United Technologies Corporation

Anthony F Giamei

Bernard H Kear

Neal P Anderson

Richard W Salkeld

Conrad M Banas

Maurice L Gell

Earl R Thompson

Edward M Breinan

Robert E Doiron

Directionally Solidified Eutectic Reinforcing Fibers Eutectic reinforcing fibers for high temperature composites include eutectic mixtures such as Al.sub.2 O.sub.3 --Y.sub.2 O.sub.3, Cr.sub.2 O.sub.3 --SiO.sub.2, MgO--Y.sub.2 O.sub.3, CaO--NiO, and CaO--MgO. The fibers may be made by several solidification processes. The edge defined film fed growth process (EFG), however, may be especially appropriate. In this process, a seed having a known composition contacts the surface of a eutectic melt in a crucible and forms a molten film. In the present invention, the composition of the seed may be equal to the composition of the eutectic melt. As the seed is pulled upward, the molten film solidifies to form a eutectic fiber. Directional solidification occurs toward the melt.

Directionally solidified eutectic reinforcing fibers and fiber

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.

Transverse directional solidification of metal single crystal articles

A single crystal nickel base superalloy component, such as a gas turbine blade (20, 28) is mechanically deformed at elevated temperature to improve the yield strength of a portion which is used at temperatures below 800.degree. C., compared to a portion which is used at a higher temperature. A blade (20) has a root (22) which is deformed by 2-14% at 700.degree.-1100.degree. C. and an airfoil (24) which is not deformed. The root yield strength is increased 15-50% while the airfoil creep strength is maintained.

Mechanically worked single crystal article

Single crystal nickel base superalloys of the gamma-gamma prime type are strengthened by deforming them 2-14% at temperatures in the range 700.degree.-1100.degree. C. Yield strength will be increased typically by 25-50%, depending on the crystallographic orientation. Careful control of parameters is necessary to obtain the strengthening while avoiding recrystallization. The metal is first homogenized and provided with a fine gamma prime deformation; strain rates in the range of 10.sup.-1 cm/cm/sec or less are used.

Wrought single crystal nickel base superalloy

A method of epitaxially casting single crystal metal articles in molds, which comprises causing the solidification interface velocity vector to rotate through at least 90 degrees, preferably 180-540 degrees, about the axis of overall directional solidification growth. In addition, a mold section has a small passageway configured to prevent line of sight communication between the portion where the seed is contained and the article portion of the mold. Preferably, the passageway is shaped like a helix of 0.8-1.5 turns. A second seed can be formed in the mold of an article made from a first seed, and used to make a second casting. The invention reduces the normal increase in crystallographic variability which would otherwise be associated with such practice.

Casting a metal single crystal article using a seed crystal and a helix

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.

Single crystal solidification using multiple seeds

In the manufacture of a single crystal article, by the directional solidification of a metal in a ceramic mold the melt-back of a seed crystal is controlled to provide high casting yield. The melt-back, measured as a fraction of the original length of the seed, is preferably between 25-75%, more preferably between 33-67%. Diametrical clearance between the seed and mold is also closely controlled, between 0.06-0.25 mm, to eliminate extraneous grain nucleation.

Control of seed melt-back during directional solidification of metals

An improved method for hot working materials previously considered to be difficult or impossible to hot work is described. The method consists of varying the deformation conditions in order to achieve an essentially constant energy input, to the material being worked, on a time basis.

Constant energy rate forming

An improved method of directional solidification is provided by varying the rate of withdrawal of a casting from the hot zone of a solidification furnace according to the sense of change of the perimeter to area ratio of the casting. The rates are varied to achieve desired microstructure and resultant properties in the casting. Also, the rate of withdrawal is varied according to controlled and predetermined relationships to cause the solidification interface to move through a transition section connecting sections of differing perimeter to area ratios in a manner which produces a desired microstructure in a first, transition, and second sections.

Rate controlled directional solidification method

A surface treatment for a class of metallic articles is described. The treatment involves the melting of a thin surface layer of the article by a concentrated energy source, within a narrow set of parameters. The melting step is performed in a manner which maximizes the temperature gradient between the melted and unmelted portion of the article, consequently, cooling and solidification upon the removal of the energy source is extremely rapid and can produce unique microstructures. The preferred energy source is a continuous wave laser, and in the preferred embodiment, a flowing inert gas cover is used to minimize melt contamination and plasma formation. The technique may be used to produce amorphous surface layers in a specific class of eutectic alloys. In another class of alloys, based on the transition metals and containing precipitates rich in one or more metalloids, uniquely fine microstructures may be produced.

Skin melting

This invention concerns composite articles, particularly those which contain single crystal components. A method is disclosed for joining single crystals together so that the resultant article is free from high angle grain boundaries and therefore possesses exceptional mechanical properties.

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Middletown, CT, United States of America

Anthony F Giamei