US2777768A - Alpha titanium alloys - Google Patents

Description

United States atent fiice 2,777,768 Patented Jan. 15, 1957 2,777,768 ALPHA TITANIUM ALLOYS No Drawing. Application August 3, 1953, Serial No. 372,161

7 Claims. (Cl. 75-1755) The invention relates to titanium base alloys containing only the alpha phase below 825 C. and more particularly to quaternary alloys of titanium, aluminum, vanadium and silicon.

Titanium metal transforms from a body-centered cubic or beta crystal structure or phase to a hexagonal closepacked or alpha crystal structure or phase on cooling from above 882 C. to below that temperature. An alloying element may be added to titanium to stabilize either the alpha or the beta structure. The effect of such an alloying element depends on whether the atomic diameter of the alloying element best fits into the hexagonal close-packed structure or the body-centered cubic lattice structure.

The effect of such an alloying element may be to either raise or lower the transformation temperature and there are known alpha stabilizers and beta stabilizers.

Alloying elements also may be added to titanium to develop some particular desired property or properties addition of such alloying elements may affect the alpha or beta crystal structure of titanium in different ways.

For instance, there are may alloying elements that can be added to titanium as strengtheners but many of such elements cause a lowering of the transformation temperature which may be undesirable. addition of one or more alloying elements or metals to titanium for one purpose may adversely afiect certain properties or characteristics that are desired to be present or developed in the alloy or in products formed therefrom.

Aluminum, oxygen and nitrogen stabilize the alpha structure, and increasing amounts of these elements raise the transformation temperature. Below 825 C. aluminum is soluble in alpha titanium up to 24% by weight before the formation of a second phase (probably TiAl) begins. Similarly nitrogen and oxygen have solubilities of 5% and 14%, respectively, in alpha titanium below 825 C. With these three elements, the amount which can be employed in titanium alloys, while still maintaining an all alpha structure below 825 C., is far greater than the amount which would be desired in titanium base alloys from other considerations.

Columbium and vanadium, among others, are beta stabilizers, that is, their atomic size is such that they fit more satisfactorily into the body-centered cubic lattice structure, thereby lowering the transformation temperature with increasing additions. However, there is a restricted alpha field with these alloying elements which makes possible the addition of very small amounts of these elements while preserving an all alpha structure below 825 C. Columbium and vanadium have solubilities with alpha titanium at 825 C. of approximately 1% and 1.5%, respectively.

When carbon, silicon or tungsten are added to titanium, there is a restricted alpha field; but instead of an alphabeta field to the right of the all alpha region in .the equilibrium diagram, there is an alpha plus compound region.

In other words, the

' ed in a structure intended to be In the case of carbon, this compound is titanium carbide. Although only 0.3% carbon is soluble in alpha titanium at 825 C. (the solubility decreases to 0.2% at 600 C.), additions of greater than 0.3% carbon do not change the basic alpha structure but merely cause the presence of titanium carbide particles in the alpha matrix. Carbon can be intentionally added to'titanium alloys, if desired, and it imparts useful physical properties up to increasing the tensile strength with a corresponding drop in ductility. Beyond this carbon content, ductility drops oif rapidly.

' Silicon is soluble in alpha titanium to an extent of 0.5% at 825 C. and any amount in excess of this forms the compound Ti5Si3, in the alpha matrix. High ductility titanium alloys have been made containing as much as 1.5% silicon, and having a considerable amount of intermetallic compound in the alpha matrix.

Tungsten does not form a compound as do carbon and silicon, and a tungsten content of greater than 0.4% at 825 C. results in a mixed alpha-beta structure. Below 725 C., the alpha-beta region changes to an alpha plus tungsten region but, because of the alpha-beta region present from 725 C. to the transformation temperature of 882 C., no more than 0.4% tungsten could be toleratcompletely alpha.

These considerations present a from such titanium alloy sheets. such titanium alloy sheets, the sheets must be rolled and the required hot rolling temperatures for producing such sheets are in the neighborhood of 80 C. The rolling procedure may comprise hot rolling or may include both hot and cold rolling to gauge, followed by an annealing operation so that a ductile titanium alloy sheet is produced which may be fabricated by forming or drawing to provide a desired part or end product.

