US3519503A - Fabrication method for the high temperature alloys - Google Patents

Description

3,519,503 FABRICATION METHOD FOR THE HIGH TEMPERATURE ALLOYS Joseph B. Moore, Jupiter Tequesta, and Roy L. Athey, North Palm Beach, Fla., assignors to United Aircraft Corporation, East Hartford, C-onn., a corporation of Delaware No Drawing. Filed Dec. 22, 1967, Ser. No. 692,705 Int. Cl. C22f 1/18 U.S. Cl. 148--11.5 14 Claims ABSTRACT OF THE DISCLOSURE The high strength, difficult to forge alloys, particularly those adapted to gas turbine engine use, are processed in compression under controlled conditions of temperature and reduction to place them in a temporary condition of low strength and high ductility and are subsequently forged to the desired configuration in hot dies at a temperature where the temporary condition of low strength and high ductility is maintained. The forged parts are then returned to their normal condition of high strength and hardness by conventional heat treatment. The material processing and part forging are usually accomplished below but within about 450 F. of the normal recrystallization temperature of the alloy.

BACKGROUND OF THE INVENTION The present invention relates in general to the high strength, high temperature alloy field and, more particularly, to fabrication methods utilizing such alloys.

In the gas turbine engine industry, to which the present invention has particular application, the engine design criteria require the use of alloys with good high temperature strength and oxidation-erosion resistance. In response to the need, a number of alloys have been developed and used. Unfortunately, however, while the high temperature strength demands have been satisfied, they have generally been achieved only at the expense of alloy fabricability, and in the manufacture of jet engines, comprising thousands of individual parts of intricate shape formed to close tolerance, fabricability of the alloy is a major factor in determining the extent of its utility. While in many industries the solution to the fabricability problem may be conveniently provided by alteration of the alloy chemistry, there are so many related criteria imposed on the gas turbine engine alloys that improvements in fabrication methods are necessarily made, if at all, despite the alloy chemistry.

SUMMARY OF THE INVENTION The present invention describes an improved method of fabricating the high strength, difiicult to work alloys, whereby they may be readily forged to close tolerances to product articles in a wide variety of intricate shapes. Briefly described, the present method involves initially working the alloy in compression at a temperature usually below but approaching the normal recrystallization tem perature of the alloy thereby lowering its recrystallization temperature and producing a very fine grain size; forging the material to the desired configuration in hot dies at a temperature below the normal recrystallization temperature; and subsequently heat treating the forged article to restore the alloy to its high strength condition. In some cases the grain size following the initial working of the alloy is so fine that magnification of 10,000 diameters is required to resolve the grain structure.

In a particular preferred embodiment of the invention, the high strength gas turbine alloys are: worked in compression at a temperature within about 450 F. of their United States Patent O 'ice normal recrystallization temperature, as by extrusion at a ratio exceeding about 4 to 1; forged in hot dies at a temperature between about 1400 F. and their normal recrystallization temperature; and subsequently heat treated to restore the alloy to its preferred condition of high strength and hardness.

In a more preferred embodiment, the strong precipitation hardened nickel base and titanium base alloys are worked in compression and forged below but within about 200 F. of their normal recrystallization temperature in hot dies in an inert atmosphere, and subsequently heat treated to restore their high strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The initial development work was directed to the improvement in the fabrication techniques utilized with the titanium base alloys and the precipitation-hardened nickel base superalloys. Representative of the elements of particular interest are those nickel base alloys designated in the industry as Mar M 200, IN100, Inconel 718, Waspaloy, Astroloy, Udimet 500, Rene 41, Inconel X and Inconel 625 and the titanium base alloys, Ti-6Al-4Mo, Ti-8Al-1Mo-1V and Ti-6Al-2Sn-4Zr-2Mo. In the discussion which follows it will be convenient to make reference to several of these alloys, the nominal composition, by weight, of which is as follows:

IN10% chromium, 15% cobalt, 4.5% titanium, 5.5% aluminum, 3% molybdenum, .17% carbon, .75% vanadium, .015% boron, .05% zirconium, balance nickel Waspaloyl9.5% chromium, 13.5% cobalt, .07% carbon, 3% titanium, 1.4% aluminum, 4% molybdenum, .005 boron, .08% zirconium, balance nickel Astroloy15.5% chromium, 17% cobalt, .07% carbon, 3.5% titanium, 4.0% aluminum, 5.0% molybdenum, .025 boron, balance nickel Titanium 8-1-17.9% aluminum, 1.0% molybdenum,

1.0% vanadium, balance titanium The precipitation hardened alloys are those which have been strengthened by the precipitation or aging of a second phase from a matrix that has been heated high enough to take the second phase into solid solution. In the nickel base alloy system the precipitated phase usually contains aluminum, titanium or columbium, or some combination thereof. These alloys find particular utility in the hot section of gas turbine engines, the IN100 alloy, for example, often being utilized in vanes and blades, while turbine disks may be formed of Waspaloy. In general, the alloys are strong and hard.

