US2950191A

US2950191A - Titanium base alloys

Info

Publication number: US2950191A
Application number: US229143A
Authority: US
Inventors: Milton B Vordahl
Original assignee: Crucible Steel Company of America
Current assignee: Crucible Steel Company of America
Priority date: 1951-05-31
Filing date: 1951-05-31
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

3, 1960 M. B. VORDAHL 2,950,191

TITANIUM BASE ALLOYS Original Filed Dec. 10, 1949 GOO 1 3 nvmvron Mara/v 5. Vowel/1.

/ 4 TTORNEYS Patented Aug. 23, 1960 TITANIUM BASE ALLOYS Milton B. Vortlahl, Long Hill, Conn, assignor, by mesne assignments, to Crucible Steel Company of America,

Borough of Flemington, N.J., a corporation of New Jersey Filed May 31, 1951, Ser. No. 229,143 12 Claims. ((31. 75-1755) This invention relates to the processing of alloys, particularly titanium-base alloys, and to alloys of a unique and desirable structure resulting from such processing.

In the drawings:

Fig. 1 is a photomicrograph of an alloy of commercial titanium with about 4.1% manganese after 90% work in the two-phase field.

Fig. 2 is a photomicrograph of an alloy of commercial titanium with about 6.8% manganese, the alloy havmg been extensively worked in the two-phase field, quenched from a temperature of 700 C., and stabilized at 500 C.

Fig. 3 is a partly theoretical phase diagram of the titanium-rich-end of the binary-titanium manganese system.

The low temperature or alpha phase of substantially pure titanium, which is of close-packed hexagonal structure, transforms at a temperature of about 885 C., to the high temperature or beta phase, which is of body centered cubic structure. The presence of such contaminants or alloying agents as carbon, oxygen and nitrogen, in the proportions in which they are commonly found in commercial titanium, tends to raise the beta transformation temperature, and establishes a relatively narrow zone or field of mixed alpha-beta structure. The presence of certain alloying metals, prominent among which are iron, chromium, manganese, and molybdenum, has a quite diiferent effect upon transformation. Increasing amounts of these alloying materials stabilize the beta phase at progressively lower temperatures, and establish a mixed alpha-beta field of substantial scope. A typical phase diagram for an alloy of this type is shown in Fig. 3, the system selected for the purpose of illustration being the titanium-manganese system. The dotted lines represent probable boundaries which have not been exactly determined.

The present invention comprises the discovery of a method, believed to be unique in the metallurgical art, for securing an interleaved dispersion or distribution of two efiectively stable and ductile phases, and of a unique structure resulting therefrom. An essential step in the method is the plastic deformation of the alloy at a temperature within the two-phase field. Another essential step is the selection of an alloy composition possessing two or more ductile phases stable over a suitable temperature range. Such plastic deformation of such a structure differs widely from the generally accepted practice of deforming to a desired size and configuration in a single phase field and subsequently heat treating to secure a desired set of properties. In the practice of applicants method, the essentials of the desired structure are established by plastic deformation, and while subsequent heat treatment is permissible and may be further beneficial, it must be so controlled as not to destroy the essential structure set up by plastic deformation.

The alloys amenable to the present invention are of the mixed-phase structure typified by the alpha-plusbeta field of the phase diagram, Fig. 3. They are characterized by the presence of two phases of unequal strength, both of which possess some ductility but which deform by basically difierent crystallographic mechanisms. Thus, a stress concentration in one phase tends to difiuse, rather than to propagate, when it encounters the other phase. The titanium base alloys particularly disclosed by this specification possess all of this unusual set of qualifications; their alpha phase is relatively weak but quite ductile; their beta phase is relatively strong While nevertheless maintaining some ductility; and alpha,

being a hexagonal close-packed structure, deforms in a basically different manner than does beta, which has a body-centered-cubic structure.

