US3157926A

US3157926A - Making fine grained castings

Info

Publication number: US3157926A
Application number: US344828A
Authority: US
Inventors: Robert A Horton; Richard L Ashbrook; Roy C Feagin
Original assignee: Howe Sound Co
Current assignee: Howmet Turbine Components Corp; Howe Sound Co
Priority date: 1964-02-14
Filing date: 1964-02-14
Publication date: 1964-11-24
Anticipated expiration: 1981-11-24

Description

United States Patent 3,1519% MAKING tCASTlNQS Robert A. Horton, fies/elated, Richard L. Ashbroek, t'lheatcrland, little, and Roy C. Feagin, Mountain Lakes, NJ, assiguors to Howe Sound Company, a corporation of fuel-aware No Drawing. Filed Feb. 31 i, E64, Ser. No. 344,828

12 Claims. (till. 212216.5)

This invention relates to making fine grained metal castings, particularly of alloys containing a high proportion of iron, neckel, cobalt, chromium or copper. The invention makes use of an oxidic compound of nickel or cobalt as a nucleation catalyst which is applied to the surface of the mold in which the casting is made, in order to insure that the casting will have a fine-grained structure. This application is a continuation-in-part of our application Serial No. 234,219, filed October 30, 1962, which in turn is a continuation-in-part of our application Serial No. 851,532, filed November 9, 1959, now abandoned.

It has long been known that the grain size of a metal has an important bearing on such of its physical properties as tensile strength, hardness and ductility. Fine grained metal usually is stronger, harder and less ductile than the same metal in coarse grained form. Grain size of metals is generally controlled by the extent of working and the heat treatment to which the metal is subjected in the course of being fabricated to desired form. However, refractory alloys which cannot readily be worked, that is, which are hard and lacking in ductility or malleability, cannot be produced in fine-grained form by such conventional procedures. The most practical method for making desired articles of such alloys is by casting, and cast articles ordinarily have a coarse grain structure.

It has been recognized for a considerable time that the grain size of metals and other polycrystalline materials in the as-cast condition can be refined by suitable use of nucleation catlaysts, that is substances which promote growth of crystals from the melt. An alloy melt, upon cooling to the temperature at which it becomes molten, may not solidify at once, but instead may subcocl considerably before solidification begins. This is due to the fact that solidification proceeds from tiny particles, called nuclei, which form or are present in the melt. Immediately below the melting point is a metastable temperature zone in which the alloy melt will not nucleate spontaneously. In the absence of suitable foreign particles (heterogeneous nucleation), solidification will not occur until the melt has cooled to a temperature below the metastable zone, whereupon nucleation will occur spontaneously. The final grain size obtained will depend on the relative rates of spontaneous nucleation and crystal growth. If nucleation is rapid compared to crystal growth, a fine grain size will result. If crystal growth is rapid compared to nucleation, large grains will be formed.

The present invention is based on the finding that oxidic compounds of nickel and cobalt are remarkably effective for catalyzing nucleation of alloys based on iron, nickel, cobalt, chromium or copper. The term ox-idic com: pounds includes both oxides and compounds such as carbonates, basic carbonates, and hydroxides which can be converted readily into oxides. It is not practical or desirable to incorporate these oxidic compounds in the alloy, and the invention therefore contemplates applying one or a combination of them to the surface of the mold in which the casting is to be made. Then a melt of the alloy is introduced into the mold (which first has been heated to the desired casting temperature) and is cooled in the mold to below its freezing temperature. The cast article thus produced is characterized by having a notably fine grain -sizemuch finer than could be obtained under the same casting conditions in a mold to which no nucleation catalyst have been applied.

The fine grains which characterize castings made in accordance with the invention range in size from about one-eighth inch in maximum dimension to sizes too small to be resolved by the unaided eye. Typical castings of refractory alloys made by the method of the invention have grains from a few thousands of an inch to about onesixteenth of an inch in maximum dimension. Similar castings, similarly made but without the use of a nucleation catalyst, have grains which typically exceed onequarter inch and range up to one-half inch or larger in maximum dimension.

