Showing papers on "Laves phase published in 1980"

Magnetic characteristics of Laves phase compound PrFe2

Abstract: The magnetic properties of Laves phase compound PrFe2, synthesised at high pressure, were studied by Mossbauer spectroscopy and saturation magnetisation. The ferromagnetism in PrFe2 has been confirmed. The rotation of the easy axis of magnetisation on the (110) plane to (111) with respect to (001) was observed as temperature increased. The authors have calculated the single-ion crystalline field magnetic anisotropy and have found this model to account for the experimental results in principle.

Hydrogen absorption in (ZrxTi1−x)B2 (B Cr, Mn) and the phenomenological model for the absorption capacity in pseudo-binary laves-phase compounds

Abstract: The hydrogen absorption of the systems (Zr x Ti 1− x )B 2 ( B  Cr , Mn; 0 ⩽ x ⩽ 1) was investigated as a function of x to check a previously proposed phenomenological model for the hydrogen capacities of Lavesphase AB 2 pseudo-binary compounds. The measurements were performed at pressures between 40 and 300 atm at room temperature and at liquid nitrogen temperatures. At 40 atm and 80 K the absorption capacity of the pseudo-binary compounds (Zr x Ti 1− x )Cr 2 increases linearly from 3.3 H atoms (formula unit (f.u.)) −1 in TiCr 2 to 4.5 H atoms (f.u.) −1 in ZrCr 2 . We show that the linear dependence of the hydrogen capacity in this system is in agreement with the phenomenological model, in which we consider a cluster composed of an A atom and its 12 B-type nearest neighbours. The maximum absorption capacity N H of the system (Zr x Ti 1− x )Mn 2 steeply increases from N H = 0.3 H atoms (f.u.) −1 for x = 0 to N H = 3.65 H atoms (f.u.) −1 for x = 0.4; it stays practically constant at approximately 4 H atoms (f.u.) −1 in the range 0.6 ⩽ x ⩽ 1. The non-linear dependence of N H on x in this system was accounted for in our model by taking into consideration the secondnearest neighbours (4A atoms) to an A atom in the Laves AB 2 compounds. The agreement between our experimental results and our model further emphasizes the importance of near-neighbour effects on the hydrogen absorption capacity in intermetallic compounds.

Two-dimensional lattice image of the Mg-base Friauf Laves phase and a new type of defect

Abstract: Two-dimensional lattice images have been obtained for the two-, four-, and nine-layer type structures of the Friauf-Laves phase, Mg(Cu0.535Al0.465)2. An intimate correlation is established between the lattice image and the crystal structure. With this relation, layer sequences of disordered stacking regions are determined. A new type of linear defect is found in the images and a structural model of the defect is proposed. The defect is always accompanied by a stacking fault, which is different from the usual stacking faults observed in close-packed structures.

Ferromagnetism in TiMn ternary hydrides

Abstract: The magnetic behaviour of TiMn intermetallics and their hydrides was investigated by susceptibility measurements in the temperature range 5–360 K and magnetization measurements in the temperature range 4–250 K with fields up to 7.2 T. The three TiMn intermetallics that are stable at low temperature (the C14 Laves phase with a wide range of homogeneity from Ti0.33Mn0.67 to Ti0.45Mn0.55, the ρ phase Ti0.46Mn0.54 and the φ phase Ti0.48Mn0.52) are paramagnetic with susceptibilities that are independent of temperature. The Laves-phase hydride retains the C14 structure with a lattice volume expansion of 27%. All three hydrides are ferromagnetic with Curie temperatures Tc of about 212, 87 and 155 K respectively that are slightly dependent on the hydrogen content. The susceptibilities above Tc consist of Curie-Weiss terms and very large temperature-independent terms. The onset of ferromagnetism in these TiMn ternary hydrides is due to the volume expansion and/or to the increase in the density of states at the Fermi level on hydrogenation.

