US3839025A

US3839025A - High temperature alloy

Info

Publication number: US3839025A
Application number: US00379814A
Authority: US
Inventors: H Morrow; W Danesi; D Sponseller
Original assignee: American Metal Climax Inc
Current assignee: Cyprus Amax Minerals Co
Priority date: 1973-07-16
Filing date: 1973-07-16
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01

Abstract

A carbide-strengthened castable cobalt-base superalloy possessed of excellent high-temperature properties and improved ductility and containing controlled amounts of chromium, nickel or iron, molybdenum, tungsten, tantalum, titanium, zirconium, carbon and the balance cobalt, along with conventional residual alloying elements and incidental impurities.

Description

United States Patent Morrow, III et al.

Oct. 1, 1974 HIGH TEMPERATURE ALLOY Inventors: Hugh Morrow, III; Wilbert P.

Danesi; David L. Sponseller, all of Ann Arbor, Mich.

Assignee: American Metal Climax, Inc., New

York, NY.

Filed: July 16, 1973 Appl. No.: 379,814

US. Cl. 75/171, 148/32 Int. Cl. C22c 19/02 Field of Search 75/171, 170; 148/32, 32.5

References Cited UNITED STATES PATENTS 3/1969 Wheaton 75/171 Primary ExaminerRichard 0. Dean Attorney, Agent, or FirmHarness, Dickey & Pierce 5 7 ABSTRACT 6 Claims, No Drawings HIGH TEMPERATURE ALLOY BACKGROUND OF THE INVENTION The high stresses and elevated temperatures to which components of high-performance gas turbines are subjected has prompted a continuing search for materials which provide for an optimum balance of mechanical properties over the normal operating temperature range of such engines. Among the various materials which have been developed for this purpose, so-called superalloys of a nickel or cobalt-base have been found particularly satisfactory. Of the foregoing, cobalt-base superalloys are in widespread use because of their ability to be cast, producing components which are possessed of excellent mechanical properties, including high stress-rupture and tensile strengths at elevated temperatures and excellent high-temperature oxidation and corrosion resistance. characteristically, most of the cobalt-base superalloys in commercial use are strengthened by a combination of solid solution and carbide dispersion strengthening and employ comparatively high quantities of chromium and refractory metals, of which tungsten is perhaps the most popular, although tantalum has also received some acceptance.

Typical of the several castable cobalt-base superalloys is the alloy disclosed in US. Pat. No. 3,432,294 comprising a carbide-hardened alloynominally containing about 0.6 percent carbon, about 18 percent to about 24 percent chromium, about 7 percent to about 15 percent nickel, about 6 percent to about 9 percent tungsten, about 2 percent to about 5 percent tantalum, about 0.1 percent to about 0.5 percent titanium, about 0.1 percent to about 1 percent zirconium with the balance being essentially cobalt. While alloys of the foregoing type have been found satisfactory for the fabrication of various components for high-performance gas turbine engines, the high cost of such alloys has somewhat detracted from a more widespread use thereof. In addition, continuing improvements in gas turbine engine designs, providing for still greater efficiency and performance, has resulted in a continuing need for superalloys of improved high-temperature mechanical properties which can be produced at more reasonable costs. The cobaltbase superalloy of the present invention, as a result of the careful control in type and quantity of the individual alloying constituents, provides for a still further improvement in certain moderate and high-temperature mechanical properties of such alloys, while at the same time providing cost advantages over similar type alloys heretofore known.

SUMMARY OF THE INVENTION The benefits and advantages of the present invention are achieved by a cobalt-base superalloy containing as its essential alloying ingredients from about 18 percent to about 26 percent chromium, from about 7 percent to about percent nickel or, in the alternative, from about 7 percent to about 12 percent iron; from about 2.5 percent to about 4.5 percent tungsten, from about 1 percent to about 4 percent molybdenum, from about 2 percent to about 5 percent tantalum, from about 0.1 percent to about 0.4 percent titanium, from about 0.1 percent to about 1.0 percent zirconium, from about 0.4 percent to about 0.7 percent carbon, and with the balance consisting essentially of cobalt, together with residual elements including manganese, silicon, boron, niobium and the like, present in conventional amounts normally encountered as well as conventional incidental impurities. In accordance with a preferred embodiment of the present invention, the nickel constituent is entirely replaced by iron without a significant sacrifice in the mechanical properties of the resultant alloy, but with a significant cost saving attributable not only to the elimination of an appreciable quantity of nickel, but also enabling the use of ferro-chromium and ferromolybdenum as a source of the chromium, molybdenum and iron alloying constituents.

Additional benefits and advantages of the present invention will become apparent upon a reading of the description of the preferred embodiments and the specific examples provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composition of the cobalt-base alloy comprising the present invention as herein described and as set forth in the subjoined claims is defined in terms of percentages by weight unless clearly indicated to the contrary.

