Raymond Fournelle - Academia.edu (original) (raw)

Papers by Raymond Fournelle

Research paper thumbnail of Is fatigue mechanism implicated in intraoral fracture of narrow dental implants? A retrieval analysis study

Purpose This study aimed to perform a thorough failure analysis of two fractured narrow dental im... more Purpose This study aimed to perform a thorough failure analysis of two fractured narrow dental implants (NDIs) after medium-term in vivo use. Materials and Methods The top parts of two fractured NDI fixtures were retrieved from two different locations at two different times from the same patient. The first NDI fixture (NDI-specimen-1) was 12 months in service while the second NDI fixture (NDI-specimen-2) was 17 months in service. In both cases, the top parts of the fractured NDI fixtures that were attached to prosthetic components were retrieved and subjected to thorough, non-destructive (light microscopy [LM] and scanning electron microscopy [SEM]), and destructive testing (metallography, energy dispersive X-ray spectroscopy [EDS] and hardness testing). Results LM and SEM revealed that both the retrieved fractured NDI fixtures failed because of fatigue, characterized by beach and ratchet marks. Macroscopic examination revealed that fatigue cracks initiated at the internal thread su...

Research paper thumbnail of Is Coherency Strain Energy the Driving Force for Diffusion Induced Grain Boundary Migration? / Ist die Kohärenzspannungsenergie die Triebkraft der diffusionsinduzierten Korngrenzenwanderung?

International Journal of Materials Research, 1992

ABSTRACT Diffusion induced grain boundary migration (DIGM) has been investigated in many systems;... more ABSTRACT Diffusion induced grain boundary migration (DIGM) has been investigated in many systems; however, the nature of the driving force is not yet clear. According to the coherency strain theory for the phenomena, the driving force for boundary migration is the relief of coherency strain energy in the grain in front of the migrating boundary which results from the volume diffusion of solute into it from the boundary or out of it to the boundary. This study tests this theory by determining whether or not DIGM occurs when Cu is diffused into a polycrystalline Ni-19.4 at.% Pd alloy. Because of the vanishingly small lattice parameter misfit expected in this system, little coherency strain is expected. Hence, the occurrence of DIGM is not expected in this system, if the coherency strains provide the only driving force for it. Tests were performed by isothermally annealing diffusion couples of Ni-19.4 at.% Pd electroplated with Cu at temperatures ranging from 773 to 1073 K for 48 h. DIGM was observed by light and scanning microscopy at all temperatures, whereas diffusion induced recrystallization (DIR), a related phenomenon, was observed after annealing at temperatures between 873 and 1073 K. Energy dispersive X-ray analysis of the DIGM and DIR regions showed that the Cu concentration in the DIGM zones was extremely high (50 to 60 wt.% Cu). That in the DIR zone was somewhat lower. The results suggest that something other than coherency strain is driving the reactions.

Research paper thumbnail of Proof of an Asymmetry of Grain Boundary Migration in Solid Solutions

Research paper thumbnail of MECHANISMS OF GRAIN BOUNDARY MIGRATION DURING DISCONTINUOUS DISSOLUTION IN Ni-In POLYCRYSTALS

During discontinuous dissolution (DD) a lamellar structure, which formed at lower temperature by ... more During discontinuous dissolution (DD) a lamellar structure, which formed at lower temperature by discontinuous precipitation (DP), is dissolved by grain boundary migration at temperatures near the solvus temperature. This dissolution behavior in a Ni-1. 4 at. % In alloy was studied over a large temperature range (928-1073 K). The metallographic observations show that the DD reaction occurs only by the backward migration of a precipitation front during its early stages. After a short incubation time DD reactions also occur on the original grain boundaries and on the intersecting boundaries between two precipitation seams. Only in very late stages can the lamellae be partially dissolved by a volume diffusion controlled reaction without grain boundary migration. The backward migration of the reaction front is delayed or even suppressed by this. The measured migration velocities range over about two powers of ten (1. 50 multiplied by 10** minus **9 to 1. 33 multiplied by 10** minus **7 ...