Although the oxidic compound of cobalt or nickel which is used as the nucleation catalyst in the method of the invention is applied to the mold surface and does not appear to enter the metal casting, it is nevertheless effective for nuclea-ting the growth of crystals throughout the entire mass of the casting. It is our belief that this is due to the fact that the molten metal in the mold, so long as it remains molten, is in contant motion due to convection or other currents. In consequence, metal from all parts of the melt in the mold circulate in contact with the mold surface and back to the interior of the body of the melt. As the melt reaches its freezing temperature, tiny crystals form where the melt is in contact with the nucleation catalyst at the mold surface. These tiny crystals are carried by the circulation of the melt a substantial distance into the body of the melt before the entire mass of metal has frozen and thus put an end to melt circulation. Whether or not this be the correct explanation, the fact is that castings made by the method of the invention are found to be of fine grained structure throughout their mass; and there is no evidence of any pick-up of oxidic catalyst from the mold wall and incorporation of such catalyst into the casting.

Metal castings made in a cold (e.g., room temperature) mold generally have a fairly fine grain structure due to the rapid chilling by the cold mold of the melt introduced into it. This, of course, is especially true of small castings and thin sections which are easy to cool rapidly. In making castings in such molds, the use of a nucleation catalyst does not generally result in a much finer grain structure than is obtained without it. For many purposes, however, castings must be made in hot molds (e.g., molds heated to above 1000 F.). For example, precision vacuum-cast articles made of refractory alloys must be made in preheated molds to avoid damage by thermal shock to the mold, and to achieve the desired accuracy of dimensions, good surface quality, and freedom from contamination in the casting. The invention is particularly applicable to imparting a fine grain structure to such castings; and

the invention particularly contemplates heating the mold to an elevated temperature, above 1000 F. and generally above 1500 F., prior to casting, prior molten metal into the mold. The molten metal is poured into the mold while the latter is heated to such temperature, and then is cooled in the mold to below its freezing temperature. Unnucleated castings made in refractory molds which have been heated to such elevated temperatures are invariably coarse grained, but castings similarly made with the use of oxidic compounds of nickel or cobalt as contemplated by the invention have a fine grain structure and the enhanced physical properties that such structure imparts.

The method of the invention lends itself particularly well to making fine-grained castings by the techniques of modern precision casting, involving forming a refractory mold about an expendable pattern and then, after the mold has hardened, eliminating the pattern from within it. While it is possible to apply the oxidic nucleation catato introducing the lyst to the mold surface after the pattern has been removed or otherwise eliminated from the mold, it is generally easier, and productive of better results, to apply it, in the form of a coating comprising at least about .01 percent by weight of the oxidic compound and advantageously one-quarter percent or more by weight of such compound, to at least a portion of the surface of the pattern before the mold is formed about it. Then when the pattern is removed from the mold, the catalyst remains to define (in part at least) the surface of the mold. For example, in making precision metal castings in molds by building up a mold shell of refractory composition on a fusible pattern of wax, plastic, frozen mercury, or the like, at least about .01 percent and advantageously one percent or more by weight of the oxidic nickel or cobalt compound is suspended in a liquid vehicle which can be applied as a first or prime coat on the pattern by painting it on or by dipping the pattern in it, after which a refractory mold shell is formed about the thus-coated pattern;

or the catalyst may with advantage be incorporated in a hardenable refractory composition which is coated on the pattern to form a refractory mold shell in which the casting subsequently is made.

Generally only one of the various oxidic compounds that may be used will be incorporated in the liquid coating or refractory composition, but a combination of two or more of them may be used if desired. The concentration of the oxidic compound in the composition need not be high. As indicated above, as little as .01 percent by weight of such compound in the composition is effective to cause sufficient nucleation in some cases. Good results may sometimes be had with as little as grams per liter (which in a typical dipcoat composition corresponds roughly to one-quarter percent by weight of the refractory solids content thereof); and ordinarily no advantage is obtained by using more than 75 grams per liter.

