Mark Bourke | Los Alamos National Laboratory (original) (raw)

Papers by Mark Bourke

Ceramic Engineering and Science Proceedings, 2000

Thermal residual stress (TRS) was measured using neutron diffraction during in situ heating (300~... more Thermal residual stress (TRS) was measured using neutron diffraction during in situ heating (300~1500K) of NiAlbased hybrid composites, reinforced with both AlN dispersoids and Al 2 O 3 short fibers (NiAl-AlN-Al 2 O 3 ). A finite element model was developed and validated using the measured data. Using the model, evolution of the TRS in each phase was studied systematically by varying matrix properties (elastic, elastoplastic or viscoplastic); and cooling/heating path and rate. The best description of the experimental data was achieved by using a creeping matrix in the model coupled with the actual thermo-mechanical history applied to the specimen. It was demonstrated that a methodology, which combines (i) in situ high-temperature neutron diffraction measurements and (ii) a finite element model that considers matrix viscoplasticity and path/rate-dependency, provides a reasonable prediction of the TRS in this three-phase composite both at low and high temperatures.

... DEFORMATION IN AN ALUMINIUM ALLOY WELD DJ SMITH R. H. LEGGAm G. A. WEBSTER HJ MACGILLNRAY P. ... more ... DEFORMATION IN AN ALUMINIUM ALLOY WELD DJ SMITH R. H. LEGGAm G. A. WEBSTER HJ MACGILLNRAY P. J. WEBSTER Saljord Uniuersity. G. MILLS Saljord University. The Welding Institute, Cambridge.* The Welding Institute, Cambridge. MIMechE. ...

We report the complete macroscopic average strain tensor for a cold-rolled uranium plate. The str... more We report the complete macroscopic average strain tensor for a cold-rolled uranium plate. The strain tensor was determined by the least-squares refinement of interplanar spacings for 19 Bragg reflections, as determined from the neutron TOF measurements at LANSCE. An annealed uranium plate was used as a reference sample, thus providing reference interplanar spacings for all 19 reflections. We also discuss the mathematical background for the calculation of the average macroscopic strain tensor as applied to the orthorhombic crystal symmetry and general triclinic sample symmetry of the uranium sample, based on a recently proposed method to determine texture-weighted strain orientation distribution function for arbitrary crystal and sample symmetries.

MRS Proceedings, 2004

Pseudoelasticity in monocrystalline Fe 3 Al (23 at.% Al) was investigated by roomtemperature mech... more Pseudoelasticity in monocrystalline Fe 3 Al (23 at.% Al) was investigated by roomtemperature mechanical testing along the <418> tensile and compressive axes. In tension, up to ~10% strain is recoverable whereas only ~5% strain is recoverable in compression. Straight, parallel, surface step lines were seen to appear/disappear as the specimens were pseudoelastically loaded/unloaded. In contrast, in the plastic region (ε >10%), wavy slip lines appeared on the specimen surfaces which did not disappear upon unloading. In-situ neutron diffraction was performed during compressive straining and the intensities of several diffraction peaks increase/decrease reversibly during loading/unloading. These changes are consistent with a deformation twin which produces large crystal rotations. They could also be indicative of a phase transformation. Unfortunately, we were able to sample only a limited range of 2θ in the present investigation and, within this range, none of the new peaks that appeared during the pseudoelastic deformation were disallowed peaks for the D0 3 crystal structure. Therefore we are unable at this time to distinguish between the two possible mechanisms, twinning and phase transformation.

Advances in X-Ray Analysis, 1997

ABSTRACT Rietveld refinement of X-ray diffraction patterns has been used to provide microstructur... more ABSTRACT Rietveld refinement of X-ray diffraction patterns has been used to provide microstructural information complementary to conventional X-ray residual stress measurements through a carburized layer containing a maximum vol. 25 % of retained austenite. Layers in a simple specimen were removed incrementally by electropolishing and, at each depth in addition to conventional residual stress measurements in both the martensite and retained austenite, data were collected at Ψ = 0 for Rietveld refinement. The refinements provide accurate values for the lattice parameters in the respective phases that can be related to carbon content and microstructure. Besides to providing qualitative information concerning the microstructure and possible surface decarburization, the c/a ratio of the martensite potentially offers an independent technique for determining carbon content profiles.