Research paper thumbnail of Diffusion Induced Grain Boundary Migration and Recrystallization in the Ni<sub>3</sub>Al(Cu) System

Materials Science Forum, 1993

Research paper thumbnail of Discontinuous coarsening of discontinuous precipitate in a Ni-7.5 at.% In alloy

Acta Metallurgica, 1988

ABSTRACT The morphology and growth kinetics of the discontinuous coarsening of discontinuous prec... more ABSTRACT The morphology and growth kinetics of the discontinuous coarsening of discontinuous precipitate in a Ni-7.5 at.% In alloy have for the first time been investigated at temperatures ranging from 667 to 1030 K by light and scanning electron microscopy and X-ray diffraction. At all aging temperatures the alloy was observed to decompose completely by discontinuous precipitation into a fine lamellar structure of nickel rich solid solution and θ (Ni3In) precipitate phase. This lamellar structure was then decomposed at all aging temperatures by a discontinuous coarsening reaction. This reaction occurred at a much slower rate than the first reaction and resulted in a much coarser lamellar structure of the same phases. Lattice parameter measurements showed the Ni rich solid solution in the product of the first reaction to be far from equilibrium while that of the second reaction was close to equilibrium. Analysis of the growth rates, lamellar spacings and phase compositions for both the discontinuous precipitation and discontinuous coarsening reactions showed that they were controlled by grain boundary diffusion. In analyzing the results a generally applicable procedure for calculating the driving force is presented. In this calculation the solid solution is treated as a regular solution and the actual thermodynamic data are used for the precipitate phase. The driving forces calculated in this way should be more reliable than those calculated with the approximations based on Raoult&#39;s and Henry&#39;s laws.

Research paper thumbnail of The morphology of discontinuous precipitation on the surface of NiIn and NiSn alloys

Scripta Metallurgica, 1986

Research paper thumbnail of Diffusion induced grain boundary migration and recrystallization in boron-doped Ni3Al intermetallics

Scripta Metallurgica et Materialia, 1992

Research paper thumbnail of Heavy ion bombardment of silicates and nitrides

Radiation Effects, 1981

have beenirradiated by 1019-1021 Krypton(3MeV)ions/m.' The damaged powders of original particle s... more have beenirradiated by 1019-1021 Krypton(3MeV)ions/m.' The damaged powders of original particle size less than 5 pm, have been examined by x-ray diffraction and electron microscope methods. The silicates and Si,N,O become non-crystalline by 10 x 19 ions/mz. The particles change shape, extending and bloating under prolonged irradiations of the order of 100 x lOI9 ions/m2. Silicate glass also undergoes this irradiation creep process. The nitrides and Tho, behave quite differently and even at fluences of 200 x 1019 ions/m-2 the powders remain crystalline, retaining relatively sharp edges to the particles without exhibiting irradiation creep. This difference in behavior can be related to the nature of the framework crystal structures, flexible for the silicates with variable bond angles, rigid for the nitrides with fixed bond angles. This may explain the behavior of radioactive minerals not found in a metamict condition.

Research paper thumbnail of Metamict zircon formed by heavy ion bombardment

Radiation Effects, 1979

ABSTRACT

Research paper thumbnail of Discontinuous precipitation and coarsening in Al-Zn alloys

Acta Metallurgica, 1988

ABSTRACT The morphology and kinetics of discontinuous precipitation (DP) and discontinuous coarse... more ABSTRACT The morphology and kinetics of discontinuous precipitation (DP) and discontinuous coarsening (DC) in solution treated and isothermally aged Al-Zn alloys containing 39.3 and 59.3 at.% Zn have been investigated at temperatures ranging from 323 to 523 K by light microscopy, electron microscopy and X-ray diffraction. At all aging temperatures the supersaturated α solid solution was observed to decompose rapidly by DP into a lamellar mixture of solute depleted α phase and β phase precipitate. DP occurred so rapidly in the 59.5 at.% Zn alloy that the heat of transformation raised the temperature of the alloy significantly. With further aging a slower DC reaction transformed the lamellar DP into a coarser lamellar structure of the same two phases; however, the composition of the α phase of the DC was closer to the equilibrium solvus composition than that of the DP. With still further aging a second, much slower DC reaction was observed to decompose the lamellar product of the first DC reaction in the 59.5 at.% Zn alloy into a still coarser lamellar structure. Analysis of the kinetics of both the DP and DC reactions showed them to be controlled by boundary diffusion in the advancing reaction interface. Reaction front migration rates for both DP and DC increased markedly with increasing Zn content. This increase seems to be associated partially with an increase in boundary diffusivity with increasing Zn content.