In terms of hardness, most of the nickel base superalloys have a hardness at room temperature in the range of Rockwell C 38 to 44. A low carbon structural steel is about Rockwell C 20, a high carbon tool steel about Rockwell C 65. In the condition of high ductility, as hereinafter discussed in greater detail, the nickel base superalloys are in the range of Rockwell C 38-44 at room temperature.

Of the three nickel base alloys described in detail, IN100 is the strongest. This alloy, specifically designed for casting application, is one of the most difficult to work using conventional forging practices. Because of its resistance to deformation and strength at high temperatures it is normally utilized only in the cast condition, blades and vanes being fabricated therefrom by investment casting techniques which can be adapted to provide parts of precise dimension. While it would be desirable to utilize the strength properties of this alloy in other applications, such as turbine disks, a wrought microstructure is usually preferred and, accordingly, the IN100 alloy is not presently used in the fabrication of disks or similar components. Even the lower strength materials which can be forged, such as Waspaloy, are so worked at the present time only with great difficulty in heavy presses and hammers and to relatively simple shapes. Consequently, subsequent machining of most if not 'all surfaces is required.

The initial effort was directed toward improved fabrication techniques for the IN100 alloy which, as mentioned, is one of the strongest alloys and, concomitantly; one of the most difficult to work'by conventional techniques. Despite the fact that this alloy as formulated is resistant to deformation, it was found that a certain combination of fabrication parameters could be applied to the IN100 alloy whereby it could be readily forged to close tolerances'and very complex shape. Utilizing the discovered techniques, it has been found possible to stretch IN100 test specimens to over a 1300% elongation. The results have been so promising that it is now considered perfectly feasible to forge the IN100 alloy into components such as turbine disks, and the forging may be accomplished in relatively conventional apparatus. Perhaps even more significantly, it now appears probable that not 4 only can these alloys be readily forged into components such as 'turbine'disks", but also that the disks can be'made with the blading formed integral therewith. And it will be remembered that the IN100 chemistry is such that this alloy has previously been considered virtually unforgeable. 1

Illustrative of the significance of the improvement in forgeability of the alloys processed by this technique is the fact that, while the stress required to press forge conventional Astroloy to a disk configuration at 2150 F. is in the range of 45,000 p.s.i., the processed Astroloy of the present invention can be press forged at 1900" F. and approximately 1200 p.s.i. This is a reduction in stress of greater than 37 to 1 along with a 250 F. reduction in temperature.

Representative date from a number of tests performed with the IN100 alloy to determine the preferred fabrication parameters are set forth in Table I. Similar data are provided for the Astroloy and Waspaloy materials in Tables II and III, respectively, and for titanium alloy 81-1 in Table IV. Tensile test results for the various materials are set forth in Tables V, VI and VII.

TABLE I.STRESS RUITURE TEST RESULTS IN100 BAR STOCK Test Type Reduction Reduction Test Percent Percen t No. reduction ratio temp. (F.) temp. (F.) elong. RA

1 Extgusion... 60w 1 2, 100 1, 800 326 99+ 8 do 5 3 tol 9 do 5.3t01 3 step forging at.-.

1 Plus TABLE II.STRESS RUPTURE 'SIEE IOSgKRESULTS OF ASTROLOY BAR T t T Rettlue- Rectiuc- Test es ype ion ion tem Percent P No. reduction ratio temp. (F.) (F elong. ft iql 1 Rolling 2.6-1 1, 025 1,700 515 99+ 2. 8-1 1, s25 3 525 90+ 5 0 4 d0 7. 3-1 1, 925 1, 700 420 03 1 2% 27s 99+ 98 07 5 .410 7. 3-1 1, 950 11 700 4011 00+ i038 22% 99+ 2 9 Extrusion 10-1 1,025 1, 025 64 55 1 1 Plus.