The present invention is particularly directed to sheet, wire and rod products in which service stresses are applied substantially parallel to the rolling or drawing direction and in which, therefore, the optimum distribution of the weaker phase is in thin fibrils or platelets whose longitudinal axes are parallel to the rolling or drawing direction. The presence of the Weaker phase in thin fibrils or platelets disposed parallelto the working direction presents a minimum area of weaker phase normal to the applied stress and so constitutes the strongest distribution; conventional processing procedures such as working in the all-beta region followed by cooling at any convenient rate produce a distribution of the weaker phase which presents an appreciably greater area of weaker phase normal to the applied stress than that achieved by the novel processing disclosed in this specification and so is weaker. A further important advantage of the optimum distribution is that a stress concentration arising in the stronger phase (which is making the major contribution to supporting the applied stress) tends, in starting to propagate across the fibrils and platelets of the weaker phase, to be diffused in a manner analogous to the'reaction to stress of a cable in contrast to that of a rod.

Each of the phases in the optimum distribution disclosed by this specification may be either continuous or discontinuous in the worked direction. The stronger phase should predominate in order to give higher strength and thus tends to be continuous inthe worked (and, therefore, the load-bearing) direction. Even if it is not continuous, however, its fibrils and platelets are coherent with their contiguous material and so, like the fibrils in a textile thread, act as if they were continuous. It is an essential feature of this invention that, normal to the direction of working, neither phase is continuous.

The history of the alloy prior to plastic deformation in a two-phase field is of little, if any, significance. The

efiect of plastic deformation in the two-phase field is to increase ductility at a given strength level, and this effect is quite independent of prior history. Whether the specimen had been hardened by quenching from a beta field or lower temperature or fully annealed by slow cooling from a beta field temperature or given any other treatment, extensive working in the two-phase field still dovelops its optimum properties, viz., the highest ductility at a given strength level. For example, the quenching from the all-beta field of a binary alloy of 4% manganese, balance substantially all commercial titanium, results in a structure characterized by extended martensitelike plates of alpha and irregular bodies of retained beta. The quenching from the all-beta field of a similar alloy containing about 7% manganese produces unstable beta grains. On subsequent elevated temperature aging or service there is a tendency to the growth of continuous bodies of alpha at the grain boundaries. Both structures are predisposed to fracture along the extended region of in rolling sheet or rod or in drawing Wire at a temperatureiwithin the two-phase field has the efiect not .only of breaking up 'and dispersing the continuous masses, particularly the relatively weak alpha, and reducing such continuous masses to much smaller, substantially discontinuous and discrete particles, but also of producing the interleaved structure of fibrils and platelets of alpha.

and beta which is disclosed by this specification as being optimum. 1 If one phase predominates, it tends to form a matrix in which island platelets or fibrils of the second phase are embedded. l 7

Fig.1 is a photomicrograph at 600 magnification of a longitudinal section of a sheet of an alloy of commercial titanium with 4.1% manganeseafter a 90% area reduction by rolling at a temperature of 650 C.,'and stabilization for one hour at a temperature of 550 C. The lighter colored constituent is alpha titanium; the darker one is partially transformed beta. The dispersion and discontinuity of the phases, particularly the alpha phase, are very clear and are substantially optimum for sheet, a good balance being struck between proper-' ties transverse and parallel to the working direction. The platelets, which in the longitudinal section of Fig. 1 are shown edgewise, are arranged parallel to the sheet surfaces. In ajwire, the fibrils would be arranged parallel to the axis, and the structure is comparable with that of a cable as compared with a solid rod. The individual fibers of the stronger but more brittle phase can, to some extent, yield separately and thus distribute the load throughout thewhole, while the efiect of stress-raising voids, lattice imperfections, and the like, tends to be nullified at the first junction with the weaker and more ductile phase.

