R. Portier - Academia.edu (original) (raw)

Papers by R. Portier

Acta Crystallographica Section A, 1980

Applied Crystallography, 2004

ABSTRACT Mechanical alloying of Al50Ni40Co10, Al50Ni25Co25 and Al50Ni10Co40 alloys resulted in fo... more ABSTRACT Mechanical alloying of Al50Ni40Co10, Al50Ni25Co25 and Al50Ni10Co40 alloys resulted in formation of a nanocrystalline Al(Ni, Co) B2 intermetallic solid solution after 160 h of milling. Thermal analysis of the powders shows that the increase in cobalt content favors formation of the AI(Ni, Cc) B2 intermetallic phase, shifts the thermal stability of the milled powders towards a higher temperature range and decreases the grain size after annealing. The powder particle size increases in the early stage of milling up to 20 h to 800 mu m with a layered internal structure. Prolonged milling causes a refinement of the internal layered structure by simultaneous fracturing and formation of very small (about 5 mu m) homogenous particles after 160 h. High-resolution transmission electron microscopy allowed to identify the structure of individual particles with a size of 2-10 nm. From the fringe distance and the angles in the case of fringe cross grating, the B2 crystal structure was confirmed.

Journal of Solid State Chemistry, 1990

The authors have studied the structural and microstructural changes of BiâSrâCaâCuâO{sub 16+x} on... more The authors have studied the structural and microstructural changes of BiâSrâCaâCuâO{sub 16+x} on annealing close to its melting point and correlated these with the thermal stability and the electrical properties. Thermal analyses suggest that the BiâSrâCaâCuâO{sub 16+x} phase undergoes a peritectic or peritectic-like transformation, accompanied by oxygen loss, just before complete melting. This transformation leads to the formation of the

Scripta Metallurgica et Materialia, 1993

ABSTRACT

Philosophical Magazine A, 1986

The one- and two-dimensional long-period superstructures in Cu3Pd are analysed by means of high-r... more The one- and two-dimensional long-period superstructures in Cu3Pd are analysed by means of high-resolution electron microscopy and electron diffraction. Minor, but nevertheless significant, modifications of the phase diagram are suggested from detailed microstructural observations. The half-period M varies not only with composition but also with temperature. A systematic decrease in M with increasing temperature has been established.At low Pd concentrations

Journal de Physique, 1985

Le Journal de Physique Colloques, 1986

The newly discovered long-range ordered icosahedral phase C1,23 without translational periodicity... more The newly discovered long-range ordered icosahedral phase C1,23 without translational periodicity creates new interesting problems for the understanding of high resolution electron microscopy images.

Advanced Light Alloys and Composites, 1998

Philosophical Magazine, 1977

ABSTRACT

Materials Science Forum, 2013

A short-time aging treatment (STAT) strategy has been proved to be very efficient in improving th... more A short-time aging treatment (STAT) strategy has been proved to be very efficient in improving the mechanical properties of various titanium based alloys. The mechanical properties of alloys such as Ti-Nb, Ti-Nb-Zr and Ti-Nb-Zr-Sn based alloys, are extremely sensitive to the β phase stability, microstructure and phase constitution. The concept of the short-time treatment is designed to control precisely the material structure (phase precipitation, etc…) without extensive modification of the distribution of alloying elements. This results in reliable optimization regarding the balance between elastic modulus, pseudo-(super-) elasticity and strength. Currently, the structural evolution mechanisms involved in the STAT are under systematic investigations in the aim of achieving accurate control of the microstructures and optimized balance of mechanical properties.

The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-G... more The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-Ga alloys are briefly discussed. The role of lattice tetragonality of martensite in the reduction of magnetic field needed for the observation of large magnetostrain effect is theoretically analyzed, considering the compensation of the magnetic anisotropy. The possibility of the field reduction is based on the previously observed lattice parameter dependence on the temperature and proper fit of the alloy specimen shape. The model shows that a significant reduction of the magnetic field needed for the giant MSE can take place in martensites with 0.98 < c/a < 1.04.