MRS Proceedings, 1998

NiAl-based hybrid composites containing 5, 15 and 30 volume percent of Al 2 O 3 fibers in additio... more NiAl-based hybrid composites containing 5, 15 and 30 volume percent of Al 2 O 3 fibers in addition to AlN dispersion particles were fabricated via a powder metallurgy route. The strengthening mechanisms associated with the short Al 2 O 3 fiber in NiAl-(AlN) dispersion -(Al 2 O 3 ) fiber composite were studied with an emphasis on the effect of thermal residual stress on the compressive strength at room temperature and 1300K. At 300K, the yield strength of the composites was predicted using a linear superposition of the monolithic yield strength, direct fiber strengthening and tensile matrix residual stresses. The prediction shows good agreement with the measured data. The majority of the room temperature strengthening is attributable to the residual stress. At 1300K, the strengthening was achieved only by the load sharing of the fibers and there is no direct influence from the process-induced thermal residual stresses since they were completely relaxed at this temperature.

Materials Science Forum, 2005

MRS Proceedings, 2004

HAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, w... more HAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, with a small amount (1-5 vol. %) of semi-coherent FCC carbides. Neutron diffraction experiments were performed to study the interaction of the carbides with the matrix during tensile and compressive loading. The behavior of the elastic lattice strains during in situ loading clearly showed a tension-compression asymmetry. Although the volume percentage is small, the interaction between the carbides and the matrix had a significant effect on the load sharing. In compression, the carbides began load sharing at the macroscopic yield point, while the tension test suggests no load sharing. Debonding at the carbide-matrix interface is proposed to explain the lack of load sharing during the tensile loading based on the disparities observed between the experimental results and the finite element models.

Materials Science Forum, 2002

ABSTRACT Low symmetry materials such as hexagonal metals and alloys, deform by twinning as well a... more ABSTRACT Low symmetry materials such as hexagonal metals and alloys, deform by twinning as well as by slip, with twinning making a substantial contribution to deformation, hardening and texture evolution. In this work, we present an experimental and theoretical study of hexagonal Zr, Be and Mg aggregates with an initial texture, deforming in compression. The evolution of texture and twinned volume fraction were measured using neutron diffraction. Complementarily, a polycrystal plasticity code was used to interpret texture and hardening evolution in terms of interaction between slip and twin modes. This study correlates twinning, texture, anisotropy and hardening. It represents a systematic approach for understanding the plastic response of hexagonal materials and for developing a microstructure-based constitutive description.

International Conference Neutrons in Research and Industry, 1997

ABSTRACT Phase transformations in engineering materials are inevitably related to mechanical beha... more ABSTRACT Phase transformations in engineering materials are inevitably related to mechanical behavior and are often precursors to residual stress and distortion. Neutron scattering in general is a valuable tool for studying their effects, and pulsed neutrons are of special value, because of the inherently comprehensive crystallographic coverage they provide in each measurement. At the Manuel Lujan neutron scattering center several different research programs have addressed the relationships between phase transformation/mechanical behavior and residual strains. Three disparate examples are presented: 1) stress induced transformation in a NiTi shape memory alloy, 2) cryogenically induced transformation in a quenched 5180 steel, and 3) time resolved evolution of strain induced martensite in 304 stainless steel. In each case a brief description of the principal result will be discussed in the context of using neutrons for the measurement.

MRS Proceedings, 2000

Composites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates h... more Composites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates have been shown to exhibit superior mechanical properties as compared to monolithic BMGs. To understand the role of reinforcements in this improvement, it is necessary to investigate the state of internal stresses in these composites. These stresses arise from the thermal expansion mismatch between the reinforcement and the matrix, as well as the elastic and plastic incompatibilities between the two phases. Neutron diffraction and synchrotron X-ray diffraction were used to measure these mismatch-induced stresses in BMG-matrix composites with various reinforcements: continuous W fibers, W or Ta particles, and dendritic, in-situ formed precipitates. The results are compared to numerical and analytical predictions of internal stresses.

Scripta Materialia, 2003

In-situ uniaxial compression tests were conducted on four tungsten fiber reinforced bulk metallic... more In-situ uniaxial compression tests were conducted on four tungsten fiber reinforced bulk metallic glass matrix composites using neutron diffraction. The results were interpreted with a finite element model. Both phases were seen to approximately obey the von Mises yield criterion. The fibers were observed to yield first and then transfer load to the matrix.