By use of the term mold shell, we do not mean to imply that such shell necessarily forms the complete mold. It may of course do so, but it may equally well be only one component of the completed mold assembly. The term mold shell is used mainly to denote the layer of refractory applied directly to the pattern, which forms that portion of the mold with which the melt comes in contact when it is poured into the mold cavity to form the casting. Such shell, if thick enough and strong enough, may form the complete mold; or it may be thickened by the application of additional refractory to make a thick strong shell mold; or it may serve only as the inner component of a bulky mold assembly which has been built up in a flask with either tightly packed dry unbonded granular refractory or well-bonded cementitious refractory to form a sturdy mold capable of withstanding rough handling and great stresses. The shell may also be but half, or some other fraction, of a complete mold shell, which when joined to one or more other fractional shells makes up a complete mold shell. Furthermore, the terms mold and mold shell" are used throughout this specification to include cores which are inserted into molds to form cavities in the castings.

The invention particularly contemplates using an oxide of nickel or cobalt as the nucleation catalyst, but also contemplates applying the catalyst to the mold in the form of any other compound which can readily be converted to oxide prior to forming a casting in the mold. For example, hydroxides of the specified metals may be applied to the mold surface and may be converted to oxides by heating to an elevated temperature before introducing the molten metal into the mold. Carbonates and basic carbonates of these metals may also be used, and converted to oxides by heating to a high temperature after application to the mold surface but before casting. When such compounds are used, the heating or other treatment by which they are converted to oxides should be carried out under conditions such that any gas or vapor evolved does not blemish the mold surface. Similarly, organo-rnetallic compounds in which nickel or cobalt is the metallic component may be used. Such compounds, when heated in an oxidizing atmosphere after application to the surface of the mold, are decomposed and converted to oxide form. The term oxidic compounds includes all those materials which after application to the mold shell may readily be converted to oxides.

While oxides of both nickel and cobalt are singularly effective nucleation catalysts for making fine grained castings of refractory alloys containing large proportions of chromium, nickel, cobalt, or a combination of them, we have found that somewhat more consistent and uniform results are obtained when a cobalt oxide, preferably cobalt (II) oxide, is employed.

The invention is described below in detail with respect to a preferred embodiment for the production of fine gained precision metal castings. In general the procedurc employed for making such castings entails forming an expendable pattern of the casting, then coating the pattern with a hardenable refractory slurry to form a refractory shell about the pattern, then reinforcing such shell sufiiciently to enable it to withstand the stresses of pattern elimination and casting, then eliminating the pattern by melting and pouring it from the resulting refractory mold, then heating the mold to an elevated temperature above 1000 F., then pouring a molten metal into the heated mold, and then cooling the molten metal in the mold until it has solidified. The method of the invention preferably involves applying the nickel or cobalt oxidic nucleation catalyst to the pattern preparatory to, or in the course of, applying the hardenable refractory to the pat tern to form the refractory shell (although such catalyst may be applied directly to the mold surface after elimination of the pattern without departing from the invention). Except insofar as application of a nucleation catalyst to the pattern and use of the particular catalysts mentioned are concerned, the steps of the procedure outlined are those heretofore commonly used in the precision casting art, and all the various forms and modifications of such steps may be employed in carrying out the method of the invention.

In the production of a large number of identical precision castings it is common practice to make one or a few master patterns from which one or a few master molds are prepared. Expendable production patterns, usually of wax, or other thermoplastic material or of frozen mercury or other readily fusible metal, are made in these master molds.

The preferred method of the invention entails applying a nucleation catalyst to the surface of the production pattern. A particularly advantageous procedure for doing so is to incorporate at least .01 percent by weight, and advantageously one-quarter percent or more, of the oxidic catalyst in the hardenable liquid refractory slurry composition which is coated on the pattern and allowed to harden thereon in forming the refractory mold shell. Such refractory compositions generally comprise mainly a suspension of finely divided refractory such as zircon, alumina or silica in an aqueous vehicle such as an aqueous solution of ethyl silicate, or an aqueous colloidal silica dispersion, or other substance which is capable of hardening by gelation or otherwise as the water evaporates after a coating of the composition has been applied to the patern. When the patern is of frozen mercury, the composition is of course non-aqueous, but is instead a suspension of finely divided refractory in an organic vehicle containing agents that cause it to harden after being coated on the pattern at very low temperature. For purposes of carrying out the method of this invention, at least about .01 percent by weight of the oxidic compound of inckel or cobalt, in finely divided form, is dispersed in such refractory composition. The composition is applied to the patern by the procedure of coating the composition on the pattern. Such may be done by brushing or spraying, but preferably the composition is applied by the dipcoating technique, involving dipping the pattern in a body of the liquid composition, which is common practice in the precision casting art.

