US2884323A - High-strength titanium base aluminumvanadium-iron alloys - Google Patents

Description

United States A Patent HIGH-STRENGTH TITANIUM BASE ALUlVIlNUM- VAN ADIUM-IRON ALLOYS Stanley Abkowitz, Paul E. Moorhead, and James R.

Gross, Warren, Ohio, assignors to Mallory-Sharon Metals Corporation, a corporation of Delaware No Drawing. Application May 7, 1957 Serial No. 657,501

7 Claims. (Cl. 75--175.5)

ductility and formability accompanied by high strength 7 in the as-annealed condition, and good ductility and extremely high strength in the aged condition; and this application as a continuation-in-part of the copending application of Stanley Abkowitz and Paul E. Moorhead, filed June 19, 1956, Serial No. 592,260, now Patent No. 2,819,959.

. Furthermore, the invention relates specifically to a titanium base alloy having a minimumyield strength as annealed, of about 169,000 p.s.i., with excellent elongation andbend ductility as annealed, and adequate elongation and bend ductility as aged.

Finally, the new titanium base alloy of the present invention is useful in both the annealed and age-hardened conditions and is characterized by the absence of compound embrittlement, good ductility and very high strength and depth of hardening.

H Application Ser. No. 592,260 indicates that normally an increase in strength of titanium can be obtained by the addition of a strengthener. Iron may be used as' a strengthener but it is a strong compound former.

alloy without the added high oxygen content, in the as annealed condition, and that the ultimate strength of the high oxygen content alloy can be increased by solution treatment and age-hardening to a strength in excess of 200,000 pounds per square inch, while retaining adequate elongation and bend ductility properties.

A most important and outstanding characteristic of the alloy of the present invention is its high oxygen tolerance.

Another outstanding characteristic of the improved Al-V-Fe titanium alloy described in said application Ser. No. 592,260, and also ofthe improved alloy having a high oxygen content of the present invention is that there is no apparent embrittlement resulting from compound formation following heat treatment or heating of any kind.

A further unusual characteristic of the improved alloy either with or without a high oxygen content is the ease with which it may be melted as compared with the melting problems involved in the manufacture of a manganese-titanium binary alloy which has comparable ductility, but with which the problem of segregation in melting is ever present.

The improved high oxygen content alloy, as well as the same alloy with a low oxygen content, in addition to having good elongation and bend ductility in the asannealed condition with a high minimum yield strength,

' has excellent formability. Heretofore it has been difli- Vanadium'may be used to retard the formation of the I titanium-iron compound. However, vanadium is an expensive alloying element. Nevertheless, vanadium can be obtained at a much lower cost in the form of a master alloy with aluminum. This creates further problems because while aluminum like iron is a strengthener aluminum accelerates the formation of the titanium-iron compound with resulting embrittlement.

, In addition to the discovery set forth in said application Ser. No. 592,260 that certain quaternary alloys of aluminum, vanadium and iron can be made with a minimum yield strength as annealed of as high as 130,000 p.s.i., and with tensile and bend ductility properties comparable to those in other titanium alloys now used which only have a 110,000 p.s.i. minimum yield strength in the as-annealed condition; we have further discovered that when said quaternary alloys of aluminum, vanadium and iron have a high oxygen content intentionally introduced therein, a minimum yield strength as annealed of about 169,000 p.s.i. can be obtained while still retaining the same good elongation and bend ductility properties present in the cult to obtain such a rcombination of properties in titanium alloy material.

Furthermore, the high oxygen content alloys of the present invention are characterized by the discovery that thestrength level of the alloy described in said application Ser. No. 592,260 having an oxygen content of 0.10%- 0.15% can be substantially increased by the intentional addition of oxygen to the melt or by increasing the. oxygen content of the sponge used until the total oxygen content of the alloy is about 0.48% 0 without seriously reducing elongation and bend ductility.

The attainment of the described unusual results, characteristics and properties in a titanium base .alloy is of outstanding importance in satisfying an existing need in the art. Prior commercial titanium alloys in which high strength approaching 200,000 p.s.i. ultimate. strength could be provided had little or no elongation and bend ductility in the age-hardened condition, so that such alloys could not be used where such high strength was in which 'noapparent embrittlement occurs resulting from compound formation following heat treatment, even' required. Similarly, with prior alloys, where adequate elongation and bend ductility values are present in the age-hardened condition, strength values in "excess of 180,000 p.s.i. developed.

Accordingly, it is an object of the present invention to provide a new quaternary titanium sheet and bar alloy ultimate tensile strength could not be though the alloy contains iron and aluminum as strengtheners.

