US3839024A

US3839024A - Wear and corrosion resistant alloy

Info

Publication number: US3839024A
Application number: US00332581A
Authority: US
Inventors: J Demo; D Ferriss
Original assignee: EI Du Pont de Nemours and Co
Current assignee: Stoody Co; EIDP Inc
Priority date: 1973-02-15
Filing date: 1973-02-15
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01
Also published as: GB1439049A; DE2348703A1; JPS501026A; JPS5238807B2; NL7314446A; CA1001864A; DD107076A5; IL43461A0; SE390643B; BR7308134D0; JPS52125412A; ATA889473A; DK141173B; IT998816B; HU166691B; AT333520B; ZA738120B; JPS5728734B2; DK141173C

Abstract

An alloy consisting essentially of, by weight: A. AT LEAST 45 PERCENT COBALT OR NICKEL; B. 20-42 PERCENT MOLYBDENUM; C. 17-25 PERCENT CHROMIUM IF (A) IS COBALT AND 8-22 PERCENT CHROMIUM IF (A) IS NICKEL; AND D. sufficient silicon, not in excess of 12 percent so that 1. THE ALLOY MICROSTRUCTURE CONSISTS OF 10-100 VOLUME PERCENT OF A HARD PHASE WHICH IS PREDOMINANTLY Laves phase and 0-90 volume percent of a relatively soft matrix phase, and 2. THE ALLOY MICROSTRUCTURE CONSISTS OF AT LEAST 10 VOLUME PERCENT OF A Laves phase.

Description

IJnited States Patent 1 Demo, Jr. et al.

[4 1 Oct. 1, 1974 [75] Inventors: Joseph John Demo, Jr.; Donald Platt Ferriss, both of Wilmington, Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Feb. 15, 1973 [21] Appl. No.: 332,581

[52] U.S. Cl. 75/171, 75/.5 R, 75/134 F [51] Int. Cl. C21c 19/00 [58] Field of Search 75/.5 R, .5 AB, .5 BB,

75/134 F, 171, .5 AC, .5 BC; 29/1825 [56] References Cited UNITED STATES PATENTS 3,160,500 12/1964 Eiselstein 75/171 3,228,994 1/1966 Robinson 75/171 X 3,331,700 7/1967 Severns, Jr. et a1. 117/32 3,356,542 12/1967 Smith 75/171 X 3,410,732 11/1968 Smith 148/32 Redden 75/171 Gibson 75/128 W X Primary Examiner-L. Dewayne Rutledge Assistant ExaminerArthur .1. Steiner [57] ABSTRACT An alloy consisting essentially of, by weight: a. at least 45 percent cobalt or nickel;

b. 20-42 percent molybdenum;

c. 17-25 percent chromium if (a) is cobalt and 8-22 percent chromium if (a) is nickel; and

D. sufficient silicon, not in excess of 12 percent so that l. the alloy microstructure consists of 10-100 volume percent of a hard phase which is predominantly Laves phase and 0-90 volume percent of a relatively soft matrix phase, and 2. the alloy microstructure consists of at least 10 volume percent of a Laves phase.

12 Claims, No Drawings WEAR AND CORROSION RESISTANT ALLOY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to wear and corrosion resistant alloys of molybdenum, chromium, silicon and either cobalt or nickel.

2. Description of the Prior Art Many tertiary alloys of cobalt or nickel and containing ternary silicide intermetallics called Laves phases are known to be wear resistant. Alloys having hard Laves phases dispersed in softer matrices are known to have low friction properties. Such alloys which are both wear and corrosion resistant are not readily available. U.S. Pat. No. 3,410,732 discloses that certain cobaltbased alloys containing chromium exhibit improved corrosion resistance in certain acidic media; however,

' these alloys may not be resistant, especially at elevated SUMMARY OF THE INVENTION It is an object of this invention to provide an alloy which is wear resistant and which has satisfactory corrosion resistance, especially at elevated temperatures, against the wide variety of corrosive liquids which may be encountered in the chemical processing industry. A further object is to provide an alloy which is wear and corrosion resistant when in sliding relation with a second alloy of the same composition. A still further object is to provide a nickel-based alloy which is stress corrosion cracking, wear and corrosion resistant. Another object is to provide articles which are coated with such an alloy. In summary, the alloy of this invention consists essentially of, by weight:

a. at least 45 percent cobalt nickel;

b. 20-42 percent molybdenum;

c. 17-25 percent chromium if (a) is cobalt and 8-22 percent chromium if (a) is nickel and d. sufficient silicon, not in excess of 12 percent, so

that

1. the alloy microstructure consists of 10-100 volume percent of a hard phase which is predominantly Laves phase and -90 volume percent of a relatively soft matrix phase, and

2. the alloy microstructure consists of at least volume percent of a Laves phase.