Advantageously the oxidic catalyst is incorporated in a composition capable of functioning as a priming coat for the pattern, if it is not incorporated directly in the refractory coating composition. For this purpose it may be incorporated as the sole finely divided solid in a solution of ethyl silicate or an aqueous silica sol, especially if one of these substances is used as the vehicle for the subsequently applied refractory composition.

If the oxide does not tend to remain in suspension in the refractory composition or other vehicle in which it is dispersed, any suitable dispersing agent may be employed to hold it in suspension. If such composition or vehicle does not wet or otherwise adequately adhere to the pattern, a wetting agent may be made to the composition to facilitate its preparation or to improve it for application to particular patterns or for use under particular conditions.

An oxide of nickel or cobalt preferably is used as the oxidic nucleation catalyst. Nickel (11) oxide and cobalt (II) and (III) oxides, as well as intermediate oxides such as so-called nickellic" and cobaltic oxides, all may be used with success. We have generally used the metallur gical grade of cobalt oxide, which contains about 76% cobalt (II) oxide, and have found it to be eminently satisfactory. Generally only one of these oxides will be used as the nucleation catalyst, but it is entirely practical to employ them in any desired combination. For example, a mixture of cobalt (I11) oxide and nickel (II) oxide may be employed in lieu of either of them alone. Oxides of commercial metallurgical grade are generally as satisfactory as chemically pure oxides, and are preferred because they are cheaper. While the dilference between these oxides in their effectiveness as nucleation catalysts for cobalt, nickel, and chromium alloys is not great, we have found that cobalt oxides (especially cobalt (III) oxide) yield somewhat more consistent and uniform results than the others, and are preferred for that reason.

The amount of oxide incorporated in the composition coated on the pattern need not be large. If the surface layer of the mold comprises about .01 percent of the oxide, grain refinement will be effective in some cases, and when one-quarter percent or more is present the amount of grain refining attained is sometimes substantial. Thus, significant grain refinement is attained when as little as grams per liter of any one of the oxides is incorporated in the pattern-coating composition, and near-maximum grain refinement results when the oxide concentration is grams per liter. As the concentration is increased from 10 to 26 grams per liter, there is a notable increase in the degree of grain refinement attained. Above 20 grams per liter the increase in effectiveness of the composition for promoting grain refinement becomes relatively less marked; but concentrations higher than 20 grams per liter may nonetheless be used with advantage. In fact, we prefer to employ concentrations of about to 75 grams per liter to insure consistent formation of castings with uniform fine grain size, and even higher concentrations are sometimes desirable. There is no critical upper limit on the oxide concentration that may be employed.

It is possible to employ the method of the invention to control grain size on various parts of the same castings. To do so, the oxidic catalyst is applied only to selected portions of the pattern. For example, if it is desired to produce a casting having one portion fine grained and another portion relatively coarse grained, the portion of the pattern coresponding to the fine grained part of the casting is coated with a composition containing one or more of the specified oxidic compounds, and the portion of the patern coresponding to the relatively coarse grained part of the casting receives a coating of a composition containing little or none of such compound. A similar procedure may be used to insure production of a uniformly fine grained casting under conditions that ordinarily would result in different sections of the casting having grains of markedly different size. For example, when a casting having sections differing substantially in thickness is cast in accordance with heretofore customary practices, and particularly when the casting conditions enable the thin section to cool rapidly, the grain size of the thin section may be notably finer than that of the thick section. Uniform fine grain size may be achieved in such castings by coating the thick section of the pattern with a composition containing a substantial concentration of the oxidic catalyst, and coating the thin section with a composition containing little or none of it.

When, as is generally preferred, the oxidic compound of nickel or cobalt is dispersed in the refractory composition applied to and hardened on the pattern to form the refractory shell, only the first-applied composition will contain such compound. Usually a number of coats of a hardenable refractory composition are applied successively, one over the other, to the pattern, to build up a mechanically strong refractory shell; but the oxidic catalyst is eifective only where it can come in contact with the molten metal. Consequently there is no advantage to be gained from incorporating it in the compositions that are used to form the second and subsequent coats of refractory. As a matter of fact, it is common practice to employ a dilferent composition for the first coat applied to the pattern than for the subsequent coats. The first coating composition generally contains a finer refractory, better suited to form a good mold surface, than the second and subsequent coating compositions. No departure from conventional practice is entailed, therefore, in using a different coating composition for the first coat than for the second and subsequent coats.

