AU626581B2

AU626581B2 - Nickel-base single crystal superalloys

Info

Publication number: AU626581B2
Application number: AU41640/89A
Authority: AU
Inventors: Warren Tan King; Earl Warren Ross; Carl Stephen Wukusick
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1986-03-27
Filing date: 1989-09-20
Publication date: 1992-08-06
Anticipated expiration: 2009-09-20
Also published as: GB2234521B; DE3612628A1; GB2234521A; DE3612628C2; IL91633A; FR2731714A1; FR2731714B1; CA1337624C; AU4164089A

Description

I

Our Ref: 293949 626581

AUSTRALIA

Patents Act COMPLETE SPECIFICATION FORM

(ORIGINAL)

Application Number: Lodged: Complete Specification Lodged: Accepted: Published: oaoo 9 f 0 e 0 00 0000 0 a 0 o a a00 0 0 o a o 4 Priority: Related Art: Applicant(s): Address for Service: GENERAL ELECTRIC COMPANY 1 River Road, Schenectady, New York, U.S.A.

ARTHUR S. CAVE CO.

Patent Trade Mark Attornerys Level 10, 10 Barrack Street SYDNEY NSW 2000 Complete specification for the invention entitled -k \-zse cy"na ir\oy *40.0 0 0 00 0J 0 d 0 *CO The following statement is a full description of this invention, including the best method of performing it known to me:- -1 080U/gs i? i.

BACKGROUND OF THE INVENTION 'E nickel-base superalloys castable as single crystal Sarticles of manufacture, which articles are especially useful as hot-section components of aircraft gas Sturbine engines, particularly rotating blades.

The efficiency of gas turbine engines depends significantly on th operating temperature of the various engine components with increased operating temperatures resulting in increased efficiencies. The search for increased efficiencies has led to the development of heat-resistant nickel-base superalloys 1 which can withstand increasingly high temperatures yet maintain their basic material properties. The requirement for increased operating temperatures has ou. a also led to the development of highly complex cast 20 hollow shapes, blades and vanes, which provide o efficient cooling of the material used to produce such Se shapes.

The casting processes used with early generations of nickel-base superalloys, commonly wly i 13DV-8137 -2referred to as conventionally cast nickel-base superalloys, generally produced parts whose microstructures consisted of a multitude of equiaxed single crystals (grains) of random (nonoriented) crystallographic orientation with grain boundaries between the grains. Grain boundaries are regions of highly nonoriented structure only a few atomic diameters wide which serve to accommodate the crystallographic orientation difference or mismatch 10 between adjacent grains.

A high angle grain boundary (HAB) is generally regarded as a boundary between adjacent grains whose crystallographic orientation differs by more than about 5-6 degrees. High angle grain boundaries are regions 15 of high surface energy, on the order of several hundreds of ergs/cm and of such high random misfit that the structure cannot easily be described or modelled. Due to their high energies and randomness, high angle grain boundaries are highly mobile and are o 20 preferential sites for such solid-state reactions as diffusion, precipitation and phase transformations; thus, high angle boundaries play an important role in the deformation and fracture characteristics and .0 chemical characteristics resistance to oxidation 25 and hot corrosion) of polycrystalline metals.

0 Also, due to the high energies and disorder of HABs, impurity atoms are attracted preferentially (segregated) to high angle grain boundaries to the degree that the concentration of impurity atoms at the grain boundary can be several orders of magnitude greater than the concentration of the same impurity atoms within the grains. The presence of such high concentrations of impurity atoms at high angle grain boundaries can further modify the mechanical and chemical properties of metals. For example, in .i c 13DV-8137 -3nickel-base superalloys, lead and bismuth are deleterious impurities which segregate to the grain boundaries. At high temperatures, even small amounts a few ppm) of such impurities in the grain boundaries of nickel-base superalloys degrade the mechanical properties stress-rupture strength) and failure generally occurs at the grain boundaries.

In contrast to high angle grain boundaries, low angle grain boundaries, sometimes also called subgrain boundaries, are generally regarded as boundaries between adjacent grains whose ooo: crystallographic orientation differs by less than about o'°o 5 degrees. It is to be understood, however, that the classification of a boundary as high angle or low angle 15 may vary depending upon the person or organization doing the classification. For the limiting case of a low angle boundary (LAB) where the orientation difference across the boundary may be less than 1 o9O.O degree, the boundary may be described (modelled) in 20 terms of a regular array of edge dislocations, a tilt boundary. While the mismatch is technically that between any two adjacent grains, and not that of the 4, 0 boundary per se, the extent of the mismatch is commonly assigned to the boundary; hence the terminology of, for o 25 example, a 5 degree low angle boundary, which usages o shall be used herein interchangeably.

