciting technology, focusing on four areas: 1) acetylene-based carburizing, 2) gas phase nitriding, 3) gas phase nitrocarburizing, and 4) carburizing machined fasteners.
The cut-then-stack paradigm of computer-aided manufacturing of laminated engineering materials (C... more The cut-then-stack paradigm of computer-aided manufacturing of laminated engineering materials (CAM-LEM) offers choice of feedstock material, ease of handling finely divided (and therefore sinterable) powders, and the ability to mix materials. This combination of features was exploited to process fluidic devices. CAM-LEM processing was used to render the Part in aluminum oxide, silicon nitride, and stainless steel.
For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we i... more For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we introduce a process based on pyrolysis of solid reagents, e.g., urea, performed in an evacuated closed vessel. Upon heating to temperatures high enough for rapid diffusion of interstitial solute, but low enough to avoid second-phase precipitation, the reagent is pyrolyzed to a gas atmosphere containing molecules that (i) activate the alloy surface by stripping away the passivating Cr2O3-rich surface film (diffusion barrier) and (ii) rapidly infuse carbon and nitrogen into the alloy. We demonstrate quantitatively that this method can generate a subsurface zone with concentrated carbon and nitrogen comparable to what can be accomplished by established (e.g., gas-phase- or plasma-based) methods, but with significantly reduced processing time. As another important difference to established gas-phase processing, the interaction of gas molecules with the alloy surface can have auto-catalytic ef...
... For example, Jolles and Monty [34] studied wtistite (Fel-xO) at temperatures between 850 and ... more ... For example, Jolles and Monty [34] studied wtistite (Fel-xO) at temperatures between 850 and 1150~ and determined that Q ,-~ 3 eV, independent of temperature; they interpreted this as the activation energy for oxygen self-diffusion (the slowest moving species). ...
In the absence of a corrosive environment, brittle materials such as silicon should be immune to ... more In the absence of a corrosive environment, brittle materials such as silicon should be immune to cyclic fatigue. However, fatigue effects are well known in micrometer-sized polycrystalline silicon (polysilicon) samples tested in air. To investigate the origins of this phenomenon in polysilicon, we developed a fixed-grip fracture mechanics microspecimen but could find no evidence of static stress corrosion cracking. The environmental sensitivity of the fatigue resistance was also investigated under cyclic loading. For low-cycle fatigue, the behavior is independent of the ambient conditions, whether air or vacuum, but is strongly influenced by the ratio of compressive to tensile stresses experienced during each cycle. The fatigue damage most likely originates from contact stresses at processing-related surface asperities; subcritical crack growth then ensues during further cyclic loading. The lower far-field stresses involved in high-cycle fatigue induce reduced levels of fatigue dama...
2000 Solid-State, Actuators, and Microsystems Workshop Technical Digest, 2000
A microfabricated normally-closed microvalve consisting of a flat silicon spring, a co-sputtered ... more A microfabricated normally-closed microvalve consisting of a flat silicon spring, a co-sputtered and patterned Titanium-Nickel (TiNi) shape memory alloy (SMA) actuator, and an orifice die, is presented. All three components are batch microfabricated using silicon substrates. This microvalve is designed for an actuation mechanism for a pneumatically controlled, biologically inspired six-legged microrobot. We have used a TiNi SMA thin film as an actuator since it is capable of both high strains (3%) and high forces (work density of 5 x lo7 Urn"). Flow rates of up to 0.17 lpm are achieved when the input air pressure is 34.5 kPa (5.0 psi). A CNC-machined plastic package accommodates the electrical and fluidic interconnects.
Proceedings, annual meeting, Electron Microscopy Society of America, 1982
Introduction. There is considerable interest in the effect of oxidation on the microstructure of ... more Introduction. There is considerable interest in the effect of oxidation on the microstructure of yttria-doped silicon nitride, since some compositions are unstable at low temperatures (=1000°C) despite their apparent stability at 1400°C (1). The material used in this study was the same commercial hotpressed Si3N4-8%Y2O3 (NCX-34) as one investigated previously, which had exhibited only passive oxidation during heating in air from 600° to 1400°C. Some thin (=100μm) specimens were oxidized at 800°, 1000° and 1450°C in ambient air and then ion-thinned from one side; others were ion-milled and oxidized. Specimens were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along with energy dispersive x-ray (EDX) analysis.
Two distinctly different morphologies of Mo5Si3 precipitates have been observed in a single cryst... more Two distinctly different morphologies of Mo5Si3 precipitates have been observed in a single crystal MoSi2. Both precipitates are laths elongated along the (110) direction common to the matrix and the precipitate but differ in their cross-sectional shape and lattice orientation. Type I precipitates exhibit a rectangular cross-section, with interfaces parallel to low-index planes (110)m∥(002)p and (002)m∥(220)p, while type II precipitates are parallelograms, with their major interface at 13° to the low-index planes (002)m∥(220)p (the subscripts m and p denote the MoSi2 matrix and Mo5Si3 precipitate, respectively). The orientation relation-ships corresponding to the two characteristic morphologies differ by a 1 8° rotation around the lath axis. A periodic array of dislocation loops and associated ledges enveloping the precipitates were revealed by high-resolution electron microscopy and selected area electron diffraction. The Burgers vector of these dislocations was determined unambiguously from high-resolution images in orthogonal viewing directions. The differences between the two characteristic morphologies and their orientation relationships are due to a difference in the stacking sequence of ledges.
922 SF3B1, a RNA splicing factor is frequently mutated in refractory anemia with ring sideroblast... more 922 SF3B1, a RNA splicing factor is frequently mutated in refractory anemia with ring sideroblasts (RARS) and RARS with thrombocytosis (RARS-T). Aside from its phenotypic importance, SF3B1 has been associated with good outcomes in MDS. Consistent with others, we found favorable survival outcomes in SF3B1 mutants. To explain the clinical phenotypes (good outcomes, anemia, and less progression to acute myeloid leukemia (AML)), we delved into the consequences of SF3B1 dysfunction in MDS. We hypothesized that SF3B1 mutations result in changes in RNA splicing of key genes in erythropoiesis resulting in anemia. Moreover, we postulated that SF3B1 is a founder mutation in RS formation but insufficient as a sole abnormality to induce a deleterious phenotype. The acquisition of genetic/ epigenetic aberrations may trigger the final phenotype. We reported abundant iron deposits in the mitochondria of SF3B1 mutants. We hypothesized that SF3B1 mutations change the composition/ chemical valence of...
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Papers by Arthur Heuer