Showing papers on "Directional solidification published in 1975"

Cores for investment casting process

Abstract: A porous high-silica core is disclosed for use in directional solidification casting processes having exceptional thermal stability at temperatures above 1650° C. and containing mineralizers which promote the formation of cristobalite. The cores may be made by mixing at least 75 parts of essentially pure fused silica particles with 1 to 25 parts of activating particles containing a mineralizer, such as an alkali metal or alkaline earth metal compound, may be fired at a temperature of 1000° to 1300° C. until they contain 35 percent or more of cristobalite and may then be cooled to room temperature. They may thereafter be incorporated in a shell mold in accordance with the "lost-wax" process and preheated with the shell mold at a temperature of 1300° to 1600° C. to provide a cristobalite content of 60 to 85 percent or more within a short period of time, such as 10 to 30 minutes, and before a molten superalloy is allowed to flow into the mold. The core has exceptionally high thermal stability and may be maintained at a temperature of 1550° to 1600° C. or higher for one hour or more during the directional solidification process without substantial deformation. The high ultimate use temperature of the core makes it possible to produce better castings by carrying out the D.S. process at a temperature 50° to 100° centigrade higher than previously used.

Ceramic molds having a metal oxide barrier for casting and directional solidification of superalloys

Abstract: A metal oxide barrier layer is provided at the interface between a refractory oxide-silica investment mold and a contained metal superalloy, allowing directional solidification of the contained superalloy at elevated temperatures without metal-mold reaction.

Process for forming a barrier layer on ceramic molds suitable for use for high temperature eutectic superalloy casting

Abstract: A method of forming a metal oxide barrier layer at the interface between a refractory oxide-silica investment mold and a contained metal superalloy includes the firing of the mold or the mold-metal system, in a controlled prevailing atmosphere having a predetermined amount of oxygen therein. The barrier layer enables directional solidification of the contained superalloy at elevated temperatures to occur without metal-mold reaction.

Ductile eutectic superalloy for directional solidification

Abstract: This disclosure relates to a eutectic alloy, and article made from the alloy, in the nickel-aluminum-molybdenum system which may be directionally solidified to produce a microstructure consisting of a ductile matrix phase of gamma prime or gamma prime/gamma containing a reinforcing fibrous or lamellar refractory metal alpha second phase. The nominal composition of the base alloy is 8 weight percent aluminum, 27 weight percent molybdenum, balance nickel. Minor elemental additions may be made to modify the mechanical properties of the first phase and/or the second phase. The directionally solidified alloy of the invention is characterized by exceptional anisotropic tensile properties, high isotropic ductilities, combined with good oxidation resistance and satisfactory sulfidation resistance at elevated temperatures.

Comparative thermal fatigue resistances of twenty-six nickel and cobalt base alloys

Abstract: Thermal fatigue resistances were determined from fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials with directional solidification and surface protection of definite benefit. The alloy-coating combination with the highest thermal fatigue resistance was directionally solidified NASA TAZ-8A with an RT-XP coating. It oxidation resistance was excellent, showing almost no weight change after 15 000 fluidized bed cycles.

Casting mold for directional solidification of an alloy

Abstract: A mold for obtaining metallic parts with an orientated crystalline struct by the directed solidification of an alloy is disclosed. The mould comprises a body of refractory mold that is a good heat conductor and on the inner wall of said body is provided a chemically protective lining of dense refractory metal oxide, with a high degree of purity, deposited on said body by blowpipe projection as a thin non-porous layer. The thickness of the metal oxide lining is in the order of a tenth of a millimeter to five tenths of a millimeter, the oxide being choosen in the group constituted by aluminium oxide, zirconium oxide, magnesium oxide and thorium dioxide with a degree of purity at least equal to 99.5 %.

An analysis of the mechanical behavior of Al-Al3Ni composites

Abstract: Commercial purity Al-Al3Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10-3 to 1.0 mm/s. The composites were tested in tension and in compression and the results were analyzed using a simple model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing, and discontinuity and premature fracture of fibers. The theoretically predicted values of the tangent modulus and strength in tension and compression were shown to closely fit the experimental results up to a growth rate of about 0.3 mm/s. Beyond this value, the excessive misalignment of the fibers caused some deterioration in the mechanical properties and a change in the mode of fracture. It has been concluded that the elastic constrained matrix exerts considerable effect on the mechanical properties thus providing an effective means of improving them by increasing the surface area of the fiber-matrix interface.

