US3441407A - Titanium-base alloys - Google Patents

Description

April 29, 1969 E. W. EVANS ET AL 3,441,407

TITANIUM-BASE ALLOYS Filed March 11, 1965 Sheet of 2 AQEINC: CURVES FORYTi QVQAI'MO =W-Nb- ALLOYS AT (550C.

April 29, 1969 Filed March 11, 1965 E. W. EVANS ET AL TITANIUM-BASE ALLOYS Sheet Z 0f2 TEMPERATURE( c) HARDNESS 04-. 11 36V 8 AL 5M0 ac AT ELEVATED TEMPERATURES jMa-wraes E69 W/Ll/AIM Fw /vs 4/5 aaaerffOa V United States Patent 3,441,407 TITANIUM-BASE ALLOYS Evan William Evans, Hagley, and John Robert Moon, Jesmond, Newcastle-upori-Tyne, England, assignors to Imperial Metal Industries (Kynoch) Limited, London, England, a corporation of-Great Britain Filed Mar. 11, 1965, Ser. No. 438,987 Claims priority, application Great Britain, Mar. 11, 1964, 10,307/ 64 Int. Cl. C22c 15/00 US. Cl. 75-175.5 13 Claims ABSTRACT OF THE DISCLOSURE Beta titanium-base alloys containing vanadium and aluminium and a beta stabilizer from the group tungsten, molybdenum, niobium and tantalum. The alloys possess high creep strength and ductility and considerable fire resistance.

This invention relates to titanium-base alloys, and in particular to beta phase titanium-base alloys.

According to the invention a titanium-base alloy comprises aluminium 3%-10%, vanadium 20%-35%, one or more of the following beta stabilising elements: tungsten up to 15 molybdenum up to 15%, niobium up to 15% and tantalum up to 10%, balance titanium, apart from impurities, not less than 51% by weight.

The total concentration of beta stabilising elements should be such that the beta phase is retained at room temperature on air cooling thick sections, the known equivalence between the beta stabilising effectiveness of these elements being used to ensure that this condition is met.

Since the crystallographic structure of alloys according to the invention before heat-treatment is single phase body-centered cubic, such alloys may be processed in a ductile and malleable form and have excellent cold rolling characteristics. By a suitable heat-treatment, the alloys can be strengthened by precipitation of an ordered Ti-Al compound (D019 structure) which covers a range of compositions from Ti Al to T i Al. Formation of the compound increases the concentration of beta stabilising elements in the matrix which remains body-centred cubic, and completely stable at lower temperatures.

A high aluminium content is necessary to make the alloys both stronger and lighter, optimum aluminium content being 6%-9% by weight. Few of the alloys have a density greater than gm./cc.

Other alpha stabilising elements such as tin may be substituted either wholly or in part for aluminium with some improvement in strength. The upper limit for tin additions is 5% by weight, there being a well-known equivalent between the alpha stabilising elements of 3% tin for each 1% aluminium which can be used in substituting tin for aluminium in order to obtain the (-tin+aluminium) content corresponding to selected concentrations of aluminium.

Small amounts of zirconium or hafnium exert an appreciable influence on strength and ductility at room temperature. Limits of concentration of zirconium and 3,441,407 Patented Apr. 29, 1969 hafnium are: up to 2% zirconium and up to 4% hafnium, by weight.

Small amounts of the beta eutectoid elements, for example, copper, nickel, chromium, silicon and iron, may be present in amounts up to 2%. Silicon and iron in combination, which have an adverse effect on forgeability due to hot-shortness, should be kept as low as possible, and should not exceed 0.5% in total amount.

Alloys which forge and roll well and which are sufficiently ductile at 600 C. are obtained only by using in the manufacture of the alloys vanadium stock, whether aluminothermicor calcium-reduced, which has a sufficiently low content of oxygen and nitrogen and of iron and silicon in combination. The total maximum content of oxygen and nitrogen together should not exceed 0.15% and the combined amounts of iron and silicon should not exceed 0.5

Grain refinement is obtained by the addition of one or more of the elements carbon, boron, and thorium in amounts up to 1.25% carbon, up to 0.2% boron or up to 1% thorium, some loss of strength at 600 C. being experienced with the carbon addition.

Alloys in accordance with the invention which contain-up to 8% tungsten may be prepared without risk of tungsten segregation by using, the melting process, an aluminium-tungsten master alloy and for additional amounts of tungsten over 8% a vanadium-tungsten master alloy.