Accordingly, it is a fundamental object of the present become brittle at high temperatures. 7

Another object of the present invention is to provide titanium alloys which may be hot rolled into sheets of any desired gauge without harmful embrittlement which may occur in hot rolling two phase titanium alloy sheets. This embrittlement in alpha-beta type titanium alloys, in

This transformation product is such that the transformation cannot be controlled during hot rolling and, because of this, the sheets cannot be annealed to form a consistently ductile material.

There can be no embrittlement caused by a transformation of the microstructure during hot rolling, if no transformation occurs and no transformation products are formed during hot rolling. From the standpoint of hot rolling titanium alloy sheets, it is desirable, if not necessary, to heat the sheets being hot rolled 'to a rolling temperature of above :800 C. Thus, if no transformation occurs on heating a titanium alloy to or cooling it from 800 'C;, no embrittlement during hot rolling at such temperature can occur. 7

Accordingly, it is a further object of'the present invention to provide a titanium alloy containing only the alpha phase below, say 825 0, thus raising the -trans formation temperature so that the crystal structure of the alloy does not change from alpha to beta and back from beta to alpha in heating the metal up to and rolling the metal at a rolling temperature of 800 C., and permitting such alloy to be satisfactorily hot rolled at 800 C.

More particularly, it is an object of the present invention to maintain an alpha structure in a titanium alloy which is stable at hot rolling temperature, and during hot rolling and cooling, so as to eliminate the occurrence of embrittlement during hot rolling such alloy into sheets of desired gauge.

It is a further object of the present invention to improve the welding characteristics of titanium alloys. We

believe that for the same reasons discussed concerning embrittlement during hot rolling, welds of low ductility result when welding alpha-beta type titanium alloys even though high strength may be present in such welds. Many alloying elements can be added to titanium to strengthen the same, but unfortunately many of such elements lower the transformation temperature and proand metastable beta phases, or the alpha and metastable beta-phases.

Moreover, it is an object of the present invention to provide an alpha titanium alloy containing no transformed or retained beta phase after having been hot rolled to 0.040" sheet material at 800 C.

In Table 1 below, a comparison is shown between the physical properties of sheets of an alpha-beta titanium alloy containing 2.2% iron-2.7% vanadium-balance titanium, and an alpha titanium alloy containing 2% aluminum-0.5% vanadium-0.2%siliconbalance titanium. These properties were obtained in the following conditions: hot rolled, hot rolled and annealed, and cold rolled and annealed. Higher ductility is normally expected after cold rolling and annealing rather than after hot rolling and annealing. What is probably the most important diiference in the two alloys, as regards their physical properties, is the hot rolled and annealed elongation values. The maintenance of high elongation in the alpha alloy is significant. Note the high elongation value of 18.4 in the alpha alloy, as compared to the elongation value of only 7.8 in the alpha-beta alloy.

The ratios of hot rolled and annealed to cold rolled and annealed elongation values are 89% for the alpha alloy and 72% for the alpha-beta alloy. Elongation values as low as 4% in 2" have been obtained on 0.040 thick hot rolled and annealed specimens from this particular alpha-beta alloy due to embrittlement during hot rolling.

TABLE I Comparison of the physical properties of a two phase and a single phase titanium alloy Ultimate Tensile Strength, p. s. i Yield Strength at 0.2% Offset,

P Proportional Limit, p. s. i Percent Elongation in 2 Minimum Bend Value:

Longitudinal Trauversen" Hardness, Rockwell A Modulus of Elasticity, p. s. i. 10

Alpha Beta. Alloy (2.2% Iron-- Alpha Alloy (2% Aluminum-$.50}, Vanadiu1n0.2% Silicon-Bal- 2.7% Vanadium-Balance Tianco Titanium) tanium) Hot Hot Rolled Gold Rolled Hot Hot Rolled Cold Rolled Rolled 1 Annealed 2 Annealed 9 Rolled 1 Annealed 2 Annealed 7.0 2. 5 2. 5 Brittle 2. 1 2. 1

