Intermetallic Composite Formation and Fabrication from Nitride-Metal Reactions

Abstract

In a method of making a molybdenum, molybdenum silicide and molybdenum silicon boride composite material, a boron nitride powder, a silicon nitride powder and a molybdenum powder are mixed to form a composite precursor. The composite precursor is sintered in an atmosphere consisting essentially of hydrogen and argon to form a sintered material. The sintered material is hot isostatic pressed to form the composite material into a final shape.

1 . A method of making a molybdenum, molybdenum silicide and molybdenum silicon boride composite material, comprising the actions of:
 a. mixing a boron nitride powder, a silicon nitride powder and a molybdenum powder to form a composite precursor;   b. cold isostatic pressing the composite precursor thereby forming a cold isostatic pressed precursor;   c. sintering the cold isostatic pressed precursor in an atmosphere consisting essentially of hydrogen and an inert gas to form a sintered material; and   d. hot isostatic pressing the sintered material to form the composite material into a final shape.   
   
   
       2 . (canceled) 
   
   
       3 . The method of  claim 1 , further comprising the action of exposing the final shape to an atmosphere including oxygen at a temperature greater than 1000° C. so as to form a borosilicate glass layer over at least a portion of an outer surface of the final shape. 
   
   
       4 . The method of  claim 1 , wherein each of the boron nitride powder, the silicon nitride powder and the molybdenum powder consist essentially of granules that are sub-micron in size. 
   
   
       5 . The method of  claim 1 , further comprising the action of milling the composite precursor prior to the sintering action to break up agglomerates of the boron nitride powder, the silicon nitride powder and the molybdenum powder, thereby making a homogeneous dispersion of the boron nitride powder, the silicon nitride powder and the molybdenum powder. 
   
   
       6 . The method of  claim 5 , wherein the action of making a homogeneous dispersion comprises the actions of:
 a. mixing the boron nitride powder, the silicon nitride powder and the molybdenum powder with a liquid to form a suspension; and   b. spray drying the suspension to form a homogenous powder mixture.   
   
   
       7 . The method of  claim 6 , wherein the liquid comprises an organic liquid. 
   
   
       8 . The method of  claim 7 , wherein the organic liquid comprises acetone. 
   
   
       9 . The method of  claim 6 , further comprising the action of mixing an organic dispersant and binder with the suspension prior to the spray drying action. 
   
   
       10 . The method of  claim 9 , wherein the organic dispersant and binder comprises a methyl methacrylate copolymer. 
   
   
       11 . The method of  claim 6 , further comprising the action of mixing a lubricant with the suspension prior to the spray drying action. 
   
   
       12 . The method of  claim 11 , wherein the lubricant comprises stearic acid. 
   
   
       13 . The method of  claim 1 , wherein the boron nitride powder consists essentially of BN. 
   
   
       14 . The method of  claim 1 , wherein the silicon nitride powder consists essentially of Si 3 N 4 . 
   
   
       15 . A composite material having an outer surface, comprising:
 a. a metallic phase continuous molybdenum matrix having an average grain size of less than 4.0 microns;   b. a molybdenum silicide intermetallic phase having an average grain size of less than 2.5 microns and suspended in the metallic phase continuous molybdenum matrix;   c. a molybdenum silicon boride intermetallic phase having an average grain size of less than 2.0 microns and suspended in the metallic phase continuous molybdenum matrix; and   d. a borosilicate glass layer covering at least a portion of the outer surface.   
   
   
       16 . The composite material of  claim 15 , wherein the molybdenum silicide intermetallic phase comprises A15. 
   
   
       17 . The composite material of  claim 15 , wherein the molybdenum silicon boride intermetallic phase comprises T2. 
   
   
       18 . The composite material of  claim 15 , wherein silicon is concentrated in a range of between 1 wt. % to 5 wt. %. 
   
   
       19 . The composite material of  claim 15 , wherein boron is concentrated in a range of between 1/2 wt. % to 2 wt. %. 
   
   
       20 . The composite material of  claim 15 , wherein the metallic phase continuous molybdenum matrix comprises molybdenum and up to 10% by weight of aluminum. 
   
   
       21 . The composite material of  claim 15 , having a sintered density greater than 94% of theoretical density. 
   
   
       22 . A mechanical structure having an outer surface, comprising:
 a. a composite material that includes a molybdenum silicide intermetallic phase, a molybdenum silicon boride intermetallic phase, and a metallic phase continuous molybdenum solid solution matrix, the composite material having been cold isostatic pressed into a form of the mechanical structure, sintered and hot isostatic pressed so that the composite material has a sintered density that is greater than 94% of theoretical density; and   b. a borosilicate glass layer covering at least a portion of the outer surface of the structure.   
   
   
       23 . The mechanical structure of  claim 22 , wherein the molybdenum silicide intermetallic phase comprises A15. 
   
   
       24 . The mechanical structure of  claim 22 , wherein the molybdenum silicon boride intermetallic phase comprises T2. 
   
   
       25 . The mechanical structure of  claim 22 , wherein silicon is concentrated in a range of between 1 wt. % to 5 wt. %. 
   
   
       26 . The mechanical structure of  claim 22 , wherein boron is concentrated in a range of between 1/2 wt. % to 2 wt. %. 
   
   
       27 . The mechanical structure of  claim 22 , configured as part of a gas turbine engine.