US3399059A - Titanium alloys - Google Patents

Description

Aug. 27, 1968 Filed June 14, 1965 STRESS RUPTURE LIFE (MINUTES) 2 Sheets-Sheet 1 20 mm 27, HAFNIOM 5Q O a NO CARBON owggm. \wwHoor HAF-NIUM A A 036 ONLY. 30 A v v 8030 1 ONLY.

u a cmzscn AND mo \L 3 MlNUlTt-ZS. o o 0 2 7, CAKBON mus BORON F @G. E.

/i/l fiw-aas United States Patent 3,399,059 TITANIUM ALLOYS Evan William Evans, Hagley, and Michael Duncan Smith, Shenstone, Lichfield, England assignors to Imperial Metal Industries (Kynoch) Limited, London, England, a corporation of Great Britain Filed June 14, 1965, Ser. No. 463,573 Claims priority, application Great Britain, June 23, 1964, 25,932/ 64 10 Claims. (Cl. 75-175.5)

ABSTRACT OF THE DISCLOSURE -Titanium-base alloys consisting of 1535% molybdenum, 15-35% vanadium with the total molybdenum plus vanadium content being in the range 40-55% have high stress rupture life at high temperature. The properties of the basic alloy are improved by the addition of hafnium, boron and carbon.

This invention relates to titanium alloys containing substantial quantities of the beta stabilising elements molybdenum and vanadium and possessing a stable all-beta structure. The alloys combine high creep strength at elevated temperatures with good room temperature strength and adequate ductility.

Accordingly the present invention provides a titanium alloy containing 15-35% molybdenum, 1535% vanadium, the total molybdenum plusvanadium content being in the range 4055%, 0.010.2 boron, balance titanium apartfromimpnrities. The prSenC of boroninthealloys of the present invention confers good creep'properties' and a further increase in creep strength is obtained by additions of 0.15% hafnium and 0.01-0.2% carbon.

Zirconium up to 8% preferably in the range 4-8% may be added to these alloys to strengthen them and to raise the recrystallisation temperature 'by 75 C. or more and also to modify oxidation resistance. A content of 5% has been found to be satisfactory.

Incidental alloying elements, that is those elements which are well known in titanium metallurgy and which may be added in small quantities to the alloys of the present invention without adversely affecting their properties, may be present. Examples of such elements are (It-5% tungsten, tantalum, niobium and chromium to modify the strength and O-5% chromium, and aluminium to modify oxidation resistance.

Tungsten and niobium are the best of such elements for strengthening the alloys and tungsten may with advantage be added up to 10%, as shown in Table I.

Typical impurities are up to 0.5% each of silicon and iron, derived from the starting vanadium, up to 0.3% of oxygen and up to 0.1% each of nitrogen and carbon.

Alloys in accordance with the present invention include aircraft engines within their field of application. As is well known, density plays an important part in the choice of materials for use in aircraft and alloys herein described have a favourable density with which are combined good elevated temperature properties and good fabricability.

It is necessary that sufiicient of thebeta stabilising ele ments molybdenum and vanadium, about 45%, should bepresent in the alloy to give a useful level of creep resistance, the upper limit of the amounts in the alloy being set by considerations of both density and rate of oxidation, since molybdenum has a density of about twice that of titanium. Above about 50% total molybdenum and vanadium, any advantage that is derived from increased strength is 'otfse't'by increased deiisityJMor'eover, the rate of oxidation of these alloys increases rapidly as their ti.- tanium content is decreased below 50%. I a,

Alloys containing molybdenum and vanadium in the proportions herein described provide a basic composition possessing a stable all-beta structure having good creep properties and room temperature strength with adequate ductility, as can be seen from Table II. This basic composition can be further improved by the addition of boron, particularly in respect of stress rupture. The following example demonstrates the effect of boron.

Example I 120 gm. buttons of the alloys Ti- 25 Mo-25, V. and Ti-25 Mo-25 V-'0.1 B were melted under argon in a nonconsumable arc furnace using a tungsten electrode- The buttons were hammer forged to inch square bar at 1200 C. and rod rolled to /2 "inch square bar from a furnace at 1150 C. Stress rupture specimens were machined from the bars after they had been heated for minutes at 900 C. and air-cooled. A life of 137 hours in stress rupture test at 25 tons/sq. in. at 600 C. is obtained with boron. The alloy without boron had a life of only half this under the same test conditions,

Strengthening of titanium by a dispersion of hard carbides is only possible when the matrix is stabilised by the presence of large amounts of beta promoters in the manner specified herein, otherwise the dispersion is unstable in favour of titanium carbide which is a relatively ineffective hardener at high temperatures. In a Ti-Mo-V base of the type described above, hafnium and carbon combine to form a-finely divided dispersion of carbides which appreciably strengthens the alloy when in use at temperatures between-500 and 600 C.-

The improvements in properties brought about separately by boron and by dispersion hardening can be incorporated into an alloy and thus results in a combination of good tensile properties at room temperature, excellent strength at temperatures between 500 and 600 C. and adequate ductility.

Example II A 5-pounnd ingot of the alloyl Ti-25 Mo-25 V-2 Hf-0.1 00.1 B was vacuum arc cast using a consumable electrode. The ingot was machined to approximately 2 inches diameter and extruded to 1 inch diameter at 1200 C. The 1 inch diameter rod was re-extruded to /2 inch diameter at temperatures between 1000 and 1200 C. Tensile and stress-rupture test-pieces were machined from the rod after heating for 1 hour at 900 C. and air-cooling.

