US3575736A - Method of rolling titanium alloys - Google Patents

Abstract

A METHOD FOR ENHANCING THE STRENGTH TO DENSITY RATIO OF ALPHA-BETA TYPE TITANIUM ALLOYS. THE INCREASED STRENGTH DEMONSTRATED BY THE ALLOYS OF THIS INVENTION IS ACHIEVED BY FAVORABLY ALTERING THE CRYSTALLOGRAPHIC TEXTURE OF HE ALLOY. THE ALLOY TO BE TEXTURED IS HOT ROLLED IN AT LEAST THREE DIFFERENT ORIENTATIONS AT A TEMPERATURE WITHIN A RANGE OF FROM ABOUT 700* TO 1500*F. THIS RESULTS IN A REDUCTION IN THE CROSS-SECTIONAL AREA OF THE ALLOY BY ABOUT 60 TO 90%.

Description

United States Patent 3,575,736 METHOD OF ROLLIN TITANIUM ALLOYS John M. Fitzpatrick, Los Altos, and Aloysius T. Davinroy, Redwood City, Calif., assignors to the United States gt America as represented by the Secretary of the Air orce No Drawing. Filed Nov. 25, 1968, Ser. No. 778,760 Int. Cl. B21b 1/00, 3/00; B21d 31/00; C21d 1/00 US. Cl. 148-115 3 Claims ABSTRACT OF THE DISCLOSURE A method for enhancing the strength to density ratio of alpha-beta type titanium alloys. The increased strength demonstrated by the alloys of this invention is achieved by favorably altering the crystallographic texture of the alloy. The alloy to be textured is hot rolled in at least three different orientations at a temperature within a range of from about 700 to 1500 F. This results in a reduction in the cross-sectional area of the alloy by about 60 to 90%.

BACKGROUND OF THE INVENTION This invention relates to a method for hot rolling titanium-base alloys. More particularly, this invention concerns itself with achieving favorable crystallographic texture in titanium-base alloys of the alpha-beta type by subjecting the alloy material to a multi-directional rolling process.

The formulation and fabrication of alloy materials characterized by high strength-to-density ratios has become a problem of paramount importance with the recent advances made in rocket technology. The need for such materials is obvious if further technical advances are to be made. Attempts to fully utilize the inherent potential of titanium alloys to achieve strength-to-density ratios comparable to ratios of fiberglass composites for rocket motor applications has not been successful. It is well known that deformation processing in a combination with heat hardening significantly improves the strength of metal alloys. Amongst titanium alloy the crystallographic texture which is most desirable for providing strength is one in which the basal planes of the hexagonal-alpha-phase lattice are preferentially parallel to the plane of the sheet. This texture provides strength under biaxial stress conditions greater than those in a crystallographically isotropic metal of the same composition. The all alpha alloys of titanium display this classical basal plane texturing after unidirectional rolling but these alloys do not have the potential of being heat treated in order to provide increased strength.

The alpha-beta type titanium alloys are generally rolled in one direction at temperatures of about 1700 F. with resultant textures giving rise to a less-than-isotropic biaxial strength. Although these alloys have not been considered ideally suited for texture hardening, some strength improvement can be achieved through heat hardening. The ability to properly texture harden and significantly improve the strength of alpha-beta titanium alloys is of extreme importance if the maximum utilization of titanium metal is to be realized for rocket motor applications. Previous methods of texture hardening by straight rolling, as above, and shear spinning have so far not shown any significant increase in the textured properties of these alloys.

With the present invention, however, it has been found that a heat-treatable, texture-hardened titanium alloy suitable for use in rocket motor cases can be fabricated by subjecting a sheet of the alloy to a multi-directional rolling process preferably at temperatures not to exceed about 1300 F. The alloy work piece is rolled in a direction parallel with respect to the rolling direction. After each successive rolling pass, the work piece is rotated 45 and then reheated. This provides a multi-directional rolling process in which the work piece is rolled in three orientations with respect to the rolling direction: parallel to the rolling direction, transverse to the rolling direction, and at an angle of 45 or diagonal to the rolling direction.