After the first hardenable refractory composition has been applied to the pattern (whether or not it contains a dispersed oxidic catalyst) and before it has hardened, it is preferably sanded or sprinkled with relatively coarse refractory particles. These particles become embedded in the refractory coating composition and help to bond the second refractory coat to the first. Preferably each successive coat of refractory composition, except the last, is similarly sanded.

Formation of the refractory mold and production of a casting therein, after the nucleation catalyst has been applied to the pattern, may follow the practices customarily used in making precision castings. After the refractory shell has been built up to desired thickness, it may be reinforced if it is not itself sufiiciently strong to withstand the stresses to which it is subjected. To this end it may be mounted in a flask and be surrounded by a densely packed cementitious refractory (secondary investment) or by a tightly packed but unbonded filling of refractory particles (unbonded back-up). Thick strong shells, or shells which are not to be subjected to substantial stresses, may notneed to be reinforced.

Next the pattern is eliminated from the mold. Usually this is accomplished by heating the mold with pattern therein to above the fusion temperature of the pattern while the mold is inverted to facilitate out-flow of the pattern material. When the pa cm is of wax or other thermoplastic material, heating of the mold is continued sufficiently to insure elimination by oxidation or volatilization or both of the residual pattern material adhering to its surface. Instead of fusion and volatilization, solvent extraction may be used to eliminate the pattern. The pattern may be thus extracted using either a liquid or vapor solvent extraction process.

However the pattern is eliminated, it is necessary that the nickel or cobalt compound remain on and define at least in part the mold surface. No special step need be taken to insure this result, however. If, as is preferred, the catalyst was applied by incorporating it in the refractory composition forming the inner coat of the shell, or in a prime coatcomprising a hardenable composition,

a then of course it remains there when the pattern is eliminated. It is only necessary to use reasonable caution in eliminating the pattern from the mold to insure that the catalyst will transfer from the pattern and remain behind on the surface of the mold.

If a hydroxide, carbonate, or organo-rnetallic compound has been employed as catalyst, the mold after elimination of the pattern preferably is heated sufficiently to convert such compound to oxide form and to eliminate gases and vapors that otherwise might impair the casting.

Next the mold is heated to casting temperature. Such heating may be elfected by simply continuing the heating step whereby the pattern material is eliminated from the mold, or it may be effected in a separate step. In either case it involves heating the mold to above 1000 F., and generally to above 1500 F. For example, in making precision castings of refractory alloys which are cast at about 26002900 R, the mold should be preheated to 1700-1900 F.

Next the molten alloy is run into the heated mold, and is allowed to cool until it has solidified. The resulting casting usually is allowed to cool in the mold until it has reached a low enough temperature for handling, after which the refractory shell is broken away and the desired cast shapes are separated from the gates and risers.

As heretofore noted, nickel and cobalt oxides are especially effective as nucleation catalysts for inducing fine grain size in castings made of alloys containing high proportions of one or more of the metals iron, nickel, cobalt, chromium and copper; and the invention particularly contemplates the use of the oxidic compounds of these elements for making castings of such alloys. The invention is not limited to making fine grained castings of any specific lloy compositions, however. Significant grain refinement may be attained in accordance with the invention in castings of any of a wide variety of iron, nickel, cobalt, chromium and copper alloys. Alloys which we have found to be very effectively cast in finegrained form by the method of the invention are for the most part based on iron, nickel, cobalt, chromium or copper (i.e., one of these metals is the principal component) and contain a combined total upwards of 85%, and sometimes upwards of 90%, of them. However, the invention may be used with success in casting alloys containing a smallereven a substantially smaller-combined total concentration of these metals.

Table I lists by way of example the nominal compositions (in percent by weight) of several alloys which have been successfully cast in fine grained form by the method of the invention.