It has been found that although rather higher forging temperatures than are used for current commercial titanium alloys are required in the initial breakdown of the ingots, processing temperatures may thereafter be lowered to about 1000 C.

Examples of alloys in accordance with the invention and their stress-rupture and density properties are shown in the table.

The alloys may be heat-treated to develop good creep properties. Hardening over and above the increase in strength which has been brought about by elements in solution may be obtained by heat-treating at 650 C. to precipitate an ordered Ti-Al phase (D019 structure) in the form of extremely small platelets. The best creep strength is obtained when precipitation has been allowed to progress almost to completion. Typical ageing curves are shown in FIGURE 1 of the accompanying drawings.

Alloys in accordance with the invention have good resistance to softening at elevated temperatures. FIG- URE 2 of the accompanying drawings shows how hardness varies with temperature and compares the hardness/temperature curve of an alloy containing 35% vanadium, 8% aluminium, 5% molybdenum and 1% carbon with the probable curve of an alpha alloy (A) and an alpha-i-beta alloy (B) of the 11% tin, 2%% aluminium, 0.2% silicon types containing molybdenum and optionally zirconium. At 600 C. the points A and B, which were experimentally determined, are markedly lower than the hardness of the alloy in accordance with the invention which maintains a high level of hardness up to 600" C.

Alloys of the invention have considerable fire resistance.

TABLE [The efieet of composition on stress-rupturfi priliperties and density of 'Ii-V-Al-MO-W-Nb a oys Alloy composition. (wt. percent) Stress-rupture test,

30 t.s.l., 600 C. (Den/sit}; Allo No. gm. cc.

y V Al W Mo Nb Life, Strain, hours percent We claim:

1. Beta titanium-base alloys possessing high creep strength and ductility at 600 C. and considerable fire resistance, said alloys consisting essentially of 25-30% vanadium; 89% aluminium; l0% tungsten; at least one beta stabilizing element selected from the group consisting of about 5% molybdenum and about 5% niobium; oxygen and nitrogen together not exceeding 0.15% and iron and silicon together not exceeding 0.5%; balance titanium in an amount not less than 51%.

2. Beta titanium base alloys as claimed in claim 11, said alloy containing at least one grain refining element selected from the group consisting of up to 1.25% carbon, up to 0.2% boron, up to 1% thorium.

3. A beta titanium-base alloy as claimed in claim 1 consisting essentially of about 30% vanadium, about 9% aluminium and 5% tungsten, balance titanium.

4. A beta titanium-base alloy as claimed in claim 1 consisting essentially of about 30% vanadium, about 9% aluminium and 10% tungsten, balance titanium.

5. A beta titanium-base alloy as claimed in claim 1, consisting essentially of about 30% vanadium, about 9% aluminium, about 5% tungsten and about 5% molybdenum, balance titanium.

6. A beta titanium-base alloy as claimed in claim 1 consisting essentially of about 30% vanadium, about 9% aluminium, about 5% tungsten, and about 5% niobium, balance titanium.

7. A beta titanium-base alloy as claimed in claim 1, consisting essentially of about 25 vanadium, about 9% aluminium, and about 10% tungsten, balance titanium.

'8. A beta titanium-base alloy as claimed in claim 1, consisting essentially of about 25% vanadium, about 9% aluminium, about 10% tungsten and about 5% molybdenum, balance titanium.

9. A beta titanium-base alloy as claimed in claim 1, consisting essentially of about 25% vanadium, about 9% aluminium, about 10% tungsten and about 5% niobium, balance titanium.

10. A beta titanium-base alloy as claimed in claim ll, consisting essentially of about 30% vanadium, about 8% aluminium, and about 10% tungsten, balance titanium.

11. A beta titanium-base alloy as claimed in claim 1, containing up to 2% zirconium.

12. A beta titanium-base alloy as claimed in claim 1, containing up to 4% hafnium.

13. Beta-titanium alloys as claimed in claim 1, containing at least 5% tungsten.

References Cited UNITED STATES PATENTS 2,754,203 7/ 1956 Vordahl -175.5 2,754,204 7/1956 Jaffee et a1. 75-1755 2,769,707 11/1956 Vordahl 75-175.5 2,880,087 3/1959 Jatfee 75--175.5 2,880,088 3/1959 Jaffee et a1. 75175.5 2,892,705 6/1959 J atfee et a1. 75175.5

OTHER REFERENCES Journal of Metals, January 1957, pp. 43-46 relied on.

CHARLES N. LOVELL, Primary Examiner.

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