Research paper thumbnail of Biotribological behavior of two retrieved implant abutment screws after long-term use in vivo

The International journal of oral & maxillofacial implants

To evaluate the effect of functional cyclic loading on two retrieved abutment screws used with si... more To evaluate the effect of functional cyclic loading on two retrieved abutment screws used with single implant supporting cement-retained porcelain-fused-to-metal crowns by characterizing the structure, properties, and biotribologic behavior after long-term use in vivo. Two abutment screws were retrieved from the same patient and same implant at two different times. An external hex implant was used to replace a missing central incisor. A traumatic incident occurred 9 months after insertion and displaced the implant palatally by bending the screw. A second, similar incident occurred 31 months after insertion. In both cases, the abutment screws were retrieved and subjected to thorough nondestructive and destructive testing. Light and scanning electron microscopic examinations revealed very minimal surface deterioration of the thread profile for the first screw (in service for 9 months) and demonstrated advanced metal adhesive wear in the form of galling for the second screw (in service...

Research paper thumbnail of Cyclic stress strain relations and strain-controlled fatigue of 4140 steel

Research paper thumbnail of High-Temperature Digm in an FE-5 AT-PERCENT-A1 Bicrystal During ZN Diffusion

Scripta Metallurgica Et Materialia, 1992

Research paper thumbnail of Criteria for the Occurrence of the Diffusion-Induced Grain Boundary Migration

Interface Science - INTERFACE SCI, 1998

Recent experimental data on diffusion-induced grain boundary migration (DIGM) are reviewed. For t... more Recent experimental data on diffusion-induced grain boundary migration (DIGM) are reviewed. For the case of the coherency strain driving force, quantitative criteria for the occurrence of DIGM are suggested, which establish the relationship between the net driving force for grain boundary migration, the diffusivity in the vicinity of the grain boundary, the enthalpy of the grain boundary segregation, the misfit parameter for the solute atoms in the matrix and the solubility of the diffusing element in the matrix. It is shown that an upper limit for the grain boundary velocity during DIGM exists due to the solute drag effect.

Research paper thumbnail of Effect of strontium modification on near- threshold fatigue crack growth in an Al-Si-Cu die cast alloy

Metallurgical and Materials Transactions A, 1996

Abstract The effects of strontium modification on microstructure and fatigue properties in a die ... more Abstract The effects of strontium modification on microstructure and fatigue properties in a die cast com-mercial aluminum-silicon alloy are demonstrated. Strontium additions of 0.010 and 0.018 wt pct drastically change the morphology of the eutectic silicon. The influence of ...

Research paper thumbnail of Low cycle fatigue behavior of a quenched and tempered niobium bearing HSLA steel

Metallurgical Transactions A, 1980

The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high streng... more The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high strength low alloy steel heat treated to give tempered martensitic microstructures presumably with and without fine niobium carbides was studied by transmission electron microscopy, stress relaxation, X-ray diffraction line broadening and strain-controlled fatigue testing. The steel without the niobium carbides cyclically softened rapidly at all strain amplitudes studied. This softening was attributed to the rearrangement of the dislocation substructure into a cell structure and to the accompanying decrease in internal stress. The steel presumably containing the fine niobium carbides cyclically softened to a lesser extent. This correlated with the observation that dislocations in this steel did not rearrange themselves into a cell structure and, hence, there was less change in the internal stress during cycling. The steel without the niobium carbides exhibited somewhat better strain-life behavior at large strain amplitudes. This was attributed to the cell structure being able to accommodate a greater amount of plastic strain in that steel.