A preferred embodiment of this invention includes the aforesaid alloy wherein the hard phase is at least 10 volume percent (preferably -75 volume percent), the molybdenum content is 22-36 percent, the silicon content is at least 1.5 percent (usually not above 5 percent and, preferably, 2-3 percent) and, alternatively, the cobalt content is 45-59 percent and the chromium content is 17-25 percent or the nickel content is 48-63 percent and the chromium content is 8-22 percent. Other preferred embodiments include the above and consist essentially of 50-55 percent cobalt, 22-29 percent molybdenum, 17-22 percent chromium and 1.5-4 percent silicon; 48-63 percent nickel, 24-36 percent molybdenum, 8-16 percent chromium and 2-5 percent silicon; 53 percent cobalt, 28 percent molybdenum, 17 percent chromium and 2 percent silicon; 51 percent cobalt, 25 percent molybdenum, 22 percent chromium and 2 percent silicon; 62 percent nickel, 28 percent molybdenum, 8 percent chromium and 2 percent silicon; 50 percent nickel, 32 percent molybdenum, 15 percent chromium and 3 percent silicon; and 53 percent nickel, 35 percent molybdenum, 9 percent chr0- mium and 3 percent silicon. Still other preferred embodiments include the alloy in rod or powder form; articles obtained by bonding alloy particles to each other at elevated pressures and temperatures, followed by cooling; coated articles obtained by applying the fused alloy to a metal substrate, followed by cooling of the alloy; and coated articles obtained by applying partly fused particles of the alloy to a substrate at elevated temperature, followed by cooling of the alloy.

DETAILED DESCRIPTION OF THE INVENTION The alloy of this invention, as defined above, is based on the discovery of an alloy composition having the high wear resistance of known wear resistant alloys, which have low corrosion resistance, and having the high corrosion resistance of known corrosion resistant alloys, which have low wear resistance. It also has been discovered that the nickel-based alloy of this invention is resistant to stress corrosion cracking. The defined alloy can be produced by melting a mixture of the elemental components or subcombinations of the elements at a temperature sufficient (for example, l,250-1,850C.) to provide a molten composition, and thereafter solidifying the melt by cooling. The resulting product is an alloy of nickel or cobalt, molybdenum, chromium and silicon in the proportions specified above and consists essentially of a cobaltor nickelbased matrix which is strengthened by the formation of intermetallic compounds and by the alloying of the matrix. The alloy is characterized by having two major phases which are detectable by metallographic, chemical and X-ray diffraction techniques. Specifically, the alloy contains at least 10 volume percent of a hard phase which provides at least 10 volume percent of a Laves phase and up to volume percent of a relatively soft matrix phase. The matrix phase in the alloy is formed from the same alloy components as the hard phase. The matrix can be substantially the base metal, a solid solution, an intermetallic compound other than Laves phase or a mixture of solid solution and intermetallic compound. Silicides of the alloy metal components also can be present in the matrix.

It is important that the hard phase of the alloy be predominantly Laves phase. A Laves phase contains one or more metallographical constituents that have the C, (hexagonal), C (cubic) or C (I-Iexagonal) crystal structure as described in International Tables for X-Ray Crystallography," Symmetry Groups, N. F. M. Henry and K. Lonsdale, International Union of Crystallography, Kynoch Press, Birmingham, England (1952). Prototypes of the Laves phase crystal structures are, respectively, MgZn MgCuand MgNi Such phase structures are unique crystal structures that permit the most complete occupation of space by assemblages of two sizes of spheres. Fundamentally, the Laves phase can be represented by the formula AB- the large atom A occupying certain sets of crystallographic sites and the small atoms B occupying other sites, in which the ratio of atomic radii AB is in the range 1.05-1.68. Laves phases occur as intermediate phases in numerous alloy systems. Laves phases generally have a homogeneity range, that is, they can have any of a range of elemental compositions while maintaining their characteristic crystal structure. The atom ratio B:A can vary from slightly lsss to slightly more than 2, possibly the result of some vacant sites in the crystal structure. Also, more than one kind of atom can occupy the large atom sites, the small atom sites, or both. Such Laves phases can be represented stoichiometrically by the formula (A ,C,)(B u) where C represents the atoms of one or more kinds that substitute for the large atoms, D represents the atoms of one or more kinds that substitute for the small atoms, of the binary Laves formula AB And x and y have values in the range -1.