Ceramic Engineering and Science Proceedings, 2000

Thermal residual stress (TRS) was measured using neutron diffraction during in situ heating (300~... more Thermal residual stress (TRS) was measured using neutron diffraction during in situ heating (300~1500K) of NiAlbased hybrid composites, reinforced with both AlN dispersoids and Al 2 O 3 short fibers (NiAl-AlN-Al 2 O 3 ). A finite element model was developed and validated using the measured data. Using the model, evolution of the TRS in each phase was studied systematically by varying matrix properties (elastic, elastoplastic or viscoplastic); and cooling/heating path and rate. The best description of the experimental data was achieved by using a creeping matrix in the model coupled with the actual thermo-mechanical history applied to the specimen. It was demonstrated that a methodology, which combines (i) in situ high-temperature neutron diffraction measurements and (ii) a finite element model that considers matrix viscoplasticity and path/rate-dependency, provides a reasonable prediction of the TRS in this three-phase composite both at low and high temperatures.

... DEFORMATION IN AN ALUMINIUM ALLOY WELD DJ SMITH R. H. LEGGAm G. A. WEBSTER HJ MACGILLNRAY P. ... more ... DEFORMATION IN AN ALUMINIUM ALLOY WELD DJ SMITH R. H. LEGGAm G. A. WEBSTER HJ MACGILLNRAY P. J. WEBSTER Saljord Uniuersity. G. MILLS Saljord University. The Welding Institute, Cambridge.* The Welding Institute, Cambridge. MIMechE. ...

We report the complete macroscopic average strain tensor for a cold-rolled uranium plate. The str... more We report the complete macroscopic average strain tensor for a cold-rolled uranium plate. The strain tensor was determined by the least-squares refinement of interplanar spacings for 19 Bragg reflections, as determined from the neutron TOF measurements at LANSCE. An annealed uranium plate was used as a reference sample, thus providing reference interplanar spacings for all 19 reflections. We also discuss the mathematical background for the calculation of the average macroscopic strain tensor as applied to the orthorhombic crystal symmetry and general triclinic sample symmetry of the uranium sample, based on a recently proposed method to determine texture-weighted strain orientation distribution function for arbitrary crystal and sample symmetries.

MRS Proceedings, 2004

Pseudoelasticity in monocrystalline Fe 3 Al (23 at.% Al) was investigated by roomtemperature mech... more Pseudoelasticity in monocrystalline Fe 3 Al (23 at.% Al) was investigated by roomtemperature mechanical testing along the <418> tensile and compressive axes. In tension, up to ~10% strain is recoverable whereas only ~5% strain is recoverable in compression. Straight, parallel, surface step lines were seen to appear/disappear as the specimens were pseudoelastically loaded/unloaded. In contrast, in the plastic region (ε >10%), wavy slip lines appeared on the specimen surfaces which did not disappear upon unloading. In-situ neutron diffraction was performed during compressive straining and the intensities of several diffraction peaks increase/decrease reversibly during loading/unloading. These changes are consistent with a deformation twin which produces large crystal rotations. They could also be indicative of a phase transformation. Unfortunately, we were able to sample only a limited range of 2θ in the present investigation and, within this range, none of the new peaks that appeared during the pseudoelastic deformation were disallowed peaks for the D0 3 crystal structure. Therefore we are unable at this time to distinguish between the two possible mechanisms, twinning and phase transformation.

Advances in X-Ray Analysis, 1997

ABSTRACT Rietveld refinement of X-ray diffraction patterns has been used to provide microstructur... more ABSTRACT Rietveld refinement of X-ray diffraction patterns has been used to provide microstructural information complementary to conventional X-ray residual stress measurements through a carburized layer containing a maximum vol. 25 % of retained austenite. Layers in a simple specimen were removed incrementally by electropolishing and, at each depth in addition to conventional residual stress measurements in both the martensite and retained austenite, data were collected at Ψ = 0 for Rietveld refinement. The refinements provide accurate values for the lattice parameters in the respective phases that can be related to carbon content and microstructure. Besides to providing qualitative information concerning the microstructure and possible surface decarburization, the c/a ratio of the martensite potentially offers an independent technique for determining carbon content profiles.

