AU751281B2 - Titanium-aluminum-vanadium alloys and products made therefrom - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFCATION FOR A STANDARD PATENT

ORIGINAL

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Name and Address of Applicant: Oregon Metallurgical Corporation 530 34th Avenue, Southwest Albany Oregon 97321 UNITED STATES OF AMERICA Yoji Kosaka Actual Inventor(s): Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Titanium-aluminum-vanadium Alloys and Products made Therefrom Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845 1.

Titanium-Aluminium-Vanadium Alloys and Products Made Therefrom Field of the Invention This invention concerns titanium alloys comprising aluminium, vanadium, iron and a relatively high oxygen content, and products made using such alloys, including ballistic armour.

Background of the Invention In 1950, Pitler and Hurlich concluded that titanium showed promise as a structural armour against small-arms projectiles. Pitler et afs Some Mechanical and Ballistic Properties of Titanium and Titanium Alloys, Watertown Arsenal Laboratory (March, 1990). Titanium alloys are now being investigated for the same purpose. Ti-6AI-4V alloys, for example, have been used to form ballistic armour.

See, for example, Hickey Jr. et al.'s Ballistic Damage Characteristics and Fracture Toughness of Laminated Aluminium 7049-773 and Titanium 6AI-4V Alloys, Watertown Arsenal Laboratory (March, 1980). The Ti-6AI-4V alloys comprise, as the name implies, titanium, 6 weight percent aluminium and 4 weight percent vanadium. Most of the Ti-6AI-4V alloys have relatively lowoxygen concentrations of less than 0.20% by weight [all percents stated herein with respect to alloy compositions are percents relative to the total weight of the alloy, unless stated otherwise]. Ti-6AI-4V alloys having higher oxygen concentrations also are known, and such alloys have been used to produce ballistic plates. US. 5 332 545, for example, describes ballistic plates made from a Ti-6AI-4V alloy. This alloy has a preferred composition of 6.2% aluminium, 4.0% vanadium and 0.25% oxygen.

Another titanium alloy that has been used to produce ballistic armour is discussed in J.C. Fanning's Terminal Ballistic Properties of TIMETAL®62S, Titanium '95: Science And Technology (1996). Fanning describes a titanium alloy having 6.0% aluminium, 2.0% iron, a relatively low oxygen content of 0.18%, less than 0.1 weight percent vanadium and perhaps other trace elements. One measure of the effectiveness of ballistic plates is the average velocity (V 50 of a shell, such as a 20mm fragment-simulated projectile (FSP), required to penetrate such plates.

Plates fashioned from Fanning's alloy were tested using the US army's 20mm FSP test. The V 50 Fanning reported for such plates is 548m/s. Id., Table III, page 1691.

This V 50 value is representative of most titanium alloys, which generally have V 50 values for plates having thicknesses similar to Fanning's of less than 600m/s.

The current military minimum V 50 for a 15.6mm thick plate made from Ti-6AI- 4V ELI (extra low interstitial oxygen) using a 20mm FSP test is 583m/s. See military standard MIL-A-46077. For armour plates having a thickness of 16.1mm to 16.9mm, the V 50 values currently required by the military range from 591m/s to 612m/s.

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2 The Ti-6AI-4V alloys have been used to produce ballistic armour because they provide better ballistic results using less mass than steel or aluminium alloys against most ballistic threats.

Titanium alloys are therefore referred to as being "more mass efficient" with respect to ballistic properties than steel or aluminium alloy. But, the V 5 0 values of known titanium alloys are not entirely satisfactory, and such alloys are expensive to produce. As a result, there is a need for titanium alloys that can be formed less expensively than conventional titanium alloys, and which can be formed into ballistic plates having V 50 values that meet or exceed current military standards.

Summary of the Invention According to a first aspect, the present invention consists in a titanium alloy for armour plate, 1o comprising: from 2.9% to 5.0% aluminium; from 2.0% to 3.0% vanadium; from 0.2% to 2.0% iron; from 0.2% to 0.3% oxygen, and less than 0.5% of other elements, the balance being titanium.

According to a second aspect, the present invention consists in a process for producing a titanium alloy for armour plate comprising: forming an ingot comprising from 2.9% to aluminium, from 2.0% to 3.0% vanadium, from 0. 2% to 2.0% iron, from 0.2% to 0.3% oxygen, less than 0.5% of other elements, and the balance being titanium, and a-3 processing the ingot to provide an a-1 alloy.

According to a third aspect, the present invention consists in a titanium alloy prepared by the process of the second aspect.

According to a fourth aspect, the present invention consists in an armour plate comprising an a-1 processed titanium alloy comprising from 2.9% to 5.0% aluminium, from 2.0% to vanadium, from 0.2% to 2.0% iron, from 0.2% to 0.3% oxygen, and less than 0.5% of other elements, the balance being titanium.

According to a fifth aspect, the present invention consists in an armor plate comprising an alloy according to the first or the third aspect.

According to a sixth aspect, the present invention consists in a process for making armour plates, comprising: providing a titanium alloy comprising from 2.9% to 5.0% aluminium, from 2.0% to 3.0% vanadium, from 0.2% to 2.0% iron, from 0.2% to 0.3% oxygen, and less than of other elements, the balance being titanium; and forming armour plates from the alloy.

According to a seventh aspect, the present invention consists in a process for making armour plates, comprising: providing a titanium alloy comprising from 2.9% to 5.0% aluminium, from to 3.0% vanadium, from 0.2% to 2.0% iron, from 0.2% to 0.3% oxygen, and less than of other elements, the balance being BFF] 10208speci.do:njc [R:\LB FF] lO02O8speci.doc :njc 2a titanium; a-P processing the alloy to form an a-P alloy; and forming armour plates from the a-P alloy.

According to an eighth aspect, the present invention consists in a method for making armor plates, comprising the steps of: producing titanium alloy in accordance with the process of the second aspect and forming armour plates from the alloy.

The present invention provides novel titanium alloys and ballistic plates made from such alloys. These alloys can be produced less expensively than conventional Ti-6A1-4V or Ti-6A1-4V ELI alloys. Furthermore, ballistic plates made from such alloys have Vs 0 values equal to or exceeding plates made from most conventional titanium alloys, as well as the current military standards, as determined by FSP ballistic tests.

The titanium alloys of the present invention comprise from about 2.9% to about aluminium, from about 2.0% to about 3.0% vanadium, from about 0.2% to about 2% iron, and at least 0.2% to about 0.3% oxygen. Such alloys also can comprise elements 15 selected from the group consisting of chromium, nickel, carbon, nitrogen, perhaps other trace elements, and mixtures thereof, wherein the weight percent of each such element is about 0.1% or less, and wherein the total weight of such elements generally is about or less.

A method for producing titanium alloys also is described comprising a-p 20 processing a titanium ingot having the composition stated above. a-P processing generally includes, but is not limited to, the following steps: P forging the ingot above Tp to form an intermediate slab; a-P forging the intermediate slab at a temperature below Tp; a-p rolling the slabs to form plates; and annealing the plates. The o method also can involve the step of p annealing the intermediate slab prior to the step of 25 -P3 forging.

The step of heating the ingot to a temperature greater than Tp generally comprises heating the ingot to a temperature of from about 1037 0 C to about 1260 0 C, with 1149 0

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being a currently preferred temperature for this step. The step of oa- forging the intermediate slabs at a temperature below Tp comprises forging the slabs at a temperature of from about 621°C to about 968 0 C, and more generally from about 927 0 C to about 968 0

C.

a-P processing also can comprise P forging the ingot to form intermediate slabs, a- 1 p forging the intermediate slabs at a temperature below Tp, and a-P rolling the final slabs Sto produce plates, whereby the steps of a-P forging and rolling the final slabs to form plates achieves a percent reduction of at least about 50% in an [R:\LIBFF] 8speci.doc:nj [R:\LIBFF]10208speci.doc:njc cx-1 temperature range. The plates are then annealed. The step of a-P forging the slabs at a temperature below Tp and rolling the slabs to produce plates preferably achieves a percent reduction of from about 70% to about 92% in an a-1 temperature range.

Alloys produced according to the present invention have been used to make ballistic plates. Alloys with the best ballistic properties when formed into plates have comprised from about 2.9% to about 5.0% aluminium, from about 2.0% to about vanadium, from about 1.45% to about 1.7% iron, and from about 0.23% to about 0.3% oxygen. Such armour plates with thicknesses of from about 15.9 to about 17.2mm have V 50 values of at least as high as 575m/s, generally greater than about 600m/s, and preferably greater than about 620m/s, as determined by FSP ballistic tests.

Brief Description of the Drawing Fig. 1 is photomicrograph illustrating the x-3 microstructure of alloys made according to the present invention.

Detailed Description of the Preferred Embodiments The present titanium alloys can be fashioned into a variety of useful devices, including structural devices and ballistic armour. The present alloys are particularly useful for forming ballistic armour plates that, when fashioned into plates of about 16mm thick, have V 50 values of about 600m/s or greater. The composition of such alloys, ie., the elements used to form the alloys and the relative weight percents thereof, as well as the methods for making armour plates using such alloys, are described below. Ballistic tests were conducted on plates fashioned from the alloys I: to determine, amongst other things, V 50 values. These results also are provided 25 below.

SI. Composition The alloys of the present invention comprise primarily titanium, and if only the other alloying elements are stated it is to be understood that the balance is titanium.

Other than titanium, the present alloys also generally include aluminium, vanadium, iron, oxygen, chromium, nickel, carbon, nitrogen, and perhaps other elements in trace amounts.

A. Aluminium The titanium alloys of the present invention generally include less than about 5.4% aluminium, and preferably equal to or less than about 5.0% aluminium. Alloys having good ballistic properties when formed into plates have from about 2.5% to about 5.4% aluminium. Plates with the best V 50 values have been made using alloys having from about 2.9% to about 5.0% aluminium, and even more preferably from about 2.9% to about 4.0% aluminium.

libc/03459 B. Vanadium The titanium alloys of the present invention generally include less than about 3.4% vanadium. Alloys having good ballistic properties when formed into plates have had from about 2.0% to about 3.4% vanadium. Plates with the best V 5 0 values have been made using alloys having from about 2.0% to about 3.0% vanadium, and preferably from about 2.0% to about 2.6%.

C. Iron The alloys of the present invention differ significantly from the common Ti-6 AI-4V alloys in a number of respects, including the iron and oxygen concentrations.

Common Ti-6 AI-4V alloys have relatively low iron concentrations of about 0.2% or less, whereas titanium alloys of the present invention have iron concentrations generally equal to or greater than about Plates having good ballistic properties can be made from alloys having from about 0.2% to about 2.0% iron, typically from about 0.25% to about 1.75%, with the best ballistic results currently being obtained using alloys having from about 1.45% to about 1.6% iron.

D. Oxygen The alloys of the present invention include relatively high oxygen concentrations. "High oxygen" concentration is defined herein as greater than or equal to The oxygen concentration of the present titanium alloys generally is greater than about 0.2% and generally less than about with the best ballistic results currently being obtained using alloys having from about 0.24% to about 0.29% oxygen.

E. Other Elements As stated above, alloys of the present invention also generally include 25 elements other than aluminium, vanadium, iron and oxygen. These other elements, and their percents by weight, typically are as follows: chromium, 0.1% maximum, generally from about 0.001% to about 0.05%, and preferably to about 0.03%; nickel, 0.1% maximum, generally from about 0.001% to about 0.05%, and preferably to about 0.02%; carbon, 0.1% maximum, generally from about 0.005% to about 0.03%, and preferably to about 0.01%; and nitrogen, 0.1% S" maximum, generally from about 0.001% to about 0.02%, and preferably to about 0.01%.

A summary of the compositions of alloys made in accordance with the present invention is provided below in Table 1.

Table 1 Alloy Composition Alloying Element Percent by Weight Aluminium from about 2.5% to about 5.4% Vanadium from about 2.0% to about 3.4% Iron from about 0.2% to about -Oxygen from 0.2% to about 0.3% 3 -v

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-o 104 T O 1J libc/03459 Alloying Element Percent by Weight Chromium 0.1% maximum, and generally from about 0.001% to about 0.05% Nickel 0.1% maximum, and generally from about 0.001% to about 0.05% Carbon 0.1% maximum, and enerall from about 0.005% to about 0.03% Nitrogen 0.1% maximum, and generally from about 0.001% to about 0.02% Titanium and trace elements balance II. cx-P Processing Alloys having the elements discussed above, and the relative weight percents thereof, are processed to obtain products having desired characteristics and a mixed (x p microstructure. See, Fig. 1. The general processing steps for forming armour plates in accordance with the present invention are referred to herein as a(-3 processing steps. The (a-p processing steps include: forming ingots from alloys having the compositions discussed above; forging the ingots to form intermediate slabs; rolling the slabs to form plates; and annealing the plates.

The alloys also may be subjected to other, generally less important, processing steps. For example, plates made from such alloys also may be subjected to surface treatments.

A. Forming Ingots One object of the present invention is to decrease the cost of producing armour plates by using scrap and waste materials to form ingots. A principle source of metal for forming the ingots is scrap metal from Ti-6AI-4V alloys. The ingots need not be formed solely from scrap and/or waste material. Previously unused metals, referred to as virgin materials, also can be used. Thus, ingots having the compositions stated above are formed by conventional methods from raw materials selected from the group consisting of scrap metals and alloys, recycled metals and 20 alloys, virgin metals and alloys, and mixtures thereof. Scrap and/or waste metals and alloys currently are preferred primarily because such materials reduce the cost of making ingots.

B. Forging and Rolling 1. Forging Temperatures 25 Armour plates having excellent ballistic properties have been made using two primary forging steps. The first P forging step forms intermediate slabs andis carried out above p transus p transus is the lowest temperature at which 100% of the alloy exists as the p phase. The cc phase can exist at temperatures lower than Tp.

The second a-p forging step is at temperatures below Tp.

For the first p forging step above Tp, ingots generally are heated to temperatures above about 1037°C. The maximum temperature for this first forging step is not as important. It currently is believed that the temperature can be at least as high as about 1260 0 C. 1149 0 C is a currently preferred temperature for forging ingots above Tp.

libd03459 Slabs forged above Tp are subjected to the second a(-13 forging step in an a-13 temperature range. Temperatures of from about Tp minus 27.50C to about Tp minus 1110C, such as from about 8150C to about 968 0 C, and more generally from about 9290C to about 968 0 C, provide a working temperature range for performing the second forging step.

An optional 13 annealing and water quenching step also can be used to produce the alloys of the present invention. The 13 annealing and water quenching step generally is implemented after the 13 forging step and prior to the (-13 forging step. The purpose of the 13 annealing step is to recrystallise 13 grains.

2. Percent Reduction Instead of stating particular forging temperatures, the intermediate forging step also can be specified with reference to the "percent reduction" achieved bythe forging step and subsequent rolling steps, which are discussed below. Percent reduction is calculated by subtracting the final slab thickness from the beginning slab thickness, dividing the result by the initial slab thickness and multiplying the result by 100. For example, if a 3cm slab is forged to a 1cm slab, the percent reduction is 3 1 2 3 0.67 X 100 67.0%.

For cc-13 forging at temperatures below Tp and for the subsequent a-13 rolling steps, the percent reduction should be at least about 50.0%, more commonly about 60.0%, and preferably from about 70.0% to about 92.0%. Plates having good ballistic properties have been made by achieving a percent reduction of about 87.0% during the a-13 forging and subsequent rolling steps.

The slabs can be cross rolled, long rolled, or both, during production and still have good ballistic properties. "Cross rolled" and "long rolled" are defined relative to the rolling direction used to roll the final plate. Cross rolling is rolling at 900 to the final rolling direction; long rolling is rolling parallel to the final rolling direction. There does appear to be some difference in the ballistic properties depending upon the rolling regimen, as illustrated in the examples provided below.

C. Annealing Plates processed as discussed above are then annealed, and particularly mill annealed. Mill annealing is one type of annealing commonly practiced to provide an article having even x 13 microstructure throughout. Armour plates having good ballistic properties have been mill annealed at temperatures of from about 7040C to about 8150C. 760-788°C is a common temperature range selected for mill annealing using a vacuum creep flattener.

D. Surface Treatments Plates fashioned as described above can be subjected to various, and generally conventional, surface conditioning treatments. Examples of such surface conditioning procedures include, without limitation, grinding, machining,

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7 shotblasting and/or pickling bathing a metal in an acid or chemical solution to remove oxides and scale from the metal surface).

II. Examples The following examples illustrate particular alloys and the processing steps to which such alloys were subjected to form plates having good ballistic properties.

These examples are provided solely to illustrate certain features of the invention and should not be construed to limit the invention to the particular features described.

Example 1 An ingot was produced from compacts made from raw materials using double vacuum arc remelt (VAR) technology. A sample was taken from the middle surface of the ingot for chemical analysis. The composition of this alloy No. 1, and its Tp are stated below in Table 2. Alloy No. 1 also is referred to as Ti-5AI-3V-High O (high oxygen) to reflect weight-percent approximations for the constituent elements.

Table 2 Chemical Analyses AI V Fe Cr Ni 0 C N Tp(F) Allot #1 4.95 3.04 0.26 0.001 0.012 0.242 0.007 0.007 1825* An ingot having the chemical composition stated in Table 2 was then forged into slabs using a 500 ton forgepress. The slabs were soaked at 1149°C for 4h and then 0 forged from 196.85mm to 127mm. An intermediate slab was a-p forged to 3 20 inches after heating the slab at 968 0 C for about 2h. The surfaces of the slabs were conditioned.

The slabs were then a-p hot rolled to form plates. Different hot rolling regimens were used to investigate the effects of rolling on ballistic properties.

These hot rolling procedures are summarised in Table 3.

25 Table 3 Pass Schedule For Hot Rolling Plates Alloy Plate A Alloy Plate B First Rolling 1) 927*C x 2h 1) 927°C x 2 h CROSS ROLL LONG ROLL mm (63.5) 58.4 53.3 -48.3 43.2 38.1 33 58.4 53.3 48.3 43.2 38.1 33 Second Rolling 2) 927°C x 2 h 2) 927*C x 2 h LONG ROLL LONG ROLL mm 27.9 22.9 -20.3 17.8 -16 27.9 22.9 20.3 17.8 -16 Plates produced by the stated rolling procedures were mill annealed using a vacuum creep flattener (VCF) at approximately 788°C. The plates also were shot blasted and pickled. Large square plates were then cut for ballistic tests.

Example 2 This example concerns a second alloy, referred to either as alloy number 2 (Table 4) or Ti-4AI-2.5V-1.5Fe-High O. Compacts for ingot formation were formed l SEC 104 u libc/03459 /V7 OS from raw materials and ingots were produced from such compacts by VAR. The chemical composition for alloy number 2 and its Tp are stated in Table 4.

Table 4 Chemical Analyses Al V Fe Cr Ni 0 C N ITp(F) Alloy#2 3.98 2.56 1.58 0.003 0.014 0.234 0.008 0.006 1764" Ingots having the stated chemical analysis were forged to slabs using a 500 ton forgepress. The slabs were soaked at 1149 0 C for 4h and then P forged from 197mm to 127mm to form an intermediate slab. The intermediate slab was a-p forged after heating at 927 0 C for 2h to form final slabs. The surfaces of the final slabs were conditioned.

The slabs were a-p hot rolled to form plates. These plates also were subjected to different hot rolling regimens to investigate the effects of rolling on ballistic properties. These rolling procedures are summarised in Table Table Pass Schedule For Hot Rolling Plates Alloy Plate A Alloy Plate B First Rolling 1) 871°C x 2 h 1) 927"C x 2 h CROSS ROLL CROSS ROLL mm (69.9) -66 -58.4 53.3 -48.3 43.2 38.1 33 66 58.4 53.3 48.3 43.2 38.1 33 Second Rolling 2) 871"C x 2 h 2) 927 0 C x 2 h LONG ROLL LONG ROLL mm (33) 27.9 22.9 20.3 17.8 16 27.9 22.9 20.3 17.8 16 15 After the slabs were rolled as discussed above, the slabs were mill annealed using a vacuum creep flattener (VCF) at approximately 788 0 C. The plates were shot blasted and pickled, and then large square plates were cut for ballistic tests.

The mechanical properties of plates produced as stated above in Examples 1 and 2 are provided below in Table 6.

Table 6 a.

a a a Physical Properties Tensile Property Charpy Impact Plate Rolling Alloy Type Direction 0.2% TS 2 ksi E1 3

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4 Side Surface Hardness Condition _PS ksi Not ft-lb Not ft-lb BHN Alloy#1, 927 0 C Ti-5AI-3V High LT 133.2 142.1 16 41.9 16.0 19.0 280 Plate A Cross Roll O 16.0 20.0 Alloy 927*C Ti-5AI-3V High LT 132.7 142.0 17 42.0 17.5 19.0 258 Plate B Cross Roll 0 115.5 17.0 Alloy 927"C Ti-4AI-2.5V-Fe LT 129.9 138.7 17 49.5 14.0 13.0 276 Plate A Cross Roll High O 14.0 13.0 Alloy #2 927 0 C Ti-4AI-2.5V- LT 131.8 142.7 17 44.3 11.5 15.0 272 Plate B Cross Roll 1.5Fe High O 12.0 12.5 13.5 Standard Production Ti-6AI-4V L 132.8 145.3 16 31.9 17.0 28.0 284 6:4 Alloy _Standard _16.5 29.0 DCrfr' r r,,rr r1 Ic.ICrs4 prooI stress.

RAL to reduction of area.

SSE 1- 1 -o404 w 1o reers to tensile strengm. El refers to elongation. KA reters libc/03459 The "standard" alloy referred to in Table 6 is a common Ti-6AI-4V alloy comprising 6.25% aluminium, 3.97% vanadium, 0.169% iron, 0.019% chromium, 0.020% nickel, 0.182% oxygen, 0.022% carbon and 0.006 percent nitrogen.

S Example 3 Seven laboratory ingots were produced by double vacuum arc remelting VAR.

The chemistries of ingots 5-8 and 10-12 are provided by Table 7.

Table 7 Chemistry of Alloys 5-8. and 10-12 Alloy No. Tp(°C) Al V Fe Cr Ni O C N 946 4.03 2.56 1.49 0.023 0.015 0.154 0.007 0.007 6 998 3.93 2.38 0.84 0.020 0 013 0.327 0 007 0.004 7 995 4.02 4.02 0.22 0022 0 014 0 270 0 009 0.004 8 962 3 10 2 01 1 53 0.020 0.013 0.299 0 008 0.005 983 3.97 2.52 1.52 0.015 0.012 0.318 0.004 0.004 11 959 2.98 2.03 1.48 0.015 0.011 0.260 0.006 0.003 12 946 3.86 2.55 147 0.016 0.011 0.150 0.006 0.008 Ingots having the using a 500 ton forge hours and then p forg alloy compositions stated press. Initially, these ingot, ed from about 197mm to in Table 7 were forged into slabs s were soaked at 1149 0 C for four about 127mm. The intermediate a ar a slabs were ca- forged to about 76.2mm after heating at p transus minus between about 30°C and about 500C for about two hours. After the slab surfaces were conditioned, the surface-conditioned slabs were again heated at temperatures of between p transus minus about 30°C and about 50°C for about two hours. The slabs were then hot rolled to 33mm by cross rolling. Finally, these plates were reheated at temperatures of between 0 transus minus about 30°C and about for about two hours, then hot rolled to 16mm in the longitudinal direction. These plates were mill annealed using a vacuum creep flattener at approximately 7880C, then shot blasted and pickled.

IV. Ballistic Properties Plates produced as described above were tested by the US. Army Research Laboratory, at Aberdeen Proving Ground, Maryland, to determine V50 values. US.

Army Test and Evaluation Command, Test Operating Procedure 2 2-710, was used 25 to determine the V 5 0 values.

The test projectile used was a 20mm fragment-simulating projectile.

Fragments from artillery shells generally are considered better at showing differences in titanium performance than armour-piercing projectiles. The fragment-simulating projectile (FSP) simulates the steel fragments ejected from highly explosive artillery rounds, which remain a reasonable threat for modern armours. The 20mm FSP was manufactured from 4340H steel, having Rc 29-31 hardness, in accordance with specification MIL-P-46593A, and was fired from a rifled Mann barrel.

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Projectile velocities were measured using an orthogonal flash X-ray system.

See, Grabarek et afs X-Ray Multi-Flash System for Measurements of Projectile Performance at the Target, BRL Technical Note 1634 (September, 1966).

Table 8 below lists the plate numbers, the Vso velocities, and standard deviations that were obtained by the ballistic tests for plates made from alloys 1 and 2. No cracks were observed following ballistic tests on plates made from alloys 1 and 2. The plate thicknesses vary slightly; as a result, the V 5 o results were normalised to a single reference thickness of 16.50mm Equation1 is the normalisation equation used to normalise the data.

VNORM VTEST 31.6T 521.4 Equation 1 is plate thickness in millimetres, VNORM is the normalised Vso in metres per second, and VTEST is the V 5 0 in meters per second obtained by testing the plates.

Table 8 Ballistic Properties of Plates Made from Alloys 1 and 2 Plate# Thickness(mm) Tested Vso(m/s) Std Dev(m/s) Normalised V 5 0 MIL-A-46077 [VTEST] [VNORMI (m/s) 1A 16.26 591 15 599 595 1B 16.10 611 6 624 591 2A 16.89 632 5 620 612 2B 16.23 658 2 667 594 Standard 16.59 532 7 529 604 Table 9 Ballistic Properties of Plates Made from Alloys 5-8 and 10-12 Plate No Thickness Tested Vso Standard Normalised MIL-A-46077 Difference Through (mm) Deviation V50 Tested Vso-MIL Cracks (m/s) 15.65 541 11 552 577 -36 No 6 14.83 570 8 607 551 19 Yes 7 15.82 594 9 600 582 12 No 8 16.59 635 6 616 606 21 No 10 15.95 573 N/A* 575 586 -13 Yes 16.46 653 6 639 602 51 No 12 16.54 592 21 575 605 -13 No *Standard deviation is not available.

Tables 8 and 9 show that plates produced from alloys described herein had Vso values of at least as high as 590m/s, and typically above 600m/s. The plates had V 5 0 values at least equivalent to that specified by MIL-A-46077 for Ti 6AI-4V ELI plates. The V 5 0 values for plates made from the present alloys are significantly higher than the V 5 0 reported for the standard Ti-6AI-4V alloy.

Furthermore, alloy 2, both plates A and B, had V 50 values of at least 90m/s higher than the V 50 value reported for the standard. Table 8 and the rolling regimens stated for the plates, particularly the ballistic properties reported for plates 2A and 2B, indicate that the best ballistic properties are achieved by rolling at temperatures of Tp minus less than about 55°C, such as Tp minus from about 27 0 C to about 50 0

C.

Cl 0 4 libc/03459 ^y T SE -o 1 Table 9 shows that plate numbers 7, 8 and 11 have higher V 50 values than that required by MIL-A-46077. The chemistry of the alloys used to make these plates is as stated herein for the present invention.

Alloys of the present invention typically have oxygen contents of from about 0.2% to about 0.3. Table 9 shows that plates 5 and 12, which were made using alloys having lower oxygen contents than that of alloys made in accordance with the present invention, namely 0.154 and 0.150 respectively, have lower V 5 0 values than that required by MIL-A-46077. The alloy used to produce plate 6 had an oxygen content of 0.327, ie., a higher oxygen content than that of alloys made in accordance with the present invention. Although plate 6 exhibited ahigher V 5 0 value than that required by MIL-A-46077, it also developed severe cracks during the ballistic tests. Such cracks make ballistic plates less desirable, and even unusable if the cracks are too extensive.

The alloy used to make plate 10 also had an oxygen content greater than 0.3, namely 0.318. Plate 10, which was made from alloy number 10, developedsever cracks during ballistic tests, and also had a lower V 50 value than that required by MIL-A-46077.

Thus, tables 8 and 9 demonstrate that armour plates made in accordance with the present invention typically have V 5 0 values greater than about 575m/s, many have V 5 0 values greater than about 600m/s, and some have V 5 0 valuesgreater than 625m/s. Armour plates made having oxygen contents greater than 0.3% may have reasonably high V 50 values, but the cracks that develop in such plates may be too sever to use the plates as ballistic armour. No cracks were observed in ballistic plates made from alloys 1 and 2 following ballistic tests.

25 The present application has been described with reference to preferred embodiments. It will be understood by persons of ordinary skill in the art that the invention can vary from that described herein, and still be within the scope of the following claims.

l* o o• libc/03459

Claims (33)

1. A titanium alloy for armour plate, comprising: from 2.9% to 5.0% aluminium; from to 3.0% vanadium; from 0.2% to 2.0% iron; from 0.2% to 0.3% oxygen, and less than 0.5% of other elements, the balance being titanium.

2. The alloy according to claim 1 comprising from 2.9% to 4.0% aluminium.

3. The alloy according to claim 1 or 2 comprising from 0.25% to 1.75% iron.

4. The alloy according to claim 3 comprising from 1.45% to 1.6% iron. The alloy according to any one of claims 1 to 4 comprising from 0.24% to 0.29% oxygen.

6. The alloy according to claim 1 or 2, comprising from 1.25% to 1.75% iron and from 0.23% to 0.25% oxygen.

7. The alloy according to any one of claims 1 to 6 and further comprising one or more elements selected from the group consisting of chromium, nickel, carbon, nitrogen, niobium, cobalt, and mixtures thereof.

8. The alloy'according to claim 7, wherein the weight percent of each such element is 0.1% or less, and wherein the total weight of such elements is 0.5% or less.

9. The alloy according to any one of the preceding claims, wherein the alloy is an a-p processed alloy.

10. A titanium alloy as claimed in claim 1, substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing.

11. A process for producing a titanium alloy for armour plate comprising: forming an ingot comprising from 2.9% to 5.0% aluminium, from 2.0% to 3.0% vanadium, from 0. 2% to iron, from 0.2% to 0.3% oxygen, less than 0.5% of other elements, and the balance being titanium, and ca-p processing the ingot to provide an a-p alloy.

12. The process according to claim 11 wherein the step of a-p processing comprises: forging the ingot to form a slab at a temperature greater than Tp; forging the ingot to form a slab; and forging the slab at a temperature below Tp.

13. The process according to claim 12 wherein the step of heating the ingot comprises heating the ingot to a temperature of about 1037°C or greater.

14. The process according to claim 12 or 13 wherein the step of heating the ingot comprises heating the ingot to a temperature of from 1037°C to 1260°C. The process according to claim 11 wherein the a-p processing step comprises: forging the ingot at a temperature greater than Tp to form an intermediate slab; and forging the Aj Nintermediate slab at a temperature below Tp to form a slab and rolling the slab to produce plates, o hereby achieving a percent reduction of at least [R:\LIBFF] 10208speci.doc:njc 13

16. The process according to claim 15 wherein the step of forging the ingot at a temperature below Tp to form slabs and rolling the slabs to produce plates achieves a percent reduction of from 70% to 92%.

17. The process according to any one of claims 11 to 16 wherein the ingot comprises from 2.9% to 4.0% aluminium.

18. The process according to any one of claims 11 to 17 wherein the ingot comprises from 1.25% to 1.75% iron.

19. The process according to any one of claims 11 to 17 wherein the ingot comprises from 2.9% to 4.0% aluminium, from 1.25% to 1.75% iron, and from 0.23% to o0 0.25% oxygen. A process for producing a titanium alloy as claimed in claim 11, said process being substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing.

21. A titanium alloy prepared by the process of any one of claims 11 to 15 22. An armour plate comprising an ca-P processed titanium alloy comprising (a) from 2.9% to 5.0% aluminium, from 2.0% to 3.0% vanadium, from 0.2% to iron, from 0.2% to 0.3% oxygen, and less than 0.5% of other elements, the balance being titanium.

23. The armour plate according to claim 22 having a thickness of from 15.875mm 20 to 17.25mm and having a Vso of at least as high as 575m/s.

24. The armour plate according to claim 22 having a thickness of from 15.875mm to 17.25mm and having a V 50 of at least as high as 600m/s.

25. The armour plate according to claim 22 having a thickness of from 15.875mm 9 to 17.25mm and having a V 50 of at least 620m/s. 25 26. The armour plate according to any one of claims 22 to 25 comprising from 2.9% to 4.0% aluminium, from 1.25% to 1.75% iron, and from 0.23% to 0.25% oxygen.

27. An armour plate as claimed in claim 22, substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing.

28. An armor plate comprising an alloy according to any one of claims 1 to 10 or prepared by the process of any one of claims 11 to

29. The armor plate according to claim 28, having a thickness from 15.875mm to 17.25mm and having a V 50 of at least as high as 575m/s. The armor plate according to claim 28, having a thickness of from 15.875mm I- to 17.25mm and having a V 50 at least as high as 600m/s. RLtL [R:\LIBFF] 10208speci.doc:njc 14

31. The armor plate according to claim 28, having a thickness of from 15.875mm to 17.25mm and having a V 50 of at least 620 m/s.

32. The armour plate according to any one of claims 28 to 31, wherein the alloy comprises from 2.9% to 4.0% aluminium, from 1.25% to 1.75% iron and from 0.23% to s 0.25% oxygen.

33. A process for making armour plates, comprising: providing a titanium alloy comprising from 2.9% to 5.0% aluminium, from 2.0% to 3.0% vanadium, from 0.2% to 2.0% iron, from 0.2% to 0.3% oxygen, and less than 0.5% of other elements, the balance being titanium; and forming armour plates from the alloy.

34. The process according to claim 33 wherein the step of forming armour plates comprises: forming an ingot from the titanium alloy; forging the ingot into slabs; and rolling the slabs into plates. The process according to claim 34 wherein the step of forging the ingot comprises first forging the ingot at a temperature of greater than Tp, and then forging the 15 ingot at a temperature below Tp. 0

36. The process according to claim 34 or 35 wherein the steps of forging the ingot and rolling the slabs achieve a percent reduction of at least 50.0%. 3 3rr

37. The process according to claim 36 wherein the steps of forging the ingot and rolling the slabs achieve a percent reduction of from 70.0% to 92.0%.

38. A process for making armour plates, comprising: providing a titanium alloy see comprising from 2.9% to 5.0% aluminium, from 2.0% to 3.0% vanadium, from 0 0.2% to 2.0% iron, from 0.2% to 0.3% oxygen and less than 0.5% of other elements, the balance being titanium; processing the alloy to form an c -n alloy; and forming 3 armour plates from the a-13 alloy. 0S3 3 25 39. A process for making armour plates as claimed in claim 33 or 38, substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing. A method for making armor plates, comprising the steps of: producing titanium alloy in accordance with the process of any one of claims 11 to 20 and forming armour plates from the alloy.

41. The method according to claim 40, wherein the step of forming armor plates comprises: forging the ingot into slabs; and Irolling the slabs into plates. [R:\LIBFF] 10208speci.doc:njc 14 C'

42. A titanium alloy according to any one of claims Ito 10 or 21 when used in an armour plate. Dated 7 February, 2002 Oregon Metallurgical Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON S. 9 [R:\LIBFFI I 02O8speci.doc:njc