Patented May 14, 1946 2400,255

UNITED STATES PATENT OFFICE 2,400,255 ELECTRIC RESISTANCE ELEMENTS AND TBELKE Leonard Bessemer Pfeil, Birmingham, England, assignor to The International Company, Inc., New York, N. Y., a corporation of Dela ware No Drawing. Application May 15, 1942, Serial No. 443,174. In Great Britain May 27, 1941 10 Claims. (C. 201-6) The present invention relates to heat-resisting of heat-resisting alloys and articles made there alloys and articles made therefrom and to a fron. method of producing such alloys and articles, It is also an object of the present invention and more particularly to heat-resisting alloys and to provide a method of improving the life of heat articles having an improved combination of prop resisting alloys and articles made therefrom with erties. out seriously impairing the creep resistance of It is well known to incorporate in heat-resisting the alloy or article. alloys, such, for example, as those used for elec Other objects and advantages of the invention trical resistance elements, Small quantities of one will become apparent to those skilled in the art or more elements such as the rare earth metals, 10 from the following description. particularly , the alkaline earth metals, The elements which I have found may be ap particularly calcium, , etc., in addition to plied as films are thorium, calcium, those of which the alloy is basically composed, and the rare earth elements. According to this for the purpose of improving the high tempera invention the alloys or articles that are made ture properties and in particular the service life therefrom and by their nature are necessarily of the alloys and articles made therefrom. As subjected to high temperatures in service are pro an example, the heat-resisting properties, and in vided on their Surfaces with films of one or more particular the resistance to oxidation, of alloys of these long-life elements in the elementary consisting basically of 80% nickel and 20% chro form or in the form of oxides or or mium are materially improved by the inclusion 20 in the form of salts that will decompose to Oxides of small quantities of calcium, cerium, calcium at high temperatures. and cerium or calcium and thorium. Many other The service life of the alloys or articles pro elements may be used and, for convenience, in . vided with such surface films is not always So view of their capacity for increasing the life of great as when the long-life element is included the alloy under high temperature conditions, they in the alloy, but compensating advantages are are referred to herein as 'long-life elements.' often obtained. For example, the addition of I have found that the long-life elements, when the elements to the molten alloys may be a matter incorporated in the alloys to improve their life, of difficulty, as many of the long-life elements may have an adverse effect on other properties are extremely reactive. Again, the presence of of the alloys. In an increasing number of appli 30 long-life elements in the alloys may render them cations of heat-resisting alloys, resistance to creep difficult to fabricate, and in some cases the alloys at high temperatures is an essential requirement, cannot be hot-worked. These difficulties are and long-life additions to the alloys may seriously avoided altogether by means of the invention. impair this resistance. Furthermore, the addition In an increasing number of applications of heat of the long-life elements to the molten alloys may resisting alloys, resistance to creep at high tem be a matter of difficulty, as many of the long-life peratures is an essential requirement, and long elements are extremely reactive. Again, the pres life additions to the alloys may seriously impair ence of long-life elements in the alloys may render this resistance. Surface application of the long them difficult to fabricate, and in some cases the life elements has the great advantage of allowing alloys cannot be hot worked. 40 of the production of articles and machine parts I have discovered that Some of the elements for high temperature operations having high re will produce the desired effect of an increase in sistance to oxidation and without any reduction the Service life of the basic alloys if they are in their normal resistance to creep. applied in the form of films to the surfaces of It appears that the long-life elements produce the alloys. the effect indicated by their influence on the It is an object of the present invention to pro formation of Scale on the Surface of the alloy. vide heat-resisting alloys and articles having an Whether this is so or not, I find that what is improved combination of properties. necessary is to produce a fine dispersion of the It is another object of the present invention to 50 long-life element or elements on the surface. provide heat-resisting alloys and articles made This need not be continuous, although the parti therefrom having high service life combined with cles that compose it should be uniformly dis improved resistance to creep. tributed, and it must not be a thick coating such It is a further object of the present invention as would either completely exclude oxygen from to provide a novel method of improving the life 55 the surface or would tend to flake off under rapid 2. 