A typical specimen of the 4.1% manganese alloy in the condition illustrated in Fig. 1 has a yield strength in 4 V duced by working itself promote transformations toward equilibrium at the particular temperature. If the working temperature is too close to the all-beta temperature, the tendency to beta formation is so great that a substantial part of the benefits of the invention may be lost. In general, the working; temperature should not approach the all-beta temperature within about 100 centigrade degrees.

Increasing. amounts of plastic deformation within the two-phase field efiect increasingly complete "dispersion and interleaving of the phases, and proportionately increase ductility at a given strength level. Generally stated, strength is a function of composition and conditions of stabilization subsequent to two-phase temperature working. For an alloy of given composition, it has been found possible, by appropriate stabilization, to maintain a substantially constant strength-level throughout varying amounts of plastic deformation. Any material variations in strength being thus eliminated, the progressive increase in ductility with increasing two-phase temperature deformation has been established, Without complication by other variables. The experimental work leading to the present invention was exhaustive, comprising different alloys, different treatments prior to two- 1 to sheet of four different thicknesses so chosen that the varying amounts of warm rolling reduction (to be described) res'ulted in specimens of the same thickness, i.e., all finished specimens received the same t-otal reduction from the ingot. Each of the twelve sheets was subdivided into three parts, and the three parts respectively of each sheet we're conditioned for two-phase temperature rolling by three ditferent treatments, as follows:

' Condition Q--Heated in one hour at 815 0', water excess of 120,000 p.s.i., an ultimate strength above 145,000 p.s.i.,: an elongation in /2" of 16%, and a bend ductility of 3.3T. This ratio of ductility-to-strength is definitely superior to any obtainable from this alloy with- V out extensive plastic deformation at a temperature within.

4.1% manganese alloy illustrated in Fig. 1 Prior to such warm working and after furnace cooling from 750 C., it showed a heterogeneous mass of variously oriented extended bodies of the two phases. After 75 warm rolling and stabilization for one hour at 550 C., alloys of commercial titanium with about 8% manganese show a yield strength of about 145,000 p.s.i., an ultimatestrength over 157,000 p.s.i., an elongation in /2 of about 16%, and an average bend ductility. of about 3 T.

While the broad invention contemplates plastic dc formation at any temperiature within the two-phase field at which the strength of the alloy permits such deformation, the working temperature should not too closely ape proach the boundary temperature between the mixed al.-

pha-beta field and the .betafield. The heating of the i Q alloy prior to Working, and possiblylocal' heating in-.

(The'measurement of band ductility is not standardized.

The present'applicant and his associates measure this prop erty asthe'radius over which the specimen can be bent to an angle of 7o .WIthOIIt CIaCkiIIg, the radius being expressed as a multiple of specimen thickness.)

quenched;

Condition Q- Heated in air one hour at 815 C,

water quenched, and tempered sixteen hours at 550 C.; Condition. F-CHeated in air one hour at 815 C.,

furnace cooled.

All specimens were then rolled to a uniform thickness at a two-phase field temperature, three different temperatures being used. The thickest specimens of each set were reduced 90% the next thinner the next thinner 60%, and the thinnest 30%, the final rolled thickness or" all being the same. All specimens were then stabilized for one hour at 550 C. Strength and ductility were then measured, and found to be as follows:

Com osition: 3.5% manganese-balance, commercial titanium.

Rolling temperature: 650 C Stabilized: lhour at 550 C. after rolling.

Bend Duc- Pre-Rolhng Reduc- Yield Ultimate Percent tility Condition tion, (1,0005 (1,0005 Elonga- (Least percent p.s.i.) p.s.i.) tion Favorable Direction) Composition: 4.7% manganese-balance, commercial titanium. Rolling temperature: 700 C. Stabilized: 1 hour at 550 0. after rolling.

two-phase temperature rolling; and, secocnd, a progres-- sive increase in ductility for increasing amounts of such rolling. These effects are the same at any of the three rolling temperatures. Other variables being eliminated, Pr R llln Reduc- Yield Ultimate Percent t ilig 5 increasing amounts of plasiic (.ieformatlon in I two g on, (1,0005 (1,0005 Emma- (Least phase field effect a progressive mcrease 1n ductility.

