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Showing papers on "Directional solidification published in 1981"


Journal ArticleDOI
TL;DR: In this article, a general framework is proposed to relate tip radius, interface undercooling and primary arm spacing in alloy dendrite growth, and all the growth morphologies developed between the limiting morphology at low and at high velocity are described to a first approximation, using an ellipsoid of revolution.

899 citations


Journal ArticleDOI
TL;DR: In this article, the phase spacings and transitions in microstructure are discussed in terms of diffusion processes at the monotectic front, with reference to the relative surface energies between two immiscible liquids and a third (solid) phase.
Abstract: Directional solidification methods have been used to examine the growth of fibrous, or tubular, composite samples in alloys close to the monotectic reaction: Liquid 1 Solid + Liquid 2. The binary systems Al-In, Cu-Pb and Cd-Ga have been examined and some use made of a transparent analogue, succinnonitrile-water. The solidification behavior appears to relate to the height of the miscibility gap in such systems and it is demonstrated how ternary additions which change this height (Sn to Al-In, Al to Cu-Pb) modify the microstructures dramatically. These structural changes are discussed with reference to the relative surface energies between two immiscible liquids and a third (solid) phase. The phase spacings and transitions in microstructure are discussed in terms of diffusion processes at the monotectic front.

119 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the phenomenon of solid liquid interface instability during directional solidification in In+, Ga+, Fe+, and Sb+ implanted silicon after pulsed laser annealing.
Abstract: The phenomenon of solid‐liquid interface instability during directional solidification has been studied in In+, Ga+, Fe+, and Sb+ implanted silicon after pulsed laser annealing. Interface instability results in lateral segregation which leads to the formation of cellular structures. The cellular structures have been studied using transmission electron microscopy. The critical bulk solute concentration above which instability develops, and the wavelength of instability (cell size) as a function of velocity of solidification have been calculated following the perturbation theory originally developed by Mullins and Sekerka. A good agreement between the experimental results and the calculations is obtained when the dependence of the interfacial distribution coefficient on the velocity of solidification is taken into account in the calculations.

82 citations


Journal ArticleDOI
TL;DR: LiInSe 2 single crystals were grown by directional solidification as discussed by the authors, and the lattice constants were determined to be a = 7.218 A, b = 8.441 A, and c = 6.772 A by powder X-ray diffraction.

66 citations


Journal ArticleDOI
TL;DR: LiGaSe2 has been shown to have an orthorhombic unit cell structure with an energy band gap of 3.65 eV and melting point was determined by differential thermal analysis to be 846 °C.
Abstract: Single crystals of a new ternary lithium chalcogenide LiGaSe2 were grown by an improved directional solidification technique. The typical as‐grown crystal has dimensions of about 4 mm cubed and shows a transparent light yellow color. We infer that LiGaSe2 crystallizes in the β‐NaFeO2 structure having an orthorhombic unit cell (a = 6.833 A, b = 8.227 A, and c = 6.541 A) by powder x‐ray diffraction. The melting point was determined by differential thermal analysis to be 846 °C. The energy band gap of LiGaSe2 at room temperature was determined by optical reflectance measurements to be 3.65 eV.

40 citations


Journal ArticleDOI
TL;DR: In this paper, several simple nickel alloys have been doped with sulfur prior to directional solidification and direct confirmation of preferential grain boundary oxygen penetration was obtained by exposing these specimens in air and vacuum, and they were found to have complex oxides on the boundaries at depths roughly an order of magnitude greater than those for matrix internal oxidation.
Abstract: Oxygen penetration of grain boundaries in nickel and nickel base alloys may produce severe intermediate temperature embrittlement. In the present study, several simple nickel alloys have been doped with sulfur prior to directional solidification. For specimens taken perpendicular to the growth direction, intergranular fracture at room temperature was readily achieved. By exposing these specimens in air and vacuum, direct confirmation of preferential grain boundary oxygen penetration was obtained. Complex oxides were identified on the boundaries at depths roughly an order of magnitude greater than those for matrix internal oxidation. It was shown that boron was effective in preventing the preferential grain boundary precipitation during air exposure although the experiment was complicated by dissolution of boride and associated void formation. Coatings which prevent oxygen penetration also prevent embrittlement.