2,400,255 changes of temperature. With Such a thick coat The following results have been obtained in ing the desired effect is not produced. tests on an 80/20 nickel- alloy having Of the long-life elements defined above, the a life of 33 hours at 1200° C. best results are obtained with thorium and the rare earth elements. The latter may advanta geously be used in the form of a so-called Treatinent 1200°Life atC. "mischmetall' containing cerium and other ele-, ments, for example, lanthianum. IIours Alloy dipped in solution of "mischinctall' nitrate.------59 In practice, the film may be formed in a number Alloy coated anodically with "mischmetali" oxide...... 5 of different ways. In general, it is best to form O Alloy dipped in solution of thoritual nitrate------54 it after the desired article (e. g., an electrical Alloy coated anodically with thoria (thorium dioxide).--- 65 resistance wire, tape or ribbon, or electrical re Alloy dippod in calcium-thoriuin solution------sistance heating element made therefron) has The invention is particularly applicable to the been fabricated from the alloy. When this is Well-known nickel-chromium and nickel-chro done, the preferred method is to dip the article 5 mium- alloys containing from 10 to 30% in a solution of a salt of a long-life element, or chromium, 20 to 90% nickel and 0 to 50% iron to deposit an oxide or of the element and to articles made therefrom which are sub anodically. In the former case, the finished arti jected in use to elevated temperatures below their cle should first be heated to give it a light oxide melting point. It may also be applied, however, scale as this causes more satisfactory wetting 20 of the surface and also makes the coating more to all the alloys (including austenitic steels), adherent. The oxidised article may be dipped and to articles made therefrom, that are com into the solution, e. g., into a Solution of any ap-. monly called heat-resisting, such as the iron propriate concentration, e. g. about 10%, while nickel-chromium, nickel--chromium, co hot and withdrawn while still hot enough to ... balt-iron-chromium, iron-chromium, iron-chro evaporate off the solvent, or it may be dipped 25 mium-, and complex alloys based on cold and then heated to remove the solvent and Systems such as these alloys but containing in decompose the salt of the long-life element to addition one or more of the elements molybde oxide. Solutions of the nitrates of the long-life num, tungsten, , columbium, zirconium, " ... aluminium and the like. These alloys include elements may be most conveniently used in most 30 cases and slightly solutions containing about those containing about 10 to 35% chromium, and 10% by weight of the salt give a film of the de may optionally contain from a small amount, say sired thickneSS. about 0.01%, to about 20% of one or more metals When anodic deposition is used, the article to from the consisting of molybdenum, tung bo treated should have a clean metallic Surface 35 sten, titanium, columbium, zirconium, aluminium, produced by bright annealing, pickling or sand Silicon and , and the balance substan blasting, and should be degreased before placing tially all metal of the iron group, i. e. metal of in the depositing bath. The bath may contain the group consisting of nickel, iron and cobalt. any soluble salt of the long-life elements of any As will be apparent to those skilled in the art, concentration from about 10% to saturation, and 40 these alloys may also contain small amounts of this should be made progressively more alkaline incidental elements and impurities, e. g. sulphur, until precipitation commences. Acid should then . phosphorus, etc. While the total of iron group be added until the precipitate disappears and . metals will usually exceed about 50%, the inven then a further slight excess. Again, the condi- . . tion contemplates not only those alloys in which tions may be varied over a wide range, but suc one of the iron group metals exceeds about 50% cessful deposition may be obtained by using a but also those alloys in which no one particular 10% solution, making the article to be plated the iron group metal exceeds about 50% although anode and increasing the applied voltage from the sum of all the iron group metals will exceed about 2 volts until deposition is indicated by the about 50%. evolution of gas round the article being treated. 