2 N 0 failure.

TABLE III.STRESS RUPTURE TEST RESULTS WASPALOY BAR STOCK Reduc- Reduc- Test Test Type tion tion temp. Percent Percent No. reductlon ratio temp. (F.) (F.) elong. RA

4-1 1 1,725 Plus 1, 725 99 93 4-1 1 1,725 Plus 1, 825 235 99+ 7.3-1 1,800 Plus 1, 700 225 99+ 1 Plus.

TABLE IV.STRESS RUPTURE TEST RESULTS TITANIUM ALLOY 8-1-1 BAR STOCK Reduc- Reduc- Test Test Type tion tion temp. Percent Percent No. reduction ratio temp. (F.) (F.) elong. RA

Since the rupture testing was in air, tests above 1500 creasing the strength and lowenng the ductility. This con- F. resulted 1n oxygen diffusion into the base metal 1nditlon requlred continuous uploading of specimens.

TABLE V.TENSILE TEST RESULTS ASTROLOGY BAR STOCK Test Type Reduction Reduction Test Flow Percent Percent Strain No. reduction ratio temp. (F.) temp. stress elong. RA rate, min.

1 Rolling 2.6-1 1,900 1,700 58,400 278 99.7 5.40

2.8-1 1.850 2- 2.8-1 1, 850 1, 700 28, 100 283 99. 7 0. 67 2.8-1 1, 850 1. 800 31,400 207 99. 6 5. 40 2.8-1 1, 850 1.800 35. 400 473 99. 7 5. 40 2.8-1 1, 850 1,800 14. 250 390 99.4 0. 67 2.8-1 1, 850 1, 900 22, 700 453 99. 2 5. 40 2.8-1 1,850 1, 900 13,200 1,025 99 0 0. 67 3 2.8-1 1,850 1 900 8. 450 790 98 3 0.20 0 28-1 1,850 2,000 16,250 267 99 1 5.40 2.8-1 1,850 2.000 6. 230 860 97 5 0. 67 11 2.8-1 1,850 2,100 14.050 163 99 2 5. 40 12 2.8-1 1 850 2,100 8, 250 171 99 3 0. 67 7.3-1 1,900 1,700 67,000 81 3 99 4 5. 40 14 7.3-1 1,900 1,700 40,500 145 99 7 67 1 7.3-1 1,900 00 33,700 8 99 5 5. 40 7.3-1 1, 900 1,800 14,850 447 99 6 0. 67 7.3-1 1,900 1, 900 25,000 500 99 5 5. 40 7.3-1 1,900 1,900 11,000 1,335 99 0 0. 67 19 7.3-1 1, 900 1, 900 4, 800 0. 20 20 7.3-1 1,900 1,900 2. 410 1,275 99 0 0.07 7. 3-1 1, 900 1, 900 803 0. 02 7.3-1 1, 900 2, 000 16, 660 191 99.1 5. 40 7. 3-1 1, 900 2, 000 8, 640 584 97. 0 0. 67 7.3-1 1, 900 2. 100 13, 650 159 98. 9 5. 40 7. 3-1 1. 900 2, 100 8, 250 147 99. 2 0. 67 8. 5-1 1, 900 1. 900 11, 800 470 99. 3 0. 67 8. 5-1 1, 900 1, 900 13, 600 500 99. 6 0. 67 2g 8. 5-1 1, 900 1, 900 14, 000 410 99. 5 0. 67 29 8. 5-1 1, 900 1, 900 10. 600 915 99.4 0. 67 8. 5-1 1, 900 1, 900 11,600 747 99. 7 0. 67 31. 8. 5-1 1, 900 1, 900 10,900 910 99. 7 0. 67 2 8. 5-1 1. 900 1, 900 11, 200 896 99. 7 0. 67 8. 5-1 1, 900 1. 900 10,500 685 99.6 0. 67 34 8. 5-1 1,900 1 900 13,000 460 99.7 0. 67 8. 5-1 1, 900 .900 12, 550 484 99. 6 0. 67 36 8. 5-1 1, 900 1, 900 11, 100 667 99. 5 0. 67 8. 6-1 1, 900 1. 900 14. 400 455 99. 5 0. 67 8. 5-1 1, 900 1, 900 14, 600 350 99. 5 0. 67 8. 5-1 1, 900 1, 900 10,800 668 99. 5 0. 67 8. 5-1 1. 900 1, 900 2 8, 820 530 99.4 0. 67 8. 5-1 1, 900 1, 900 7 8, 430 530 99. 5 0. 67 42- 8. 5-1 1, 900 1, 900 2 9, 730 420 99.6 0. 67 43- 3. 5-1 1, 900 1, 900 B 10, 600 732 99. 6 0. 67 8. 5-1 1, 900 1, 900 2 11,100 535 99.6 0. 67 8. 5-1 1, 900 1, 900 2 9,800 648 99. 7 0. 67 4 8.5-1 1,990 1,900 2 9 600 383 99.7 0.67 47 8. 5-1 1, 900 1, 900 2 11,500 355 99.6 0. 67 4s 8. 5-1 1, 900 1, 900 2 11, 300 302 99.8 0. 67 40 8. 5-1 1, 900 1, 900 2 11, 000 450 99. 7 0. 67 50 8. 5-1 1, 900 1, 900 7 10,700 517 99. 7 0. 67 51- 8 5-1 1.900 1 7 12,600 390 99.6 0. 67 5 do 8 5-1 1,950 .900 14,400 288 99.5 0.67