Room temperature tensile test:

0.1% PS t.s. 67.7

U.T.S. t.s.i 73.5 Percent elong. on 4 /A 31 Percent R.A. 36

Creep tests:

20 t.s.i. at 550 C.0.02% total strain in hours. 20 t.s.i. at 575 C.0.0'6% total strain in 100 hours. 10 t.s.i. at 600 C.--0.1% total strain in 100 hours.

A basic composition containing 20% molybdenum and 20% vanadium is, however, preferred and alloys having this composition have been studied in greater detail and are discussed below.

The eifect'of zirconium, tantalum, tungsten and chromium on total strain in the first five hours of the stress rupture test are shown in Table III. Experience has shown that the creep strength of the alloys can be judged from such figures with reasonable accuracy. The carbon is also varied in alloys in the table and, whilst zirconium and tungsten improve strength, tantalum appears to have little or no effect.

" Additions of carbon and boron 'botliin" the presence of and in the absence of hafnium are shown in FIGURE 1 We claim:

in which the basic composition is Ti-20 Mo-20 V and is 1. A titanium-base alloy having high creep strength stress rupture tested at 30 tons/sq. in. at 600 C. It will consisting essentially of 15-35% molybdenum, 15-35% be seen that hafnium increases stress rupture life convanadium, the total molybdenum plus vanadium content siderably and carbon and boron alone produce the best 5 being in the range 40-55%, 0.01-0.2% boron, 0.1-5% results. In FIGURE 2 the effects of various amounts of hafnium, 0.01-0.2% carbon and the balance titanium hafnium, carbon and boron are shown on the stress rupapart [from impurities said alloy being characterized by ture life of Ti-20 Mo-20 V tested at 20 tons/sq. in. at containing a fine dispersion of hafnium carbide.-

575 C. In general, increase in the amounts of these three 2. A titanium-base alloy according to claim '1 containelements increases the life. ing in addition up to 8% zirconium.

- 0f the range of alloys herein disclosed, the preferred 3. A titanium-base alloy according to claim 2 containcompositions are Ti-20 Mo-ZO V-2 H'f-S W-0.2 B and ing in addition 4-8% zirconium.

Ti-2O Mo-20 V-2 Hf-S W003 00.03 B and Ti-20 Mo-20 4. A titanium-base alloy according to claim 2 contain- V-2 Hf-4 Zr-0.03 C. These alloys combine good creep g in addition 11p o 5% zi conium.

strength and ductility with good fabricability. 15 5. A titanium-base alloy according to claim 1 contain- TABLE L-EFFECT or ALLOYING ELEMENTS ON THE 1 addltlon to i i to 5% tantalum STRESS-RUP'IURE LIFE OF 'Ii-20 Mov TESTED AT 20 IllOblllm, chromium and aluminium.

T.S.I, AT 600 C. 6. A titanium-base alloy according to claim 5 contain- Alloy composition Stress-rupture life Elongation percent ing up to 5% tungsten.

(wt. percent) (hours) e 20 7. A titanium-base alloy having high creep strength con- 'Ii-20 Mo-20V 7.8 33 sisting of m-oylbdenum, 25% vanadium, 2% haf- 13 7 Q3 nium, 0.1% carbon, 0.1% boron, balance titanium and 5 Nb-.. 22 26 impurities, said alloy being characterized by containing a figi 5 g fine dispersion of hafnium carbide. 1 CL. 11 31 25 8. A titanium-base alloy having high creep strength Pg g 32 consisting of 20% molybdenum, 20% vanadium, 2% haf- 0.25 Br. 10 35 nium, 5% tungsten, 0.03% carbon, 0.03% boron, balance 8:? g; titanium apart from impurities, said alloy being char- 1.5 1 acterized by containing a fine dispersion of hafnium car- 0.25 B 9 81 30 bide.

TABLE II.--HOT HARDNESS AND STRESS-RUPTURE OF Tl-M0-V ALLOYS CONTAINING UP TO BY WEIGHT Composition, Hardness value (D.P.N.) Stress rupture test,

percent 600 0. Button Density, number Mo V gmJcc. Increasing temperature Decreasing temperature Elong.

Lite under percent R.I. 500 0. 600 C. 700 0. 700 0. 600 0. 500 C. R.T. 25t.s.i. (hrs) on 11st: gta uge eng 1 Flaws revealed on machining.

TABLE IIL-TOTAL STRAIN IN THE FIRST 5 HOURS OF THE STRESS-RUPTURE TEST FOR VARIOUS ALLOYS BASED ON Ti-20 Mo-20 V-2 Hf TESTED AT 20 T.S.I. AT 576 C.

Y Total strain, Ti Mo V Hf Zr W Ta Cr C B ins/ms. in

5 hours Balance in each 20 20 2 0. 1 0. 00% alloy. 20 20 2 0. 03 0. 1 0. 01

5 6 9. A titanium-base alloy having high creep strength 2,819,960 1/1958 Bomberger 75175.5 consisting essentially of 20% molybdenum, 20% vana- 2 933 7 9- 5 195 j ff 75 175 5 drum, 2% hafnium, 4% ZlI'COl'lluIIl, 0.03% carbon, bal- 3,306,739 2/1967 Evans et a1.

ance essentially titanium apart from impurities said alloy being characterized by containing a fine dispersion of 5 hafnium carbide. OTHER REFERENCES 10. A titanium-base alloy as in claim 1 wherein the Development of a Alloy for Use at 1200 total molybdenum plus vanadium content is in the range 18000 Armour Research Foundation March 1952 45-50%. 36

References Cited 10 pages' UNITED STATES PATENTS CHARLES N. LOVELL, Primary Examiner.

2,596,489 5/1952 Jalfee et a1. 75-1755

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