50 Although the present invention has been de If the voltage is increased further the deposi scribed in conjunction with preferred embodi tion becomes more rapid, but the gas evolution ments, it is understood that modifications and tends to strip off the film. The gelatinous film variations may be resorted to without departing deposited should have a thickness of a few thou from the spirit and scope of the invention, as sandths of an inch. After Coating the article is 55 those skilled in the art will readily understand. heated to dehydrate the film and to convert it Such variations and modifications are considered to oxide. to be within the purview and scope of the ap Sometimes I may apply the film to the alloy pended claims. or partly-fabricated article and thereafter fabri claim: cate, or complete the fabrication of, the article, 60 1. A method of improving the high tempera and then I may use other methods of forming ture Service life of chromium-containing heat the film. For instance, the surface of the alloy resisting alloys substantially free from long-life or partly-fabricated article may be provided with elements which comprises providing such alloys an integral film by cementation, brought about with an adhering surface film of at least one by heating the alloy in a powdered long-life ele 65 member selected from the group consisting of ment in an inert atmosphere, or in a mixture of thorium, calcium, zirconium and the rare earth an oxide or other compound of the element with elements, oxides and hydroxides thereof and salts a reducing agent. Again, the alloy or partly-fab thereof that will decompose to oxides at high ricated article may be passed through a bath of temperatures. the molten element or this may be electrolytically 70 2. An article subjected in use to elevated tem deposited from a bath of a molten salt of it. Of peratures made of a chromium-containing heat course these methods may also be used to form resisting alloy and having a surface film of at films on finished articles, but for this purpose the least one member selected from the group consist two methods first described are preferred because ing of thorium, calcium, Ziconium and the rare of their simplicity. 75 earth elements, oxides and hydroxides thereof 200,255 3 and salts thereof that will deCOmpose to Oxides at 8. A method of increasing the service life of an high temperatures. article that is made from a heat-resisting chro 3. Electrical resistance wires, tapes, ribbons and mium-containing alloy and that by its nature is the like made of a chromium-containing heat necessarily subjected to high temperatures in resisting alloy and having a surface film of at service, comprising forming a film on the surface least one member selected from the group con of said article by anodic deposition thereon of sisting of thorium, calcium, zirconium and the at least one member of the group consisting of the rare earth elements, oxides and hydroxides there Oxides and hydroxides of thorium, calcium, zir of, and salts thereof that will decompose to oxides COnium and the rare earthmetals. at high temperatures, 10 9. A method of increasing the service life of an 4. An alloy composed essentially of chromium, article that is made from a heat-resisting chro nickel and iron and containing from 10 to 30% mium-containing alloy and that by its nature is chromium, 20 to 90% nickel and 0 to 50% iron, necessarily subjected to high temperatures in said alloy being provided on its surface with a service, comprising applying to the alloy a film film comprising at least One member selected from 5 of at least One member selected from the group the group consisting of thorium, calcium, Zir consisting of thorium, calcium, zirconium and the conium and the rare earth elements, oxides and rare earth elements, oxides and hydroxides there hydroxides thereof and salts thereof that will of and salts thereof that will decompose to oxides decompose to Oxides at high temperatures. at high temperatures, and thereafter fabricating 5. A heat-resisting chromium-containing al the article from said alloy. loy provided on its surface with a film Compris 10. A method of increasing the service life of an ing a member selected from the group consisting article that is made from a heat-resisting chro of "mischmetal' or compounds thereof. mium-containing alloy and that by its nature is 6. A heat-resisting chronium-containing al necessarily subjected to high temperatures in loy provided on its surface with a film comprising service, comprising partly fabricating the article a member selected from the group consisting of 25 from said alloy, applying to the partly-fabricated thorium and compounds thereof. alloy a film of at least one member selected from 7. A method of increasing the service life of an the group consisting of thorium, calcium, zir article that is made from a heat-resisting chro conium and the rare earth elements, oxides and mium-containing alloy and that by its nature is hydroxides thereof and salts thereof that Wilde necessarily subjected to high temperatures in 30 compose to Oxides at high temperatures, and service, comprising forming a film on the sur thereafter completing the fabrication of said ar face of Said article by dipping Said article in a tice. solution of at least one member of the group con sisting of the salts of thorium, calcium, zirconium LEONARD BESSEMER PEEL. and the rare earth metals.