Single crystal tungsten alloy penetrator and method of making

Abstract

High density single crystal penetrators are made from alloys containing at least 90% tungsten, with the remainder being 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 alloy material.

What is claimed is:  
     
         1 . A high density penetrator designed to be propelled from the muzzle of a weapon, which penetrator is generally circular in cross-section, has a diameter of at least 3 mm and a length to diameter ratio of at least about 5 to 1 and comprises a shaped single-crystal alloy body consisting essentially of at least 90% tungsten with the remainder being essentially tantalum, rhenium, niobium, molybdenum or a mixture thereof, said single-crystal body being aligned with [100] orientation with respect to its long axis and being encased in a metal or metal alloy material, which has a ductility and strength greater than the ductility and strength of said single-crystal alloy, said encasing material surrounding a head end portion of said single-crystal alloy body and at least substantially the entire length thereof.  
     
     
         2 . The penetrator according to  claim 1  wherein said single-crystal alloy contains at least about 93% tungsten and at least a major portion of the remainder of said single-crystal alloy is tantalum or rhenium.  
     
     
         3 . The penetrator according to  claim 1  wherein said single-crystal alloy has a density of at least about 98% of the theoretical density of said single-crystal material.  
     
     
         4 . The penetrator according to  claim 1  wherein said encasing material includes an aerodynamically-shaped head end.  
     
     
         5 . The penetrator according to  claim 1  wherein said body consists of a rod having a diameter of at least 8 mm.  
     
     
         6 . The penetrator according to  claim 1  wherein a plurality of said single crystal bodies are embedded in parallel, spaced-apart orientation in said encasing more ductile and stronger material.  
     
     
         7 . The penetrator according to  claim 1  wherein said encasing material is a metal alloy including a major portion of tungsten alloyed with minor portions of nickel, iron and cobalt.  
     
     
         8 . The penetrator according to  claim 1  wherein said encasing material includes at least about 1% by weight of a pyrophoric metal selected from the group consisting of hafnium, zirconium, titanium and mixtures thereof.  
     
     
         9 . 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 stable single-crystal substrate within said chamber,    providing a vapor mixture of chlorides or fluorides of tungsten and said alloying metal in said CVD chamber, with the optional inclusion of H 2 , and heating said single-crystal substrate to a temperature between 1600° C. and 2200° C. 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.    
     
     
         10 . The method according to  claim 9  wherein said substrate is a thin wire which is aligned with the [100] orientation with respect to its long axis.  
     
     
         11 . The method according to  claim 10  wherein said single-crystal substrate is formed of a metal or an alloy of metals having a body-centered cubic crystal structure.  
     
     
         12 . The method according to  claim 11  wherein said substrate is molybdenum, tungsten, niobium or tantalum, or an alloy thereof.  
     
     
         13 . The method according to  claim 9  wherein said heating is continued until said single-crystal body has grown to have a diameter of at least about 3 mm.  
     
     
         14 . An economical 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) which can be periodically closed to outlet flow therefrom,    locating a stable, single-crystal substrate within said chamber,    providing a solid feedstock in the form of a major amount of elemental tungsten and a minor amount of said elemental alloying metal in said CVD chamber,    heating said substrate to at least about 800° C. and heating said solid feedstock to a temperature of at least about 700° C but below that of said substrate, and    initially introducing vapor into said chamber containing chlorine or fluorine and then discontinuing vapor flow into or out of said chamber to cause the deposition of a single-crystal alloy of elemental tungsten and said alloying metal upon said substrate with the simultaneous creation of C 1   2  or F 2  vapor which reacts with said heated solid feedstock to form metal halide vapors that then react at said substrate.    
     
     
         15 . The method according to  claim 14  wherein said chamber is periodically evacuated and the atmosphere of said evacuated chamber is resupplied with said vapor initially introduced.  
     
     
         16 . The method according to either  claim 14  wherein said vapor contains chlorine, wherein said single-crystal substrate and said growing single-crystal alloy body are heated to a temperature between about 1600° C. and about 220° C., and wherein said feedstock is heated to a temperature which is not above about 900° C.  
     
     
         17 . The method according to either  claim 14  wherein said vapor contains tungsten fluoride and hydrogen, causing the deposition of elemental tungsten and said alloying metal upon said substrate with the simultaneous creation of HF, which HF subsequently reacts with said heated solid feedstock to form additional metal vapors.  
     
     
         18 . The method according to  claim 14  wherein said substrate is a thin wire which is aligned with the [100] orientation with respect to its long axis.  
     
     
         19 . The method according to  claim 18  wherein said single-crystal substrate is formed of a metal or an alloy of metals having a body-centered cubic crystal structure.  
     
     
         20 . The method according to  claim 14  wherein said heating is continued until said single-crystal body has grown to have a diameter of at least about 3 mm.