Low angle grain boundaries are more highly ordered and have lower surface energies than high angle grain boundaries. Higher order and lower energy result in boundaries with low mobility and low attraction for impurity atoms which, in turn, results in a lesser effect on properties, mechanical and chemical, compared to high angle grain boundaries. Thus, while no grain I boundaries constitute a preferred condition, low angle boundaries are to be preferred over high angle grain boundaries,

T--

13DV-8137 -4- Improvements in the ability of conventional superalloys to withstand higher temperatures without impairing other needed qualities, such as strength and oxidation resistance, was achieved through alloy development and the introduction of improved processing techniques. These improvements followed from findings that the strength of such superalloys, and other important characteristics, were dependent upon the strengths of the grain boundaries. To enhance such 10 conventional superalloys, initial efforts were aimed at strengthening the grain boundaries by the addition of various grain boundary strengthening elements such as carbon boron zirconium and hafnium (Hf) SI and by the removal of deleterious impurities such as 15 lead (Pb) or bismuth (Bi) which tended to segregate at and weaken the grain boundaries.

Efforts to further increase strength levels in conventional nickel-base superalloys by preferentially orienting the grain boundaries parallel to the growth or solidification direction were subsequently initiated. Preferential orientation of the grains t'.

1 6 generally results in a columnar grain structure of long, slender (columnar) grains oriented in a single crystallographic direction and minimizes or eliminates grain boundaries transverse to the growth or solidification direction. The process used, i.e., directional solidification had long been used for other purposes such as the manufacture of magnets and grain-oriented silicon steel for transformers. That process has been described and improved upon, for instance, in U.S. Patent 3,897,815 Smashey. The disclosures of all the U.S. Patents referred to herein are hereby incorporated by reference. 13 DV -8137 Compared with conventionally cast superalloy articles, directionally solidified (DS'd) articles exhibited increased strength when the columnar grains were aligned parallel to the principal stress axis due to the elimination or minimization of grain boundaries transverse to the direction of solidification. In addition, DS provided an increase in other properties, such as ductility and resistance to low cycle fatigue, due to the preferred grain orientation. However, reduced strength and ductility properties still existed in the transverse directions due to the presence of longitudinal columnar grain boundaries in such DS'd articles. Additions of Hf, C, 13, and Zr were utilized to improve the transverse grain boundary strength of 15 such alloys as was done previously in conventional oequiaxed nickel-base superalloys. However large additions of these elements acted as melting point depressants and resulted in limitations in heat treatment which did not allow the development of maximum strengths within such directionally solidified o superalloys.

It has been recognized for some time that o articles could be cast in various shapes as a perfect single crystal, thus eliminating grain boundaries altogether. A logical step then was to modify the DS 4, process to enable solidification of superalloy articles as single crystals to eliminate longitudinally extending high angle grain boundaries previously found in DS'd articles.

In the single crystal metallic alloy arts, it has heretofore been conventional teaching that elements such as boron, zirconium, and carbon are to be avoided, i.e. kept to the lowest levels possible with commercial melting and alloying practice and technology. For example, U.S. Patent 3,494,709 recites 13DV-8137 -6the deleterious effect of B and Zr, proposing limits of 0.001% and 0.01% for those elements, respectively.

U.S. Patent 3,567,526 teaches that the fatigue properties of single crystal superalloy articles can be improved by the complete removal of carbon.

In U.S. Patent 4,116,723, there is disclosed homogeneous single crystal nickel-base superalloy articles having no intentional additions of cobalt B, Zr or C which are said to have superior mechanical properties, creep and time to rupture, compared to similar nickel-base superalloys containing Co, C, B, and Zr. Therein it is taught that cobalt should be restricted to less than about and more preferably to less than about to preclude the 15 formation of deletcrious topologically close packed phases (TCP) o- and Further, it is taught therein that no single element of the group carbon, boron, and zirconium should be present in an amount greater than 50 ppm, that preferably the total of such 20 impurities be less than 100 ppm and, most preferably, that carbon be kept below 30 ppm and that B and Zr each be kept below 20 ppm. In any event, it is taught that carbon must be kept below that amount of carbon which will form MC type carbides. Subsequently, in U.S.

Patent 4,209,348 it was shown that 3-7% Co could be included in the single crystal nickel-base superalloys disclosed therein without forming TCP.

Another purpose in limiting C, B, and Zr is to increase the incipient melting temperature in relation to the gamma prime solvus temperature thus permitting solutionizing heat treatments to be performed at temperatures where complete solutionizing of the gamma prime phase is possible in reasonable times without causing localized melting of solute-rich regions.

Recently, however, it has been recognized, U.S. Patent 4,402,772, that the addition of hafnium in small 13DV-8137 -7amounts to certain of nickel-base superalloys for the casting of single crystal articles is effective, for example, in providing enhanced properties and enhanced heat treatability in that such articles have a greater temperature range between the gamma prime solvus and incipient melting temperatures than do most prior art single crystal articles.

