US3457068A - Titanium-base alloys - Google Patents

Description

United States Patent 3,457,068 TITANIUM-BASE ALLOYS Howard D. Cox and Harry W. Rosenberg, Henderson, Nev., 'assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 449,313, Apr. 19, 1965. This application Feb. 8, 1966, Ser. No. 525,825

Int. Cl. C22c 15/00; C22d 1/18; CZlc 1/30 11.5. C1. 75-1755 4 Claims ABSTRACT OF THE DISCLOSURE A titanium base alloy consisting essentially of about 1.5 to 3% Al, 1 to 4% Sn, the percent of Al plus Sn present not to exceed 3.5%, 2 to 4% Mo, up to 5% Zr, up to 0.5% Be, up to 0.4% in total amount of C, 0 and N balance titanium. The titanium alloy exhibits good weldability and immunity from stress corrosion in the presence of a halide or halogen environment.

This application is a continuation-in-part of our copending application Ser. No. 449,313, filed Apr. 19, 1965, now abandoned.

This invention pertains to titanium-base alloys and provides alloys of this type involving novel and critical proportions for imparting immunity to stress-corrosion cracking together with excellent strength and adequate ductility at room and elevated temperatures.

The alloys of this invention constitute a valuable improvement over titanium-base alloys heretofore in extensive, commercial use, all of which are subject to stresscorrosion cracking when exposed to elevated temperatures under stress in the presence of a halide or halogen environment, such as an atmosphere containing chlorine gas, hydrochloric acid or a chloride or other halogen salt, for example, sodium chloride. The attack manifests itself by surface-cracking of such alloys, resulting in fissures which increase in depth with time of exposure at temperatures usually above 500 F. Commercial alloys subject to this attack include such widely-used types as Ti-6Al-4V, Ti-8Al-1V-1Mo, T i-5Al-2.5Sn, Ti-4Al-3Mo-1V, etc.

As part of our investigation of this phenomenon, we have confirmed that unalloyed titanium metal including the commercial grades containing the interstitials carbon, oxygen and nitrogen within commercial tolerances as Well as considerably in excess thereof, is immune from stresscorrosion cracking. We have also confirmed that this immunity is retained within extremely critical upper limits when other metals are individually alloyed with titanium, these limits varying widely with the particular metal so alloyed. We have found, for example, that binary Ti-Zr alloys retain immunity to stress-corrosion cracking for zirconium additions up to about 40% by weight of the total, whereas for molybdenum additions the upper limit occurs at about 12% Mo, and for beryllium at the low value of about 1.5%. For the alpha promoter tin the upper limit is about 11% and for aluminum about 3.5%.

Based on this information, we have devised a series of strong, ductile, Weldable and creep-resistant alloys which are wholly immune to stress-corrosion cracking and which constitute the present'invention. These alloys consist es- 3,457,068 Patented July 22, 1969 sentially of about 1.5 to 11% of metal of the group aluminum and tin, the percentage of aluminum present plus the percentage of tin present not to exceed 3.5%, the alloys also containing about 2 to 4% molybdenum and may also contain up to 5% zirconium and up to 0.5% beryllium, these alloys being characterized as forged and annealed by an ultimate strength of at least 110,000 p.s.i., a tensile elongation of at least 3%, by good weldability and by immunity to stress-corrosion cracking. The preferred alloys of the invention will contain about 1 to 4% zirconium or about 0.1 to 0.25% beryllium, or both. With respect to the alpha promoters aluminum and tin, these alloys may contain only aluminum within limits of about 1.5 to 3.5% and preferably under 2.5%; or only tin within limits of about 4.5 to 11%; or may contain both of these elements within the broad limits abovestated, but preferably within limits of about 0.5 to under 2.5% aluminum plus about 1 to 4% tin. As regards its strengthening effect on these alloys, about 3% by weight of tin is equivalent to about 1% of aluminum, but in order to maintain the alloy immune to stress-corrosion cracking the equivalent aluminum content, i.e. the percentage by weight of aluminum present plus /3 the percentage by weight of tin present should not, as abovestated, exceed about 3.5%.

Additions of zirconium to the alloys of the invention, provides a means of enhancing alpha-strengthening without impairing immunity to stress-corrosion cracking, since as above pointed out large additions of this element may be made to an otherwise immune alloy without affecting this property. Beryllium additions strengthen the alloy by compound formation thereby to enhance elevated temperature creep resistance. Molybdenum, a beta promoter isomorphous with titanium, is included in these alloys as an essential constituent for enhancing the strength thereof without materially affecting ductility. At least 2% of this element is required for imparting the requisite strengthening while more than about 4% impairs weldability.