Also, it is an object of the present invention to provide a new quaternary titanium alloy which is easy to produce without segregation during melting, Which has high strength and good elongation and bend ductility and formability in the as-annealed condition and which may be age-hardened to in excess of 200,000 p.s.i. ultimate tensile strength while retaining adequate elongation and bend ductility.

Furthermore, it is an object of the present invention to provide a new high-strength heat treatable sheet and bar titanium alloy with which hardening to a considerable depth is possible.

In addition, it is an object of the present invention to provide a new quaternary titanium sheet alloy which is lighter in weight, or has a lower density than other titanium alloys presently used which have less favorable properties from the standpoint of minimum yield strength, as annealed, but which other alloys may have comparable bend, tensile and ductility properties.

Finally, it is an object of the present invention to provide a new quaternary titanium base sheet alloy containing about 1.5% aluminum, 8% vanadium, and 3%5% iron; and to provide a new high-oxygen content quaternary titanium base sheet and bar alloy containing 0.8%- -1.8% A1, 7.5%8.5% V, 4.5%5.5% Fe and 0.30% 0.50%

These and other objects and advantages apparent to those skilled in the art from the following description and claims may be obtained, the stated results achieved, and the described difficulties overcome by the discoveries, principles, compositions and alloys which comprise the present invention, the nature of which is set forth below illustrative of the best modes in which applicants have contemplated applying the principlesand which are particularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The alloys of the present invention may be prepared from either commercial titanium or high-purity titanium. Where prepared from commercial titanium, a typical analysis of the material in addition to titanium, alumi num, vanadium and iron is 0.02% C, 0.01% N 0.10% 0 and 0.005% H In other words, presently available sponge having a sponge hardness of 120 BHN is suitable. However, since the high oxygen content alloys of the present invention contain substantially more oxygen than present in 120 BHN commercial titanium sponge, it is necessary to provide the additional total oxygen content in the alloy either by using a sponge having a much higher interstitial oxygen content or by adding commercially pure T10 to the melt.

In practice, the titanium is preferably melted by the electric arc process in a water-cooled copper crucible either in a vacuum or in an atmosphere such as argon, and the alloying elements are added to the melt either separately or in alloying combinations of vanadium and aluminum, vanadium and iron, or vanadium, iron and aluminum, as well as TiO where a high interstitial sponge having the desired high oxygen content is not used.

In general, the alloys of the present invention may comprise 0.8%1.8% Al, 7.5%-8.5% V, 4.5%-5.5% Fe and 0.30%0.50% 0 the balance being titanium. More particularly, the preferred high oxygen content alloy of the present invention may have a nominal composition of 1.3% A1, 8% V, Fe and 0.4% O with the balance titanium.

The alloys of the present invention after melting and casting may be processed in the usual manner and forged or rolled to form the desired semi-finished or finished product. For instance, ingots of the improved quaternary alloys may be forged or bloomed to slab form, .hot rolled to sheet bar, and the sheet bar may be rolled to form finished sheets, say, .020" to .090 thick, say for example 0.40" sheet. Alternately, bars may be produced by forging or blooming to billets and hot rolling the bars to the desired size, for example, bars.

Several examples of alloys disclosed in said application Ser. No. 592,260 without a high oxygen content but otherwise comprising the improved Al-V-Fe quaternary alloy of the present invention are as follows:

TABLE I Nominal or Intended Composition Example No. Heat N 0.

Percent;

Percent Percent Percent V Fe Al Ti 8 Bal. DM 455 8 3 1.5 5 1.5 Bel.

The mechanical properties of annealed sheet fabricated from alloys in Table I as determined by evaluation, are indicated in Table II below:

tility with a minimum as-annealed yield strength of 122,200 p.s.i. and higher with larger amounts of iron, and with freedom from embrittlement resulting from compound formation following heating or heat treatment.

These alloys likewise have a relatively low density of about 0.169 pound per cubic inch for the alloy of Example 2 which compares favorably with a higher 0.172 density for the 8% binary manganese alloy which has a lower minimum yield strength in the as-annealed condition and which is more diflicult to make because of the segregation problem in melting.

These sheet alloys of Tables I and II accordingly provide quaternary titanium alloys which are relatively easy to make, which may have a 130,000 p.s.i. minimum yield strength or higher, as annealed, with good tensile and bend ductility, which have good forming characteristics, which have relatively low density, and which have a combination of the indicated properties heretofore not obtained in any known prior titanium alloy.

In accordance with the further discoveries of the present invention, if increasing amounts of oxygen are added to the alloys of Tables I and H the higher oxygen content alloys are characterized by a number of improved properties.