See footnotes at end of tables.

TABLE V-Cntinued Test Type Reduction Reduction Test Flow Percent Percent Strain No. reduction ratio temp. (F.) temp. stress eiong. RA rate, min.

8. -1 1, 950 1, 900 16, 400 248 99. 0. 67 8. 5-1 1, 950 1, 900 16,300 410 99.2 0. 67 8. 5-1 1, 950 1, 900 14, 300 402 99. 4 O. 67 8. 5-1 1, 950 1, 900 13, 800 365 99. 5 0. 67 8.5-1 1,950 1, 900 11, 800 522 99. 4 0. 67 8. 5-1 1, 950 1, 900 16, 100 448 99. 4 0. 67 8. 5-1 1, 950 1, 900 19, 000 270 99. 1 O. 67 8. 5-1 1, 950 1, 900 15, 200 500 99. 2 0. 67 8. 5-1 1, 950 1,900 14, 300 363 99. 5 0. 67 8. 5-1 1, 950 1, 900 13, 500 367 99. 5 0. 67 8. 5-1 1, 950 1, 900 15. 500 321 99. 5 0. 67 8. 5-1 1, 950 1, 900 20, 400 220 99. 4 0. 67 8. 5-1 1, 950 1, 900 15, 600 460 99. 4 0. 67 8. 5-1 1, 950 1, 900 14,200 532 99. 5 0. 67 8. 5-1 1,950 1, 900 2 13, 200 315 99. 6 0. 67 8. 5-1 1, 950 1, 960 2 13, 200 500 99. 7 0. 67 8. 5-1 1, 950 1, 900 2 13, 500 215 99. 6 0. 67 8. 5-1 1, 909 1, 900 2 14, 500 272 99. 6 0. 67 8. 5-1 1, 900 1,900 2 13, 000 260 99.6 0.67 8.5-1 1,900 1,900 2 14,400 182 99. 6 0.67 8. 5-1 1, 900 1, 900 2 14, 400 345 99. 5 0. 67 8. 5-1 1, 900 1, 900 2 13,800 202 99. 5 0. 67 8. 5-1 1, 900 1,900 2 13, 800 452 99. 5 0. 67 8. 5-1 1, 900 1, 900 2 14, 300 340 99. 5 0. 67 8. 5-1 1, 900 1, 900 2 14, 600 381 99. 6 0. 67 8. 5-1 1, 900 1, 900 2 14, 200 313 99. 6 0. 67 1 Plus. 2 Transverse specimens.

TABLE VI.-TENSILE TEST RESULTS WASPALOY BAR STOCK Test Type Reduction Reduction Test Flow Percent Percent Strain No. reduction ratio temp. (F.) temp. stress elong. RA rate, min