As above pointed out, the interstitial content of the alloys of the invention is not a controlling factor within relatively wide limits, i.e. up to about 3% carbon, 0.8% oxygen and 0.4% nitrogen as regards immunity to stresscorrosion cracking. However, from the standpoint of retention of good ductility the alloys should not contain more than about 0.05% of carbon and nitrogen and about 0.3% oxygen, the total interstitial content not to exceed about 0.40%. Total incidental impurities in these alloys including the interstitials and extraneous metallic and other elements should not exceed about 0.70%.

The alloys of this invention may be produced by conventional methods in which titanium metal is rendered molten in admixture with the desired proportions of recited alloying metals. Titanium metal in the form of sponge of commercial purity may be thoroughly mixed with the alloying elements as subdivided metal particles, and the admixture compressed into compacts which are then welded into a consumable electrode. This electrode may be melted in a suitable type of cold mold arc furnace and the resulting ingot may be remelted to provide improved uniformity and homogeneity. The so-produced alloy ingot may be processed by conventional techniques such as forging, extruding, rolling and other working finished articles, such as bar, sheet, strip, wire or tubing methods to produce intermediate mill products and semiand other shapes which may later be converted by additional working or forming procedures into final products or articles. After forging, rolling or working in the mill product stage, the alloy may be annealed to place it in best condition for further forming and fabrication and also for stress relief. Annealing at about 1300 F. for 1 hour followed by air cooling will be found to be effec tive for this purpose. The precise temperature and time may be dependent on the specific proportions of alloying elements.

Table 1, following, shows typical annealed tensile properties and stress-corrosion resistance of typical alloys according to this invention, together with, for comparison, a commercial titanium-base alloy of 4%Al-3%Mo- 1%V:

TABLE 1 Ult. 0.2% Elong., Stress 2 Alloy 1 Composition, Stu, YS, Percent Corrosion PercentBal. Ti K s.i. K s.i. in 1 Cracking 1.8 A1 -l 2J1 Mm 103 .0 None. 2.05 l 2.11 117 21 Do. 0.22 2.3 71--.. 2. 0. 4'0 Zr 123 23 Do. 0.22 Be 2 Al- 2 M 110 24 Do. a 3 ML" 112 Do. 2 Al- 2 Sn. 130 14 D0 4 Mo... 3 83 3 8 4 Zr. 2 Al- 4 Sn 135 15 Do. 4 Mo 3 87 3 7 4 Zr. 4 Al- 3 M0... 118 14 Dellnite 1 V Cracking.

1 Alloys melted and remelted to form an ingot which is forged then rolled to about 0.050-inch sheet and annealed at 1,300 F. for 1 hour and air cooled.

2 Stress-corrosion cracking determined by clamping a strip specimen into a U shape so that the outside fibers of the restrained bend are highly stressed. The stressed specimen is then exposed to a chlorine atmosphere for 2 hours at a temperature of 800 F. Such treatment will result in readily apparent stress-corrosion cracking in susceptible alloys, such as presently known commercial titanium-base alloys. The alloys of Table 1 that show no stress-corrosion cracking under test conditions would be immune in service.

3 Tested at 800 F.

To determine weldability, sheet section specimens were butt welded together. A section of the weld was then bent around a mandrel to determine the minimum radius around which the Welded specimen could be bent without cracking. This was compared with the minimum bend radius of the unwelded base metal. A separate tensile specimen was cut from a portion of the Welded sheet so that the weld metal lay transversely across the central portion of the specimen. The specimen was then pulled in a tensile machine, and tensile strength and ductility (tensile elongation) of the Weld metal thus determined.

Below in Table 2 are shown weld test results on the alloys of Table 1:

Cir

The alloys of this invention and articles produced therefrom are useful in the production of parts and components for structures requiring light-weight and high strength, such as airframes and jet engines, missiles and space vehicles. In addition these alloys, because of their immunity to stress-corrosion cracking in a chloride atmosphere, are particularly valuable when the end uses thereof involve exposure under stress to elevated temperature in a chloride or other halide environment. This may occur when aircraft or missiles are operated under conditions that their parts or surfaces reach relatively high temperatures while exposed, for example, to salt spray or ocean atmospheres.

What is claimed is:

1. An alloy consisting essentially of about: 1.5 to 3.0% aluminum, 1 to 4% tin, the percent of aluminum plus /3 the percent of tin present not to exceed 3.5%, 2 to 4% molybdenum, up to 5% zirconium, up to 0.3% beryllium, up to 0.4% in total amount of carbon, oxygen and nitrogen, balance substantially titanium, characterized by room temperature properties as forged and annealed, of at least 110,000 p.s.i. in ultimate strength and at least 3% in tensile elongation, and characterized further by good Weldability and high resistance from stress-corrosion cracking in the presence of a halide or halogen environment.

2. An alloy according to claim 1 containing about 1 to 4% zirconium.

3. An alloy according to claim 1 containing about 0.1 to 0.25% beryllium.

4. An alloy according to claim 1 containing about 1 to 4% zirconium and 0.1 to 0.25% beryllium.

References Cited CHARLES N. LOVELL, Primary Examiner