The effect of molybdenum on high-temperature properties of 9 pct Cr steels

Abstract: Heat-resistant 9 Cr steels with 1, 2, and 3 pct Mo were tested for mechanical properties, weldability, and creep-rupture properties The elevated-temperature and rupture strengths increase with increasing molybdenum content While the 9 Cr-1 Mo steel is martensitic and is precipitation strengthened with carbides, the 9 Cr-2 Mo and 9 Cr-3 Mo steels receive added benefits from precipitation of Laves phase and solid-solution strengthening The latter cause little decrease in ductility and impact resistance The 9 Cr-2 Mo and 9 Cr-3 Mo steels are characterized by a duplex microstructure which aids weldability Weld cracking tests show no need for preheating the latter steels, although the martensitic 9 Cr-1 Mo steel is known to be susceptible to weld cracking if not preheated Both duplex-structure steels have good resistance to stress-relief cracking Anisotropy of mechanical properties, due to the orientation of the duplex structure in the rolling direction, is less than that observed in the fully martensitic 9 Cr-1 Mo steel

The ageing characteristics of an Fe-19 wt% Ni-9 wt% Co-5 wt% W alloy

Abstract: In the present paper, we compare the behaviour during ageing in the temperature range 380 to 530° C of the two martensitic alloys Fe-18.65 Ni-8.99 Co-4.87 Mo and Fe-18.65 Ni-8.99 Co-4.87 W (wt %). The kinetics of precipitation were followed by measurements of hardness, by resistometric measurements and electron microscopy. In the case of the alloy with Mo, Mo at first concentrates in local clusters, then an ω phase is formed, and above 450° C, finally a Ni3Mo or Laves phase (Fe, Ni, Co)2 Mo is formed. In the case of the alloy with W, ω phase formation was not observed but an intermetallic precipitate isomorphous with Ni3Mo, (Fe, Ni, Co)3 W = A3W was found. The precipitates are rod-shaped, of several nm in length. The preferred direction of growth of these precipitates is 〈1 1 1〉 of the martensitic matrix and the orientation relationship with the martensitic matrix is (0 1 1)M ∥ (0 1 0)A3W and [1 1 1]M ∥ [1 0 0]A3W, identical to that found for the Ni3Mo precipitate in the (Fe, Ni, Co, Mo, Ti) industrial maraging steel.

Titanium-manganese-vanadium based laves phase material - with hexagonal structure, used as hydrogen storage material

Abstract: A novel hydrogen storage material has the formula Ti1-aZraMn2-x Crx-y(VzM1-z)y in which M is one or more of Ni, Co and Cu; a is 0-0.3; x is 0.2-1.0; y is 0.2 to x; z is 0.6-0.9; and the ratio of V:M is 9:1 to 3:2. The material is useful as a hydrogen storage material in the cooling water circuit of hydrogen-fuelled vehicles. It shows a hydrogen pressure of more than 1 bar in the range -30 to +80 deg.C, extremely rapid hydrogen desorption and absorption even at low temps. and no poisoning on using hydrogen of only 99% purity, and requires no special initial activation.

Ni base alloy with superior stress corrosion resisting property and manufacture thereof

Abstract: PURPOSE: To improve strength, toughness and stress corrosion crack resisting property of an alloy in pure water under high temperature and pressure by means of a specified heat treatment in the manufacture for Ni base alloy containing Cr and Nb etc. CONSTITUTION: An Ni austenite alloy containing 0.01W0.15% C, less than 2% Si, less than 2% Mn, 15W25% Cr, 1W5% Mo, 0.1W2% Al, 0.1W2% Ti, 2W7% Nb less than 0.01% B and residual Ni is used for structual members in a nuclear reactor. The ingot of the Ni alloy is primarily homogenized at 1,130W1,200°C and formed by hot plastic working with reduction of area more than 30%. Since then, said alloy is aged at 600W760°C, after the solution heat treatment has been achieved at 920W1,080°C. Consequently, Laves phase composed of intermetallic compounds between metals containing Ni mainly and Nb, is removed, and austenite structure including fine precipitated particles, is obtained. Thus, Ni alloy with high strength, toughness and stress corrosion crack resisting property in pure water, may be used for manufacturing parts of a nuclear reactor. COPYRIGHT: (C)1982,JPO&Japio

Hydride of beryllium-based intermetallic compound

Abstract: Alloys of beryllium with Group IV or V metals of C22 Aluminum Boride, C15 Laves or C14 Laves phase structures and an atom ratio of 2:1 form hydrides reversibly. Either beryllium or the Group IV or V metal or both are in some instances substituted for in part by selected metals up to the solubility limit in the phase structures. Exemplary systems are based on Be 2 Ti with substitutions made to increase the stability of the hydride, or are based on Be 2 Zr with substitutions made to decrease the stability of the hydride.

Neutron Scattering Studies of Hydrides of the Laves Phase Rare Earth Compounds RFe2

Abstract: We have used neutron scattering to study the structure and magnetic ordering of a series of hydrides and deuterides of the rare earth-iron compounds RFe2. The parent RFe2’s have the cubic close packed Laves phase (C15) structure for R Heavier than Nd and order ferrimagnetically at ∿600 K with the full free ion moment on each R and ∿1.6μB/Fe at saturation. The stable hydride phases with ∿2 and ∿3.5 H(D) per formula unit are known from x-ray and neutron diffraction to retain the C15 cubic structure, with lattice parameters increased by ∿5% and ∿7%. The RFe2H4 phase is rhombohedrally distorted and is not ordered at 4.2 K (1).

Process Optimization of Cast Alloy 718 for Water Cooled Gas Turbine Application

Abstract: Several quantitative tools were utilized to optimize the microstructure of cast alloy 718. Quantitative metallography indicated that the cast structure can contain about 1 l/2 volume % carbide and nitride phase, about 0.4 volume % porosity and up to about 17 volume % Laves phase, a Cb rich segregant that readily forms in this alloy. With the proper hot isostatic pressing (HIP) cycle, segregation and porosity could be reduced to zero percent, allowing ultimate tensile strengths up to 1240 MPa (180 Ksi) to be obtained. Furthermore, differential thermal analysis showed that with the presence of Laves phase, an incipient melting point 100°C (180’F) below the true melting {point was possible. HIP was also shown to increase the rate of homogenization. A dislocation structure was documented that is thought to contribute to the increased strength of the alloy. It was found that y ” nucleated on the dislocation lines, separating the original cast grain into tiny subgrains. Thes% subgrains were determined by TEM to be misoriented Y, lo-12 between themselves, effectivc?ly reducing the grain size to 10 20 microns from the original grain size which was determined to be 2, 3000 microns.

Effect of silicon on the phase composition of nickel-base alloys

Abstract: 1. The addition of silicon to nickel-base alloys has a large effect on the nature and formation rate of precipitating carbides and intermetallic phases. 2. The ν carbide of the M6C type formed in alloys with silicon has a smaller lattice constant than in alloys without silicon or the ν carbide of the M12C type. Silicon accelerates the formation of carbides of the M12C type. 3. Silicon favors the formation of Laves phase in nickel alloys. After aging for 1000 h, Laves phase is formed in alloy EI929 with 1% Si and in alloy EP220 with 0.4% Si.

High pressure Mössbauer studies of magnetic Np intermetallics

Abstract: A high pressure (50 kbar) Mossbauer spectrometer for the 60 keV resonance in 237Np for temperatures between 1.4 and 100 K is described. It was used to study the magnetic properties of some neptunium intermetallics under pressure. For the cubic Laves phase compounds NpOs2 and NpAl2 a drastic decrease of the ordering temperature, the hyperfine field, and the isomer shift under increasing pressure was observed. It shows that their magnetic properties are primarily determined by the Np-Np separation which controls the width and hybridization of the 5f band. In contrast, an increase of ordering temperature coupled with a decrease of isomer shift with pressure was found in tetragonal NpCo2Si2, while the hyperfine field remains constant. This suggests that its magnetic properties must arise from different sources.

Exchange and Crystal Field Excitations in Rare-Earth Iron and Rare-Earth Cobalt Laves-Phase Compounds

Abstract: We have examined the magnetic excitations in a series of Laves-phase (Fd3m structure) compounds of heavy rare earths with Fe (RFe2) and Co (RCo2). These are prototype compounds for the study of magnetic interactions in a material with two magnetic atoms from several aspects: (1) the unit cell contains only two inequivalent sites, one for the transition metal and one for the rare earth; (2) the static structure factor separates reflections into six classes, two of which contain contributions from only one atom type, which simplifies determination of the sublattice magnetization; and (3) as shown below, the dynamic structure factor also selects out modes involving only one type of excitation (in-phase or out-of-phase spin precession) thereby greatly simplifying the analysis of spin wave data.

Magnetostrictive properties of rare earth-iron Laves phase materials prepared by powder metallurgy techniques

Abstract: A powder metallurgical approach has been utilized for preparation of highly magnetostrictive rare earth-iron Laves phase compounds. The results of dilatometric studies indicate that the liquid-phase sintering kinetics are in reasonable agreement with the concept of a phase boundary reaction as the rate-limiting factor. Magnetic powder orientation prior to sintering is found to improve magnetostriction of these compounds substantially.

Method of estimating the residual life of heat resistant parts made of 12% Cr steele

Abstract: Disclosed is a method of measuring the deterioration degree of heat resistant parts made of a 12% Cr steel containing at least one of Mo and W and used under high temperatures on the basis of the amount of Laves phase precipitated within said 12% Cr steel.

Magnetization and Mössbauer studies of (UxZr1−x)Fe2

Abstract: An attempt is presented to correlate the results of magnetic measurements and 57Fe Mossbauer studies performed on the pseudobinary (UxZr1−x)Fe2 intermetallic system (crystallizing in the cubic C15 Laves phase structure). The interpretation of the Mossbauer spectra obtained at 4.2, 78, and 300 K over the whole concentration range is based on the analysis of the distribution of hyperfine fields caused by the different local environment effects on the Fe nuclei. The concentration dependence of the mean hyperfine field and ordered magnetic moments may be explained by the strong influence of varying numbers of U atoms on the magnetic moment of Fe due to a transfer of 5f and/or 6d electrons of U to 3d states of Fe. An additional discussion of the temperature dependence of the initial susceptibilities measured in the neighbourhood of the magnetic transition temperatures appropriate to each U concentration is also given.

Magnetic Anisotropy and Spin Reorientations in HoxTb1−xFe2, DyxTb1−xFe2, and HoxTbyDy1−x−yFe2

Abstract: The properties of ternary and quaternary rare earth-iron Laves phase intermetallic compounds have been the subject of extensive investigation in recent years, in part because for certain compositions they exhibit both very high magnetostrictive strains and relatively low magnetic anisotropy at room temperature — characteristics which are desirable for magnetostrictive device applications. They also exhibit a complex set of spin reorientations as a function of composition and temperature.

Magnetic Excitations in TbFe2

Abstract: Magnetic inelastic scattering studies have been performed as a function of temperature on ErFe2 (1), HoFe2 (2) and TbFe2. All the heavy rare earth iron compounds of composition RFe2 crystallize in the C15 Laves phase structure with lattice constants a ≈ 7.3 A They have Curie temperatures in the range 575 K to 700°K and exhibit a ferrimagnetic alignment of iron and rare earth spins. The iron moment is typically 1.5 µBand the rare earth has the full free ion moment at 0 K.