8. 5-1 1, 765 1,800 22, 400 101 99. 7 0. e7 8. 5-1 1, 765 1, 800 18, 650 228 99. 8 0. 67 8. 5-1 1, 765 1, 800 21, 600 169 99. 8 0. 67 8. 5-1 1, 765 1, 800 24, 700 114 99. 7 0. 67 8. 5-1 1, 765 1, 800 28, 600 99. 6 0. 67 8. 5-1 1,765 1,800 29, 400 45 9s. 5 0. 67 8. 5-1 1, 765 1, 800 19, 300 119 99. 4 0. 67 8. 5-1 1, 765 1, 800 22, 400 156 99. 6 0. 67 8. 5-1 1, 765 1,800 24, 700 83 99. 1 0. 67 8. 5-1 1, 765 1, 800 23, 700 84 99. 3 '9. 67 8. 5-1 1, 765 1, 800 400 99. 6 0. 67 8. 5-1 1,765 1, 800 20,600 so 99. 7 0. 67 8. 5-1 1, 765 1, 800 28, 300 99. 1 0. 67 8. 6-1 1, 765 1, 800 32, 900 81 97. 2 0. 67 8. 5-1 1, 765 1, 800 16, 000 295 99. 8 0. 67 8. 5-1 1, 765 1, 800 1 17, 500 99. 8 0. 67 8.5-1 1,765 1,800 1 15, 700 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 16, 800 113 99. 8 0. 67 8. 5-1 1, 765 1, 800 1 16, 350 166 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 23,000 72 99. 6 0. 67 8. 5-1 1, 765 1, 800 1 19, 850 135 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 17, 167 99. 8 0. 67 8. 5-1 1, 765 1, 800 1 23, 800 70 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 17, 200 131 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 18, 350 147 99. 7 0. 67 8. 5-1 1, 765 1, 800 1 18, 500 117 99. 7 0. 67 8. 6-1 1, 765 1, 800 1 15, 500 107 99. 6 0. 67 8. 5-1 1, 775 1, 800 32, 700 76. 5 99. 7 0. 67 8. 5-1 1, 775 1, 800 23, 900 83. 5 99. 8 0. 67 8. 5-1 1, 775 1, 800 24, 100 150 99. 8 O. 67 8. 5-1 1, 775 1, 800 23, 600 104 99. 8 0. 67 8. 5-1 1, 775 1, 800 28, 900 85. 6 99. 7 0. 67 8. 5-1 1, 775 1, 800 27, 100 106 99. 8 0. 67 8. 5-1 1, 775 1, s00 26, 100 114 99. 7 0. e7 8. 5-1 1, 7 75 1, 800 300 119 99. 8 0. 67 8. 5-1 1, 775 1, 800 22, 600 104 99. 8 0. 67 8. 5-1 1, 775 1, 800 22, 500 133 99. 8 0. 67 8. 5-1 1, 775 1, 800 26, 960 94 99. 7 0. 67 8. 5-1 1, 775 1, 800 24, 200 118 99. 7 0. 67 8. 5-1 1, 775 1, 800 20, 800 182 99. 8 0. 67 8. 5-1 1, 775 1, 800 200 177 99. 8 0. 67 8. 5-1 1, 775 l, 800 29, 906 87 99. 7 0. 67 8. 5-1 1, 775 1, 800 1 23, 200 75. 7 99. 6 0. 67 8. 5-1 1, 775 1, 800 1 20, 406 93. 5 99. 7 O. 67 8.5-1 1, 775 1,800 1 20, 300 103 99.8 0. 67 8. 5-1 1, 775 1, 800 1 22, 100 75 99. 8 0. 67 8. 5-1 1, 775 1, 800 1 21, 809 97. 5 99. 6 0. 67 8. 5-1 1, 775 1, 800 1 22, 000 110 99. 7 0. 67 8.5-1 1, 775 1, 800 1 22, 200 85 99. 7 0. 67 8. 5-1 1, 775 1, 800 1 23,860 82 99. 5 0. s7 8. 5-1 1, 775 1, 800 1 24, 500 62 99. 6 0. 67 8. 5-1 1, 775 1, 800 1 18, 700 119 99. 7 0. 67 8. 5-1 1, 775 1, 800 1 19, 750 128 99. 6 0. 67 8. 5-1 1, 775 1, 800 1 22, 600 73 99. 5 0. 67

1 Traverse specimen.

TABLE VIL-TENSILE TEST RESULTS Ti 8-1-1 BAR STOCK Test Type Reduction Reduction Test Flow Percent Percent Strain No. reduction ratio temp. temp. stress elong. RA rate, min.