TABLE I Alloy A Alloy 11 Alloy Percent Percent Perccnt Chromium 25. 13. 0 5 Nickel... 10. 5 Balance Dal-once Cobalt Carbon Manganese Silicon Other alloys which have been successfully cast in line grained form by the method of the invention include cast iron (nominally about 3% carbon, balance iron) and cartridge brass (nominally 70% copper, balance zinc).

Castings made in accordance with the invention are characterized by having a grain size notably smaller, in those sections corresponding to the parts of the mold surface to which the oxide catalyst had been applied, than similar castings made in the same manner but in a mold not similarly treated. It is easily possible by the method of the invention to produce metal castings having grains too small to be resolved with the naked eye, when identical shapes cast under the same conditions but without use of a nucleation catalyst have grains averaging from one-quarter inch to one-half inch across.

It is interesting and 0f significant importance that the grain refinement achieved by the method of the invention penetrates quite deep into the casting. Although nucleation catalysis applied by this method is primarily a surface phenomenon, its effect is not limited to the surface of the casting. Many more grains which clearly did not originate at the surface are seen in sections cut through castings nucleated in accordance with the invention than in similar sections cut through unnucleatecl castings. As noted above, we believe this effect is due to circulation of the melt in the mold prior to its solidification.

Following are examples of the production of finegrained castings by the method of this invention:

Example I.A hardenable refractory slurry composition was prepared by suspending about 30 parts by weight of finely milled zircon in about 8 parts by weight of a 30% silica sol to which a small amount of wetting agent had been added. Metallurgical grade black cobalt (III) oxide was added to the resulting slurry, in the concentration of grams per liter. A wax pattern of a cluster of turbine blades was dipped in the resulting composition, and the coating thus applied to the pattern was sanded with to SO-mesh Alundum (fused aluminum oxide). Three additional dipcoats of a similar hardenable refractory containing no cobalt oxide or equivalent were then applied, each coat being sanded with ground fused fireclay and allowed to harden before the next was applied. The coated pattern was mountcd in a flask and backed up with a ccmentitious secondary investment. After the secondary investment had hardened, the resulting mold was inverted and heated to melt the wax pattern and burn out the residue of wax which adhered to the surface of the mold cavity. Heating was continued until the mold temperature attained 1840-" F. A melt of alloy C as set forth in Table I above, at a temperature of 2650" E, was then poured into the mold. The casting thus formed was alloyed to solidify and cool to a convenient handling temperature in the mold, after which the mold was broken away and the turbine blades were separated from the gates and risers to which they were joined. These castings were found to have a notably fine grain structure. Individual grains were so small as to be barely discernible to the naked eye. In contrast, like turbine blades cast under identical conditions at the same time in molds in which no cobalt oxide or equivalent material had been incorporated were characterized by having grains up to a quarter inch acros.

Example H.--A mold for a test bar one-eighth inch in diameter was made substantially as described in Example I. The composition with which the pattern was initially dipcoated contained five grams of cobalt (Ill) oxide per ml. of liquid. The mold was heated to 1700 F., and a cobalt-base surgical alloy melt at 2950 F. was poured into it. After cooling and breaking away the mold, the bars were found to have a very fine grain structure, the largest grains being no more than about one thirty-second inch in diameter. The ultimate tensile strength of these bars was found to be 123,000 pounds per square inch, and the yield strength was found to be 86,000 pounds per square inch. Test bars similarly made of the same alloy in molds to which no nucleation catalyst was applied had a much coarser grain structure, and under test showed an ultimate tensile strength of only 108,000 pounds per square inch and a yield strength of only 78,000 pounds per square inch.

Quarter-inch test bars made and nucleated as described in Example II had an ultimate tensile strength of 116,000 pounds per square inch, a yield strength of 82,000 pounds per square inch, 10% elongation in one inch, and a reduction in area of 10.4%. Corresponding unnucleated test bars were coarse-grained and had an ultimate tensile strength of 100,000 pounds per square inch, a yield strength of 77,000 pounds per square inch, an elongation of 8% in one inch, and a reduction in area of 8.2%. All these values were determined in the as-cast condition. Except for the presence of cobalt (III) oxide in the first dipco-at used to make the molds .for the nucleated castings, and the absence of any nucleation catalyst from the molds used to make the unnucleated castings, all test bars were made of the same alloy and under identical conditions. Thus it is apparent that the nucleation catalysts of the invention, used in accordance with the method of the invention, make it possible to produce markedly improved metal castings.

