Single crystal tungsten penetrator and method of making

Abstract

High density single crystal penetrators are made from tungsten or from alloys containing at least 90% tungsten, and a remainder of essentially tantalum, rhenium, niobium, molybdenum or a mixture thereof. The penetrator will generally be circular in cross-section and have a length to diameter ratio of at least about 10 to 1, with the single crystal body being aligned so the crystalline axis having the [100] orientation is parallel to the longitudinal axis of the penetrator. A penetrator having such desired crystalline characteristics can be formed by CVD about a heated substrate of body-centered cubic crystal material. One particularly efficient process utilizes static CVD in a closed chamber and employs a solid feedstock of polycrystalline tungsten material.

Description

[0001] This application is a continuation-in-part of U.S. Ser. No. 10 / 046,096, filed Jan. 11, 2002, which was a continuation of International Application No. PCT / US00 / 19031, filed Jul. 12, 2000, which claimed priority from U.S. Ser. No. 60 / 143,827, filed Jul. 13, 1999, the disclosures of all of which are incorporated herein by reference.[0002] There may be environmental and occupational hazards associated with the manufacture, deployment and use of depleted uranium (DU) as a ballistic penetrator. It would be desirable to have an alternative, benign material having penetration characteristics at least about equal to DU. [0003] When a penetrator interacts with armor, it generates an aerosol and particles which are respirable and which may reach the gas exchange region of the human lung. In addition, penetrator impact fragments are deposited into the soil and can eventually find their way into the human food chain. DU is known to be toxic to the kidney, and it is also theoretically car...

AI Technical Summary

Benefits of technology

[0006] After much research, it is now believed that material flow and failure mechanisms, not strength and ductility, are key properties in determining penetration performance. As a penetrator strikes armor, a high deformation rate in the penetrator causes heat to be generated. Because there is not enough time to conduct / diffuse this heat away from the deformation area, thermal softening occurs which overcomes the effect of previous hardening mechanisms, such as strain hardening. As a result, gross penetrator deformation occurs in locally softer material, along adiabatic shear bands, and the rapid failure along these adiabatic shear bands allows the penetrator to rapidly shed excess material. This rapid, localized deformation allows material to slough off and thus maintains a small diameter at the penetrator / armor interface. Without such localized shearing, the penetrator would form a large-diameter, blunt-nosed head that is much less effective. For a given value of kinetic energy, the small diameter penetrator will need to move less armor material, and will penetrate farther, than a larger, blunt-nosed penetrator.

[0012] It is an object of the present invention to provide high density penetrators that will meet the foregoing criteria and to provide methods for efficiently and economically fabricating such Penetrator. SUMMARY OF THE INVENTION

[0018] Also provided are methods for economically and efficiently producing such high density penetrators using CVD. By using an appropriate single crystal substrate and CVD, it has been found that a single crystal body suitable for use as a high density penetrator can be fabricated from tungsten. In addition, a generally closed CVD system is also provided which makes very efficient use of raw materials and minimizes the creation of reaction by-products that would otherwise require processing and / or other clean-up treatment prior to being discarded.

[0020] In another particular aspect, the invention provides a method for making a single crystal, high density alloy body containing a major amount of tungsten and a minor amount of tantalum, rhenium, niobium and / or molybdenum as an alloying metal, which body is suitable for use as a high density penetrator, said method comprising providing a chamber suitable for carrying out chemical vapor deposition (CVD), locating a single crystal substrate which is stable at a temperature of at least about 800° C. within said chamber, introducing (a) tungsten chloride or fluoride vapor or (b) a vapor mixture of chlorides or fluorides of tungsten and said alloying metal into said CVD chamber, with the optional inclusion of H2, and heating said single crystal substrate to at least about 800° so as to cause a single crystal tungsten alloy body of desired composition to grow upon the exterior surface of said single crystal substrate and create a high-density tungsten alloy body suitable for use as a penetrator.

Problems solved by technology

There may be environmental and occupational hazards associated with the manufacture, deployment and use of depleted uranium (DU) as a ballistic penetrator.

DU is known to be toxic to the kidney, and it is also theoretically carcinogenic because of its residual radioactivity.

Known tungsten heavy alloys, besides being inferior in penetration performance versus DU, contain nickel and cobalt alloying constituents that are also known to be toxic.

As a result of the foregoing, the testing of munitions with DU penetrators is limited to a few testing ranges within the U.S., and essentially, warfighters cannot train with the actual ammunition they will use in wartime because of the severe restrictions placed on training exercises at even these limited testing ranges in the U.S. After DU munitions are used in war (e.g. Desert Storm), a subsequent cleanup effort should be conducted to recover DU from the soil and prevent it from entering a food chain.

Despite developments that led to some increases in strength and toughness, the basic penetration performance of these materials did not significantly improve and did not approach that of DU.

As a penetrator strikes armor, a high deformation rate in the penetrator causes heat to be generated.

As a result, gross penetrator deformation occurs in locally softer material, along adiabatic shear bands, and the rapid failure along these adiabatic shear bands allows the penetrator to rapidly shed excess material.

Without such localized shearing, the penetrator would form a large-diameter, blunt-nosed head that is much less effective.

However, single crystal unalloyed tungsten has a high muzzle-launch failure rate; it appears to lack sufficient strength and ductility to reliably remain intact after launching.

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