An alloy, as the term is used herein, is a substance having metallic properties and containing in its elemental composition two or more chemical elements of which at least two are metals. The alloy of this invention has at least three metallic elements. Other elements (which are non-essential) can be present in the alloy of the invention provided they do not have a substantially adverse effect on the wear and corrosion resistance of the alloys. Following are examples of typical non-essential elements. Manganese is sometimes present up to about 0.6 percent and iron is tolerable up to about 2 percent. Moreover, cobalt-based alloys typically contain about 0.5 percent nickel, and nickelbased alloys typically contain about 0.5 percent cobalt. Up to about 3 percent of all such non-essential elements can be present in the alloy of this invention. It is to be understood that the previously-disclosed weight percentages of the essential elements are based only on the weights of the four essential elements in the alloy.

In the alloy of this invention the hard phase is almost exclusively Laves phase at about an 8 percent chromium content. At 12-25 percent chromium contents an additional phase may appear. This additional phase may surround Laves phase particles and may constitute a significant, though minor, part of the hard phase. This additional hard phase component is normally harder than the dispersing matrix phase and may constitute up to volume per cent of the alloy. In an alloy which has a hard phase consisting predominantly of a Laves phase and a non-matrix surrounding phase, the Laves phase constitutes at least 50 volume percent and, usually, greater than 75 volume percent of the hard phase. The alloy in all cases has at least 10 volume percent Laves phase.

Table I contains metallographic data on representative compositions of the alloy of this invention. The table shows the volume per cent of phases present, the bulk Rockwell C hardness and the microhardness values of the hard and matrix phases.

TABLE I.

Articles can be formed from the alloy of this invention by melting and casting the alloy using conventional furnaces, molds and techniques. The alloy can be pre formed or, as already disclosed, it can be formed from unalloyed mixtures of the necessary components. In the latter case, conventional prior art alloy conditions and techniques are chosen so as to form the alloy in situ. The preformed alloy can be physically reduced to particle sizes adapted to make articles by powder metallurgy procedures. In such procedures, powder particles of the preformed alloy are positioned in a mold and subsequently compressed at elevated pressures and temperatures to partly fuse them until a complete body of the alloy is produced (a powder metallurgy part) and thereafter cooled. Such parts are wear and corrosion resistant.

Coatings of the alloy on various substrates can be made by known procedures, for example, as disclosed in US. Pat. No. 3,331,700; by overlaying metal substrates with melts of the alloy provided in rodform; or by plasma spraying coatings of partly fused particles of the alloy on metal substrates and thereafter cooling the coatings. The aforesaid rod can consist of solid preformed alloy which is a continuous structure or it can consist of a combination of a continuous metal sheath which is filled with the necessary components so that the alloy is formed in situ during fusion. It is to be understood that the coatings may need dimensional finishing to prepare them for use. Such coatings are wear and corrosion resistant.

The alloy of this invention is especially useful for providing one or, preferably, both of two surfaces which are in sliding contact with each other and exposed to corrosive liquids. Typical sliding surface applications include rotating and axially movable shafts sliding inside cylindrical bushings and against end restraining surfaces such as thrust bearings. Bearings and seals provided with surfaces of the alloy of this invention resist corrosion by oxidizing liquids, such as ferric chloride and nitric acid solutions, and reducing liquids, such as aqueous hydrochloric, formic and sulfuric acids. Although the alloy may resist a few corrodants less than some known alloys, it exhibits superiority in its overall resistance to both wear and corrosion.