The usable proportions and the preferred proportions of the individual alloying constituents comprising the nickel-containing cobalt-base alloy in accordance with one embodiment of the present invention is set forth in Table 1.

TABLE 1 Nickel-Type Cobalt-Base Alloy Composition as low as possible Similarly, the usable proportions as well as the preferred proportions of the individual alloying elements comprising the so-called ferrous-type cobalt-base alloy in accordance with a second embodiment of the present invention is set forth in Table 2.

TABLE 2 Ferrous-Type Cobalt-Base Alloy Composition Usable Range Preferred Range Ingredient (percent) (percent) Chromium 18 26 23 25 Nickel up to 2 up to 1 Iron 7 12 9 l 1 Molybdenum 1 4 1 3 Tungsten 2.5 4.5 3.2 3.8 Tantalum 2 5 3 4 Titanium 0.1 0.4 0.2 0 3 Zirconium 0.1 1.0 0.3 0.6

TABLE 2-Continued Fcrrous'l' \pc Cobalt-Base Allo Composition as low as possible The principal distinctions between the so-called nickel-type and ferrous-type cobalt-base alloys as set forth in Tables 1 and 2, respectively, resides in the quantity of iron and nickel present in the alloys. The nickel-type alloy contains residual quantities of iron up to about 2 percent in combination with from about 7 percent to about 12 percent nickel, while the ferrous-type alloy contains nickel as a conventional residual in amounts up to about 2 percent, and with iron substituted therefor in an amount ranging from about 7 percent to about 12 percent. In addition to the foregoing differences, the nickel-type alloy has permissible manganese and silicon contents of up to about 0.5 percent, whereas the irontype cobalt-base alloy may contain manganese and silicon in amounts as high as about 1 percent.

A principal distinction between the alloys defined in Tables 1 and 2 from prior art type cobalt-base alloys is the presence of molybdenum in amounts of from about 1 percent to about 4 percent and preferably, from about 1 percent to about 3 percent in combination with lesser quantities of tungsten providing therewith unexpected improvements in certain high-temperature mechanical properties of the alloys, as well as an appreciable reduction in their costs. In both instances, the cost savings achieved by a substantial reduction in the tungsten content and the replacement thereof with lowercost molybdenum has been achieved without substantially modifying the stress-rupture, tensile strength,

thermal expansion and solidification characteristics of the alloys. At the same time these modifications provide for an improved stress-rupture and tensile ductility and a lower room temperature density of the alloy. The inclusion of molybdenum, therefore, as a partial replacement for the tungsten constituent provides for definite unexpected benefits in the properties of the cobalt-base alloys accompanied by a cost savings which is particularly marked in connection with the ferroustype cobalt-base alloy of Table 2, permitting the use of lower-cost ferro-chromium and ferro-molybdenum as the source of the chromium, molybdenum and iron alloying constituents.

As set forth in Tables 1 and 2, the essential alloying constituents of the improved cobalt-base superalloys of the present invention comprise chromium, nickel or iron, molybdenum, tungsten, tantalum, titanium, zirconium, and carbon with the balance essentially cobalt and with the remaining constituents being present as residuals and incidental impurities which can generally be tolerated in the amountsas specified, at which level they do not adversely affect the high-temperature physical and chemical properties of the alloys. The manganese and silicon constituents, for example, comprise conventional residuals in ferro-chromium, which preferably is employed for preparing the alloy as set forth in Table 2 because of economic considerations. It is for this reason that the manganese and silicon contents of the ferrous'type cobalt alloy are higher than that of the nickel-type cobalt alloy. The silicon constituent is present as a conventional residual in nominal amounts of about /2 percent in both the ferro-chromium and ferromolybdenum materials of the types normally employed for preparing the ferro-type cobalt alloy. A typical lowcarbon ferro-chromium alloying material nominally contains about 30.8 percent iron, 0.45 percent silicon, 0.64 percent manganese and about 0.04 percent carbon, with the balance consisting essentially of chromium. A typical ferro-molybdenum alloying material nominally contains about 38.6 percent iron, 0.62 percent silicon, 0.04 percent carbon, and the balance comprised essentially of molybdenum. As previously mentioned, the high permissible iron content of the ferroustype cobalt-base alloy set forth in Table 2 permits the use of the two lower-cost ferro-chromium and ferromolybdenum materials, providing for substantial further cost savings in preparing the alloys and accordingly, constitutes a preferred practice.

