C.H. Allibert

Thermodynamic study of the LaNi5−xCux system

Abstract The enthalpies of formation of LaNi 5− x Cu x compounds ( x = 0, 1, 2, 3, 4, 5) were measured using a calorimetric method and were found to increase linearly from LaNi 5 to LaCu 5 . A relation taking the substitution of copper for nickel into account is proposed to explain this behaviour. The enthalpies of hydrogenation are calculated from these values for the enthalpies of formation using relations established previously and are compared with experimental data.

Structural and thermodynamic data on the pseudobinary phases R(Co1−xCux)5 with R≡ Sm, Y, Ce

For the phases R(Co1−itxCuitx)5 with R ≡ Sm, Y, Ce, homogenized at 950 °C, the enthalpies of formation were determined by a calorimetry technique involving dissolution in molten tin and the lattice parameters were measured using X-ray diffraction in a focusing camera. In order to study the effect of substitution of cobalt for copper, the lattice parameters were corrected for the contribution of the departure of R from stoichiometry. For the R(Co1−itxCuitx)5 phases with R ≡ Sm, Y, the lattice parameters were also measured after heat treatment at 400 °C. The x dependences of the enthalpies of formation and lattice parameters indicate an ideal behaviour for the mixing of SmCo5 and SmCu5 on one hand, and for YCo5 and YCu5 on the other hand. This result is consistent with the homogeneous state found for Sm(Co1−itxCuitx)5 and Y(Co1−itxCuitxon the whole x range at 400 °C. For the mixture of CeCo5 and CeCu5, the enthalpies of formation exhibit a slightly positive deviation which predicts the solid state miscibility gap previously evidenced in the CeCo5-CeCu5 section below 800 °C.

Enthalpies of formation of SmCo alloys in the composition range 10–22 at. % Sm

Abstract Several intermetallic compounds exist in the composition range 10–22 at.% Sm(Sm 2 Co 17 , SmCo 5 , Sm 2 Co 7 ) but their preparation as single-phase specimens is very difficult. In order to determine the enthalpies of formation of these compounds, measurements were carried out on four alloys containing respectively 12.9 at.% Sm, 16.4 at.% Sm, 17 at.% Sm and 19.8 at.% Sm, annealed in the temperature range 950–1100 °C. The compositions of the phases present in each specimen were deduced from the characterization of the measured alloys by scanning electron microscopy, electron microanalysis and X-ray diffraction. The heats of formation were deduced from solution calorimetry in molten tin. The variation of the experimental results as a function of the samarium content enabled the enthalpy of formation of SmCo 5 ( − 40.8 kJ mol −1 ) to be determined. The same ΔH f value as determined for the phase quenched from 950 °C was measured for SmCo 5 kept at room temperature after very slow cooling. This result did not confirm the eutectoid decomposition previously reported for SmCo 5 . The extrapolation of the measured values for the higher and lower samarium contents leads to the evaluation of the enthalpies of formation of Sm 2 Co 17 (−152 kJ mol −1 ) and Sm 2 Co 7 (−99kJ mol −1 ).

Enthalpies of formation of the LaCu intermetallic phases

Abstract The enthalpies of formation of the various intermetallic phases of the LaCu binary system were measured by a calorimetric method involving the dissolution of the compounds in molten Al. The experimental results were compared with the values predicted by the Miedema representation.

Redetermination of the phase equilibria in the system Sm-Co-Cu for Sm content 0–20 AT.% AT 850°C

Abstract A reinvestigation of the phase equilibria is carried out at 800°C in the system Sm-Co-Cu for Sm content up to 20 at.%. The experimentation involves the electron microanalysis and X-ray diffraction study of heat-treated specimens and some DTA. The new features exhibited are, on the binary Sm-Co limit, the existence of the compound Sm5Co19 with the rhomboedral structure, and on the Sm-Cu boundary, the solid state decomposition of SmCu5 forming SmCu6 and a phase Sm2Cu9 not previously identified, at about 850°C. In the Cu-rich part of the Sm-Co-Cu system, the pseudobinary phase Sm(Co1−xCux)5 with the hexagonal CaCu5 structure type is shown to have an existence range extended towards Sm-deficient compositions. The lattice parameters indicate that the stoichiometry departure likely results from the disordered substitution of Cu or Co atom pairs for Sm atoms in Sm(Co1−xCux)5.

Thermodynamic study of the valence state of cerium and hydrogen storage in Ce(Ni1−xCux)5 compounds☆

The enthalpies of formation of the pseudo-binary Ce(Ni1−xCux)5 compounds, measured by the calorimetric method, were found to increase linearly from CeNi5 to CeCu5. The valence state of cerium in Ce(Ni1−xCux)5 is discussed by comparison with the La(Ni1−xCux)5 system. The enthalpies of hydrogenation of Ce(Ni1−xCux)5 are calculated from their enthalpies of formation using relations previously established, and compared with experimental data from literature.

The influence of zirconium on Sm(CoFeCuZr)7,2 alloys for permanent magnets. I:Identification of the phases by transmission electron microscopy

Abstract An Sm(Co 0.69 Fe 0.22 Cu 0.06 Zr 0.03 ) 7.2 alloy cast from the melt was exposed to various heat treatments at 1050-850 °C. The aged alloys were studied by transmission electron microscopy and energy dispersive X-ray-scanning transmission electron microscope microanalysis. The specimens treated at 1050 °C contain a mixture of Sm 2 Co 17 and Sm 2 Co 7 type phases. Prolonged aging at 850 °C provokes the additional precipitation of Sm 5 Co 19 type phase. A treatment similar to that designed for magnet preparation induces the characteristic cellular morphology described in the literature. Such a microstructure is formed by cells of rhombohedral 2:17 type phase containing thin lamellae of 1:3 type. A boundary consisting of a stacking of 2:7 and 5:19 type phases enriched in zirconium surrounds the iron-rich 2:17 cells.

Effect of Nb and Zr on the phases present in Nd-Fe-B alloys for permanent magnets

Identification des phases formees par le niobium et le zirconium dans les alliages Nd-Fe-B, apres un long recuit a des temperatures proches de celles du frittage et des traitements thermiques effectues sur ces materiaux

Phase equilibria in the CeCo5-CeCu5 system and structural characterization of the Ce(Co1−xCux)5 phases☆

Abstract The phase equilibria of the CeCo5-CeCu5 system were determined by DTA and isothermal annealings. Except for the mixtures very rich in Cu, a pseudo-binary behaviour and direct melting of the phases are deduced from the results. A solid state miscibility gap is present below about 800 °C. For the Ce(Co1−xCux)5 phases homogenized at 900 °C, the irregular increase of the lattice parameter as a function of x is attributed to a change of the valence state of Ce. The Cu and Co substitution entails a drastic decrease of the Curie temperature of the phases.

Elaboration of (Steel/Cemented Carbide) Multimaterial by Powder Metallurgy

A steel/cemented carbide couple is selected to generate a tough/hard two layers material. The sintering temperature and composition are chosen according to phase equilibria data. The choice of optimal sintering conditions needs experimental studies. First results evidence liquid migration from the hard layer to the tough one, leading to porosity in the hard region. The study of microstructure evolution during sintering of the tough material (TEM, SEM, image analysis) evidences the coupled mechanisms of pore reduction and WC dissolution, and leads to temperature and time ranges suitable to limit liquid migration. The sintering of the two layer material is then shown to need further compromises to avoid interface crack formation due to differential densification.