In addition to the aforementioned tests, a number of actual forgings were made. In one test an IN100 alloy bar was extruded at 2050 F. using 5.3 to 1 reduction to provide a cylindrical billet two inches in diameter and four inches in length. It was pressed in heated dies at 1900 F. and 40 tons pressure with no dwell time to produce a shaped pancake 5 /3 inches in diameter. A Similar specimen forged at 1900 F. in heated dies at 60 tons pressure with a three minute dwell produced a 6 inch diameter pancake. Following one such test it was discovered that the die had developed a hairline crack which was exactly reproduced in the pressed pancake in the form of a thin walled fin. A further indication of the ductility of the material was the fact that grain structure evident on the surface of the die was reproduced on the exterior of the pancake. In later forging experiments a similarly produced billet was forged in a die designed to cause metal flow diametrically inward and then axially forward into the die to form a thin annular flange portion on the end of the pressed article. This particular forging experiment was selected as representative of one of the more difiicult types of forging, and the inward and forward flow of the IN100 material was effected.

It is evident that a particular combination of temperature and compressive working places the material in a condition of very high temporary ductility, very high relative to the ductility in the unprocessed condition. The ductility is temporary in the sense that it is maintained only as long as grain growth is prevented and thus it is present only during the alloy fabrication process. Once the fabrication process has been completed and the article is heat treated to produce grain growth and to restore the alloy to its original high strength condition, no temperature thereafter encountered in its operating environment will restore it to a condition of very high ductility.

In the fabrication process, therefore, significant grain growth of the alloy should be avoided not only during the initial working of the billet but also during the forging process. It has been found that the alloy billet should be worked in compression preferably at a temperature within about 450 F. of the normal recrystallization temperature of the material. In addition, the forging must be performed at a temperature approaching the normal recrystallization temperature. For this reason, a departure from the normal forging practice is dictated. Except in exceptional circumstances, the forging will be accomplished utilizing dies heated to the forging temperatures in an inert atmosphere and with the use of high temperature lubricants.

The hot dies used in the forging operations to date were made from TRW 2278, a nickel base casting alloy similar in composition and strength to MAR M 200. Other suitable materials will be evident to those skilled in the art. Since an inert gas cover is preferentiallly utilized in the forging process, alternative die materials such as TZM molybdenum alloy will also be suitable. Further, because of the use of an inert atmosphere, the dies have been heated by induction coils. Numerous alternative die heating methods will, however, be found satisfactory.

The fabrication parameters for production of billet stock are selected so that the combined effect of heating resulting from that applied from an external heat source and that generated internally of the material as a function of the working does not result in a temperature rise sutficient to cause substantial grain growth. As a general rule, therefore, the greater the extent of the working in a single pass, the lesser the preferred working temperature. In the more preferred processes, the total required reduction is effected in a plurality of passes.

In the original work, because of the evident relationship of the process parameters to the alloy recrystallization temperature, it was initially thought that recrystallization should be avoided in the hot coldaworking and forging steps. Subsequent analysis of the hot cold-worked material revealed it to be hot-worked, hence, recrystallized even though the grain size was too small to be visible by conventional light microscopy. Recrystallization apparently takes place simultaneously with the hot cold-working but with substantial inhibition of grain growth. Further, it is apparent that the hot cold-working lowers the recrystallization temperature of the alloy very significantly below that found in the same material as conventionally processed. Because processing as taught herein does inhibit grain growth short transients of up to 10 minutes above the normal recrystallization temperature, while preferably avoided, are yet not fatally detrimental to the achievement of the intended advantages.

With respect to the total reduction necessary to achieve the desired temporary ductility, it appears that a reduction of at least about 4 to 1 is the practical minimum necessary at the most preferred working temperature. No maximum working limit has been discovered except, of course, insofar as it results in an internal heat buildup during processing as previously discussed.

Initially, the compressive working was provided by extrusion, particularly in the case of the IN alloy- Utilizing these results for background information, Astroloy, Waspaloy, and titanium alloy 8-1-1 were similarly extruded. Astroloy extruded at 1925 F. using an extrusion ratio of 10 to 1 did not exhibit the desired high temporary ductility. Similarly, Waspaloy extruded at 1825 F., 1775 F., and 1725 F. at an extrusion ratio of 6 to 1 was not satisfactory. However, Waspaloy extruded at 1725 F. with an extruseion ratio of 4 to 1 and double extruded at 4 to 1 followed by 4 to 1, showed a degree of ductility suitable for close tolerance forging. Also, titanium alloy 8-1-1 extruded at 1700 F., 1600 F., 1500 F., and 1400 F. with an extrusion ratio of 10 to 1 and at 1400 F. and 1300 F. with an extrusion ratio of 4 to 1 shows the desired degree of ductility.