Research paper thumbnail of Fatigue behavior of a precipitation hardening Ni−Al−Cu medium carbon steel

Metallurgical Transactions A, 1976

Research paper thumbnail of The effect of repeated torque and salivary contamination on the preload of slotted gold implant prosthetic screws

The Journal of Prosthetic Dentistry, 2002

Screw loosening and/or fracture is common and has been attributed to many factors, including impr... more Screw loosening and/or fracture is common and has been attributed to many factors, including improper torque and preload. Purpose. This study evaluated the effect of repeated preload torque and salivary contamination on the preload of the slotted gold implant prosthetic screw. Fifteen slotted gold prosthetic screws were tested in an unused stack of components consisting of an implant, an abutment cylinder, and a screw and gold cylinder. A custom load frame and load cell and associated electronics were used. The component stack was lubricated with human saliva. Each screw was tightened to 10 Ncm with a hand-held torque wrench fitted with strain gauge electronics and then removed 10 times. Preload values at the first (Group 1X), fifth (Group 5X), and tenth (Group 10X) repetition were measured. Repeated-measures 1-way analysis of variance (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.05) and paired comparisons were used to analyze the data. The mean preload value increased from Group 1X (184.3 N +/- 28.9) to Group 5X (202.5 N +/- 27.7) to Group 10X (220.2 N +/- 29.0). The differences among these groups were significant (P=.004). Within the limitations of this study, higher preload was achieved after the repeated use of a saliva-lubricated gold prosthetic retaining screw.

Research paper thumbnail of Solidification shrinkage defects in electronic solders

JOM, 2005

Lead-Free Solder Overview Alloys that undergo solidifi cation over a wide range of temperatures g... more Lead-Free Solder Overview Alloys that undergo solidifi cation over a wide range of temperatures generally exhibit a difference in the contraction behavior of the ensuing solid and liquid phases. Furthermore, dissolution of substrate metals during process refl ow can lead to shifts in phase composition, additional primary phases, and volumetric contraction artifacts. The extent and frequency of surface roughness, shrinkage voids, fi llet lifting, and hot tearing seen in lead-free solders are different than for eutectic tin lead solder. Shrinkage effects have been reported in Sn/Pb, Sn/Pb/Ag, Sn/Ag/Cu, and Sn/Cu/Ni solders for various components, but few studies have examined their impact on solder joint reliability. Nevertheless, they warrant proper identifi cation due to the shift toward lead-free solders. This article is a review of the effects of shrinkage in Sn-Pb and lead-free solders as well as a discussion of some of the factors that contribute to their formation. Visit the site regularly and click on "What's New" to fi nd out the most up-to-date information on meetings, publications, membership activities, and more.

Research paper thumbnail of Is fatigue mechanism implicated in intraoral fracture of narrow dental implants? A retrieval analysis study

Purpose This study aimed to perform a thorough failure analysis of two fractured narrow dental im... more Purpose This study aimed to perform a thorough failure analysis of two fractured narrow dental implants (NDIs) after medium-term in vivo use. Materials and Methods The top parts of two fractured NDI fixtures were retrieved from two different locations at two different times from the same patient. The first NDI fixture (NDI-specimen-1) was 12 months in service while the second NDI fixture (NDI-specimen-2) was 17 months in service. In both cases, the top parts of the fractured NDI fixtures that were attached to prosthetic components were retrieved and subjected to thorough, non-destructive (light microscopy [LM] and scanning electron microscopy [SEM]), and destructive testing (metallography, energy dispersive X-ray spectroscopy [EDS] and hardness testing). Results LM and SEM revealed that both the retrieved fractured NDI fixtures failed because of fatigue, characterized by beach and ratchet marks. Macroscopic examination revealed that fatigue cracks initiated at the internal thread su...

Research paper thumbnail of Is Coherency Strain Energy the Driving Force for Diffusion Induced Grain Boundary Migration? / Ist die Kohärenzspannungsenergie die Triebkraft der diffusionsinduzierten Korngrenzenwanderung?

International Journal of Materials Research, 1992

ABSTRACT Diffusion induced grain boundary migration (DIGM) has been investigated in many systems;... more ABSTRACT Diffusion induced grain boundary migration (DIGM) has been investigated in many systems; however, the nature of the driving force is not yet clear. According to the coherency strain theory for the phenomena, the driving force for boundary migration is the relief of coherency strain energy in the grain in front of the migrating boundary which results from the volume diffusion of solute into it from the boundary or out of it to the boundary. This study tests this theory by determining whether or not DIGM occurs when Cu is diffused into a polycrystalline Ni-19.4 at.% Pd alloy. Because of the vanishingly small lattice parameter misfit expected in this system, little coherency strain is expected. Hence, the occurrence of DIGM is not expected in this system, if the coherency strains provide the only driving force for it. Tests were performed by isothermally annealing diffusion couples of Ni-19.4 at.% Pd electroplated with Cu at temperatures ranging from 773 to 1073 K for 48 h. DIGM was observed by light and scanning microscopy at all temperatures, whereas diffusion induced recrystallization (DIR), a related phenomenon, was observed after annealing at temperatures between 873 and 1073 K. Energy dispersive X-ray analysis of the DIGM and DIR regions showed that the Cu concentration in the DIGM zones was extremely high (50 to 60 wt.% Cu). That in the DIR zone was somewhat lower. The results suggest that something other than coherency strain is driving the reactions.

