Methods for making aluminum nitride armor bodies

Abstract

A method of making aluminum nitride armor bodies is provided. The method starts with low cost bulk raw material, in the form of aluminum or aluminum alloy, cryogenically mills the raw material into a precursor powder, which is essentially free of oxides and other undesirable impurities. The precursor powder is formed into a pre-form using low cost, short residence time molding processes. Finally, the pre-form is exposed to a nitriding process to convert the pre-form into the aluminum nitride armor body. In this manner, the method avoids the use of high cost aluminum nitride as a starting material and avoids the need for the high cost, single axis densification processes of the prior art.

1 . A method of making an aluminum nitride armor body, comprising:
 obtaining a precursor powder of pure aluminum or aluminum alloy that is essentially free of oxides and nitrides;   forming the precursor powder into a pre-form having a desired shape of the armor body; and   exposing the pre-form to a nitriding process to form the aluminum nitride armor body.   
     
     
         2 . The method of  claim 1 , wherein the step of obtaining the precursor powder comprises:
 selecting a raw material comprising substantially pure aluminum or an aluminum alloy; and   cryogenically milling the raw material in the presence of a substantially inert liquid cover to protect the raw material from exposure to, and reaction with, outside contaminants to a desired particle size.   
     
     
         3 . The method of  claim 2 , wherein the liquid cover comprises cryogenic liquid. 
     
     
         4 . The method of  claim 4 , wherein the liquid cover comprises liquid nitrogen. 
     
     
         5 . The method of  claim 2 , wherein the raw material is an aluminum alloy pre-alloyed with rare earth, alkyl metals, and any combinations thereof. 
     
     
         6 . The method of  claim 2 , wherein the desired particle size is between 400 nanometers and 50 microns. 
     
     
         7 . The method of  claim 1 , wherein the step of forming the precursor powder into the pre-form comprises a room temperature forming process. 
     
     
         8 . The method of  claim 1 , wherein the step of forming the precursor powder into the pre-form comprises multi-axis forming process. 
     
     
         9 . The method of  claim 1 , wherein the step of forming the precursor powder into the pre-form comprises a molding process selected from the group consisting of a cold press process, a dry press process, a slip cast process, an injection molding process, an extrusion process, an isopressing process, and any combinations thereof. 
     
     
         10 . The method of  claim 1 , wherein the desired shape comprises a plate-like or panel-like shape. 
     
     
         11 . The method of  claim 1 , wherein the step of exposing the pre-form to the nitriding process comprises exposing the pre-form, in a pressure vessel, with controlled vapor pressure of nitrogen or dissociated ammonia. 
     
     
         12 . The method of  claim 11 , wherein the nitrogen or dissociated ammonia flows into pores within the pre-form to result in a nitride reaction filling in the pores towards theoretical density with substantially no shrinkage of the pre-form. 
     
     
         13 . The method of  claim 12 , wherein the desired shape has a maximum thickness of about 25 millimeters. 
     
     
         14 . A method of making an aluminum nitride armor body, comprising:
 producing a slurry having a precursor powder that is essentially free of oxides and other undesirable impurities and a cover liquid that essentially prevents the oxidation of the precursor powder, the precursor powder comprises pure aluminum or aluminum alloy;   introducing the slurry into an interior of a mold having a desired shape;   precipitating the precursor powder from the slurry to form a pre-form having the desired shape; and   placing the pre-form in a pressure vessel with controlled vapor pressure of nitrogen or dissociated ammonia to form aluminum nitride in the pre-form.   
     
     
         15 . The method of  claim 14 , wherein the precursor powder comprises aluminum alloyed with rare earth metal, alkyl metal, and combinations thereof. 
     
     
         16 . The method of  claim 14 , wherein the step of producing the slurry comprises milling a raw material of pure aluminum or aluminum alloy with the cover liquid in an evacuated mill. 
     
     
         17 . The method of  claim 14 , further comprising applying a delaminating layer to an interior surface of the mold before introducing the slurry into the interior of the mold. 
     
     
         18 . The method of  claim 14 , further comprising replacing the cover liquid with a second inert cover in the mold by warming the cover liquid above its boiling point in the presence of the second inert cover, thereby allowing the cover liquid to evaporate and separate from the precursor powder. 
     
     
         19 . The method of  claim 14 , further comprising vibrating the mold to encourage deposition of a uniform layer of the precursor powder along a bottom interior portion of the mold. 
     
     
         20 . A method of making an aluminum nitride armor body, comprising:
 producing a slurry having a precursor powder that is essentially free of oxides and other undesirable impurities and a cover liquid that essentially prevents the oxidation of the precursor powder, the precursor powder comprises pure aluminum or aluminum alloy;   separating the precursor powder from the slurry and covering the precursor powder to preclude oxidation;   compacting the precursor powder into a pre-form having a desired shape; and   placing the pre-form in a pressure vessel with controlled vapor pressure of nitrogen or dissociated ammonia to form aluminum nitride in the pre-form.