Thus, a high oxygen content alloy having a nominal composition of 1.3% Al--8% V5% Fe and 0.4% 0 has the typical properties set forth in Tables HI through VII below:

MECHANICAL PROPERTIES .In 2 inches.) 2 In 1. inch.)

TABLE IV Typical room temperature properties 0) heat treated .040" sheet bar Comparing the values in Table III with those in Table 11, the presence of 0.4% 0 in the alloy of Table III does not produce any detrimental eifects on the elongation and bend ductility of'the alloy in sheet form or on the elongation and reduction of area ductility of the alloy in bar form. However, the improved high oxygen content alloy has high strength and exceptionally good ductility in the annealed condition (178,000 p.s.i. U.T.S., 18.3% elongation in bar, and 178,000 p.s.i. U.T.S. and 12.9% elongation with a 2.2-4.2 T minimum bend radius in sheet) in spite of the high oxygen. The high oxygen alloy also has very high strength and good ductility in the age-hardened condition (195,000 p.s.i. U.T.S., 190,000 p.s.i., 0.2% olfset Y.S., 12% elongation and 30.1 RA in bar and 206,000 p.s.i. U.T.S. 195,000 p.s.i., 0.2% offset Y.S., 5.8% elongation and 6.1-5.9 T bend radius in sheet).

Examination of the creep properties of the improved h gh oxygen content alloy indicates that the material may beqused safely up to 700 F. without encountering a large amount of permanent deformation.

Further, the improved high oxygen content alloy has satisfactory fatigue properties in sheet form, comparable to those of annealed manganese binary alloy sheet.

It has heretofore been believed that titanium alloys with a high interstitial content have been subject to notch embrittlement, that is, the notched to unnotched ratio may be 1 and below. We have discovered, however, that the high oxygen content alloy of the present invention has very satisfactory properties in this respect as shown in-- TABLE VI Typical n tched and unnotched tensile properties of bar Notched Unnotched Notched/ Condition UTS (p.s.i.) UTS (p.s.i.) Unnotched Ratio Annealed 230, 000 178, 000 1. 29 Age hardened 223, 000 195, 000 1. 14

In Table VI, the notched to unnotched ratio is above 1 in either the annealed (1.29) or age-hardened (1.14) condition, and thus the alloy is insensitive to notch embrittlement even though it has the indicated high oxygen content.

Furthermore, the new high oxygen content alloy of the present invention is not subject to compound embrittlement as indicated by the values given in Table VII An increase in the ultimate tensile strength and yield strength and in the minimum bend values and a decrease in the elongation values in the last two lines of Table VII would indicate the presence of compound embrittlement. However, these values in Table VII show marked stability, and the absence of compound embrittlement.

Investigation of the additions of increasing amounts of oxygen from the 0.08% 0 present in the alloys of Table II to the 0.4% 0 in the alloys of Tables III to VII shows that the yield strength of annealed 0.040" sheet material increases with the addition of oxygen up to a total oxygen content of about 0.4% 0 then decreases somewhat until the oxygen content is about 0.5% and then again increases until the total oxygen content is about 0.6% after which the material is completely brittle. The ultimate tensile strength of annealed material varies in a similar manner with an increasing total oxygen content.

The ultimate tensile strength and yield strength of 0.040" sheet material which has been age-hardened vary in a similar manner with increasing amounts of total oxygen content, the material showing the highest values with an oxygen content of about 0.4%.

The elongation values for 0.040" annealed sheet material remains relatively fixed with increasing amounts of total oxygen content up to about 0.4% 0 and the elongation values then drop off to about 10% with 0.5% 0 and about 7% with about 0.6% 0 Similarly, in' the age-hardened material the elongation values are relatively constant until a total oxygen content of about 0.4% 0 and then drop 011 with further increasing amounts of oxygen.

Finally, the minimum bend radius values (T in 0.040" sheet in annealed condition are relatively low until the total oxygen content of about 0.5% 0 is reached, after which these values rise rapidly and a similar curve applies to the minimum bend radius values for age-hardened material.

Consequently, a total oxygen content in the improved Al-V-Fe alloy of about 0.4% 0 produces the best combination of mechanical properties. The sheet material may be formed to desired shape in annealed condition where elongation (12.9%) and bend (2.2-4.2) ductility values are excellent after which formed parts may be solution-treated and age-hardened to provide finished parts having an ultimate strength of 206,000 p.s.i. and a yield strength of 195,000 p.s.i.

As indicated in the foregoing tables, the improved high oxygen content alloy may be annealed by soaking at 1250 F., then furnace cooling to 900 F. and then air cooling. Thirty minutes at temperature is a suitable soaking time for sheet whereas one hour of temperature is satisfactory for bar material.