One major class of corrodants widely encountered in the chemical processing industry comprises acidic media, including dilute and concentrated mineral and organic acids and solutions of acidic salts, such as aqueous hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid and ferric chlo- Metallographic Data on Representative Compositions of the Alloy of this Invention Rc Rockwell C Hardness VHN Vickers Hardness No. greater than ride. Such acidic media are especially corrosive at elevated temperatures, for example, 50100C.

1n the following examples the alloys tested had compositions as given below, including phase volumes. The number preceding each element of an alloy composition is percent by weight. Hard phase volumes are expressed as alloy percent and are determined by relative areas under intensity graphs generated by X-ray diffraction analyses of characteristic alloy phases, as is well known in the metallurgical art. Alloys A through H were prepared by mixing the elements in the specified weight proportions, heating each mixture in air until completely molten, pouring off scum which formed on the surface and allowing the melt to cool to room temperature. Alloys C through H are alloys of the invention; alloys A, B and I through Q are commercially available prior art alloys.

A 62 Co/28 Mo/2 Si/8 Cr, having 50 percent hard phase. B 62 Co/24 Mo/2 Si/l 2 Cr, having 45 percent hard phase. C 53 Co/28 Mo/2 Si/17 Cr, having 54 percent hard phase. D 51 Co/25 Mo/2 Si/22 Cr, having 50 percent hard phase. E 62 Ni/28 Mo/2 Si/8 Cr, having percent hard phase F 53 Ni/35 Mo/3 Si/9 Cr, having 56 percent hard phase. G 50 Ni/32 Mo/3 Si/l5 Cr, having 50 percent hard hase. H 50 Ni/ Mo/3 Si/22 Cr, having 50 percent hard phase. The hard phase in each alloy above contains at least 75 percent Laves phase.

1 316 stainless steel, having the composition 12,

(max) Mn/balance Fe, having no LP and known as corrosion resistant. K A superstainless steel, Carpenter 20Cb3, of composition 34 Ni/2.5 Mo/20 Cr/3.5 Cu/balance position 5 Fe/16 Mo/7 Cr/balance Ni, having no LP and known as corrosion resistant.

O Hastelloy C, another nickel superalloy of composition 54 Ni/16 Mo/16 Cr/l Si/5 Fe/4 W, having no LP and known as corrosion resistant.

P Hastelloy B, another nickel superalloy of composition 6 Fe/28 Mo/l Si/balance Ni, having no LP and known as corrosion resistant.

O Stellite 68, a well known alloy of composition 29 Cr/1.5 (max.) Mo/2 Si/3 Fc/4.5 W/0.9-l .4 C/balance Co, having no LP and known as wear rcsistant.

Examples 1-11 The following well known Rider and Drum test procedure was used to compare corrosion and wear on alloy compositions of the invention and certain known corrosion and wear resistant alloys. For the test, a flat rider of test material 1 inch by 9/32 inch by 1 1/32 inch was loaded against a 3% inch diameter rotating drum providing a peripheral surface of like or different material. The rider bore down in line contact along a 9/32 inch by 1 inch face. Prior to the test run both rider and drum surfaces were polished to 10 microinch finishes. For the test the drum, with its lowest 1 inch in 5 percent aqueous HCl, was rotated at 25C. and at 400 peripheral surface feet per minute while the rider was under a 15 pound load. After 1 hour the weight changes of both rider and drum were recorded. The surface of each tested element was rated according to the following scale:

microcracks; severe corrosion.

Table I1 shows the weight losses of the riders and drums and the surface ratings of the worn riders and Fe, having no LP and known as corrosion resistant. drums of alloys which were rubbed together.

TABLE II Concurrent Effects of Wear and Corrosion Rider Drum Weight Losses tmg.) Surface Ratin s Example Alloy Alloy 1 er rum Rider Drum 1 A A 13 23 g g 2 B B 27 0 g g 3 c c 87 a g g 4 D D 13 23 g g 5 F F 44 79 g f 6 o o 78 22 f f 7 H H 106 25 f f 3 Q Q 82 93 p p 9 (a) Q 1718 285 p p 10 O O 156 (gain) p p 1 1 Q l 317 (gain) p p (a) chromium plated steel L lnconel 600, a nickel-based alloy of composition 77 Ni/16 Cr/7 Fe, having no LP and known as corrosion resistant.

M Monel 400, a nickel-based alloy of composition 1.4 Fe/32 Cu/balance Ni, having no LP and generally known as corrosion resistant.