Philosophical Magazine, 1977

Taking into account the symmetry properties of enantiomorphic crystals, we have deduced from the ... more Taking into account the symmetry properties of enantiomorphic crystals, we have deduced from the Howie–Whelan equations the following new results about the relative intensities of the diffracted beams of electrons: (i) In the two-beam and systematic reflection cases, the deviation from Friedel's law may be observed only if g belongs to a non-centric star. In the two-beam case this possible deviation is related to the phase change between the Fourier coefficients of crystal absorption potentials. (ii) Extinction conditions of inversion boundaries have been established in the case of systematic reflection in relation to the location (with respect to the elements of symmetry of the structure) of inversion centres.The absolute determination of LiFe5O8 ordered enantiomorphic structures is performed by comparison between observed and calculated electron diffraction intensities. In particular the exact operating diffraction conditions are carefully examined.

Philosophical Magazine A, 1980

ABSTRACT A MODEL FOR STACKING FAULTS IN PYRITEA model for stacking faults laying in the (001) pla... more ABSTRACT A MODEL FOR STACKING FAULTS IN PYRITEA model for stacking faults laying in the (001) plane of pyrite is proposed which is in accord with previously published experimental observations. This stacking fault has an a [0, x, 1/2] vector not parallel to the fault plane. It has a coherent and conservative character and half of the sulphur atoms are located on a coincidence sublattice. Through the fault, the atoms take the positions of the marcassite structure.

Le Journal de Physique Colloques, 1982

A la suite des travaux de Bollmann, de nombreux modèles géométriques ont été proposés pour décrir... more A la suite des travaux de Bollmann, de nombreux modèles géométriques ont été proposés pour décrire les joints de grains. Ces modèles ne s'appliquent qu'aux structures symorphiques ne contenant qu'un atcme par maille. Les restrictions peuvent être facilement évitées en introduisant quelques concepts élémentaires de cristallographie qui conduisent à une description unifiée des interfaces hcmophases. La notion d'extrema imposés par la symétrie est discutée pour la relaxation de la translation rigide en relation avec les travaux originaux de G. Kalonji et J.W. Cahn.

Acta Crystallographica Section A, 1980

Applied Crystallography, 2004

ABSTRACT Mechanical alloying of Al50Ni40Co10, Al50Ni25Co25 and Al50Ni10Co40 alloys resulted in fo... more ABSTRACT Mechanical alloying of Al50Ni40Co10, Al50Ni25Co25 and Al50Ni10Co40 alloys resulted in formation of a nanocrystalline Al(Ni, Co) B2 intermetallic solid solution after 160 h of milling. Thermal analysis of the powders shows that the increase in cobalt content favors formation of the AI(Ni, Cc) B2 intermetallic phase, shifts the thermal stability of the milled powders towards a higher temperature range and decreases the grain size after annealing. The powder particle size increases in the early stage of milling up to 20 h to 800 mu m with a layered internal structure. Prolonged milling causes a refinement of the internal layered structure by simultaneous fracturing and formation of very small (about 5 mu m) homogenous particles after 160 h. High-resolution transmission electron microscopy allowed to identify the structure of individual particles with a size of 2-10 nm. From the fringe distance and the angles in the case of fringe cross grating, the B2 crystal structure was confirmed.

Journal of Solid State Chemistry, 1990

The authors have studied the structural and microstructural changes of BiâSrâCaâCuâO{sub 16+x} on... more The authors have studied the structural and microstructural changes of BiâSrâCaâCuâO{sub 16+x} on annealing close to its melting point and correlated these with the thermal stability and the electrical properties. Thermal analyses suggest that the BiâSrâCaâCuâO{sub 16+x} phase undergoes a peritectic or peritectic-like transformation, accompanied by oxygen loss, just before complete melting. This transformation leads to the formation of the

Scripta Metallurgica et Materialia, 1993

ABSTRACT

Philosophical Magazine A, 1986

The one- and two-dimensional long-period superstructures in Cu3Pd are analysed by means of high-r... more The one- and two-dimensional long-period superstructures in Cu3Pd are analysed by means of high-resolution electron microscopy and electron diffraction. Minor, but nevertheless significant, modifications of the phase diagram are suggested from detailed microstructural observations. The half-period M varies not only with composition but also with temperature. A systematic decrease in M with increasing temperature has been established.At low Pd concentrations

Journal de Physique, 1985

Le Journal de Physique Colloques, 1986

The newly discovered long-range ordered icosahedral phase C1,23 without translational periodicity... more The newly discovered long-range ordered icosahedral phase C1,23 without translational periodicity creates new interesting problems for the understanding of high resolution electron microscopy images.