The texture hardening multidirectional rolling process of this invention provides a means for utilizing the full potential of alpha-beta type titanium alloys by favorably altering the crystallographic texture of the alloy. The resultant alloy possesses higher strength under biaxial stress conditions and consequentially enable the fabrication of lighter weight structures.

SUMMARY OF THE INVENTION In accordance with this invention, texture hardening of alpha-beta type titanium alloys can be accomplished by multi-directional rolling process in which alloy metal sheets are hot holled in three different orientations at temperatures ranging from about 700 F to 1500 F. The sheets are subjected to successive rolling operations, each of which is alternately oriented along three different directions with respect to the rolling direction: parallel to the rolling direction, transverse to the rolling direction, and at a 45 angle or diagonal to the rolling direction.

Texture hardening in accordance with the process of this invention results in a significant improvement in the strength to weight ratios of alpha-beta titanium alloys as compared to the results achieved by previously known hardening processes. After multi-directional rolling, the alloys display the favorable basal plane texturing in which the basal planes of the hexagonal-alpha-phase lattice are preferentially oriented parallel to the plane of the sheet. This results in the fabrication of a high strength alpha-beta type titanium alloy.

Accordingly, the primary object of this invention is to provide a method for favorably texturing alpha-beta titanium alloys by preferentially orienting the basal plane of the alloys crystal lattice parallel to the plane of the sheet.

Another object of this invention is to provide a method for fully utilizing the inherent characteristics of titanium alloys to achieve high strength-to-density ratios.

Still another object of this invention is to provide a method for inducing high strength in alpha-beta type titanium alloys through a combination of processing parameters which includes heat treating and deformationprocessing.

The above and still further objects and advantages of this invention will become apparent upon consideration of the following detailed description thereof;

3 DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is predicated on the discovery that the crystallographic texture of alpha-beta titanium alloys can be favorably altered to produce a classical basal plane texture in order to provide an alpha-beta type titanium alloy having a high strength to density ratio. The favorable alteration is achieved by subjecting an alloy Work piece to a series of hot rolling steps oriented in three different directions to reduce its cross-sectional area..The cross-sectional area is ultimately reduced by about 60 to 90 percent and the rolling steps are conducted at temperatures of from about 700 to 1500 F. Preferably the work piece is rolled at a temperature of about 1300 F. and reduced in cross-sectional area by about 90 percent.

Specific examples of alpha-beta type titanium alloys subjected to the rolling process of this invention were of two compositions, Ti-6Al-4V and Ti-7Al-2.5Mo. The Ti- 6Al-4V alloy was obtained in the form of /1 in.-thick strip, 6 in. wide. It had been a ring-rolled forging with a wall thickness of approximately 1 /2 in. The ring was cut open, straightened on a forge press at 1750" F., and then rolled from a furnace temperature of 1750 F. to A in. thick. This strip was conditioned to remove oxide and surface irregularities by machining in. from both surfaces. The resulting plate, in. thick, was used for processing in accordance with this invention. A second form of a Ti-6Al-4V alloy used in the rolling process was 1 /2 in.-thick plate.

The Ti-7Al-2.5Mo alloy was obtained in the form of 2-in. thick plates. This material was converted to thicknesses that could be used on a two-high Fenn rolling mill. Conversion was performed in two ways by a vendor forge shop. The first way was to roll slabs from 2 in. thick to approximately 1 in. thick at a furnace temperature of 1750 F. The second way was to hammer-forge some of the 2-in. thick material to approximately 1 in. thick, also at a furnace temperature of 1750 F. The rolled material was further reduced by rolling on the Penn mill to Aa-in. thickness at a furnace temperature of 1750 F. Both the rolled and forged materials were used in preparing multi-directional rolled sheet for test evaluation.

The starting size of the Work piece multi-directional rolling was a regular octagon, 4 /2 in. across the parallel edges. These starting blanks were prepared from the thick plates (l /z-in. thick Ti-6Al-4V and l-in. thick Ti-7Al- 2.5Mo) by cutting the required shape on an abrasive cutoff wheel. Typical rolling schedules are illustrated in Tables I and II for T i-6Al-4V and Ti-7Al-2.5Mo respectively. On each successive rolling pass, the octagon was rotated 45 and reheated after every pass.