N A nickel-based superalloy, Hastelloy N, of com- It can be seen that the alloys of the invention (Exs. 3-7) in sliding contact against themselves are superior to Stellite 68 against itself (Ex. 8) chromium plated steel (Ex. 9), stainless steel 316 (Ex. 11) and l-lastelloy C (Ex. 10) with the coba1t-based alloys (Exs. 3-4) being somewhat superior to the nickel-based alloys (Exs. 5-7) under these conditions.

Examples 12-28 The superiority of the alloy of the invention over similarly constituted alloys of the prior art (Examples 1 and 2) under a wider variety of corrosive conditions is indicated by the results of the following examples. The following test was used to compare the corrosion resistance of the alloy of the invention and known corrosion nd wear resistance alloys in contact with a variety of corrosive liquids. It consisted of a. immersing a weighed Vs inch X 1 inch X 1 /2 inch coupon of metal wet belt ground to an 80 grit finish in a liter of a testing liquid for 24 hour intervals at the indicated temperature,

b. removing the coupon and measuring its weight loss,

c. replacing the old testing liquid with the same volume of fresh testing liquid and reimmersing the coupon for another 24 hours,

(1. repeating (b) and (c) until three to five 24-hour intervals of exposure are completed, and

e. converting weight losses to rate of metal thickness losses, using average values where the daily losses are about the same but detailing a loss for each day which greatly deviates from the average daily loss.

Table 111 shows the corrosion performance as mils/year of metal thickness loss in the alloys tested in the aqueous liquids at the exposure temperatures shown in column headings.

seen that the cobalt-based alloys of the invention (Exs. 14-15) have corrosion resistance superior to stainless steels (Exs. 20-21) and Stellite B (Ex. 28) and generally equivalent to Monel (Ex. 24), the Hastelloys (Exs. 25-27) and Carpenter 20Cb3 (Ex. 22). The nickelbased alloys of the invention (Exs. 16-18) can be seen to perform in similar comparative relation to the known alloys cited. It can further be seen that alloys of the invention (Exs. 14, 15, l7, l8 and 19) show corrosion resistance against the oxidizing ferric chloride and- /or nitric acid media superior to Monel 400 (Ex. 24), Hastelloy N (Ex. 25) and Hastelloy B (Ex. 27). Although they are somewhat inferior to stainless steels (Exs. 20-22), lnconel 600 (Ex. 23), Hastelloy C (Ex. 26) and Stellite 6B (Ex. 28), their overall corrosion and wear performance is satisfactory and useful in the chemical processing industry. Examples 29-31 The following test was used to compare the stress corrosion cracking resistance of the nickel-based alloy of this invention and a known wear resistant Laves phase-containing alloy. The procedure used was that described by M. A. Streicher and A. .1. Sweet in Corrosion, 25, No. 1, 1-6 (1969). Each sample used was a 3 inch X 0.5 inch X 0.065 inch strip machine from a cast 3 inch X 1 inch X 0.25 inch block. The 0.065 inch thickness was deflected at its ends and across its mid- TABLE 111 Corrosion Performance of Alloys (mils/year loss) 45% Formic 10% 10% FeCL, 65% HNO 5'72 HCl Acid H 80 Example Alloy 25C(a) 66C. 66C. Boiling BOllll'lg 12 A 101 1365 194 1.5 218 13 B 212 240 1.2 2.3 114 14 C 9.2 492 (b) 1.5 1.6 34

39 (c) 15 D NT 41 1.0 3.8 19 16 E NT NT 13 NT 3.4 17 F 499 290 13 2.5 16 18 G 84 420 (b) 30 NT NT 60 (c) 19 H NT 163 (b) 308 3.8 48

20 (c) 20 l 1000 11 500 500 900 21 J 1000 8 1000 1700 5000 22 K 165 1 80 5.9 38 23 L 440 26 123 37 220 24 M 1000 5000 26 0.8 16 25 N 1000 970 17 NT 22 26 O l 22 18 3.1 26 27 P 102 9860 10 0.9 2.0 28 Q 80 8.0 4100 28 240 (a) Average of 5-7 24 hr. cycles (b) Rate for first 24 hr. cycle (0) Average rate for next 2-4 cycles NT not tested greater than point in a jig of lnconel 600, a stress corrosion crack resistant material, to apply a maximum applied 60,000

psi. stress in the outer surface of the strip. The jig with sample was immersed in boiling 45 percent aqueous magnesium chloride. Periodically, the surface of the stressed sample was examined at 20X magnification to see the beginning and propagation of surface cracks. Failure occurred when the sample fractured into two pieces. Table IV shows alloys used and their time to failure.