SUMMARY OF THE INVENTION There is provided by the present invention nickel-base superalloys for producing single crystal articles having improved tolerance to low angle grain boundaries. The improved tolerance to low angle grain boundaries arises from the discovery that nickel-base superalloys suitable for casting as single crystal articles can, contrary to the teachings of the prior art, be improved by the addition of small, but G 6 oA° controlled, amounts of boron and carbon, and optionally hafnium, and is manifested principally by improved grain boundary strength. Additionally, the superalloys of this invention also possess an improved balance o between cyclic oxidation and hot corrosion resistance due primarily to the carbon and hafnium and an increased Al to Ti ratio.

I As one result of this increased grain boundary strength, grain boundary mismatches far greater than A o the 60 limit for prior art single crystal superalloys can be tolerated in single crystal articles made from the nickel-base superalloys of this invention. This translates, for example, into lower inspection costs and higher yields as grain boundaries over a broader range can be accepted by the usual inspection techniques without resorting to expensive X-ray techniques. The superalloys of this invention are especially useful when directionally solidified as i hot-section components of aircraft gas turbine engines, particularly rotating blades.

Y-rrn l^U~ 13DV-8137 -8- Broadly, the single-crystal superalloys of this invention consist essentially of about, by weight, 7-12% Cr, 5-15% Co, 0.5-5% Mo, 3-12% W, 2-6% Ta, Ti, 3-5% Al, 0-2% Cb, 0-2.0% Hf, 0.03-0.25% C and 0.002-0.050% B, the balance being nickel and incidental impurities.

DETAILED DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective schematic view of a blade member for use in a gas turbine engine; 10 FIGURE 2 is a perspective schematic view of a 0000 directionally solidified slab-like single crystal ingot marked for removal of blanks to be processed into oo0 Soo mechanical property test specimens; FIGURE 3 is a graph of comparative S0 15 stress-rupture life versus alloy boron content; o. FIGURE 4 is a graph of comparative stress-rupture life versus grain boundary misfit; and FIGURE 5 is a graph of external metal loss in .cyclic oxidation as a function of exposure time.

0 20 DETAILED DESCRIPTION OF THE INVENTION Nickel-base superalloys castable as single crystals have typically been used to manufacture p o n airfoil members, rotating blades and stationary vanes, for the hot section of aircraft gas turbine 25 engines. Such a blade member 10 is shown schematically Sin FIG. 1 and includes base (or root) portion 12 (shown 1 machined to a "fir-tree" configuration for attachment to a disk), platform portion 14, and aerodynamically curved airfoil portion 16. Blade member 10 may also be provided with an internal passage or passages through which a fluid (generally air) is circulated during operation of the turbine for purposes of cooling the blade. Frequently, the fluid is forced out of holes situated at the leading and trailing edges of the airfoil to effect skin cooling by laminar flow of the 13 DV -8 137 fluid over the surface of the airfoil portion 16.

Details of such cooling provisions are known in the art and are not shown here since they are unnecessary to an understanding of this invention. The art of directionally casting such blades is also known in the art as shown, for example, by U.S. Patent 3,494,709 and, therefore, also shall not be described here in detail.

Following directional solidification, which typically progresses downwardly toward base 12, in the direction indicated by arrow 18, the solidified blade ':4%,member 10 is inspected for the presence of grain *Poo4 boundaries and verification of the axial growth direction 18. The axial growth direction is determined by X-ray analysis (typically by the well-known Laue method) and for nickel-base superalloys is preferably plus or minus 15 degrees of the (001] crystal direction.

Heretofore, only low angle grain boundaries, Zo such as the one shown schematically at 20, up to a o maximum of about 60 mismatch across adjacent grains have been permitted in single crystal blades Skilled observers can generally visually detect LABs on the order of 0-30. Towards the maximum permissible ~25 mismatch of 60, however, visual techniques become unreliable and additional Laue patterns on either side of the boundary in question must be made. The Laue patterns are not inexpensive and due to current single crystal practice 3 to 4 Laue patterns generally are required per casting. Presently, due in part to uncertainties in detecting low angle grain boundaries, the yield of castings is only about It has now been discovered that nickel-base superalloys suitable for casting as single crystal articles can be improved by the addition of small, but 4 l13DV-8 137 controlled, amounts of boron and carbon, and optionally hafnium, yielding a new family of single crystal nickel -base superalloys.