The beta transus for the 0.4% 0 Al-V-Fe alloy of the present invention is 1525:25 F., and metallographic examination discloses a structure which is consistently an alpha-beta structure with relatively small particle size.

Age-hardening may be achieved with a maximum combination of strength and ductility by using heat treat- '7 merits indicated in the tables, that is, for 0.040" sheet, the material is solution treated for one-half hour at 1375 F. and water-quenched after which the material is aged for two hours at 1000 F. and air cooled. A similar treatment is used for bar except that the solution treatment at 1375 F. is for one hour.

End quench data indicates that hardening to a considerable depth is possible. This is of particular significance for bar stock, particularly where it is desired to use large size bars because a substantial depth of hardness (hardening of sections up to at least 2%" diameter) may be obtained. Thus, high-strength bars formed of the material may be used as structural meinbers because of the more-than-adequate elongation and reducti'on-of-area values in the age-hardened condition.

Furthermore, the high oxygen content alloy of the present invention has a low density of 0.168 pound per cubic inch.

It is to be understood that in the foregoing tables, where intended composition is indicated, there may be some variation in actual composition determined by chemical analyses. Compositions usually are close to the nominal or intended composition but may vary slightly either way from the intended values, depending upon the ability to control the exact amount of alloying additions made.

The high oxygen content alloys of the present invention accordingly provide quaternary titanium alloys which are relatively easy to make, which may have a minimum yield strength as annealed of about 169,000 p.s.i. with excellent elongation and bend ductility values, which have good forming characteristics, which have relatively low density, "and which may be age-handened to about 200,000 p.s.i. ultimate strength while still retaining satisfactory elongation and bend ductility values.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the .prior art, because such terms are used for descriptive purposes herein and are intended to be broadly construed.

Having now described the invention, the features, discoveries, and principles thereof, the characteristics of the new alloys, several examples of preferred embodiments of the new alloys, and the new and useful results obtained; the new and useful compositions, combinations, products, discoveries and principles, and reasonable me- 8 chanical equivalents thereof obvious to those skilled in the art are set forth in the appended claims.

We claim:

1. A titanium base alloy c onsisting o f 0.8 l.f Al, 7.5% 8.5% V, 4.5%5.5% Fe, 0.30%0.50% O and the balance titanium with incidental impurities.

2. A titanium base alloy consisting of 1.3% A1, 8% V, 5% Fe and 0.4% O and the balance titanium with incidental impurities.

3. A titanium base alloy consisting of 0.8%-1.8% A1, 7.5%-8.5% V, 4.5%5.5% Fe, and 0.30%0.50% '0 and the balance titanium with incidental impurities, and said alloy having as-annealed an elongation in excess of 12% and a minimum yield strength varying from in excess of 122,200 p.s.i. to 169,000 p.s.i., determined by the oxygen content within the range indicated. N I

4. A titanium ibase alloy consisting of 0.8%-1.8% Al, 7.5%-8.5% V, 4.5%5.5% Fe and 0.30%0.50% Q the balance titanium with incidental impurities, and said alloy being free from embrittlement resulting from compound formation following heat treatment.

5. A titanium base alloy consisting of 0.8%1.8% Al, 7.S%8.5% V, 4.5%5.5% Fe and 0.30%0.50% O and the balance titanium with incidental impurities, and said alloy having as age-hardened following heating and water'- quenching, an ultimate tensile strength of about 200,000 psi. and 5.8% elongation in 0.040" sheet form.

6. A titanium base alloy consisting of 0.8%'-1.8% Al, 7.5%'8.5% V, 4.5%5.5% Fe and 0.30%'0.50% O and the balance titanium with incidental impurities, and said alloy having as age-hardened following heating and water-quenching, an ultimate tensile strength of about 200,000 p.s.i. and 12.0% elongation in A" bar form.

7.-A titanium base alloy consisting of 0.8%l.8% Al, 7.5%8.5% V, 4.5%5.5% Fe and 0.30%0.50% O and the balance titanium with incidental impurities, and said alloy having as age-hardened following heating and water-quenching, an ultimate tensile strength of about 200,000 p.s.i. and 12.0% elongation in bar form and being hardenable to a considerable depth of the order of sections up to at least 2%" in diameter.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A TITANIUM BASE ALLOY CONSISTING OF 0.8%-1.8% AL, 7.5%-8.5% V, 4.5%-5.5% FE, 0.30%-0.50% 02 AND THE BALANCE TITANIUM WITH INCIDENTAL IMPURITIES.