MRS Proceedings, 1998

NiAl-based hybrid composites containing 5, 15 and 30 volume percent of Al 2 O 3 fibers in additio... more NiAl-based hybrid composites containing 5, 15 and 30 volume percent of Al 2 O 3 fibers in addition to AlN dispersion particles were fabricated via a powder metallurgy route. The strengthening mechanisms associated with the short Al 2 O 3 fiber in NiAl-(AlN) dispersion -(Al 2 O 3 ) fiber composite were studied with an emphasis on the effect of thermal residual stress on the compressive strength at room temperature and 1300K. At 300K, the yield strength of the composites was predicted using a linear superposition of the monolithic yield strength, direct fiber strengthening and tensile matrix residual stresses. The prediction shows good agreement with the measured data. The majority of the room temperature strengthening is attributable to the residual stress. At 1300K, the strengthening was achieved only by the load sharing of the fibers and there is no direct influence from the process-induced thermal residual stresses since they were completely relaxed at this temperature.

Materials Science Forum, 2005

MRS Proceedings, 2004

HAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, w... more HAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, with a small amount (1-5 vol. %) of semi-coherent FCC carbides. Neutron diffraction experiments were performed to study the interaction of the carbides with the matrix during tensile and compressive loading. The behavior of the elastic lattice strains during in situ loading clearly showed a tension-compression asymmetry. Although the volume percentage is small, the interaction between the carbides and the matrix had a significant effect on the load sharing. In compression, the carbides began load sharing at the macroscopic yield point, while the tension test suggests no load sharing. Debonding at the carbide-matrix interface is proposed to explain the lack of load sharing during the tensile loading based on the disparities observed between the experimental results and the finite element models.

Materials Science Forum, 2002

ABSTRACT Low symmetry materials such as hexagonal metals and alloys, deform by twinning as well a... more ABSTRACT Low symmetry materials such as hexagonal metals and alloys, deform by twinning as well as by slip, with twinning making a substantial contribution to deformation, hardening and texture evolution. In this work, we present an experimental and theoretical study of hexagonal Zr, Be and Mg aggregates with an initial texture, deforming in compression. The evolution of texture and twinned volume fraction were measured using neutron diffraction. Complementarily, a polycrystal plasticity code was used to interpret texture and hardening evolution in terms of interaction between slip and twin modes. This study correlates twinning, texture, anisotropy and hardening. It represents a systematic approach for understanding the plastic response of hexagonal materials and for developing a microstructure-based constitutive description.

International Conference Neutrons in Research and Industry, 1997

ABSTRACT Phase transformations in engineering materials are inevitably related to mechanical beha... more ABSTRACT Phase transformations in engineering materials are inevitably related to mechanical behavior and are often precursors to residual stress and distortion. Neutron scattering in general is a valuable tool for studying their effects, and pulsed neutrons are of special value, because of the inherently comprehensive crystallographic coverage they provide in each measurement. At the Manuel Lujan neutron scattering center several different research programs have addressed the relationships between phase transformation/mechanical behavior and residual strains. Three disparate examples are presented: 1) stress induced transformation in a NiTi shape memory alloy, 2) cryogenically induced transformation in a quenched 5180 steel, and 3) time resolved evolution of strain induced martensite in 304 stainless steel. In each case a brief description of the principal result will be discussed in the context of using neutrons for the measurement.

MRS Proceedings, 2000

Composites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates h... more Composites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates have been shown to exhibit superior mechanical properties as compared to monolithic BMGs. To understand the role of reinforcements in this improvement, it is necessary to investigate the state of internal stresses in these composites. These stresses arise from the thermal expansion mismatch between the reinforcement and the matrix, as well as the elastic and plastic incompatibilities between the two phases. Neutron diffraction and synchrotron X-ray diffraction were used to measure these mismatch-induced stresses in BMG-matrix composites with various reinforcements: continuous W fibers, W or Ta particles, and dendritic, in-situ formed precipitates. The results are compared to numerical and analytical predictions of internal stresses.

Scripta Materialia, 2003

In-situ uniaxial compression tests were conducted on four tungsten fiber reinforced bulk metallic... more In-situ uniaxial compression tests were conducted on four tungsten fiber reinforced bulk metallic glass matrix composites using neutron diffraction. The results were interpreted with a finite element model. Both phases were seen to approximately obey the von Mises yield criterion. The fibers were observed to yield first and then transfer load to the matrix.