The principal benefit, in addition to an improved balance betw,,en cyclic oxidation and hot corrosion resistance, following from this discovery is that low angle grain boundaries in single crystal articles made from the superalloys of the invention herein are stronger than their prior art single crystal articles. Therefore, LABs having greater than 60 of mismatch may be tolerated and accepted in such articles compared to about 60 maximum previously considered acceptable. Reduced inspection costs and increased yield of acceptable articles follows from the aforesaid improved tolerance to low angle grain boundaries. It will be appreciated that neither LAIBs nor HABs will be present in a true "single crystal." It will further be appreciated, however, that although there may be one or more low angle boundaries present in the single discussed herein reference shall still be made to single crystals.

as ladeAs noted above, single crystal articles such as bade10 are subjected to an X-ray test to determine orientation and to a visual test to determine the 25 presence (or absence) of low angle grain boundaries.

::*While the X-ray test must still be used with the new superaJlloys of this invention to determine orientation, the number of X-ray tests required to distinguish between HABs and LABs is expected to be greatly reduced or eliminated.

stated another way, any LAB may be greatex than 0 0 and the tolerance limits for accepting LABs visually can be increased up to about 20 0 for the airfoil articles made from the new superalloys of this invention and Laue determinations are only expected to be required for ruL, y 13DV-8137 -11boundaries greater than about 90. It should be noted that large boundary mismatches are acceptable in the new superalloys when compared to the approximately mismatches allowed in the prior ar alloys. In the root and platform areas, there will be no limitation on the boundaries, HABs will be acceptable, due to the increased strength of the boundaries in articles made from the superalloys of this invention and in recognition of the lower temperatures in the platform 10 and root portions compared to those in the airfoil o*7, portion. Thus, reference to a "single crystal article" herein shall be to an article at least a portion of o o o which shall be in the nature of a "single crystal." So Overall, the estimated casting yield of articles made 15 from the new superalloys is expected to increase to 75-85%.

It will be appreciated, therefore, that the new superalloys of this invention possess exceptional properties even when processing by DS techniques 20 results in articles having oriented high angle grain boundaries throughout. Exceptional properties are anticipated even when the superalloys of this invention are conventionally cast CCC) to produce articles having a plurality of randomly oriented grains with high angle S 25 grain boundaries therebetween.

o Accordingly, there is provided by this invention a new family of nickel-base superalloys castable as single crystal articles having improved tolerance to low angle grain boundaries consisting essentially of chromium, cobalt, molybdenum, tungsten, tantalum, titanium, aluminum, columbium, hafnium, carbon, boron and (optionally) hafnium in the percentages (by weight) set forth in Table I, below, the balance being nickel and incidental impurities.

1 13 DV-8137 -12- TABLE I ALLOY COMPOSITIONS (weight 40000.

640

GOOD

000 0000 o 0 00 0 00.0 00:, 0 0 0 00 41 0

QWO

Elements Cr Co Mo w Ta Ti Al Cb Hf

C,

B

Base Pr e fe rred 7-12 5-15 0.5-5 3-12 2-6 2-5 3-5 0-2 0-2.0 0.03-0.25 0.002-0.050 7-10 5-10 1-3 4-8 3-5 3-4 4-4.5 0-1 0105-0.5 0.03-0.1 0.002-0.020 9.5-10.0 7.0-8.0 1.3-1.7 5.75-6.25 4.6-5.0 3.4-3.6 4.1-4.3 0.4-0.6 0.1-0.2 0.05S-0. 07 0.003-0.005 Most Preferred In Table II there is set forth the compositions of the various alloys, including those of the present invention, referred to herein.

0 0 o 4, 0 04 4.

0 4.

4.

0 0 0 a 00~ 0. 4. 0 C *4 4 U~ 0 4' 4 4' 0.

C 4. 44 4 0 4 4' 0. 0.

404.. a TABLE II ALLOY COMPOSITIONS' (weight HEAT Cr Co 140 W Ta, TI Al Cb Hf C B Base 2 18 44 47 48 49 50 59

AA

BB

R125 RO3 1 Th 2

A

3 P1 9.3 9.2 9.8 9.6 9.8 9.7 9.7 9.6 9.7 10.1 8.0 9.0 14.0 7.5 7.5 7.5 7.5 7.6 7.5 7.5 7.4 7.5 5 .4I ,4.5 10.0 9.5 0 2 1 .5 6.0 .6 6.0 -5 6.0 .5 6.

6.0 .5 6.0 .5 6.1 .5 6.0 .5 6.0 4.2 .5 8.0 .0 7.0 .0 4.0 4.0 4.2 5.0 3.8 1.8 3.6 4.7 3.5 4.7 3.5 4.7 3.5 4.8 3.5 4.7 3.4 4.8 3.5 11.9 1.3 6.0 1.0 3.8 2.5 5.0 3.7 41.1 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.9 5.6 4.8 3.0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.10 0 0.15 0.15 0.15 0.20 0.19 0.15 0 0.06 0.06 0.05 0.05 0.05 0.05 0.0038 0 0.0018 0.0043 0.0030 0.0076 0.0046 0.0150 0.0150 0.1 1.5 0.11 0.17 e balance nickel plus erage of several heats us 0.030 Zr incidental impurities lr i 13DV-8137 -14- Shown schematically in FIG. 2 is the top portion of a slab-like ingot 30 directionally solidified in the direction of arrow 18' to produce material for testing. The material produced was either a single crystal which had no LABs or, as depicted in FIG. 2, had at least one LAB 20' parallel to solidification direction 18', or was conventionally DS'd to produce ingots having a plurality of HABs oriented parallel to solidification direction 18' (not 10 illustrated). The ingots produced so as to have a S"0 plurality of oriented HABs were .ikewise produced by the same DS process but without the use of the o techniques required to produce single crystals and will 0 0 be referred to herein simply as DS or DS'd material.