percen p firm 3 Stabilization, as above described, is desirable under nee on most conditions, and can be performed at temperatures 30 119 137 8 m up to about 550 C., Without materially altering the 60 123 141 6 10 10 mrcrostructure typ1fied by Fig. 1. 5 g- While the optium combination of strength and ductility 3O 133 '1 is secured by extensive plastic deformation in the two- 60 124 137 6 phase field, fabrication problems frequently render it 75 121 130 9 3.4 a 90 111 132 21 ,3 1mposs1ble to roll sheet to the strength level desired in g8 39 lg g g-g 15 the fabricated product. Bending, forming, drilling, and 75 11? 135 10 3:1 like operations, cannot be satisfactorily performed at the 90 113 135 17 desired high strength. It has been found that the alloys processed according to the present invention can be ancomposmom manganeskbalanee, commercial titanium, nealed to the low strength level nececssary for fabrication, Rolling temperature: 505 0. 20 and, after fabrication, quenched to the desired high stabmzedzlhom at 590 after rolling strength, and still retain the essentials of the dispersed phase structure. The alpha phase is spheroidized, but Beaming Ream Yield Ultimate Percent 55 33 remains as discrete bodies rather than continuous masses. Condition tion, (1,000.4 (1,000s Elonga- (Least 1 1g. 2 1s a photomicrograph of an alloy contamrng Pment 1151-) 6.8% manganese, balance commercial titanium, which, after extensive plastic deformation in the two-phase field, 117 140 3 10 had been heated for 1 hour at 700 C., and water 00 130 144 3 10 quenched; it will be seen to consist of a beta matrix con- 53 fig, 2:3 taining very numerous relatively small and substantially 30 110 130 4 10 30 discrete globules of alpha. This specimen, after stabilizagg if; ii 2 tion for 1 hour at 500 C., showed a yield strength of 90 123 134 13 3.3 about 140,000 p.s.i., an ultimate strength of about 170,000 g8 3 2 p.s.i., and elongation in /2" of about 12%, and a bend 75 109 132 14 4.0 ductility of about 3 T. 90 113 132 18 While in the foregoing description the binary alloys of titanium and manganese have been used for the purpose The temperature of 815 C., to which all of the alloys of illustration, it has been found as the result of very exwere heated prior to the two-phase rolling, if not within tensive work that the novel processing is equally applicathe all-beta field lies so close to the all-beta field as to ble to any alloys comprising two ductile phases, both of destroy the efiect of previous Working. The tabulated which are relatively stable at normal temperatures. results definitely show for each alloy rolled from each of Prominent among these are the binary alloys of titanium three pre-rolling conditions, first, a negligible variation with molybdenum, chromium and iron, as Well as manin yield and ultimate strength with varying amounts of ganese; and the ternary and higher alloys of titanium with Tensile Properties Composition (Balance As Warm Rolled As Stabilized at 600 0.

Titanium) 0.2% Yield Ultimate Elongation Bend 0.2% Yield Ultimate Elongation Bend in $6" Radius in Radius 51, 000 70, 000 21 0. 3 Mn 3.4 o 0.23 153,000 173,000 12 0.5 133,000 149,000 18 3.3 Mn 44 3:? 152,000 175,000 13 5.5 144,000 100,000 22 4.9 Mn 0.1 ,9, g; 159,000 134,000 2 4.1 132,000 140,000 12 2.9 Mn 13.2 C 0.15 170,000 137,000 0 0.2 155, 000 100,000 12 4.0 01* 7.4 o 0.34 134,000 154,000 7 4.0 132,000 143,000 14 2.7 01* 12.4 0 0.17 141,000 100,000 5 7.0 133,000 142,000 11 2.7 Fe 2.4 117,000 140,000 12 2.7 93,000 125,000 19 1.7 Fe 5.0 o 0.25 133, 000 104,000 3 3.3 119,000 141,000 3 0.5 M0 4.7 135,000 159,000 10 7.5 122,000 145,000 20 0.2 g: 140,000 170,000 3 0.1 135,000 159,000 10 5.3 8: 127,000 154,000 14 4.3 117,000 134,000 21 2.0 3:; g 8: 130,000 104, 000 3 4.9 127,000 139,000 19 2.7 g; 8: 127,000 153,000 0 5.2 117, 000 134,000 22 3.0 il; o 0.2 155,000 175,000 10 0.5 133,000 150,000 20 0.0 Mn 5.5