5. 0 2. 0 2. 5 Brittle 2. 1 2. l

1 The normal 'hot rolling procedure is as follows: hot roll thick plate transverse to the forging direction at 800 C. Reductions of approximately 0.050" per pass are taken to a thickness of 0.150 and reductions of approximately 25% per pass are taken thereafter. These sheets were hot rolled to 0.04

3 Annealing consists of heating in air at 700 O. for 1 hour and air cooling. I 3 These sheets were hot rolled to 0.100, sandblasted, cold rolled to 0.063, annealed, cold rolled to 0.040

and annealed.

vide low ductility. We have discovered that by raising the transformation temperature and by narrowing the alpha-beta field-that is the temperature range through which both alpha and beta can exist-to be as small as possible, there is an absence of any acicular transformation product in the alpha titanium alloy, providing ductile and high strength Welds.

Moreover, it is an object of the present invention to provide an alpha titanium alloy having improved high I temperature physical properties over titanium alloys containing metastable beta or mixed alpha and beta, which may lose strength rapidly and become brittle at temperatures above 400 C. In accordance with the present invention, the alpha titanium alloys comprehended are stable up to 825 C. in the annealed condition.

Furthermore, it is an object of the present invention to provide an alpha titanium alloy characterized by the absence of beta or the transformed beta phase below 825 C. which results in the elimination of brittleness obtained in hot rolled annealed titanium alloy sheets containing both the alpha and'beta phases and the alpha Accordingly, it is a further object of the present invention toprovide an alpha titanium alloy in which the hot rolled and annealed elongation values of sheets, such as 0.040 thick sheets, are exceedingly high due to the absence of embrittlement during hot rolling.

A picture of the microstructure of the two phase titanium alloy set forth in Table 1, hot rolled to 0.040" sheet at 800 C. and annealed at 700 C. for one hour with air cooling, shows a definitely two phase structure, with very small particles, and no large grains evident. There is a medium amount of. small to medium size carbides, and the structure is typical-of one in which a brittle transformation product occurs on hot rolling.

In comparison, a picture of the microstructure of the alpha titanium alloy set forth in Table I, after hot rolling to 0.040" at 800 C., annealing at 700 C. for one hour and air cooling, shows a structure which is single phase with a few medium size carbides. Such pictures show clearly that no harmful embrittlement has taken place in this single phase structure during hot rolling at 800 C.

2,772,708 ;I1lustra tive compositions and properties of alpha titave'lop certain properties .or characteristics if carbon, nium alloys'embodying the invention appear in Table II oxygen and nitrogen are completely absent or only pres ent in very small quantities.- For instance, where a so= as follows:

TABLE II Minimum Bend Value Percent Con- Ult. en- N (lition sile Stu,

p. s. i.

Percent Percent Percent Percent I 1 v o 10.7 68.8 2 3.0 72.0 1 .4 07.0 2 i 3 0 2 l 0.5 0.2 17.7 05.7 2 0.5 0.2 17.7 07.0 2 0.5 0.2 12.9 05.7 2 I 0.5 0.2 11.; 00.4 14. 00.0 1 11.5 09.0