0:"2 15 For comparative purposes, some of the alloys of Table I were also cast conventionally to produce ingots having a plurality of randomly oriented grains with high angle grain boundaries in between.

The heat treatment method used with the 20 superalloys of the present invention to substantially 0 fully develop a duplex gamma prime structure was to slowly heat the as DS'd ingot (or article) to about 2310° F and hold thereat for about 2 hours to place the gamma prime phase into solid solution; cool at a rate of 1000 F to 150° F per minute to below about 19750 F then at a rate of about 75° F to 150 F per minute to o about 12000 F; reheat to about 1975' F for about four hours; cool at a rate of about 75° F to 1500 F per minute to about 1200" F; heat to about 16500 F for about 16 hours; and, lastly, cool to ambient temperature.

The aforementioned specimens for physical property measurements were fabricated in conventional fashion from bar-like sections 32 taken transverse to 4 13DV-8137 solidification direction 18' of the heat treated ingots. Each single crystal specimen from section 32 contained either no LABs or an LAB of known orientation established by X-ray analysis. Similarly, specimens from DS'd slabs contained a plurality of oriented grains and oriented high angle grain boundaries and specimens from CC slabs contained a plurality of randomly oriented grains and randomly oriented high angle grain boundaries.

10 By reference to FIG. 3 and Table III, it may 0o O, be seen that boron has been discovered, contrary to the teachings of the prior art, to be beneficial to the stress-rupture strength of single crystals and, with carbon, strengthens any LABs present in single crystals 15 made from the alloys of this invention. In FIGS. 3 and 4 and Tables III and IV, reference is made to of Perfect Crystal Life" which is the stress-rupture life of an alloy of the Base composition (Table II) DS'd to form no LABs and tested with its [110] direction 20 perpendicular to the DS direction (and parallel to the specimen stress axis) at the same conditions of stress and temperature as the superalloy for which it serves as the comparative standard. Also in some Tables, there is set forth for comparative purposes the stress-rupture lives of specimens of the Base composition having a LAB with the degree of mismatch shown and for specimens of the Base composition in the DS'd condition.

13DV-8137 -16- TABLE 111-A

TRANSVERSE

1 STRESS-RUPTURE PROPERTIES I STRESS-RUPTURE PROPERTIES NO. HEAT B Hf LAB S (ppm) (deg) TEMP STRESS LIFE ELONG (ksi) (hrs) R OF

A

C%)

I

0.0 0 01 o 0 to o a -0 p p *s 9 a a 0 0 4t 4 o o' o 0 0 1 2 3 4 6 7 8 15 9 11 12 13 20 14 16 17 18 25 19 21 22 23 47 47 48 48 so50 49 49 49 49 49 59 90 90 90 49 49 49 49 50 90 90 90 90 0.15 0.15 0.15 0.15 0.20 0.15 14.0 0.15 14.0 0.15 ~31 0.15 ,-31 0.15 15 0.20 13.6 0.15 11 0.15 14 0.15 16 0.15 14.0 0.15 14 0.15 15 0.15 15 0.20 12 0.15 11 0.15 14 0.15 14 0.15 16 12.6 11.9 9.2 12.2 12.03 1600 1600 1600 1600 1600 1500 1600 1600 1600 1600 1600 1600 1600 1600 1700 1800 1800 1800 1800 1800 1800 1800 1800 58 58 58 58 -55 75 58 58 58 58 58 58 58 58 45 30 24 30 28 30 24 30 30 24.6 0.4 0.0 10.3 0.6 1.2 146.0 0.6 0 77.7 1.3 0 175.1 2.4 1.8 185.02 2.1 304.04 3.8 48.8 1.3 0.6 46.3 1.8 0.6 109.8 0.9 1.2 347.9 1.9 1.8 380.1 3.9 24.9 171.4 1.8 168.0 2.5 3.7 92.2 2.5 0.7 108.7 1.9 1.3 124.7 2.5 0.6 33.3 0.9 0.0 234.05 NA NA 118.8 2.6 0.6 296.1 1.8 0 51.0 1.6 73.1 3.3 0.8 30 1 Transverse across LABs (or HABs) and transverse to solidification direction.