Research paper thumbnail of Proof of an Asymmetry of Grain Boundary Migration in Solid Solutions

Research paper thumbnail of MECHANISMS OF GRAIN BOUNDARY MIGRATION DURING DISCONTINUOUS DISSOLUTION IN Ni-In POLYCRYSTALS

During discontinuous dissolution (DD) a lamellar structure, which formed at lower temperature by ... more During discontinuous dissolution (DD) a lamellar structure, which formed at lower temperature by discontinuous precipitation (DP), is dissolved by grain boundary migration at temperatures near the solvus temperature. This dissolution behavior in a Ni-1. 4 at. % In alloy was studied over a large temperature range (928-1073 K). The metallographic observations show that the DD reaction occurs only by the backward migration of a precipitation front during its early stages. After a short incubation time DD reactions also occur on the original grain boundaries and on the intersecting boundaries between two precipitation seams. Only in very late stages can the lamellae be partially dissolved by a volume diffusion controlled reaction without grain boundary migration. The backward migration of the reaction front is delayed or even suppressed by this. The measured migration velocities range over about two powers of ten (1. 50 multiplied by 10** minus **9 to 1. 33 multiplied by 10** minus **7 ...

Research paper thumbnail of Diffusion Induced Grain Boundary Migration and Recrystallization in the Ni<sub>3</sub>Al(Cu) System

Materials Science Forum, 1993

Research paper thumbnail of Discontinuous coarsening of discontinuous precipitate in a Ni-7.5 at.% In alloy

Acta Metallurgica, 1988

ABSTRACT The morphology and growth kinetics of the discontinuous coarsening of discontinuous prec... more ABSTRACT The morphology and growth kinetics of the discontinuous coarsening of discontinuous precipitate in a Ni-7.5 at.% In alloy have for the first time been investigated at temperatures ranging from 667 to 1030 K by light and scanning electron microscopy and X-ray diffraction. At all aging temperatures the alloy was observed to decompose completely by discontinuous precipitation into a fine lamellar structure of nickel rich solid solution and θ (Ni3In) precipitate phase. This lamellar structure was then decomposed at all aging temperatures by a discontinuous coarsening reaction. This reaction occurred at a much slower rate than the first reaction and resulted in a much coarser lamellar structure of the same phases. Lattice parameter measurements showed the Ni rich solid solution in the product of the first reaction to be far from equilibrium while that of the second reaction was close to equilibrium. Analysis of the growth rates, lamellar spacings and phase compositions for both the discontinuous precipitation and discontinuous coarsening reactions showed that they were controlled by grain boundary diffusion. In analyzing the results a generally applicable procedure for calculating the driving force is presented. In this calculation the solid solution is treated as a regular solution and the actual thermodynamic data are used for the precipitate phase. The driving forces calculated in this way should be more reliable than those calculated with the approximations based on Raoult&#39;s and Henry&#39;s laws.

Research paper thumbnail of The morphology of discontinuous precipitation on the surface of NiIn and NiSn alloys

Scripta Metallurgica, 1986

Research paper thumbnail of Diffusion induced grain boundary migration and recrystallization in boron-doped Ni3Al intermetallics