The cobalt and chromium alloying constituents impart the requisite high-temperature strength and corrosion and oxidation resistance to the cobalt-base alloy. Chromium contents above the upper limits specified in Tables 1 and 2 are generally undesirable due to the precipitation of phases resulting in brittleness of the resultant alloy, whereas amounts below the lower limits usually result in inadequate oxidation resistance and a sacrifice in the physical strength properties of the alloy.

The mechanisms by which the cobalt-base superalloy is strengthened include carbide strengthening and solid-solution strengthening. The former effect derives mainly from the MC carbide-forming constituents tantalum, titanium and zirconium. These elements form carbides that are located in the interdendritic regions or are dispersed in the matrix. The latter effect consists of solid-solution strengthening of the matrix mainly by tungsten, molybdenum and chromium. The stability of the resultant microstructure provides for superior durability of the alloy when subjected to stresses at elevated temperatures as high as 2,000F and above, which are characteristic of peak temperatures attained in the hot section of modern, high-performance gas turbine engines. The refractory-type carbide-forming metallic elements are interrelated in type and quantity within the limits as set forth in Tables 1 and 2 to provide for optimum physical and chemical properties of the resultant cobalt-base alloy. In this connection, the carbon content of the alloy is carefully controlled within the limits specified to produce the required quantity of carbides.

In addition to the foregoing important alloying elements, the remaining alloying constituents enumerated comprise residuals whose presence is not essential, but which can be tolerated up to the amounts specified without adversely affecting the properties of the alloy. For example, the niobium constituent comprises a residual usually associated with tantalum and while permissible in amounts up to 2 percent, preferably is controlled to levels below about 1 percent due to the improved oxidation resistance of the resultant composition. Other conventional residuals may also be present in usual minimal quantities along with incidental conventional impurities of the types which do not adversely affect the moderate and high-temperature physical and chemical properties of the alloy.

In order to further illustrate the alloy compositions comprising the present invention, the following examples are provided. it will be understood that the examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as herein described and as set forth in the subjoined claims.

EXAMPLE 1 A cobalt-base superalloy of the nickel type in accordance with Table l was prepared employing vacuum melting techniques to provide a nominal composition of 24 percent chromium, percent nickel, 1.9 percent molybdenum, 3.5 percent tungsten, 3.5 percent tantalum, 0.2 percent titanium, 0.5 percent zirconium, 0.6 percent carbon, and with the balance cobalt along with conventional residuals and incidental impurities. The resultant vacuum melted composition was investment cast into test specimens and subjected to tests at elevated temperatures.

EXAMPLE 2 A cobalt-base superalloy of the so-called ferrous-type in accordance with the composition as set forth in Table 2 was prepared employing vacuum melting techniques to provide a nominal composition of 24 percent chromium, 10 percent iron, percent molybdenum, 3.5 percent tungsten, 3.5 percent tantalum, 0.2 percent titanium, 0.5 percent zirconium, 0.6 percent carbon and the balance cobalt and conventional residuals and incidental impurities. The vacuum melted alloy was investment cast into test specimens and subjected to physical tests at elevated temperatures as in the case of the test specimens of Example 1.

Room and elevated temperature tensile properties and stress rupture properties of the alloys prepared in accordance with Examples 1 and 2 were determined and the data are set forth in Table 3.

TABLE 3 Alloy- Alloy- Property Example 1 Example 2 Ultimate Tensile Strength,

psi 74F [09,300 112,700 1400F 85,000 79,100 1800F 35,000 30,000 2000F 19.100 18.300

0.2% Yield Strength, psi

74F 77,200 78,200 1400F 44,800 41,800 1800F 29,500 22,500 2000F 15.300 15.800

71 Elongation 74F 3.0 2.0 1400F 15.2 20.0 1800F 26.8 37.6 2000F 21.6 25.2

71 Reduction Area 74F 2.9 3.0 1400F 12.4 16.6 1800F 25.7 39.1 2000F 21.6 29.9

IOU-Hour Rupture Strength,

psi 1600F 27,500 25,000 1800F 15,500 13.600 2000F 7,000 6,400

TABLE 3-Continued Alloy- Alloy- Property Example 1 Example 2 100-Hour Rupture Elongation. 7(

1600F 9.0 24.3 1800F 12.0 20.0 2000F 11.0 13.3

As will be noted, the alloy of Example 1 has superior high-temperature tensile strength properties in comparison to the alloy of Example 2 due to the presence of nickel in lieu of iron. Both alloys possessed excellent rupture strength and excellent intermediate temperature, tensile and stress rupture ductility, the latter properties being generally superior to those of similar cobalt-base alloys of the types heretofore known. In addition to the foregoing properties, the coefficient of thermal expansion of the two alloys were substantially the same as that of prior art cobalt-base alloys. For example, the alloy of Example 1 has an average thermal expansion coefficient (10" inches/inch/C) of 14.28 from room temperature to 500C and 16.18 from room temperature to 1,000C; while the alloy of Example 2 has average coefficients of 14.58 and 16.26, respectively, for the same two temperature ranges. Similarly,

- the alloy of Example 1 has a density at room temperature of 8.53 g/cc (0.308 lbs./in while the alloy of Example 2 has a density of 8.58 g/cc (0.309 lbs/in).