2 No failure in time shown was step loaded to 104.8 ksi/3 hrs then step loaded to 134.7 ksi/ failure in 1 min.

3 In radius section of specimen 4 No failure in time shown step loaded to 78 ksi/ failure in 4.7 addn'l hrs.

No failure in time shown step loaded to ksi/failure.

a a a a a a a a a p a a a a a a a.

a C a G. Q a a a a o Sb i b A A 4 4 a ba! U A a a a 44 a sac a a a TABLE III-B COMPARATIVE STRESS RUPTURE PROPERTIES NO. HEAT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

LIFE

(hrs) 24.6 10,3 146.0 77.7 175.1 185.02 304.04 48.8 46.3 109.8 347.9 380.1 171.4 168.0 92.2 108.7 124.7 33.3 234.05 118.8 296.1 51.0 73. 1 BASE ALLOY NO LA (hrs) W% BASE ALLOY LAB LI~E (deg) (hrs) BASE ALLOY DS'd (hrs) cc R (hrs) 150 150 150 150 150 150 150 150 150 150 150 150 150 150 90 100 375 100 250 100 375 100 100 16.4 6.9 97.3 51.8 116.7 123.3 202.7

HAD

73.2 231.9 253.4 114.3 112.0 102.4 108.7 33.3 33.3 93.6 118.8 79.0 51.0 73.1 2 2 15 2 2 2 2 2-15 3 3 3 3 3 3 3 3 3 3 11 36

NA

1 il- i J 13DV-8137 -18- That the superalloys of the invention have superior stress-rupture strengths compared to conventional single crystal superalloys at any given angle of mismatch from 0 to about 180 is shown in FIG.

4. Similarly, at any given level of of no LAB rupture life the superalloys of the invention can tolerate larger degrees of misfit, on the order of about 2 times, than can single crystal superalloys of the prior art. As may be noted from Table IV, even when DS'd to form HABs, the superalloys of the invention have superior stress-rupture strengths.

9 0 6 o a I 06 0e 6i

V

4 .4 ~4 4', I S I1~

I..

4 4 13DV-8137 -19- TABLE IV STRESS-RUPTURE STRENGTHS 1 (DS'd High Angle Boundary Specimens)

COMPARATIVE

STRESS-

RUPTURE

LIVES (HRS) STRESS-RUPTURE PROPERTIES BASE R OF NO DS CC HEAT B TEMP STRESS LIFE ELONG A LAB BASE (ppm) (ksi) (hrs) 110 47 0 1400 90 4.0 0.9 0.0 220 NA 100 1600 55 1.9 1.0 0.0 230 <3 1800 26 2.3 2.1 2.7 250 <1 2000 12 3.1 1.0 0.0 250 <4 48 20 1400 90 3.3 0.8 0.0 220 NA 100 1600 55 15.6 0.6 0.8 230 <3 1800 26 9.2 1.1 0.0 250 <1 2000 12 4.5 0.0 0.0 250 <4 30 1400 90 184.42 1.9 3.8 220 NA 100 1600 55 69.2 1.5 0.0 230 <3 .1800 26 65.6 1.0 0.0 250 <1 2000 12 9.1 1.6 1.3 250 <4 49 43 1400 90 92.53 3.7 6.2 220 NA 100 1600 55 133.8 1.3 2.5 230 <3 1800 26 50.0 1.2 0.0 250 <1 2000 12 2.9 1.9 2.0 250 <4 2000 12 1.8 NA 0.0 250 <4 59 75 1400 90 9Z.44 10.8 32.0 220 NA 100 1600 55 54.1 0.9 0.0 230 <3 1800 26 98.1 1.7 0.6 250 <1 2000 12 4.1 NA 0.6 250 <4 AA 1600 50 0.3 1 All transverse to DS direction except for CC 2 Step Loaded 3 Step Loaded 4 Step Loaded to 100 KSI to 110 KSI 110 KSI 21.8 hrs 2.2 hrs 21.9 hrs 120 KSI 2.2 hrs to 110 KSI 120 KSI 2.1 hrs 130 KSI .1 hrs .8 hrs 130 KSI .2 hrs 140 KSI .2 hrs to 120 KSI 140 KSI 1.3 .2 hrs 150 KSI .3 hrs 4 4

A

I atI ft it 4 41 '4 d^ 0 4 4% 6 4 a hi 13DV-8137 Table V presents the results of cyclic oxidation tests on uncoated 1/4" x 3" long round pin specimens conducted under the conditions shown in the table using a natural gas flame at Mach 1 gas velocity. The specimens were rotated for uniform exposure and cycled out of the flame once per hour to coul the specimens to room temperature. External metal loss was measured on a section cut transverse to the length dimension of the specimen. Metal loss per side was found by dividing the difference between the pin diameter before and after test by two. The data in the table are the average of two such measurements at o 0 to each other across the diameter of the specimen.