A review of the microstructure of various of the Waspaloy and Astroloy extrusions revealed that in some cases the expected ductility was not achieved due to a buildup of internal heat resulting from the compressive working. In other words, the combination of externally applied heat together with that generated internally during working resulted in excessive grain growth.

This extrusion work indicated that, depending to some extent upon the working temperature, the total reduction may advantageously be made in two or more extrusion operations. Furthermore, since the buildup of internal heat during rolling or forging operations is much less than that developed in extrusion, these forms of compres sive working may in some instances advantageously be utilized to provide the requisite reduction, particularly in the case of Waspaloy and Astroloy, or to supplement the work produced by other methods.

Application of the described techniques to commercial quantities and sizes of the various materials was undertaken and the temporary ductility was produced. A series of 12 inch diameter ingots of both Waspaloy and Astroloy were reduced to 9 inch round-cornered squares using conventional rolling temperatures. From the 9 inch square stock, the material was reduced to 3 /2 inch round stock by a combination of rolling and press forging.

The particularly preferred process parameters for the IN100, Astroloy, Waspaloy and Titanium 8-1-1 alloys are set forth below. A variety of starting materials have been utilized, including a powder product of IN100 and a vacuum induction melted fine grain ingot of IN100, a vacuum induction followed by a vacuum consumable melted controlled grain size ingot of both Waspaloy and Astroloy, and a double vacuum consumable ingot of Titanium 8-1-l.

In the case of IN100 a minimum reduction in billet stock of 5 to 1 is required in the temperature range of 2000-2100 F. Press forging is accomplished with a die temperature and material temperature of 1900-2000 F. in an inert atmosphere with a strain rate of approximately 0.5 in./in./min.

With Astroloy the minimum reduction in billet stock is 4 to 1 in the temperature range of 18252000 F. Press forging is done at 1900 F. at a strain rate of 0.5 in./in./min.

Waspaloy is reduced in billet form at least 4 to 1 at 1725-l825 F. and forged at 1800 F. at a strain rate of 0.5 in./in./min.

Titanium 8-1-1 is reduced at least 4 to l in the temperature range of 13001700 F. and forged at about 1700 F. with a strain rate of 0.5 in./in./min.

For the achievement of very close tolerances there appears to be an advantage for all alloys in the use of very low strain rates of perhaps 0.05 in./in./min.

The precise metallurgical mechanism by which the aforementioned results are attained has not as yet been completely resolved. 'It has been reported in the literature that a phenomena referred to as superplasticity exists in some materials. See, for example, an article in the Transactions of the ASM, vol. 53 (1965) by D. H. Avery and W. A. Backofin. In the present case, however, the basic considerations leading to the development of the alloy chemistry are inimical to a condition of superplasticity. The present invention provides a method whereby the strong, high temperature alloys may be placed in a condition of low strength and high temporary ductility and forged into useful configurations, not because of their chemistry, but despite it. And this is of fundamenal importance, since an inherent condition of low strength and high ductility which exists because of the alloy chemistry at any temperature within a jet engine operating regime cannot be tolerated. In other words, it is of the utmost importance that the condition of low strength and high ductility be temporary and hence present only during the fabrication process.

To restore the particular alloy to its normal condition of high strength and hardness subsequent to the forging operation, the conventional solution, stabilization, and precipitation heat treatment is all that is required. In the case of the INlOO alloy having a normal recrystallization temperature of about 2100 F., the preferred heat treatment involves solution heat treatment at about 2175 F. to produce grain growth which is followed by stabilization and precipitation heat treatment. The solution heat treat temperature of the various other alloys specifically mentioned herein are set forth in Table VIII.

TABLE VIII Normal recrystallization Solution temperature, heat treat,

Wrought alloy (F). (F.)