In Table II, the designation HR means hot rolled to called strong titanium sponge is used, that is a raw -040 at 800 C. and the designation HRA means hot material which has higher than average oxygen and nitrorolled and annealed at 700 C. for one hour and air gen contents, an alloy containing 2% aluminum1% cooled after hot rolling. The percentages of alloying vanadium0.2% siliconbalance titanium is very satiselements indicated in Table 11 are intended composition, factory. wet chemical analyses of bro 'en specimens sometimes It has been found that carbon, say from 0.050% to being at variance with the intended composition. 0.6%, with or Without 0.010% to 0.1% nitrogen or Illustrative compositions and properties of alpha ti- 0.050% to 0.5% oxygen, or both oxygen and nitrogen, tanium alloys embodying the invention and including may be used. Alpha titanium alloys of the invention zirconium as an alloying element appear in Table III may include either the minimum amounts of such elewhich also includes properties of unalloyed titanium ments made with high purity titanium, or selected which does not have the improved properties of the alpha amounts thereof added to high purity titanium, or titanium alloys of the present invention, as follows: amounts thereof within the ranges stated when the alloy TABLE III Properties of. alpha titanium alloy sheets made from titanium base with zirconium as an alloying element in percentages indicated l 1 Yield $00. Minimum Bend Percent Percent Percent Percent] Percent. Percent U10. Tenat 0.2% Pro. Percent Hard. Value 1 y Zr Si l C l N Condition sile Stu, Offset, Limit, Elong. Rockp.'s. i. p. s. i. p. s. i. in 2" well A I L. T. I I g 2 l 2 0. 5 29 0115 HRA 125, 400 123, 400 116, 200 14. 4 69 0 3 6 5 2 2 2 0. 2 2, 5 l 1 2 36 0196 ERA 103, 900 98, 700 85, 350 15. 0 67 0 3. 6 2 1 3 1. 5 1 40 0155 ERA 110, 800 102, 700 92, 400 14. 5 64 3 2.1 2 1 Unalloyed Titanium 61 0123 HRA 105, 800 96, 900 84, 400 13. 5 64. 2 3. 6 2 1 Unalloyed Titanium 38 0098 HRA 74, 150 62, 100 50, 200 23. 8 59. 9 0. 5 O 5 Unalloyed Titanium 53 0273 HRA 83, 600 74, 100 66, 100 18. 7 58. 5 2. 1 1 0 The titanium base metal used in making the alpha titanium alloys of the present invention may be high purity titanium metal or commercial titanium as normally produced. In either event, the titanium base metal may contain substances or impurities normally found in either high purity titanium or commercially pure titanium such as carbon, oxygen and nitrogen in amounts varying with the degree of purity.

Sometimes one or more of the elements, carbon, oxygen or nitrogen, may intentionally be introduced in the alpha p titanium alloys of the present invention. For example, 10 elements, can be included in one titanium alloy which all of the alpha stabilizers are potent strengtheners in will still be all alpha. This is important because the connection with carbon, oxygen and nitrogen, but they strength level of the resulting alloy depends on the amount are not so potent when carbon, oxygen and nitrogen are of alloying agents added, and a wide range of tensile absent. Thus, as a general rule, a greater amount of strengths may be obtained, depending on the amount or ,one or more alloying elements may be necessary to deamounts of alloying elements present. For instance, if

is made from commercial titanium containing varying amounts of such substances or impurities.

In the examples given in Tables II and III, the alloys in each instance, unless otherwise shown, contain approximately 0.02% nitrogen, 0.2% oxygen and 0.3% to 0.6% carbon.

We have unexpectedly discovered a most interesting and significant characteristic regarding the alpha titanium found in combination in a titanium alloy.

1.5% v.ot' X element,..and.0.5% of Y element, and, 3%

Atypical annealing operation of 0.040" sheets rolled from alpha titanium alloys of the present invention may be carried outin amuflietype-air-fur-nace at 700 C..for

one hour with air cooling. Annealing of alloysof the present invention in semi finished or finished form, other than sheets of the stated thickness, may be carried out in the manner just described.

In the foregoing tables the bend characteristics are measured as the radius upon which the sheets can be bent without fracture to an angle of 75 the radius being stated as a multiple of the specimen thickness.

Although preferred percentages and combination percentages of the various addition elements in the alpha titanium alloys of thepresent invention are given in Table ll, aluminum may be present in amounts of from 0.50%

to 5.0%;vanadium may be present in amounts of from 0.50% to 3.0%; and silicon from 0.05% to 1.5%. The maximum for vanadium is 3.0% since up to such an amount with the other alloying elements, vanadium hasa good and not a detrimental affect on the alloy as awhole. Silicon has a tendency to hold the elongation at a certain level andto obtain increased strength; and the percentage of silicon can be on the high side it the percentages of aluminum and vanadium are on the low side.