We claim:

l. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) forming a refractory mold having a surface layer comprising at least about 0.01 percent by Weight of an oxidic compound of a metal selected from the group consisting of nickel and cobalt,

(b) heating the mold to a temperature above 1000" F.,

(c) introducing a melt of the alloy into the heated mold, in contact with the surface comprising said oxidic compound, and

(d) cooling the alloy in the mold to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidification of the melt.

2. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) applying to at least a portion of the surface of a pattern of the article to be cast a coating comprising at least 0.01 percent by weight of an oXidic compound of a metal selected from the group consisting of nickel and cobalt,

(b) forming a refractory mold about the pattern to which such compound has been applied,

() removing the pattern from the mold while leaving such compound to define at least a part of the mold surface,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into said heated mold, and

(f) cooling the alloy in the mold to below its freezing temperature whereby nucleation of said alloy is catalyzed by said OXldiC compound during initial solidification of the melt.

3. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) coating the surface of an expendable pattern of the article to be cast with a composition comprising at least 0.01 percent by weight of an oXidic compound of a metal selected from the group consisting of nickel and cobalt,

(b) forming a mold by applying a hardenable refractory composition to the coated pattern,

(0) eliminating the pattern from within the mold after said refractory composition has hardened while leaving such compound to define the mold surface at least in part,

(d) heating the mold to a temperature above 1000" F.,

(e) introducing a melt of the alloy into said heated mold, and

(f) cooling the alloy in the mold to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oXidic compound during initial solidification of the melt.

4. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) coating the surface of a fusible pattern of the article to be cast with a composition comprising at least one-quarter percent by weight of an oXidic compound of a metal selected from the group consisting of nickel and cobalt,

(12) forming a mold by applying a hardenable refractory composition to the coated pattern,

(c) heating the pattern to above its fusion temperature to eliminate it from the mold after said refractory composition has hardened, whereby such compound remains to define at least in part the surface of the mold cavity,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into said heated mold, and

5. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) dispersing at least 0.01 percent by weight of an oxidic compound of a metal selected of the group consisting of nickel and cobalt in a hardenable refrac tory composition,

(b) applying a coating of said composition to a pattern of the article to be cast,

(0) allowing the coating to harden on the pattern,

(d) subsequently removing the pattern from within said hardened coating to form a mold cavity,

(e) heating the mold to a temperature above 1000 F.,

(f) introducing a melt of the alloy into said heated mold cavity, and

(g) cooling the alloy therein to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidfication of the melt.

6. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) coating a thin film of a liquid composition containing at least about 10 grams per liter of an oxidic compound of a metal selected from the group consisting of nickel and cobalt on the surface of an expend able pattern of the article to be cast,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into contact with the thus-defined heated mold surface, and

(f) cooling the alloy to below its freezing tempenature while it remains in contact with said mold surface whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidification of the melt.

7. The method of making a fine grained cast metal article of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) coating on the surface of a fusible pattern of the article to be cast a thin film of a hardenable liquid refractory composition in which there is suspended from 20 to 75 grams per liter of an oxide of a metal l 1 selected from the group consisting of nickel and cobalt,

(1)) allowing such composition to harden on the pattern,

() building up a mold by applying successive coats of hardenable refractory composition to the pattern,

(:1) heating the pattern to above its fusion temperature to eliminate it from the mold after said coats of refractory composition have hardened, whereby said oxide remains to define at least in part the surface of the mold ]cavity,

(e) heating the mold to a temperature above IOU-6 F.,

(f) introducing a melt of the alloy into contact with the thus-defined heated mold surface, and

(g) cooling the alloy to below its freezing temperature while it remains in contact with such mold surface whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidification of the melt.

8. The method of making a fine grained casting of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) forming a refractory mold having a surface layer comprising at least aobut one-quarter percent by weight of an oxidic compound of cobalt,

(b) heating the mold to a temperature above 1000 F.,

(c) introducing a melt of the alloy into such heated mold, and

(d) cooling the alloy in the mold to below its fr ezing temperature whereby nucleation of said alloy is catalzed by said oxidic compound during initial solidification of the melt.