The data of Table V are presented in graphical 15 form in FIG. 5. It may be noted that while the o:.oo: resistance of the superalloys of the invention to cyclic oxidation is not as good as exemplary alloy BB, the superalloys of the invention possess highly acceptable resistance to cyclic oxidation which is an improvement over the cyclic oxidation resistance of the Base alloy and R125. The improved cyclic oxidation o O. resistance of the superalloys of this invention compared to that of the Base superalloy is believed to be due primarily to the increased Al to Ti ratio.

Comparison of the data for heats 44 and 49/50 shows the further increased cyclic oxidation resistance provided by the addition of hafnium.

o P-mIR a a a a a a a 0 a a a a *C 0 a to at a a.

a a an a C a C. C a a a a 0 0 0. C 0 o 0,0 C a a an. a 0 C Coo a a TABLE V CYCLC OXIDATION TESTS (MACH 1) CYCLED TO RT ONCE/HR EXTERNAL METAL LOSS (I4ILS/SIDE)

HEAT

47 48 59 Base 1

AA

47 48 49 59 Base 1 R125 TIME (H-RS) 157 181 200 TEMP 2075 2075 2075 2075 2075 2075 2150 2150 2150 2150 2150 2150 2150 71 89 a 0 [7.5] 0.25 0 15.0 4.0 0.5 3.7 0.5 0.3 99 133 207 5.5 6.0 5.7 5.5 13.5 36.1 39.5 0.25 0.5 [10.5] 0.5 0.25 22.5 6.5 20.3 21.3 18.8 18.5 23.8 53.5 58.8 0.25 [7.5)2 1.0 [18.3) 0.5 36.5 *10.0 23.5 25.8 25.G 24.8 30.8 25.5 29.5 27.1 28.3 34.0 73.2 83.8 22.2 26.3 1 Average of' several heats 2 I indicates depth of single pit (mils) 13DV-8137 -22- Table VI presents the results of hot corrosion tefsts on uncoated 1/8" x 2" long round pin specimens conducted under the conditions shown in the table using a JP-5 fuel-fired flame with salt in parts per million (ppm) shown added to the combustion products. The specimens were rotated for uniform exposure and were cycled out of the flame to room temperature once every day. The data of Table VI show that the presence of carbon in the superalloys of the invention is required for hot corrosion resistance and that the hot corrosion resistance of the superalloys of the invention is superior to that of alloys AA and BB prior art single crystal alloys.

The superalloys of the invention thus have an improved balance between cyclic oxidation and hot corrosion resistance due primarily to the carbon and hafnium and an increased Al to Ti ratio in comparison to the Base alloy.

TABLE VI C C HOT CORROSION TESTS TEMP SALT TIME METAL LOSS HEAT (ppm) (H-rs) (mils/side) 44 1600 1 613 1.7 Base 1600 1 613 18 1600 2 40Z 36.0 44 1600 Z 620 Base 1600 2 620 AA 1600 2 470 11.8 BB 1600 2 620 28.0 44 1700 5 478 6.6 Base 1700 S 478 11.3 AA 1700 S 478 30.1 c ca ra~aur~-~-r~ 13DV-8137 -23- There being extant evidence that the inventive concepts herein of adding small, but controlled, amounts of boron and carbon, and optionally hafnium, to improve the low angle grain boundary tolerance of nickel-base superalloys suitable for casting as single crystal articles are applicable to other nickel-base single crystal superalloys, it will be understood that various changes and modifications not specifically referred to herein may be made in the invention herein described, and to its uses herein described, without departing from the spirit of the invention particularly as defined in the following claims.

Sooo 00oo00 00ooo 6 0 0000 0ooo 0 o 000 000 a i a 0 0 0 uo a e or e ;D a 0r 0 o 0 0 00 OVu4 «u o 0o w 0 e 0u 0 000$« 600 0 6 00U i 1 i ii

Claims

1. A nickel-base superalloy consisting of, in percentages by weight, 7-12 Cr, 5-15 Co, 0.5-5 Mo, 3-12 W, 2-6 Ta, Ti, 3-5 Al, 0-2 Cb, 0-2.0 Hf, 0.03-0.25 C and 0.002-0.-050 B, the balance being nickel and incidental impurities.