Zirconium has been indicated in several of the examples in Table III as an alloying element. along with aluminum .and silicon or vanadium. Up to 3% zirconium produces a good butanot outstanding strength-ductility relation.

The alpha titanium alloys of the present invention incorporate in combination-a number of desirable and outstanding, characteristics and properties heretofore not Thus sheets hot rolled from such alloys have a good combinationof strength and ductility, providing as an averagev a 115,000 p. s. i. minimum yield strength, with approximately 15% elongation in 2" as hot rolled or as hot rolled and annealed; along with a 3T minimum bend in sheets from 0.015" to 0.125; and provide weldability and lack of embrittlement at elevated temperatures up to 650 C. for --four hours.

In addition to the foregoing, the alloys possess a workable degree of reproduc'bility so as to be suitable for production if'proper specification requirements of the spongeraw material are met.

Another matter wort-hyof comment is the fact that aluminum and siliconare good addition elements from the standpoint of lightness since they do not tend to increase the density of the resulting alloy.

aluminum, 0.50% ..to 3% hot rolled to 0.0 -.700 C- for onehourand air cooled, a115,000 p. s. i. v.minimum yield strength and about 15% elongation in2".

.Q ysen ans ai tn enh r bee in spia ld wss a .ills sl hIi 'sh' small amounts as impurities in'titaniurn alloys; I to stabilize the hexagonal alpha structure and may be intentionally added for improvement of physical properties.

lficcordinglu the present invention provides new alpha titanium alloys having outstanding new characteristics and avoiding :d fliculties, defects and undesirable characteristics heretoi o'r eipresent in unalloyed titanium sheets or titanium alloy sheets, the examples given being typical of the alloys andtheirproperties comprehended by the present invention.

We claim:

1. Analphatitanium .alloy composed of. in excess of 90% titanium, 0.50% to 5% aluminum, and the balance of said alloy being substantially only vanadium and silicon.

An alpha titanium alloy comprising 50% to 5.0% aluminum, .50% to 3%. vanadium, 05% to 1.5% silicon and the balance being substantially only titanium.

3. An alpha titanium alloy consistingessentially of 2 aluminum, 0.5% vanadium, 0.2% silicon and the balance substantially v only titanium.

,4. .An alpha titanium alloy consisting essentially of 2% aluminum, 1% vanadium, 0.2% silicon and the balance substantially only titanium.

5. An alpha titanium alloy comprising 0.50% to 5% aluminum, 0.50%v to.3%.vanadium,0.05% to 1.5% silicon and the balance titanium with carbon, nitrogen and oxygen. as incidental impurities.

. 6..An alpha titaniumalloy comprising 0.50% to 5% vanadium, 0.05% silicon and .the balance titanium with incidental impuritiesofnot over 0.6% carbon," 0.1% nitrogenand 0.5%

v oxygen.

7. Analphatitanium alloy comprising 050% to5% aluminum, 0.50%Yto.3%' vanadium, 0.0 '5% to 1.5% silicon and the balance being substantially only titanium, the alloy being characterized by-the absence of the beta orthe trans formedbetaphase below 825 C. and by the absence of brittleness present in hot rolled annealed-titaniumalloysheets containingboththe alpha and beta phases, and being further characterized'by having, as sheet at 800 C. and annealed at References Cited in the fileof this patent UNITED STA TES PATENTS 'Swazyet a1. Dec. 1, 1953 OTHER REFERENCES Titanium Project, Navy Contract No. Noa (5) 51- 006-c;- Report No. 9 Final Report. Released asPB ;107l50,-Sept, 12, 1952, pages 44 and 45, are most pe rtinent.

to.1.5% I

Claims (1)

1. AN ALPHA TITANIUM ALLOY COMPOSED OF IN EXCESS OF 90% TITANIUM. 0.50% TO 5% ALUMINUM, AND THE BALANCE OF SAID ALLOY BEING SUBSTANTIALLY ONLY VANADIUM AND SILICON.