9. The method of making a fine grained casting of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) applying a coating comprising at least about onequarter percent by weight of an oxidic compound of cobalt at least a portion of the surface of a pattern of the desired casting,

(b) forming a mold about the pattern to which such compound has been applied,

(c) removing the pattern from the mold while leaving such compound to define at least a part of the mold surface,

(:1) heating the mold to a temperature above 1000 F.

(e) introducing a melt of the alloy into said heated mold,

and

(7) cooling the alloy in the mold to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oxiclic compound during initial solidification of the melt.

10. The method of making a fine grained casting of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) dispersing at least about one-quarter percent by weight of an oxidic compound of cobalt in a hardenable refractory composition,

(b) applying a coating of said composition to a pattern of the desired casting,

(0) allowing the coating to harden on the pattern,

(d) subsequently removing the pattern from within said hardened coating to form a mold,

(e) heating the mold to a temperature above 1000 F.,

(f) thereafter introducing a melt of the alloy into such heated mold, and

(g) cooling the alloy therein to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oXidic compound during initial solidification of the melt.

11. The method of making a fine grained casting of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) coating on the surface of a fusible pattern of the desired casting a thin film of a hardenable liquid composition containing from 20 to grams per liter of cobalt oxide,

(b) forming a mold by applying a hardenable refractory composition to the resulting coated pattern,

(c) heating the pattern to above its fusion temperature to eliminate it from the mold after said refractory composition has hardened, whereby said oxide remains to define at least in part the surface of the mold cavity,

([1) heating the mold to a temperature above ltl00 F.,

(e) thereafter introducing a melt of the allo into such heated mold cavity, and

(f) cooling the alloy therein to below its freezing temperature whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidification of the melt.

12. The method of making a fine grained casting of an alloy containing at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and copper which comprises (a) forming a refractory mold having a surface layer comprising at least about one-quarter percent by weight of an oxidic compound of nickel,

(b) heating the mold to a temperature above 1000" R,

(c) introducing a melt of the alloy into such heated mold, and

(d) cooling the alloy in the mold to below its freez ing temperature whereby nucleation of said alloy is catalyzed by said oxidic compound during initial solidification of the melt.

References Cited in the file of this patent UNITED STATES PATENTS 335,628 Riddle Feb. 9, 1836 1,454,068 Myers May 8, 1923 2,592,337 Robertson et a1. Apr. 8, 1952 3,019,497 Horton Feb. 6, 1962 OTHER REFERENCES The Iron Age, vol. 169, No. 26, pages ll2 to 116, June 26, 1952.

Journal of institute of Metals, vol. 80, pages 93 to 93, October 1951, part II,

Disclaimer 3,157,926.R0be1"t A. H Orton, Cleveland, and Richard L. Ashbwook, Chesterland, Ohio, and Roy 0. F eagz'n, Mountain Lakes, NJ. MAKING FINE GRAINED CASTINGS. Patent dated Nov. 24, 1964. Disclaimer filed Oct. 24, 197 2, by the assignee, H owmet Gowpomtion. Hereby enters this disclaimer to claims 1 through 11 of said patent.

[Ofli'cz'al Gazette Mamh 13,1973]

Claims

1. THE METHOD OF MAKING A FINE GRAINED CAST METAL ARTICLE OF AN ALLOY CONTAINING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL, COBALT, CHROMIUM AND COPPER WHICH COMPRISES (A) FORMING A REFRACTORY MOLD HAVING A SURFACE LAYER COMPRISING AT LEAST ABOUT 0.01 PERCENT BY WEIGHT OF AN OXIDIC COMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT, (B) HEATING THE MOLD TO A TEMPERATURE ABOVE 1000*F., (C) INTRODUCING A MELT OF THE ALLOY INTO THE HEATED MOLD, IN CONTACT WITH THE SURFACE COMPRISING SAID OXIDIC COMPOUND, AND (D) COOLING THE ALLOY IN THE MOLD TO BELOW ITS FREEZING TEMPERATURE WHEREBY NUCLEATION OF SAID ALLOY IS CATALYZED BY SAID OXIDIC COMPOUND DURING INITIAL SOLIDIFICATION OF THE MELT.