Scripta Metallurgica et Materialia, 1992

Research paper thumbnail of Heavy ion bombardment of silicates and nitrides

Radiation Effects, 1981

have beenirradiated by 1019-1021 Krypton(3MeV)ions/m.' The damaged powders of original particle s... more have beenirradiated by 1019-1021 Krypton(3MeV)ions/m.' The damaged powders of original particle size less than 5 pm, have been examined by x-ray diffraction and electron microscope methods. The silicates and Si,N,O become non-crystalline by 10 x 19 ions/mz. The particles change shape, extending and bloating under prolonged irradiations of the order of 100 x lOI9 ions/m2. Silicate glass also undergoes this irradiation creep process. The nitrides and Tho, behave quite differently and even at fluences of 200 x 1019 ions/m-2 the powders remain crystalline, retaining relatively sharp edges to the particles without exhibiting irradiation creep. This difference in behavior can be related to the nature of the framework crystal structures, flexible for the silicates with variable bond angles, rigid for the nitrides with fixed bond angles. This may explain the behavior of radioactive minerals not found in a metamict condition.

Research paper thumbnail of Metamict zircon formed by heavy ion bombardment

Radiation Effects, 1979

ABSTRACT

Research paper thumbnail of Discontinuous precipitation and coarsening in Al-Zn alloys

Acta Metallurgica, 1988

ABSTRACT The morphology and kinetics of discontinuous precipitation (DP) and discontinuous coarse... more ABSTRACT The morphology and kinetics of discontinuous precipitation (DP) and discontinuous coarsening (DC) in solution treated and isothermally aged Al-Zn alloys containing 39.3 and 59.3 at.% Zn have been investigated at temperatures ranging from 323 to 523 K by light microscopy, electron microscopy and X-ray diffraction. At all aging temperatures the supersaturated α solid solution was observed to decompose rapidly by DP into a lamellar mixture of solute depleted α phase and β phase precipitate. DP occurred so rapidly in the 59.5 at.% Zn alloy that the heat of transformation raised the temperature of the alloy significantly. With further aging a slower DC reaction transformed the lamellar DP into a coarser lamellar structure of the same two phases; however, the composition of the α phase of the DC was closer to the equilibrium solvus composition than that of the DP. With still further aging a second, much slower DC reaction was observed to decompose the lamellar product of the first DC reaction in the 59.5 at.% Zn alloy into a still coarser lamellar structure. Analysis of the kinetics of both the DP and DC reactions showed them to be controlled by boundary diffusion in the advancing reaction interface. Reaction front migration rates for both DP and DC increased markedly with increasing Zn content. This increase seems to be associated partially with an increase in boundary diffusivity with increasing Zn content.

Research paper thumbnail of Biotribological behavior of two retrieved implant abutment screws after long-term use in vivo

The International journal of oral & maxillofacial implants

To evaluate the effect of functional cyclic loading on two retrieved abutment screws used with si... more To evaluate the effect of functional cyclic loading on two retrieved abutment screws used with single implant supporting cement-retained porcelain-fused-to-metal crowns by characterizing the structure, properties, and biotribologic behavior after long-term use in vivo. Two abutment screws were retrieved from the same patient and same implant at two different times. An external hex implant was used to replace a missing central incisor. A traumatic incident occurred 9 months after insertion and displaced the implant palatally by bending the screw. A second, similar incident occurred 31 months after insertion. In both cases, the abutment screws were retrieved and subjected to thorough nondestructive and destructive testing. Light and scanning electron microscopic examinations revealed very minimal surface deterioration of the thread profile for the first screw (in service for 9 months) and demonstrated advanced metal adhesive wear in the form of galling for the second screw (in service...

Research paper thumbnail of Cyclic stress strain relations and strain-controlled fatigue of 4140 steel

Research paper thumbnail of High-Temperature Digm in an FE-5 AT-PERCENT-A1 Bicrystal During ZN Diffusion

Scripta Metallurgica Et Materialia, 1992

Research paper thumbnail of Criteria for the Occurrence of the Diffusion-Induced Grain Boundary Migration

Interface Science - INTERFACE SCI, 1998

Recent experimental data on diffusion-induced grain boundary migration (DIGM) are reviewed. For t... more Recent experimental data on diffusion-induced grain boundary migration (DIGM) are reviewed. For the case of the coherency strain driving force, quantitative criteria for the occurrence of DIGM are suggested, which establish the relationship between the net driving force for grain boundary migration, the diffusivity in the vicinity of the grain boundary, the enthalpy of the grain boundary segregation, the misfit parameter for the solute atoms in the matrix and the solubility of the diffusing element in the matrix. It is shown that an upper limit for the grain boundary velocity during DIGM exists due to the solute drag effect.