Advanced Light Alloys and Composites, 1998

Philosophical Magazine, 1977

ABSTRACT

Materials Science Forum, 2013

A short-time aging treatment (STAT) strategy has been proved to be very efficient in improving th... more A short-time aging treatment (STAT) strategy has been proved to be very efficient in improving the mechanical properties of various titanium based alloys. The mechanical properties of alloys such as Ti-Nb, Ti-Nb-Zr and Ti-Nb-Zr-Sn based alloys, are extremely sensitive to the β phase stability, microstructure and phase constitution. The concept of the short-time treatment is designed to control precisely the material structure (phase precipitation, etc…) without extensive modification of the distribution of alloying elements. This results in reliable optimization regarding the balance between elastic modulus, pseudo-(super-) elasticity and strength. Currently, the structural evolution mechanisms involved in the STAT are under systematic investigations in the aim of achieving accurate control of the microstructures and optimized balance of mechanical properties.

The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-G... more The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-Ga alloys are briefly discussed. The role of lattice tetragonality of martensite in the reduction of magnetic field needed for the observation of large magnetostrain effect is theoretically analyzed, considering the compensation of the magnetic anisotropy. The possibility of the field reduction is based on the previously observed lattice parameter dependence on the temperature and proper fit of the alloy specimen shape. The model shows that a significant reduction of the magnetic field needed for the giant MSE can take place in martensites with 0.98 < c/a < 1.04.

Philosophical Magazine, 1977

Taking into account the symmetry properties of enantiomorphic crystals, we have deduced from the ... more Taking into account the symmetry properties of enantiomorphic crystals, we have deduced from the Howie–Whelan equations the following new results about the relative intensities of the diffracted beams of electrons: (i) In the two-beam and systematic reflection cases, the deviation from Friedel's law may be observed only if g belongs to a non-centric star. In the two-beam case this possible deviation is related to the phase change between the Fourier coefficients of crystal absorption potentials. (ii) Extinction conditions of inversion boundaries have been established in the case of systematic reflection in relation to the location (with respect to the elements of symmetry of the structure) of inversion centres.The absolute determination of LiFe5O8 ordered enantiomorphic structures is performed by comparison between observed and calculated electron diffraction intensities. In particular the exact operating diffraction conditions are carefully examined.

Philosophical Magazine A, 1980

ABSTRACT A MODEL FOR STACKING FAULTS IN PYRITEA model for stacking faults laying in the (001) pla... more ABSTRACT A MODEL FOR STACKING FAULTS IN PYRITEA model for stacking faults laying in the (001) plane of pyrite is proposed which is in accord with previously published experimental observations. This stacking fault has an a [0, x, 1/2] vector not parallel to the fault plane. It has a coherent and conservative character and half of the sulphur atoms are located on a coincidence sublattice. Through the fault, the atoms take the positions of the marcassite structure.

Le Journal de Physique Colloques, 1982

A la suite des travaux de Bollmann, de nombreux modèles géométriques ont été proposés pour décrir... more A la suite des travaux de Bollmann, de nombreux modèles géométriques ont été proposés pour décrire les joints de grains. Ces modèles ne s'appliquent qu'aux structures symorphiques ne contenant qu'un atcme par maille. Les restrictions peuvent être facilement évitées en introduisant quelques concepts élémentaires de cristallographie qui conduisent à une description unifiée des interfaces hcmophases. La notion d'extrema imposés par la symétrie est discutée pour la relaxation de la translation rigide en relation avec les travaux originaux de G. Kalonji et J.W. Cahn.