When the size of the work piece reached an effective diameter of 9 in., the octagonal plate was cut into two equal sections from each of which was prepared another regular octagon measuring approximately 4% in. across. These pieces were then multi-directionally rolled in the same manner as before to a final thickness of approximately /3 in. A production summary of multi-directional rolling is given in Table III.

TABLE I [Multi-directional rolling sehediilgotg rlli-6Al-4v; Preheat Temperature TABLE I.Continued Per- Exit Pass Material cent/ temp. N 0. thickness pass F.) Remarks 960- 1,000 Slight dishing of plate occurred on 21st pass and persisted through final pass. 22 0.445 5. 3 23 0.426 4. 3 980 24 0. 406 4. 7 25 0. 389 4. 7 1, 000 26 0. 365 5. 7 27 0.347 4. 0 1,000 Air-cool plate. Plate was cut in half to enable continued rolling. Preheat both plates at 1,300 F.

[or 30 min. 0. 331 4. 6 0. 316 4. 5 960 0. 297 6. 0 920 0. 281 5. 4 930 0. 268 4. 6 890 0.253 5. 6 900 34 0.239 5.5 900 35 0. 228 4. 6 900 36 0.218 4. 4 900 37 0. 206 5. 5 890 38 0. 200 2. 3 840 39 0. 187 6. 5 840 40 0. 175 6. 4 860 41 0.168 4. 0 860 42 0. 156 7. 1 840 43 0. 139 8. 5 820 44. 0. 136 2. 2 800 45 0. 130 4. 3 780 46 0. 127 2. 3 Aircool after final pass.

TABLE II [Muiti-direetional rolling schedulle1 gag ii7A1-2.51\I0; preheat temperature Per- Exit Pass Material eent/ temp. No. thickness pass F.) Remarks 1. 000 Preheat block at 1,450 F.1'or 1hr.- 1. 0.926 5. 6 1,100 2 0.871 5. 9 1, 3. 0. 818 6. 1 1, 4. 0.768 6. 1 1,100 5. 0.722 6.0 1,100 6 0. 679 6. 0 7. 0. 637 6. 2 1, 100 8. 0. 600 5. 8 1, 100 9. 0. 563 6. 2 1,100 10 0. 530 5. 9 11 0. 498 6. 0 1, 080 12 0.467 6. 2 13 0. 440 5. 8 1, 070 14 0. 414 5. 9 15 0. 390 5. 8 1, 040 16 0. 367 6. 0 1,040 17-- 0. 344 6. 3 1,040 18 0. 326 5. 2 1,040 19.- 0.307 5.8 1,040 20 0. 290 5. 5 980 Slight dishing of plate occurred on 20th pass and persisted through final pass. 21 0. 272 6 2 22 0.262 3 7 1,020 Air-cool plate. Plate was cut in half to enable continued rolling. Preheat both plates at 1450 F. tor 30 min. 0. 249 5. 0 940 0. 234 6. 0 960 0. 221 5. 0 0. 210 5. 0 900 0. 200 4. 8 900 0. 188 6. 0 940 0. 182 3. 2 040 0. 173 5. 0 0. 164 5. 2 800 0. 5. 5 880 0. 148 4. 5 880 0. 143 3. 4 860 0. 136 4. 9 O 129 5. 1 840 0 127 1. 6 840 0 123 3. 1

800 Air-cool sheet after final pass.

TABLE III Ti-6 Al-4V and Ti-7Al-2.5Mo multi-direetional roll production summary] Material Pre- Sheet starting heat Total re- Total desi gthickness tem duetion rolling Alloy nation (in.) F. 1 (percent) passes Remarks Ti-6Al4V 38 RR 1. 5 1 3 93 47 Two plates obtained with a diameter of 8 in.

Ti-6Al-4V 4SRR 1. 5 1: 300 91. 5 49 Four plates obtained with a diameter of 7% in.

T1-6Al-4V SSRR .624 1, 300 80 25 Straight rolled at furnace temperature 1,700 F. from 11111. dthilek; to $325 ir. pr'igr to round rolling. Two 11115 e Ti-6A1-4V 10SRR 0. 624 1,100 so 27 D0. p a 850 we W1 dlametero Ti-6Al-4V 13SRR 0.370 1,300 70 20 Straight rolled at furnace temperature 1,700 F. from iljgafinghilclg to 33702111. pritin;1 to roundfro lling. Two

e a e o gi-figljll; 0.370 1,188 70 22 Do. p S ame Wlt lametero 7/2 m i-6 7 1.5 ,4 92 43 Two lates obt d h Twivvii 0 Y 92 40 1pc. aine wit a. diameter of 7% 1n Ti7 -2 51 o 2 80 24 One late obta ed 'th 10' Ti-7A1-2.5M0 21SRR 1.000 1,450 87 38 1 30. m W1 adlameter of m 1 The preheat temperature is that at which the material was allowed to soak. This soaking was performed in a 40 kw. resistance box furnace for 15 min. pIlOl' to each rolling pass. Whenever the material was allowed to air cool, it was preheated for a period of not less than 30 mn. prior to the next rolling pass.

No conditioning was necessary for the Ti-6Al-4V alloys other than that described heretofore. The 1 /2 in. thick plate was received as bright, fiat, and locally conditioned material. The hammer-forged Ti-7Al-2.5Mo alloy required milling approximately in. from both surfaces to prepare clean, flat surfaces for rolling.

All rolling procedures were done on a Penn, type 081, two-high rolling mill. The mill had a ground, roll-face width of 9 in. Unidirectional rolling (also termed straight rolling) was conducted on starting plates (sheet-bars) of the Ti-6A1-4V having the following dimensions: 7 /2 by 8% by 1 /2 in. Unidirectional rolling was carried out with the 7 /2-in. dimension in the rolling direction. Rolled sheets were edge trimmed by shearing or abrasive wheel cutting to 8-in. widths in order to pass through the Stanat Roller Leveler. The roller-leveler was employed following the final roll pass to achieve necessary flatness in the sheets. In some cases, the work had a tendency to curl on exit from the rolls, particularly at thicknesses between /2 and A in. When this occurred, it was necessary to flatten the pieces on a hydraulic press between platens. Prior to a flattening or roller leveling operation, the work was heated to the same temperature as it would be for a rolling pass. Typical unidirectional rolling schedules are shown in Tables IV and V and were conducted to provide comparative results achieved between unidirectional and multi-directional rolling. All rolling was done at a constant roll speed of 29 ft/min which was chosen only for convenience in handling the material on exit from the mill. The actual temperature of the metal on exit from the rolls was monitored periodically with a surface contact pyrometer. The work was reheated to the furnace temperature after each pass. Percentage reduction per pass was determined by a limit imposed by the strength of shear pins in the drive train of the rolling mill. A production summary of straight rolling is given in Table VI.

TABLE IV [Unidirectional rolling schednle18 rF1ii-6Al-4V; preheat temperature Exit temp F. Remarks Preheat block at 1,100 I. for 1 hr.

Percent/ pass Per- Exit Material cent/ temp. thickness pass F.) Remarks 2 8 0. 796 2. 4 0. 778 2. 3 0. 758 2. 6 0. 738 2. 6 Press-straighten plate after th pass. 0. 718 2. 7 900 0.700 2. 5 Press-straighten plate after 42nd 40 pass.

0. 676 3. 4 920 0. 658 2. 7 Press-straighten plate after 44th pass. 0. 639 2. 9 920 0. 621 2. 7 Press-straighten plate after 46th pass. 0. 601 3. 2 920 g 0. 583 3. 0 Press-straighten plate after 48th pass.

0. 564 3. 3 0. 550 2. 5 900 Press-straighten plate after 50th pass. 0. 531 3. 3 920 0. 516 2.8 Press-straighten plate after 52nd pass. Plate new measures 26% 50 in. long and will be cut in half for continuation of rolling. 53 0. 500 3 1 820 5 0. 483 3. 4 900 Press-straighten plate after 54th pass. 0. 469 2. 9 900 1 O. 456 2. 8 880 0.441 3. 3 880 Press-straighten plate after 57th pass. 0. 428 3. 0 860 0. 414 3. 3 860 0. 400 3. 4 880 0.389 2.8 880 Press-straighten plate alter 61st pass. 0. 375 3. 6 880 0. 365 2. 7 880 0. 351 3. 8 Press-straighten plate after 64th pass. 65 0. 345 1. 7 66 0. 337 2. 3 840 67 0. 324 3. 9 880 68 0. 317 2. 2 860 69 0. 305 3. 8 880 65 70 0. 293 3. 9 860 71 0. 282 3. 8 800 72 0. 270 4. 2 880 73 0. 262 3. 0 860 74 0. 253 3. 4 860 75 0. 241 4. 7 76 0. 230 4. 6 840 70 77 0. 220 4. 3 820 78 0. 210 4. 5 820 79 0. 199 5. 2 820 80 0. 189 5. 0 820 81 0. 179 5. 3 82 0. 168 6. 1 820 83 0. 157 6. 5 800 84 0. 149 5. 1 780 Air-cool sheet alter final pass.

TAB LE V [Unidirectional rolling schedufggfgrEi-SMAV; preheat temperature Uniaxial tension test data for the Alan-thick Ti-6Al-4V alloy material are presented in Table VII. Here, the uniaxial test data for the as-received plate, as well as data on straight-rolled and multi-directional rolled plates are Per- Exit Pass Material cent/ te mp. 5 shown. On the basls of the R values, this material appears No thmlness pass Remarks to be capable of developing substantial textures during 1. 5 Preheat block for 1 hr. at 1300 F. rolling to 'a total reduction of about 80% {332 ""55,-

Uniaxial tension test data for the Ti-7A1-2.5Mo alloy 1.380 3.2 1n the hammer-forged condition are presented in Table {333 g VIII. In this case, we find that R is slightly greater than 1, 1.230 3.0 1,050 and that substantial R values are achieved by multig? i; directional rolling to total reductions of less than 90% 1. 059 4. 25 1. 0 0 5 ,050 977 5' 1 TABLE VII 0.926 5.2 1,050 8-3;; Unlaxlal tenslon data on preliminary materlal 0:775 1 I: (T1-6A1-4V) in indicated condition 0.725 6.5 8:228 0. 3 I: Longitudinal 0,591 6.5 Press-straighten plate after 19th 20 Yield strength at 0.2% (k.s.i.) 102,2 0.559 pass Engineering tensile strength (k.s.i.) 142.0 11522 Youngs modulus (p.s.i. 10 13,45 M94 giz plate after 22nd Plastic strain at maximum load (percent) 4.6 gigg Total elongation (Z-in. gage) (percent) 13.3 0: 409 0:6 I: Press-straighten plate after 25th 25 Elastlc POISSOHS ratlq 0-349 0 384 6 1 P R at 0.2% long. plastlc strain 0.3 0:362 5171111111. Press-straighten plate after 27th Calculated blaXlal Y5 113.6

D358- 0. 342 5.5 0320 6A As received. 0. 308 3.8 30 0.302 4.7 980 Press-straighten plate after 31st Yield strength at 02% (ksi) 150.3

ass. 0.284 6.0 080 p Engineering tensile stren th k.s.1. 168,7

2 0.270 4.9 960 Press-straighten plate after 33rd Youngs modulus (PSLXHFG) 148 DZLSS. 0.252 6.7 Press-straighten plate after 34th Plastic strain at maxlmum load (percent) 2,6 0 235 6 7 Pass' Total elongation (Z-in. gage) (percent) 4,0 01223 5.1 1:...1: Elastic Poissons ratio 0,39 8' 2'? 900 R at 0.2% long. plastic strain 3,07 0:183 6.2 s40 Calculated 1:2 biaxial YS (k.s.i.) 214.0 .171 9.3 880 59 0.152 0.4 Alt-cool Sheet after final pass. 40 Straight ro1led-80% furnace temperature 1100 F.,

as-rolled.

TABLE VI [Ti-GAMV unidirectional sheet production summary] Material Prestarting heat Total re- Total Sheet desigthickness temp. dnction rolling nation (in.) (F.) (percent) passes Remarks 15791-1 1.5 1,300 00 44 Sheet length, in. 15791-2 1.5 1,100 89 97 slighttslurzztce cracking noted on finished sheet. Sheet;

eng 1n. 15791-3 1.5 1, 300 00 42 Sheet length, in. 15791-4 1.5 1,300 42 Sheet length, 76 in. 15791-411 0. 150 RT 10 8 15791-4 sheet was cut in 2 pieces. One pleee 37 in. long was solution treated at 1600 I.15 min. and WQ, followed by 10% cold reduction 15791-4B 0.150 RT 10 7 Second sheet, 39 in. long, from 15791-4 was solution treated at 1,700 F.-15 min. and WQ, followed by a 10% cold reduction. 15701-2 0.152 RT 10 7 15791-2 sheet was out in 2 pieces solution treated at 1700 F.15 min. and WQ, followed by a 10% cold reduction. 15791-5 1. 5 1, 90 S7 Slight surface cracking noted on fininshed sheet. Sheet length, 83 m.

l The preheat temperature is that at which the material was allowed to soak. This soaking was performed in a 40 kw. resistance box furnace for 15 min. prior to each rolling pass. Whenever the material was allowed to air cool, it was preheated for a period of not less than 30 min. prior to the next rolling pass.

In the following tables of data summarizing the uniaxial tension test results for the alloys of this invention, the notation R indicates a practical measure of the texture achieved by any thermal-mechanical process. It measures the ratio of the plastic lateral strains, at 0.2% longitudinal plastic strains, measured in a nniaxial tension test performed on the alloy work piece regardless of the angular relation of the major axis of the work piece to the rolling direction. R is defined either as e /e or, alternatively, as de /a e, where 6 is the natural or logarithmic strain measured in the width dimension, and q; is the similar measurement in the thickness dimension of the uniaxial tension test work piece. The same notation R is also used in the following discussion.

TABLE VIII 1 [Uniaxial tension data on Ti-7Al-2.5Mo alloy] P astlc Stram 3 maxlinum load (percent) 5 Total elongation (2-1n. gage) (percent) 6.5 Cmditwns Elastic Poissons ratio 0.359 Mechanical property A B c R at 0.2% long. plastic strain 1.98 5 Calculated 1'2 biaxial YS (k si 192 8 Yield strength at 0.27 (k.s.l.) 108.3 134.2 136.2 137.4 Engineering tensile stiiength (k.s.i.) 121.8 156.5 157.2 155.3 Rolled 1500 F., annealed 1400 F., STA Youngs modulus (p.s.i. 10-) 16.2 16.4 16.0 16.45 glastiiclstrair'iiat r12aximum )1o(ad (P61851112). -4 9 g Mechanical property:

a eonga on -ln. gage ercen Elastic Poisson's ratio, n 0.368 0. 420 0.382 0. 388 YlelFl strfmgth 02% 1475 Rat 0.2% longitudinal plastic strain 1.17 4.3 4.6 4.0 10 Engineering tensile strength (k.s.i.) 165.6 Calculated 1:2 biaxial YS (k.S.l.)- 128.5 203.0 208. 1 204. 8 y gas modulus s i X10 6) 6 Explanation of conditions: A-Han1mer forged from 2in. Plasnc Stram maximum load (percent) thick pateBto r n thiIckAPlateHtfQrnMie te i 7g0 1n (as Total elongation (2-1n g g (p 8.6 receive 1' 3. eria 11111 1 11'80 1011a 1'0 8 111113.09 temp. 1,450" F. from 1 in. thick to in. thick. Annealed at Elastlc Polsson S m i-"i 0356 ,4%o; llrgtsT 1.7 50; 1 111, o ln s itige tit/900 15 R at 0 l ng. plast c strain 1.75 r. raig r0 e rom -in. tlic pa e to 5 -in. ttvllicklplaltle 1fufrnace teznp. 1,;54(50FFS1%bsequ0erg1i multi-dflieqc- Calculated 1 2 blaxlal YS (k S1 188.2

lona 1'0 er urnace emp. rom in. to 5 in. Annealed at 1,400 F.1 hr., ST at 1,750 FAA, hr. WQ urilaxlal tension tes.t Work Places were msirilmenteid plus age at 1 1m wlth strain gages to provide the test results. Initially, SIX

TABLE IX [Uniaxial tension data on Ti-6A1-4V, straight rolled, 90% reduction] Annealed at 1,400 F.-l 111'. ST 1,700 F. hr. WQ,

As-rolled, 90% reduction 1 Annealed at 1,400.1 hr. plus STA aged at 900 F.-24 hr.

Longltu- Diag- Trans- Longitu- Diag-Trans- Longitu- Diag- Trans- Longitu- Diag- Transdinal onal verse dinal onal verse dinal onal verse dinal onal verse Yield strength at 0.2% (k.s.i.) 127. 0 126. 0 140. 0 126. 0 124. 0 141.0 145. 2 145. 0 153. 0 158. 2 146.0 150. 6 Engineering tensile strength (k.s.i.) 152. 2 128. 0 146. 7 151. 0 127. 5 146. 0 171. 5 159. 0 172. 0 179. S 162. 0 172.0 Young's modulus (I).S.l.X" 14. 9 18. 3 17. 3 15. 16. 19. 0 15. 75 16. 8 15. 75 15. 9 16. 65 16. 8 Plastic. strain at maximum load (percent). 5. 8 5. 7 2. 2 8. 0 8. 0 5.0 3. 6 4. 0 2. 4 4. 8 -13. 0 5. 0 Total elongation (percent) 9. 0 17. 8 4. 5 18. 1 18. 5 14. 2 10. 4 11. 0 8. 7 7. 1 11. 0 l0. 3 Elastic Poissons 0. 350 0. 378 0. 395 0. 341 0. 380 0. 406 0. 353 0. 391 0. 391 0. 317 0. 346 0. 334 R at 0.2% longitudinal strain 1. 33 4. 08 0. 9 1. 17 4. 2 0. 83 1.66 3. 32 1. 76 0. s5 2. 0 1. 22 Calculated 1:2 biaxial YS (k.s.i.) 154. 0 188. 2 158. 8 149. 7 186. 5 158. 0 183. 5 208. 5 195. 2 177. 6 191. 0 180. 0

1 From furnace temperature of 1,300 F. In performing the several rolling schedules, the primary objective has been to achieve the highest possible lateral strain ratios through the development of a favorable crystallographic texture. Such a texture gives rise to 40 high lateral strain ratios in uniaxial tension tests performed on work piece samples taken parallel to the rolling direction and transverse to the rolling direction. Thus, from the sheet materials that were rolled, emphasis was placed on measuring R in the rolling direction.

On the basis of a heat-treatment study and an indication that a 1400 F. anneal stabilizes the crystallographic texture, a standard heat treatment (STA) was adopted so that the influence of other processing parameters might be noted. This treatment consisted of a 1400 F .-1 hr. anneal, a 1700 F. solution treatment for A hr., water quenching, and aging at 900 F. for 24 hr.

TABLE X strain gages were employed; two in the width dimension, on opposite faces; two in the thickness dimension on opposite edges; and two in the longitudinal dimension, on opposite faces. One-sixteenth-inch gage length, foil-type strain gages were used in the thickness direction and oneeighth-inch gage length foil-type strain gages were used in the length and width directions. All gages were bonded to the specimen surface with Eastman 91'0 contact adhesive. A 2-in. gage length extensometer was also employed as a check of longitudinal strain. During each test, the load, the extensometer, and the six strain gages were read-out on eight channels of a light-beam oscillograph. From the resulting data, lateral strain ratios were calculated at a number of points following the onset of plastic deformation.