A 1 .1 1 0 0.32 155, 000 173,000 4 7.5 149,000 160,000 14 4.4 Mn 610 Or 4.3 o 0.42 153,000 171,000 0 7.3 143,000 153, 000 13 0.2 Mo 2. 9 Mn 3. 3 C M iii 1 N M2 127, 000 153,000 10 5.7 113,000 133,000 15 2.2

' Stabilized at 700 o.

7 various metals of this group. Likewise included are the ternary andhigher alloys of titanium with the metals of thisigrou'p, andwith aluminum; While in the titanium aluminum alloys the beta phase is not stable at normal temperatures, it iss'tabilized by the additionof one or more of the'metals, manganese, molybdenum, chromium and iron. 'The weight percentages ofthe different metals of the group,-manganese,molybdenum, chromium and iron, which; when added to titanium'produce a two-phase structure, varywiththe particular metalthe maximum for manganese, for example, being about 13%, but the atomic percentages fall within therange of about 2 to about 15 atomic percent. Below'ab 'out atomic percent the beta phase is either absent altogether or present only in a negligible amount; while above about 15 atomic percent the alloys show an all-beta structure. Typical alloys and their properties as worked in the twophase field, both with and without subsequent stabilization, are shown in'the' preceding table. I

The present invention is beiievedto be of broad scope in that a desired structure having desired properties is secured by plastic deformation in the two-phase fie1d,'and not by any heat treating sequence of an article which has been fabricated to a desired 'form by deformation in a single-phase field with little if, any regard to the properties desired in the finished article. While the examples in the foregoing specification are all from two-phase systems, the method is obviously applicable to systems containing more than two phases, all of which possess the requisite stability and ductility.

This application is a division of applicants prior copending application, Serial 'No. 132,327, filed December 10, 1949, now abandoned.

What is claimed is: I g

1. An improved titanium base alloy which contains about 1 to 4% iron, up to about 30% maximum of each ofthe gases oxygen and nitrogen, and at least two metals within the ranges specified from'the group con-.

less than about 5%; the alloy being characterized by its good'ductility and impact strength with relatively high tensile strength. 7,

2. An improved titanium base alloy as defined in claim 1 as heat treated by working aboveand Within its alpha-..

beta phase range of about 1800 to 1000 F., followed g by annealing in a lewegpemon of itsalpha-beta region of about 900? to 1400 F., and wherein its structure has .50

alpha islands in amatfix of retained beta.

3. An improved 'titaniumbase alloy as defined 'in claim l as treatedby rapidly.v coolingit froman upper portion to slightly above its alpha-beta phase range of about 1400 to 1800-F., followed by reheating to the lower portion of such range, about 900 to 1400 F .',.and wherein its structure has alpha islands in a matrix of retained beta.

4. An improved titanium base alloy which contains about 1 to 4% iron, up to about .30% maximum of each of the gases oxygen and.nitrogen, at least two metals within the ranges specified from the group consisting of: chromium about .5 to 5%, manganese about .5 to 6%, and molybdenum about .5 to 5%, the iron-plus-alloying metal content being less than 10% but not less than about 5%, andthe balance titanium with incidental impurities.