MAR M200 2, 225 2, 200 Inconel 718. 1, 775 1, 750 Waspaloy 1, 850 1, 865 Astroloy... 2, 050 2, 050 Udimet 500 1, 925 1, 975 Rene 41." 1, 925 1, 950 Inconel X--- l, 750 1, 800 Inconel 625 1, 750 1, 800

below but within about 450 F. of its normal recrystallization temperature to a compressive strain 12 equivalent to that provided by at least about a 4 to 1 reduction in cross-sectional area todepress the recrystallization temperature below the normal alloy recrystallization temperature, producing a recrystallized microstructure having a grain size not exceeding about 35 microns; and forging the alloy to the desired configuration in hot dies at a forging temperature within about 350 F., of but not exceeding on a sustained basis the normal crystallization temperature of the alloy, while inhibiting substantial grain growth. 2. The method of fabricating articles from the high strength, precipitation hardened alloys of nickel or titanium which comprises the steps of:

working the alloy in compression at a temperature within about 450 F. of its normal recrystallization temperature, the working parameters being selected to permit the alloy temperature to approach but not exceed the normal recrystallization temperature of the alloy as a result of work-generated heating;

forging the alloy to the desired shape in hot dies at a temperature within about 350 F. of but not ex-' ceeding on a sustained basis the normal recrystallization temperature of the alloy;

and heat treating the forged alloy to restore it to its normal condition of high strength and hardness.

3. The method according to claim 2 wherein: in the working step, the alloy is worked to a compressive strain equivalent to that provided by at least a 4 to 1 reduction in cross-sectional area.

4. The method according to claim 3 wherein: the alloy is in the form of a dense, sintered po-wder metallurgical billet.

5. The method of fabricating articles from the strong, high temperature nickel base alloys which comprises the steps of:

working the alloy in compression at a temperature of at least 1650 F., the working parameters being selected to permit the alloy temperature to approach but not exceed the normal recrystallization temperature of the alloy as a result of work-generated heatmg;

forging the alloy to the desired shape in hot dies at a temperature between 1725 F. and the normal recrystallization temperature of the alloy;

and heat treating the forged alloy to eifect grain growth and restore its normal strength and hardness.

6. The method according to claim 5 in which: in the working step, the alloy is worked to a total compressive strain equivalent to that provided by at least a 4 to 1 reduction in cross-sectional area.

7. The method according to claim 6 in which: the forging is conducted in an inert atmosphere.

8. The method of fabricating articles from the strong titanium base alloys which comprises the steps of:

working the alloy in compression at a temperature of at least 1300 F., the working parameters being selected to permit the alloy temperature to approach but not exceed the normal recrystallization temperature of the alloy as a result of work-generated heat- 111g;

forging the alloy to the desired shape in hot dies at a temperature between 1400 F. and the normal recrystallization temperature of the alloy;

and heat treating the forged alloy to effect grain growth and restore its normal strength and hardness.

9. The method of fabricating turbine engine compo nents from the INlOO alloy which comprises:

working the alloy in compression at a temperature of about 1900-2100 F. to at least about a 5 to 1 reduction in areas;

forging the alloy to the desired shape in hot dies at a temperature of about 18002000' F. in an inert atmosphere;

and heat treating the forged alloy at about 2175 F.

to effect grain growth.

10. The method according to claim 9 in which: the alloy to be worked in compression is in the form of a dense, sintered powder metallurgical billet.

11. The method according to claim 9 in which:

the working in compression is an extrusion process;

and the extrusion is performed sequentially in at least two steps to effect a total extrusion ratio of at least 16 to 1. 12. The method of fabricating turbine engine components from Waspaloy which comprises the steps of working the alloy in compression at a temperature of about 15501775 F. to a total reduction ratio of at least 4 to 1;

forging the alloy to the desired shape in hot dies at a temperature of about 16501825 F. in an inert atmosphere;

and heat treating the alloy at a temperature of about 1865 F. to effect grain growth.

13. The method of fabricating turbine engine components from Astroloy which comprises the steps of:

working the alloy in compression at a temperature of about 1650-1950 F. to a total reduction ratio exceeding about 6 to 1;

14 forging the alloy to the desired shape in hot dies at a temperature of about 1700-1950 F. in an inert atmosphere; and heat treating the alloy at a temperature of about 205 0 F. to effect grain growth. 14. The method of fabricating articles from the titanium alloy 8-1-1 which comprises the steps of:

working the alloy in compression at a temperature of about 13001800 'F. to a total reduction ratio exceeding about 4 to 1; forging the alloy to the desired shape in hot dies at a temperature of 16001800 F. in a non-contaminating atmosphere; and heat treating the alloy at 1675-1825 F. to effect grain growth.

References Cited UNITED STATES PATENTS 2,666,721 1/1954 Bechtold et a1. 148l1.5

L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner