US2754205A - Titanium base alloys - Google Patents

Description

United States Patent "Ofifice 2,754,205 Patented July 10, 1956 TITANIUM BASE ALLOYS Robert I. Jaifee, Worthington, and Horace R. Ogden and Daniel J. Maykuth, Columbus, Ohio, assiguors, by mesne assignments, to Rem-Cru Titanium, lnc., Midland, Pa., a corporation of Pennsylvania No Drawing. Application December 28, 195-3, Serial No. 400,745

3 Claims. (Cl. 75-175.5)

This invention pertains to titanium base alloys containing as essential constituents aluminum and zirconium in proportions as specified below.

The use of titanium as a structural material is limited by its relatively low tensile strength and high cost, and it therefore becomes desirable to alloy with titanium such other metals as will increase the strength to acceptable levels, and preferably at the same time effect some reduction in total material cost. Aluminum is a metal well suited to the attainment of these objectives, being low in weight, relatively low in cost, and having a material strengthening effect on titanium. However, the amount of aluminum alone that can be added to titanium is limited by its adverse effect on ductility. Binary alloys of titanium with more than about 8% of aluminum are somewhat brittle, while those containing less than about aluminum are of reduced strength as compared to those containing upwards of 5% aluminum. A further strengthening as well as an increase in the content of relatively inexpensive aluminum that may be employed, is highly desirable.

The present invention comprises the discovery that additions of zirconium to titanium-aluminum alloys, effects a marked improvement in properties, and likewise enables the aluminum content to be increased to as much as about 10%, with material increase in strength, while maintaining adequate ductility for fabrication purposes.

We have found that additions of zirconium in amounts ranging from as low as about 0.5% to as high as about 40%, effectively strengthen titanium-aluminum alloys, containing aluminum over the range of about 0.5 to 10%, without appreciable impairment of the ductility characteristics. A preferred range analysis is about 3.5 to 10% aluminum with about 1 to 20% zirconium, as the alloys throughout this range are extremely strong and ductile. For securing an optimum combination of strength combined with good ductility, the zirconium should be on the high side of its range when the aluminum is on the low side of its range, and vice versa.

The alloys of the invention are further strengthened without undue loss of ductility by controlled and limited additions of the interstitials carbon, oxygen and nitrogen. To this end carbon may be added in amounts up to about 0.3%, and oxygen and nitrogen up to about 0.2% each.

As is known, the metal titanium, in the pure state, is capable of existing in either of two allotropic forms. Below about 885 C. or 1625 F., it assumes a closepacked, hexagonal micros-tructure known as the alpha phase, while at this temperature and above, it assumes a body centered, cubic structure known as the beta phase.

Certain substitutional alloying additions to the titaniumbase metal, among which are included aluminum as well as the interstitials carbon, oxygen and nitrogen, tend to stabilize the alpha phase, and thus may be referred to as alpha promoters.

Other substitutional alloying elements, when added in progressively increasing quantities, stabilize the beta phase at progressively lower temperatures, until a mixed alpha-beta or all-beta microstructure is obtained at normal or atmospheric temperatures, or the beta phase undergoes an eutectoid reaction, depending on the character and amount of the beta stabilizers added.

Zirconium forms a continuous series of solid solutions with titanium, since the beta forms of both elements are isomorphous, and since the alpha forms of both elements are likewise isomorphous, it thus forms an alpha-beta isomorphous system with titanium. The addition of zirconium tends to stabilize or promote the beta phase of titanium in that the lowest temperature at which the alloy is entirely beta becomes progressively lower with increasing amounts of zirconium until a point is reached at which this so called beta transus temperature starts to increase again with further additions of zirconium. While zirconium thus lowers the transformation temperature of titanium, the alloys eventually revert to the alpha phase at lower temperatures unless other beta promoters are present. However, in view of the fact that zirconium forms an alpha-beta isomorp'hous system with titanium, where the beta reverts to alpha on cooling, the resulting alloys are characterized by high thermal stability, in that the beta phase stabilized by zirconium does not form eutectoid decomposition products.

Thus the titanium-aluminum-zirconium alloys of the invention are characterized by high strength and ductility combined with high thermal stability.

The alloys of the invention may be prepared by meltcasting in an atmosphere of argon, rolling at a suitable temperature, say 980 C., and annealing under condi- -ti0ns which will effect recrystallization, but not substantial grain growth or re-solution of carbides. A typical but by no means universal annealing treatment comprises soaking at a temperature of about 850 C. for about 3 /2 hours. The titanium base metal employed should be of acceptable purity. such as iodide" base titanium as produced, for example, in accordance with Patent No. 1,671,213 to Van Arkel, or the commercial purity product obtained by magnesium reduction of titanium tetrachloride in accordance with the process described in Patent No. 2,205,854 to Kroll.

The properties of selected alloys in accordance with the invention made from iodide base titanium, as annealed 3 /2 hours at 850 C. are given below in the following table.

Table l Composition, Per- Tensile Properties-p. s. i. X 1,000

cent (Balance Vickers Titanium) Hardness 0.2% Ultimate Percent Bend Ofiset Strength Elongaw Al Zr Yield tlon in l" L 5 268 62 79 17 5 l 291 65 78 2O 0. 7 5 2. 5 28S 71 84 17 0. 3 5 5 303 83 96 17 l. 0 5 l0 322 92 103 14 l. 3 7.5 361 101 101 20 3.0 7.5 2.5 33G 99 100 17 1.2 7. 5 2. 5 O 25 375 127 131 10 0. 8 7. 5 5 349 114 22 O. 9 7.5 7 5 371 113 116 22 0.9 10 1 307 1O 2. 5 38-1 121 123 5 B1 2 0. 5 3O 309 1 114 5 6. 2

I As east hardness.

Y Rolled 850 0., annealed V4 hour at 850 C. and quenched. The 'liO.5Al-30Zr alloy, after aging 48 hours at 400 C. was found to have a minimum bend radius of -2.0 T longitudinal and 3.0 'I transverse.

1 Brittle.

As shown by the data in the table, the alloys according to the invention are quite ductile, having tensile elongations of at least 5% and minimum bend ductilities, in general, under 2. These alloys are quite ductile with minimum bend ductilities up to 7. Where the alloys are to be used in the form of sheets the minimum bend ductilities may range as high as 20, and where they are to be used in massive form, as in forgings, the percent tensile elongations may range as low as about 2%.

It will be also noted from the data in the table that the alloys according to the invention have tensile strengths at least 10% in excess of that of the unalloyed titanium base metal. The tensile strengths of the zirconiurnscontaining alloys are also substantially higher than for the corresponding binary titanium-aluminum alloys, and are also in general more ductile, panticularly as regards bend ductility. Furthermore, brittle binary titanium-aluminum alloys are rendered strong and ductile as shown by the data for the Ti-lO Al analysis.

The alloys of the invention may be welded without appreciable impairment of ductility in the welded as compared to the non-welded portions, by reason, among others, of their thermally stable characteristics above mentioned.

This application is a continuation-in-pant of our application Serial No. 209,904, filed February 7, 1951, and now abandoned, and our copending application Serial No. 327,422, filed December 22, l952.

What is claimed is:

1. An alloy consisting essentially of: about 0.5 to 10% aluminum, about 0.5 to 40% zirconium, aluminum being present on the low side of its range when zirconium is present on the high side of its range and vice versa, up to about 03% carbon, up to about 0.2% each of oxygen and nitrogen, and balance substantially titanium characterized in having a minimum bend ductility of no more than 20T, and a tensile strength at least 10% in excess of that of the corresponding titanium-aluminum binary alloy.

2. An alloy consisting of: about 0.5 to 10% aluminum, about 0.5 to 40% zirconium, carbon up to about 0.3%, oxygen and nitrogen up to about 0.2% each, balance titanium.

3. A titanium base alloy consisting essentially of about: 3.5 to 10% aluminum, 0.5 to 40% zirconium, up to 0.3% carbon, up to 0.2% each of the oxygen and nitrogen, characterized in having in the annealed condition, a minimum bend ductility of not over 7 T, a tensile elongation of at least 5% and a tensile strength of at least 80,000

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Report No. 5, The Manufacture of Titanium Alloys,"

prepared by PR Mallory and 00., Indianapolis, under Navy Contract No. NOa (S) 10,683, Oct. 20, 1950. 30 Pages '40 and 44.

Claims (1)

1. AN ALLOY CONSISTING ESSENTIALLY OF: ABOUT 0.5 TO 10% ALUMINUM, ABOUT 0.5 TO 40% ZIRCONIUM, ALUMINUM BEING PRESENT ON THE LOW SIDE OF ITS RANGE WHEN ZIRCONIUM IS PRESENT ON THE HIGH SIDE OF ITS RANGE AND VICE VERSA, UP TO ABOUT 0.3% CARBON, UP TO ABOUT 0.2% EACH OF OXYGEN AND NITROGEN, AND BALANCE SUBSTANTIALLY TITANIUM CHARACTERIZED IN HAVING A MINIMUM BEND DUCTILITY OF NO MORE THAN 20T, AND A TENSILE STRENGTH AT LEAST 10% IN EXCESS OF THAT OF THE CORRESPONDING TITANIUM-ALUMINUM BINARY ALLOY.