While it will be apparent that the invention herein disclosed is well calculated to achieve the benefits and advantages set forth, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

What is claimed is:

l. A cobalt-base alloy consisting essentially of about 18 percent to about 26 percent chromium, about 7 percent to about 12 percent nickel, up to about 2 percent iron, about 1 percent to about 4 percent molybdenum, about 2.5 percent to about 4.5 percent tungsten, about 2 percent to about 5 percent tantalum, about 0.1 percent to about 0.4 percent titanium, about 0.1 percent to about 1.0 percent zirconium, about 0.4 percent to about 0.7 percent carbon and the balance cobalt along with conventional residual alloying elements and conventional incidental impurities.

2. The alloy as defined in claim 1, in which the conventional residual alloying elements and conventional incidental impurities include manganese present in an amount up to about 0.5 percent, silicon up to about 0.5 percent, boron up to about 0.1 percent and niobium up to about 2 percent.

3. The alloy as defined in claim 1, in which said chromium is present in an amount of about 23 percent to about 25 percent, said nickel is present in an amount of about 9 percent to about 11 percent, said iron is present up to about 1 percent, said molybdenum is present in an amount of about 1 percent to about 3 percent, tungsten is present in an amount of about 3.2 percent to about 3.8 percent, tantalum is present in an amount of about 3 percent to about 4 percent, titanium is present in an amount of about 0.2 percent to about 0.3 percent, zirconium is present in an amount of about 0.3 percent to about 0.6 percent, carbon is present in an amount of about 0.55 percent to about 0.65 percent and with the balance consisting essentially of cobalt.

4. A cobalt-base alloy consisting essentially of about 18 percent to about 26 percent chromium, about 7 percent to about 12 percent iron, up to about 2 percent nickel, about 1 percent to about 4 percent molybdenum, about 2.5 percent to about 4.5 percent tungsten, about 2 percent to about 5 percent tantalum, about 0.1 percent to about 0.4 percent titanium, about 0.1 percent to about 1.0 percent zirconium, about 0.4 percent to about 0.7 percent carbon and with the balance cobalt along with conventional residual alloying elements and conventional incidental impurities.

5. The alloy as defined in claim 4, in which said conventional residual alloying elements and said conventional incidental impurities include manganese up to about 1 percent, silicon up to about 1 percent, boron up to about 0.1 percent, and niobium up to about 2 percent.

6. The alloy as defined in claim 4, containing about 23 percent to about 25 percent chromium, about 9 percent to about 11 percent iron, up to about 1 percent nickel, about 1 percent to about 3 percent molybdenum, about 3.2 percent to about 3.8 percent tungsten, about 3 percent to about 4 percent tantalum, about 0.2 percent to about 0.3 percent titanium, about 0.3 per cent to about 0.6 percent zirconium, about 0.6 percent carbon with the balance consisting essentially of cobalt.

Claims

1. A COBALT-BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT 18 PERCENT TO ABOUT 26 PERCENT CHROMIUM, ABOUT 7 PERCENT TO ABOUT 12 PERCENT NICKEL, UP TO ABOUT 2 PERCENT IRON, ABOUT 1 PERCENT TO ABOUT 4 PERCENT MOLYBDENUM, ABOUT 2.5 PERCENT TO ABOUT 4.5 PERCENT TUNGSTEN, ABOUT 2 PERCENT TO ABOUT 5 PERCENT TANTALUM, ABOUT 0.1 PERCENT TO ABOUT 0.4 PERCENT TITANIUM, ABOUT 0.1 PERCENT TO ABOUT 1.0 PERCENT ZICRONIUM, ABOUT 0.4 PERCENT TO ABOUT 0.7 PERCENT CARBON AND THE BALANCE COBALT ALONG WITH CONVENTIONAL RESIDUAL ALLOYING ELEMENTS AND CONVENTIONAL INCIDENTAL IMPURITIES.

6. The alloy as defined in claim 4, containing about 23 percent to about 25 percent chromium, about 9 percent to about 11 percent iron, up to about 1 percent nickel, about 1 percent to about 3 percent molybdenum, about 3.2 percent to about 3.8 percent tungsten, about 3 percent to about 4 percent tantalum, about 0.2 percent to about 0.3 percent titanium, about 0.3 percent to about 0.6 percent zirconium, about 0.6 percent carbon with the balance consisting essentially of cobalt.