From a comparison examination of the test results dis- [Uniaxial tension data on Ti fiAl-4V, multi-direetional rolled 90%, furnace temperature 1,300 F.l

Annealed 1,400 F.-1 Annealed hr., ST 1,700 FHA hr., ST 1,700 F.1/; h1.,

As- 1,400 F. WQ, aged at 900 F. WQ, Aged at 900 Mechanical property rolled 1 hr. 24 hr. F.24 hr.

Yield strength at 0.2% (k.s.i.) 121. 3 110. 9 146. 0 143. 0 148. 3 Engineering tensile strength (k.s.i.) 130. 8 114. 5 160. 5 161. 0 163.1 Young's modulus (p.s.i. l0-) 14. 25 15. 0 16. 6 15. 1 15. 87 Plastic strain at maximum load (percent) 1. 9 5. 7 4. 5 3. 0 3. 2 Total elongation (2-in. gage) (percent) 11.1 15. 3 10.6 10.4 10. 1 Elastic Poissons ratio 0. 490 0.478 0.495 0.403 0.399 R at 0.2% longitudinal plastic strain. 3. 35 4. 72 4. 94 2. 94 2. 26 Calculated 1:2 biaxial YS (k.s.i.) 175.1 170.0 225. 5 201. 4 198. 7

Note.Uniaxial tension data on Ti-GAl-4V, multi-directional rolled 90%, furnace temperature 1,300 F.

TABLE XI Uniaxial Tension Data on Ti-6Al-4V, Multi-Directional Rolled 90% Reduction at 1400 F. and 1500 F.

Rolled 1400 F., annealed 1400 F., STA

Mechanical property:

Yield strength at 0.2% (k.s.i.) 147.5

Engineering tensile strength (k.s.i.) 166.0 Youngs modulus (p.s.i. 10-

closed in Tables IX and X, it can be seen that the multidirectional rolling process of this invention provides an alpha-beta type titanium alloy having a high strength to density ratio as indicated by the calculated R values. Table XI presents data resulting from a multi-directional rolling process conducted at temperatures of 1400 F. and 1500 F., respectively.

The invention has been described with particular refer- 15.9 once to specific embodiments thereof. It is to be understood, however, that the description of the present invention is for the purpose of illustration only, and it is not intended to limit the invention in any way.

What is claimed is:

1. A method for rolling an alpha-beta titanium alloy sheet which comprises the steps of rolling said sheet to reduce its cross-sectional area by passing said sheet in a planar first direction parallel to the rolling direction in a single rolling pass while heated to temperature between about 700 F. to 1500 F., continuing said rolling until the cross sectional area of the sheet is reduced by about 60 percent to 90 percent of its original cross-sectional area by performing a plurality of such rolling passes, angularly rotating said alloy sheet in the plane of said first direction subsequent to each repeated rolling pass such that rolling is effected in at least three differently oriented directions relative to said rolling direction and then cooling said rolled sheet to room temperature.

2. A method for rolling an alpha-beta titanium alloy sheet which comprises the steps of rolling said sheet to reduce its cross-sectional area by passing said sheet in a planar first direction parallel to the rolling direction in a single rolling pass while heated to a temperature of 1300 F., continuing said rolling until the cross-sectional area of the sheet is reduced to about 90 percent of its original cross-sectional area by performing a plurality of such rolling passes, rotating said alloy sheet 45 in the 12 plane of said first direction subsequent to each repeated rolling pass such that rolling is effected in at least three differently oriented directions relative to said rolling direction and then cooling said rolled sheet to room temperature.

3. A method in accordance with claim 2 wherein the rolled sheet is further annealed at a temperature of about 1400" F. for one hour, solution heat treated at 1700 F. for about 15 minutes, water quenched, and aged at 900 F. for 24 hours prior to cooling to room temperature.

References Cited UNITED STATES PATENTS 691,565 1/ 1902 Norton. 2,165,027 7/ 1939 Bitter. 3,169,085 2/1965 Newman 148-115 3,492,172 1/1970 Sauvageot et al. 14811.5 3,496,755 2/1970 Guernsey et al. 72364 3,489,617 1/1970 Weurfel 14811.5

CHARLES W. LANHAM, Primary Examiner E. M. COMBS, Assistant Examiner U.S. Cl. X.R.