39 citations


Patent
14 Dec 1981
TL;DR: In this paper, a single crystal article is cast so that the solidification front moves transverse to the length of the article, and essentially parallel to the flange surfaces where the defects tend to occur.
Abstract: During conventional directional solidification of a single crystal article having a large overhanging flange lying along its length, crystal nucleation defects and shrinkage occur in the flange. To form articles without such defects, the part is cast so that the solidification front moves transverse to the length of the article, and essentially parallel to the flange surfaces where the defects tend to occur. The solidification front is initiated at a seed crystal oriented to produce the desired crystal structure in the cast article. Dendritic effects produce somewhat different properties in articles cast in accord with the invention, compared to those cast with prior art techniques.

37 citations


Journal ArticleDOI
TL;DR: In this article, a non-dimensional analysis of segregation during directional solidification under transient conditions is applied to different types of growth in various solidification configurations, namely Bridgman, Czochralski and floating zone.

37 citations


Patent
23 Dec 1981
TL;DR: In this article, a method for directional solidification of large single crystal metal alloy castings using multiple seed crystals is described, where solidification interfaces emanate from the separate seeds, and merge to form a unitary solidification interface which is caused to move through the article.
Abstract: Disclosed is a method for directional solidification of large single crystal metal alloy castings using multiple seed crystals. Solidification interfaces emanate from the separate seeds, and merge to form a unitary solidification interface which is caused to move through the article. The crystallographic orientation of the seeds is controlled, to avoid unacceptable mismatch of crystal structure orientation where the separate interfaces merge.

33 citations


Journal ArticleDOI
TL;DR: Using Kerr and Bitter techniques, magnetic domain patterns have been studied in various cobalt, iron, and cobalt-iron borides prepared by chill casting, directional solidification, and melt-spinning as mentioned in this paper.
Abstract: Using Kerr and Bitter techniques, magnetic domain patterns have been studied in various cobalt, iron, and cobalt‐iron borides prepared by chill casting, directional solidification, and melt‐spinning. Magnetic symmetries and metallurgical stability of the phases are discussed.

31 citations



Journal ArticleDOI
TL;DR: In this article, a model based on diffusive and convective fluxes was developed describing laminar fluid flow and segregation; an experimental correlation between segregation and the Rayleigh number was obtained.
Abstract: Convection and segregation phenomena during vertical directional solidification of Ga‐doped Ge under stabilizing vertical thermal gradients were investigated. Microscopic growth rates were determined by interface demarcation, compositional profiles by single point spreading resistance measurements, and thermal characterization of the melt by direct thermal probing. It was found that destabilizing horizontal temperature gradients, even in melts with a diameter as small as 3 mm, led to convection with pronounced effects on solidification. Turbulent convection resulted in microscopic growth rate‐controlled dopant inhomogeneities similar to those observed for solidification under destabilizing vertical gradients. Under laminar convection dopant inhomogeneities were caused by perturbations in boundary layer thickness. Macrosegregation under both turbulent and laminar convection was controlled by the boundary layer thickness. A model based on diffusive and convective fluxes was developed describing laminar fluid flow and segregation; an experimental correlation between segregation and the Rayleigh number, consistent with the model, was obtained. Indirect evidence for diametrically antisymmetric fluid flow in the melt was obtained from lateral microsegregation across the interface. Theoretical and experimental results showed that complete elimination of convective interference is virtually impossible; however, "effective" diffusion‐controlled segregation was achieved at relatively high growth rates and low Rayleigh numbers.

Journal ArticleDOI
TL;DR: In this article, a model is developed to calculate the extent of solid state diffusion effects during and after solidification of ternary additions in Fe-Ni alloys, and the resulting equilibrium partition coefficients, K x o, for elementX in FeNi-X alloys are 0.43 for Au, 0.58 for Ge and 0.87 for Ni, and 1.45 for Pt.
Abstract: A directional solidification experiment to measure partition coefficients of ternary additions in Fe-Ni alloys is described. A model is developed to calculate the extent of solid state diffusion effects during and after solidification. Ternary diffusivities of Ge and Au in Fe-Ni were measured for use in the calculation procedure. The model is used to correct the measured partition coefficients for solid state diffusion effects. The resulting equilibrium partition coefficients, K x o , for elementX in Fe-Ni-X alloys are 0.43 for Au, 0.58 for Ge, 0.12 for P, 0.87 for Ni, and 1.45 for Pt. These studies demonstrated that solid state diffusion effects are significant when the diffusivity of the third elementX, in Fe-Ni, is higher than 1 × 10−10 cm2/s at 1300 °C. The partition coefficient data is of particular interest in understanding the fractionation behavior of trace elements in iron meteorites.

Proceedings Article
01 Jan 1981
TL;DR: The Heat Exchanger Method (HEM) is a promising low-cost ingot casting process for material used for solar cells as mentioned in this paper, which is the only method that is capable of casting single crystal ingots with a square cross section using a directional solidification technique.
Abstract: The Heat Exchanger Method (HEM) is a promising low-cost ingot casting process for material used for solar cells. This is the only method that is capable of casting single crystal ingots with a square cross section using a directional solidification technique. This paper describes the chemical, mechanical and electrical properties of the HEM silicon material as a function of position within the ingot.

Patent
24 Jun 1981
TL;DR: In this article, an improved alloy for use in directional solidification casting is disclosed in which the proportions of carbon, zirconium, tungsten and molybdenum have been changed to produce a new ultra high strength casting alloy free of the problem of grain boundary cracking which has been encountered in the production of this type of alloy and to minimize M 6 C plate phase formation in turbine blades under high temperature conditions over extended operating periods.
Abstract: An improved alloy for use in directional solidification casting is disclosed in which the proportions of carbon, zirconium, tungsten and molybdenum have been changed to produce a new ultra high strength casting alloy free of the problem of grain boundary cracking which has been encountered in the production of directional solidification castings of this type of alloy and to minimize M 6 C plate phase formation in turbine blades under high temperature conditions over extended operating periods. In addition there is disclosed the unexpected characteristic of the alloy's substantial increase in fracture toughness and tensile ductility under extreme operating conditions.

Journal ArticleDOI
TL;DR: In this article, a natural submicron-size periodic structure was fabricated by directional solidification of Pb-sn eutectic thin films, and a mechanism that involves the propagation of bent plates was observed to adjust the spacing without forming faults.
Abstract: A natural, submicron‐size periodic structure was fabricated by directional solidification of Pb‐Sn eutectic thin films. Eutectic alloy films between 1 and 8 μm thick were deposited on glass and directionally solidified at rates between 0.5 and 12.6 mm/min that yielded fault‐free lamellar structures. A mechanism that involves the propagation of bent plates was observed to adjust the spacing without forming faults. Below a critical thickness comparable to the periodic spacing, the structure was observed to become irregular. The spacing control and stability of the lamellar eutectic thin films are discussed.

Patent
10 Aug 1981
TL;DR: An alloy composition casting scheme and specific heat treatment process for the production of directionally solidified single crystal articles which have exceptional properties is described in this article, where the alloy is based on the Ni-Al-Mo system, preferably with additions of Ta.
Abstract: An alloy composition casting scheme and specific heat treatment process are described for the production of directionally solidified single crystal articles which have exceptional properties. The alloy is based on the Ni-Al-Mo system, preferably with additions of Ta. The process for producing the article includes directional solidification at a high rate to produce a fine dendritic microstructure. A combined homogenizing and solution treatment is performed to provide a unique chemically homogeneous single phase microstructure. This homogeneous article is rapidly quenched and then aged at an intermediate temperature to develop a controlled uniform distribution of fine gamma prime phase particles.

Journal ArticleDOI
TL;DR: In this article, two types of instabilities were identified: (1) convective type that correspond to long wavelengths, and (2) morphological type that corresponds to short wavelengths. But while the convective instabilities depend strongly on gravity, the morphological instabilities are practically independent of gravity.

Patent
08 Sep 1981
TL;DR: In this article, a gold-based contact material fabricated by directional solidification and hibiting increased strength, hardness, wear resistance and undegraded electrical conductivity is presented.
Abstract: Gold based contact materials fabricated by directional solidification and hibiting increased strength, hardness, wear resistance and undegraded electrical conductivity, are presented. An eutectic structure comprises a matrix metal consisting essentially of gold and a second phase rich in an alloying material. The second phase rich in an alloying material is disposed within the matrix metal in a plurality of elongated zones formed by directional solidification of the alloy with each zone having an elongated axis generally normal to a contact boundary surface of the solid. The second phase is rich in an alloying material selected from a group of alloying elements consisting of Be, Ca, Sr, La, Na, Th, Zr, Hf, Sb, Ge, Mo, Si and the rare earth elements. Selected ones of the alloying elements can be subjected to internal oxidation for forming hard, oxide particles of the second phase material.

Journal ArticleDOI
TL;DR: In this article, the phase spacings and transitions in microstructure are discussed in terms of diffusion processes at the monotectic front, with reference to the relative surface energies between two immiscible liquids and a third (solid) phase.
Abstract: Directional solidification methods have been used to examine the growth of fibrous, or tubular, composite samples in alloys close to the monotectic reaction: Liquid 1 Solid + Liquid 2. The binary systems Al-In, Cu-Pb and Cd-Ga have been examined and some use made of a transparent analogue, succinnonitrile-water. The solidification behavior appears to relate to the height of the miscibility gap in such systems and it is demonstrated how ternary additions which change this height (Sn to Al-In, Al to Cu-Pb) modify the microstructures dramatically. These structural changes are discussed with reference to the relative surface energies between two immiscible liquids and a third (solid) phase. The phase spacings and transitions in microstructure are discussed in terms of diffusion processes at the monotectic front.

Journal ArticleDOI
TL;DR: The role of gravity on the directional solidification of eutectic Ri/MnBi has been studied in reduced gravity aboard NASA soundinq rocket SPAR flight experiments and contrasted with normal gravity investigations as discussed by the authors.
Abstract: The role of gravity on Bridgman-Stockbarger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA soundinq rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Ri/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnRi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed, normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50%, for the low gravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97% of the theoretical maximum. Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnRi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

Journal ArticleDOI
TL;DR: In this paper, the authors employed an efficient iteration scheme based on a fast elliptic equation solver for the quasi-steady freezing encountered in long cylindrical alloy bars, and gave results showing the two-dimensional temperature fields encountered in solidification processes subject to various input conditions.
Abstract: The material characteristics of directionally solidified superalloy crystals require carefully controlled solidification rates, temperature field distributions, and maximum temperature gradients. Experimentally, these can be determined by vacuum casting of cylindrical rods. Corresponding analytical studies yield nonlinear equation systems due to radiative boundary conditions and latent heat effects, which in the past required lengthy finite-difference or finite-element solutions. For the quasi-steady freezing encountered in long cylindrical alloy bars, we employed an efficient iteration scheme based on a fast elliptic equation solver previously reported in the literature. This paper discusses the principal aspects of the computational scheme and gives results showing the two-dimensional temperature fields encountered in solidification processes subject to various input conditions.

Patent
14 Jan 1981
TL;DR: In this article, an improved nickel base alloys for use in vacuum directional solidification casting which alloys include a plurality of elements but which, in particular, include the following elements in the percentages by weight specified: carbon.07-.09, zirconium.007-.015, tungsten 9.3-9.7, and molybdenum 0.4-0.6.
Abstract: improved nickel base alloys for use in vacuum directional solidification casting which alloys include a plurality of elements but which, in particular, include the following elements in the percentages by weight specified: carbon .07-.09, zirconium .007-.015, tungsten 9.3-9.7, and molybdenum 0.4-0.6. The new ultra high strength casting alloys are free of the problem of grain boundary cracking which has been encountered in the production of directional solidification castings of this type of alloy and minimize M 6 C acicular phase formation in turbine blades under high temperature conditions over extended operating periods. The invention also includes a turbine engine blade cast from the alloy.

Book ChapterDOI
TL;DR: In this article, two data analysis techniques for processing eddy-current signals are presented and discussed, and two techniques of data analysis for processing the eddy currents are used to identify directional solidification in a Pb-20Sn alloy.
Abstract: Even though casting technology has a 5000-year history, the understanding and control of the process still has significance to current metal producers. Nondestructive evaluation is usually applied to finished or semifinished product; however, in casting, when the evaluation is moved to the point of production, the testing procedure can be incorporated into the casting control. The metallurgical impetus for such casting control and evaluation cannot be simply stated since the needs are process and product dependent. The main technical advantage of applying eddy-current analysis to the study of solidification is that eddy currents have a reasonable sensitivity to continuous and discontinuous conductivity changes. A drawback in the examination of the liquid-solid interfaces is that the eddy-current signals are integrated over a substantial volume, which averages out detailed information such as dendrite structure. To successfully use the technique of eddy-current analysis, one must utilize postmortem metallographic examination of specimens for standards and detailed mathematical modeling of the solidification response, which cover probable morphologies. Laboratory measurements of freezing of a Pb-20Sn alloy demonstrate that directional solidification can be identified. Finally, two techniques of data analysis for processing eddy-current signals are presented and discussed.

Journal ArticleDOI
TL;DR: In this paper, a method for the analysis and control of solidification from the melt, based on the continous measurement of the transformation volume, has been proposed and its application to the growth of InSb in a vertical crucible, under a protective flux, is described.

Patent
25 Sep 1981
TL;DR: In this article, a method of casting single crystal vanes of f.c. structure involves upwards directional solidification of single columnar grain, of predetermined transverse orientation and vertical 001 direction, delivered by a selector located at the bottom of a top-poured shell mould.
Abstract: Method of casting single crystal vanes of f.c.c. structure involves upwards directional solidification of single columnar grain, of predetermined transverse orientation and vertical 001 direction, delivered by a selector located at the bottom of a top-poured shell mould. Each shell mould cavity (8) is arranged so that its axis (12) is oriented along the 111 direction of the selected crystal.

ReportDOI
01 Jul 1981
TL;DR: In this paper, a survey of the performance of field emission cold cathodes of selected refractory materials fabricated as needle arrays by unidirectional solidification is presented, and performance data has been obtained using niobium, tantalum and vanadium carbides with various cathode geometries.
Abstract: : A survey has been made of the performance as field emission cold cathodes of selected refractory materials fabricated as needle arrays by unidirectional solidification. Cathodes based upon refractory metal carbides have been fabricated and tested. Performance data has been obtained using niobium, tantalum and vanadium carbides with various cathode geometries. Life times of over 1,000 hours and current densities of up to 1 A/sq. cm. have been obtained. Preliminary experiments indicated that LaB6 can be formed into platelets by conventional cooling in an aluminum matrix and that directional solidification should produce suitable rod-like morphology.

Journal ArticleDOI
TL;DR: In this article, the effects of thermal and solute gradient, gravity induced convection during vertical directional solidification, on longitudinal macrosegregation of Bi and Mn rich off-eutectic starting compositions, has been studied as a function of composition, growth velocity and gravity vector orientation.
Abstract: The effects of thermal and solute gradient, gravity induced convection during vertical directional solidification, on longitudinal macrosegregation of Bi and Mn rich off-eutectic starting compositions, has been studied as a function of composition, growth velocity and gravity vector orientation. Since the morphology of these alloys is characterized by an aligned, rodlike permanent magnet composite when grown cooperatively, the magnetic properties were used to measure composition segregation and the transition from dendritic to composite growth. Severe macrosegregation was observed in all cases studied and the degree of convection inferred by modeling the observed composition segregation using a stagnant film approach. Morphological stability was found to follow a constitutional supercooling-type law for both Bi and Mn rich compositions.

Patent
06 Nov 1981
TL;DR: A carbide reinforced iron based superalloy material is described in this article, which consists of an austenitic matrix containing about 30 volume percent aligned M 7 C 3 phase fibers.
Abstract: A carbide reinforced iron based superalloy material is described. The material consists of an austenitic matrix containing about 30 volume percent aligned M 7 C 3 phase fibers. Fiber alignment is produced by directional solidification. A nominal alloy composition (by weight) is 20% Cr, 10% Mn, 5% Al, 3.2% C. balance iron. The alloys are characterized by the absence of strategic elements, are east to process and have superior mechanical properties to the known prior art, low nickel, iron base superalloys.

Journal ArticleDOI
TL;DR: In this paper, a floating zone method for directional solidification of the NiO-Y 2 O 3 eutectic has been proposed, and the composition and dependence of the interlamellar spacing on solidification rate have been determined.