2. The superalloy of claim 1 consisting of, in percentages by weight, 7-10 Cr, 5-10 Co, 1-3 Mo, 4-8 W, 3-5 Ta, 3-4 Ti,

4-4.5 Al, 0-1 Cb, 0.05-0.5 Hf, 0.03-0.1 C and 0.002-0.020 B, the balance being nickel and incidental impurities. 3. The superalloy of claim 2 consisting of, in percentages by weight, 9.5-10.0 Cr, 7.0-8.0 Co, 1.3-1.7 Mo, 5.75-6.25 W, 4.6-5.0 Ta, 3.4-3.6 Ti, 4.1-4.3 Al, 0.4-0.6 Cb, 0.1-0.2 Hf, 0.05-0.07 C and 0.003-0.005 B, the balance being nickel and incidental impurities. 4. A single crystal article of manufacture the overall composition of which is a nickel-base superalloy consisting o of, in percentages by weight, 7-12 Cr, 5-15 Co, 0.5-5 Mo, 3-12 W, 2-6 Ta, 2-5 Ti, 3-5 Al, 0-2 Cb, 0-2.0 Hf, 0.03-0.25 C and 0.002-0.050 B, the balance being nickel and incidental impurities, wherein any low angle grain boundaries present in said article are greater than 0°.

5. The article of claim 4 wherein any low angle grain boundaries present therein are in the range of from 0 to

6. The article of claim 5 which is an airfoil member for a S" gas turbine engine.

7. The article of claim 4 consisting of, in percentages by weight, 7-10 Cr, 5-10 Co, 1-.3 Mo, 4-8 W, 3-5 Ta, 3-4 Ti, 4-4.5 Al, 0-1 Cb, 0.05-0.5 Hf, 0.03-0.1 C and 0.002-0.020 B, oX. the balance being nickel and incidental impurities.

8. The article of claim 4 consisting of, in percentages by weight, 9.5-10.0 Cr, 7.0-8.0 Co, 1.3-1.7 Mo, 5.75-6.25 W, 4.6-5.0 Ta, 3.4-3.6 Ti, 4.1-4.3 Al, 0.4-0.6 Cb, 0.1-0.2 Hf, 0.05-0.07 C and 0.003-0.005 B, the balance being nickel and incidental impurities.

9. An article of manufacture the overall composition of which is a nickel-base superalloy consisting of, in percentages by weight, /-12 Cr, 5-15 Co, 0.5-5 Mo, 3-12 W, SRA 2-6 Ta, 2-5 Ti, 3-5 Al, 0-2 Cb, 0-2.0 Hf, 0.03-0.25 C and 0.002-0.050 B, the balance being nickel and incidental j '4'i o y 0132h:AB 25 impurities, at least a portion which is a single crystal. The article of claim 9 wherein any low angle grain boundaries present in said single crystal portion are- greater than 00.

11. The article of claim 10 wherein any low angle grain boundaries present in said single crystal portion are in the range of from 0 to

12. The article of claim 10 as an airfoil member for a gas turbine engine at least the airfoil portion of which is said single crystal portion.

13. The article of claim 10 consisting of, in percentages by weight, 7-10 Cr, 5-10 Co, 1-3 Mo, 4-8 W, 3-5 Ta, 3-4 Ti, 4-4.5 Al, 0-1 Cb, 0.05-0.5 Hf, 0.03-0.1 C and 0.002-0.020 B, the balance being nickel and incidental impurities.

14. The article of claim 13 consisting of, in percentages by weight, 9.5-10.0 Cr, 7.0-8.0 Co, 1.3-1.7 Mo, 5.75-6.25 W, 4.6-5.0 Ta, 3.4-3.6 Ti, 4.1-4.3 Al, 0.4-0.6 Cb, 0.1-0.2 Hf, 0.05-0.07 C and 0.003-0.005 B, the balance being nickel and incidental impurities. An article of manufacture the overall composition of which is nickel-base superalloy consisting of, in percentages by weight, 7-12 Cr, 5-15 Co, 0.5-5 Mo, 3-12 W, 2-6 Ta, 2-5 Ti, 3-5 Al, 0-2 Cb, 0-2.0 Hf, 0.03-0.25 C and S0.002-0.050 B, the balance being nickel and incidental impurities.

16. The article of claim 15 which is directionally solidified.

17. The article of claim 15 which is cast.

18. The article of claim 15 wherein said composition consists of, in percentages by weight, 7-10 Cr, 5-10 Co, 1-3 Mo, 4-8 W, 3-5 Ta, 3-4 Ti, 4-4.5 Al, 0-1 Cb, 0.05-0.5 Hf, 0.03-0.1 C and 0.002-0.020 B, the balance being nickel and incidental impurities.

19. The article of claim 15 wherein said composition consists of, in percentages by weight, 9.5-10.0 Cr, 7.0-8.0 Co, 1.3-1.7 Mo, 5.75-6.25 W, 4.6-5.0 Ta, 3.4-3.6 Ti, 4.1-4.3 Al, 0.4-0.6 Cb, 0.1-0.2 Hf, 0.05-0.07 C and 0.003-0.005 B, 0132h:AB -26 the balance being nickel and incidenmtal impurities. DATED this 27th day of June, 1991. GENERAL ELECTRIC COMPANY By Its Patent Attorneys ARTHUR S. CAVE CO. T44