TABLE IV Alloy Example Composition Time to Failure 29 A 40 hrs. 30 E no failure. 148 hrs. 31 G no failure. 194 hrs.

it can be seen that nickel-based alloys with 8 percent Cr (Ex. 30) and with percent Cr (Ex. 31 are superior to the prior art cobalt-based alloy with 8 percent Cr (Ex. 29). Generally, the attainment of 100 hours without failure indicates that attainability of at least 1,000 hours without failure is possible under these conditions.

We claim: 1. Alloy consisting essentially of, by weight: a. at least 45 percent cobalt or nickel; b. -42 percent molybdenum; c. 17-25 percent chromium if (a) is cobalt and 8-22 percent chromium if (a) is nickel; and d. sufficient silicon, within the range 15-12 percent,

so that, the alloy microstructure consists of 20-100 volume percent of a hard phase which is at least 75 volume percent Laves phase and 0-80 volume percent of a relatively soft matrix phase, said alloy containing no more than 3 percent nonessential elements.

2. The alloy of claim 1 wherein the hard phase is 20-75 volume percent and which consists essentially of 20-75 volume percent and which consists essentially of 48-63 percent nickel, 22-36 percent molybdenum, 8-22 percent chromium and 15-5 percent silicon.

7. The alloy of claim 6 which consists essentially of 48-63 percent nickel, 24-36 percent molybdenum, 8-16 percent chromium and 2-5 percent silicon.

8. The alloy of claim 7 which consists essentially of 62 percent nickel, 28 percent molybdenum, 8 percent chromium and 2 percent silicon.

9. The alloy of claim 7 which consist essentially of 50 percent nickel, 32 percent molybdenum, 15 percent chromium and 3 percent silicon.

10. The alloy of claim 7 which consists essentially of 53 percent nickel, 35 percent molybdenum, 9 percent chromium and 3 percent silicon.

11. The alloy of claim 1 in the form of a powder.

12. The alloy of claim 1 in the form of a rod.

Claims

1. ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT: A. AT LEAST 45 PERCENT COBALT OR NICKEL; B. 20-42 PERCENT MOLYBDENUM; C. 17-25 PERCENT CHROMIUM IF (A) IS COBALT AND 8-22 PERCENT CHROMIUM IF (A) IS NICKEL; AND D. SUFFICIENT SILICON, WITHIN THE RANGE 1.5-12 PERCENT, SO THAT, THE ALLOY MICROSTRUCTURE CONSISTS OF 20-100 VOLUME PERCENT OF A HARD PHASE WHICH IS AT LEAST 75 VOLUME PERCENT LAVES PHASE AND 0-80 VOLUME PERCENT OF A RELATIVELY SOFT MATRIX PHASE, SAID ALLOY CONTAINING NO MORE THAN 3 PERCENT NON-ESSENTIAL ELEMENTS.

2. The alloy of claim 1 wherein the hard phase is 20-75 volume percent and which consists essentially of 45-59 percent cobalt, 22- 36 percent molybdenum, 17-25 percent chromium and 1.5-5 percent silicon.

3. The alloy of claim 2 which consists essentially of 50-55 percent cobalt, 22-29 percent molybdenum, 17-22 percent chromium and 1.5-4 percent silicon.

4. The alloy of claim 3 which consists essentially of 53 percent cobalt, 28 percent molybdenum, 17 percent chromium and 2 percent silicon.

5. The alloy of claim 3 which consists essentially of 51 percent cobalt, 25 percent molybdenum, 22 percent chromium and 2 percent silicon.

6. The alloy of claim 1 wherein the hard phase is 20-75 volume percent and which consists essentially of 48-63 percent nickel, 22-36 percent molybdenum, 8-22 percent chromium and 1.5-5 percent silicon.

11. The alloy of claim 1 in the form of a powder.

12. The alloy of claim 1 in the form of a rod.