Research paper thumbnail of Effect of strontium modification on near- threshold fatigue crack growth in an Al-Si-Cu die cast alloy

Metallurgical and Materials Transactions A, 1996

Abstract The effects of strontium modification on microstructure and fatigue properties in a die ... more Abstract The effects of strontium modification on microstructure and fatigue properties in a die cast com-mercial aluminum-silicon alloy are demonstrated. Strontium additions of 0.010 and 0.018 wt pct drastically change the morphology of the eutectic silicon. The influence of ...

Research paper thumbnail of Low cycle fatigue behavior of a quenched and tempered niobium bearing HSLA steel

Metallurgical Transactions A, 1980

The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high streng... more The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high strength low alloy steel heat treated to give tempered martensitic microstructures presumably with and without fine niobium carbides was studied by transmission electron microscopy, stress relaxation, X-ray diffraction line broadening and strain-controlled fatigue testing. The steel without the niobium carbides cyclically softened rapidly at all strain amplitudes studied. This softening was attributed to the rearrangement of the dislocation substructure into a cell structure and to the accompanying decrease in internal stress. The steel presumably containing the fine niobium carbides cyclically softened to a lesser extent. This correlated with the observation that dislocations in this steel did not rearrange themselves into a cell structure and, hence, there was less change in the internal stress during cycling. The steel without the niobium carbides exhibited somewhat better strain-life behavior at large strain amplitudes. This was attributed to the cell structure being able to accommodate a greater amount of plastic strain in that steel.

Research paper thumbnail of Fatigue behavior of a precipitation hardening Ni−Al−Cu medium carbon steel

Metallurgical Transactions A, 1976

Research paper thumbnail of The effect of repeated torque and salivary contamination on the preload of slotted gold implant prosthetic screws

The Journal of Prosthetic Dentistry, 2002

Screw loosening and/or fracture is common and has been attributed to many factors, including impr... more Screw loosening and/or fracture is common and has been attributed to many factors, including improper torque and preload. Purpose. This study evaluated the effect of repeated preload torque and salivary contamination on the preload of the slotted gold implant prosthetic screw. Fifteen slotted gold prosthetic screws were tested in an unused stack of components consisting of an implant, an abutment cylinder, and a screw and gold cylinder. A custom load frame and load cell and associated electronics were used. The component stack was lubricated with human saliva. Each screw was tightened to 10 Ncm with a hand-held torque wrench fitted with strain gauge electronics and then removed 10 times. Preload values at the first (Group 1X), fifth (Group 5X), and tenth (Group 10X) repetition were measured. Repeated-measures 1-way analysis of variance (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.05) and paired comparisons were used to analyze the data. The mean preload value increased from Group 1X (184.3 N +/- 28.9) to Group 5X (202.5 N +/- 27.7) to Group 10X (220.2 N +/- 29.0). The differences among these groups were significant (P=.004). Within the limitations of this study, higher preload was achieved after the repeated use of a saliva-lubricated gold prosthetic retaining screw.

Research paper thumbnail of Solidification shrinkage defects in electronic solders

JOM, 2005

Lead-Free Solder Overview Alloys that undergo solidifi cation over a wide range of temperatures g... more Lead-Free Solder Overview Alloys that undergo solidifi cation over a wide range of temperatures generally exhibit a difference in the contraction behavior of the ensuing solid and liquid phases. Furthermore, dissolution of substrate metals during process refl ow can lead to shifts in phase composition, additional primary phases, and volumetric contraction artifacts. The extent and frequency of surface roughness, shrinkage voids, fi llet lifting, and hot tearing seen in lead-free solders are different than for eutectic tin lead solder. Shrinkage effects have been reported in Sn/Pb, Sn/Pb/Ag, Sn/Ag/Cu, and Sn/Cu/Ni solders for various components, but few studies have examined their impact on solder joint reliability. Nevertheless, they warrant proper identifi cation due to the shift toward lead-free solders. This article is a review of the effects of shrinkage in Sn-Pb and lead-free solders as well as a discussion of some of the factors that contribute to their formation. Visit the site regularly and click on "What's New" to fi nd out the most up-to-date information on meetings, publications, membership activities, and more.