5, An improved titanium base alloy which contains about 1 to 4% iron, up to about .30% maximum of each of the gases oxygen and nitrogen, about 1 to 6% chro- 8 mium, about 1 to 5% molybdenum, the iron-plus-alloying metal content being less.than 10% but notless than about 5 and the balance titanium with incidental impurities.

6. -An improved titaniumbase alloy whichcontains I about 2 to 3.5% iron, up to about oxygen and about .15% maximum nitrogen, about 2 to 5% chromium, about 1.5 to 4.5% molybdenum, the iron-plus-alloying metal content being less than 1 0% but not less than 50%, and the balance titanium with incidental impurities. 7 7 1; j J

7. An improved titanium base alloy which contains about 1 to 3%. iron, up to about 30% maximumjofjejach or the gases oxygen and nitrogen, about 1' 6% Tot chromium, about 1 to 5%;manganese, tlf1je lro' ll-plusalloying metal content beingQless than 10% but not less than about 5%, and the balance titanium withincide'ntal' impurities.

8. An improved titanium base alloy which contains about 1.5 to 2.5% iron, up to about 10% maximum oxygen and about .15 maximum nitrogemabout 2 to 4% chromium, about 2 to 4.5% manganese, the ironplus-alloying metalcontent being less than 10 but not less than about 5 and the balance titanium with incidental impurities. g

a 9. An improved titanium base alloy which contains about 1 to 4% iron, up to :about .-30% maximum of each of the gases oxygen and nitrogen, about*1-to-5% molybdenum, about 1 to 6% manganese, thence-plus alloying metal content being less than 10% but not less than about 5%, and the balance titaniumiivvith Tiiicidental impurities.

10. An improved titanium "base alloy which coh'tains about 1.5 to 3% iron, upto about .20%"maximurn oxygen and about .15 maximum nitrogenfahout 1.5

ance titanium with incidental impurities.

12. An improved titanium base alloy which contains about 1.5 to 3.5% iron, up to about .20% maximum oxygen and about .15 maximum nitrogen, about 1.5 to 3.5 each of chromium and manganese, about 1 to 3% molybdenum, the iron-plus-alloying metal content being less than 10% but not less than about 5%, and the balance titanium with incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,854 'Kroll -2 1 June 25, 1940 2,554,031 'Jafiee et .al. May 22, 1951 2,588,007 Jaffee m, Mar. 4, 1952 2,640,773 Pitler et al. June 2, 1953 ron nroN PATENTS 7 718,822 'Germany Mar. 24, 1942 I omen REFERENCES Zeitschrift fur Metallk'unde, vol. 29 (1937), pages and 191.

Transactions of the American Institute of Mining and Metallurgical Engineers, vol. 1660(1946), pages 390-396.

UNITED STATES PATENT UFFICJE @ERHHCATE @l CUHHECZFWN Patent N0a 2,950.,191 August 23 1960 Milton Ba Vordahl It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 10 for "50%" read 5% *0 Signed and sealed this 11th day 01 April 1961e (SEAL) Attcst:

ERNEST W. SWIDER ARTHUR W. CROCKER Alt-testing Oflicer A ti Commissioner of Patents

Claims

1. AN IMPROVED TITANIUM BASE ALLOY WHICH CONTAINS ABOUT 1 TO 4% IRON, UP TO ABOUT .30% MAXIMUM OF EACH OF THE GASES OXYGEN AND NITROGAN, AND AT LEAST TWO METALS WITHIN THE RANGES SPECIFIED FROM THE GROUP CONSISTING OF: CHROMIUM ABOUT .5 TO 6%, MANGANESE ABOUT .5 TO 6%, AND MOLYBDENUM ABOUT .5 TO 5%, THE IRONPLUS-ALLOYING METAL CONTENT BEING LESS THAN 10% BUT NOT LESS THAN ABOUT 5%, THE ALLOY BEING CHARACTERIZED BY ITS GOOD DUCTILITY AND IMPACT STRENGTH WITH RELATIVELY HIGH TENSILE STRENGTH.