Technique for preparing homogeneous bulk samples of concentrated alloys

Abstract: A technique has been developed for casting relatively large samples (∼100 g) of concentrated alloys. It was used to prepare Al−Mg castings having Mg concentrations near the maximum limit of solid solubility. Concentration gradients and nonequilibrium eutectic solidification were minimized by the rapid cooling and directional solidification that are characteristic of the technique.

Structure and strength of Al, Cu-Al3Ni directionally solidified composites

Abstract: A series of Al3Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 104 °C · s/mm2 (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al3Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m2 were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ’ phase. Massive Al3Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.

Heat resisting nickel alloys using directional solidification - to ppte. lamellar intermetallic cpds. which increase strength

Abstract: Nickel base alloy contg. molybdenum plus addns. 1 of the elements Co, Cr, Al, Si and B, in a concn. such that by directional solidification in a temp. gradient, a two- or multi-phase composite material is formed in which a single- or multi-component phase is embedded parallel to the direction of solidification in a matrix of nickel mixed crystals. The intermetallic phase is pref. (a) the sigma phase (Ni-Cr-Mo) or the rho phase (Ni-Cr-Mo); (b) the Laves phase Mo (Ni1-xSix)2; (c) Mo2NiB2; and the alloy may contain Mo fibres. The alloy may also contain the following maxima in atom % 10% Ti, 0.5% Zr, 0.05% Fe, 10% W, 4% Ta, 2% Hf, 0.03% Y, to increase strength and corrosion resistance, plus 2% max. Si or B in excess of that in cpds. (b) or (c). The heat resisting alloys obtd. are used e.g. for gas turbine applications. They have increased strength and corrosion resistance, e.g. when Si is added it is present in the reinforcing lamellae so the ductility of the matrix is not impaired.

Directionally solidified pseudo-binary eutectics of Ni-Cr-(Hf, Zr)

Abstract: A pseudo-binary eutectic, in which the intermetallic Ni7Hf2 reinforces the Ni-Cr solid solution phase, was previously predicted in the Ni-Cr-Hf system by a computer analysis. The experimental determination of pseudo binary eutectic compositions and the directional solidification of the Ni-Cr-Hf, Zr, and Ni-Cr-Zr eutectic alloys are discussed. To determine unknown eutectics, chemical analyses were made of material bled from near eutectic ingots during incipient melting. Nominal compositions in weight percent of Ni-18.6Cr-24.0HF, Ni19.6Cr-12.8Zr-2.8Hf, and Ni-19.2Cr-14.8Zr formed aligned pseudo-binary eutectic structures. The melting points were about 1270 C. The reinforcing intermetallic phases were identified as noncubic (Ni,Cr)7Hf2 and (Ni,Cr)7(Hf,Zr)2, and face centered cubic (Ni,Cr)5Zr. The volume fraction of the reinforcing phases were about 0.5.

Method of growing composites of the type exhibiting the Soret effect

Abstract: A predetermined amount of segregation is introduced into a molten sample of a composite that exhibits the Soret effect, such amount approximating the amount of segregation resulting from directional solidification of the sample. The molten sample is then directionally solidified starting at the end opposite the end richer in the constituent that would migrate toward the cooler part of a liquid solution of the composite maintained in a temperature gradient. Since solidification commences at the end deficient in such constituent, its migration toward the interface between the solid and liquid during the solidification will compensate for the deficiency yielding a more homogeneous product.

Chill-cast aluminium alloy pistons mfr. - using directional solidification to obtain fine structure and high fatigue strength

Abstract: The parent patent described the prodn. of castings, esp. Al or Al-alloy pistons for internal combustion engines, using a round mould with an outer insulating jacket and a base-plate plus, if required, a core suspended in the mould. The melt solidifies from the base-plate due to indirect cooling and, after an adequate solid layer is formed, direct cooling is applied to the bottom of the casting. In the present invention, a limited, dosed amt. of molten metal at the correct temp. flows into the mould followed by heat-extn. at constant speed independent of the casting height so the temp. gradient in the solid layer near the junction with the molten metal remains constant. Provides directional solidification along the axis of the piston so a fine-grained structure is obtd. which, after heating for 5 hours at 230 degrees C gives an increased fatigue strength of 10.5-13 kp/mm2.

An apparatus for directional solidification with high thermal gradients in the molten zone

Abstract: An apparatus which uses RF induction heating and a liquid metal cooling jacket has been developed. It has been used to produce aligned composites from eutectic alloys with melting points of up to 1800K.