Boron carbide based materials and process for the fabrication thereof

Abstract

Disclosed is a method for fabricating a solid article from a boron carbide powder comprising boron carbide particles that are coated with a titanium compound. Further disclosed herein are the unique advantages of the combined use of titanium and graphite additives in the form of water soluble species to improve intimacy of mixing in the green state. The carbon facilitates sintering, whose concentration is then attenuated in the process of forming very hard, finely dispersed TiB2 phases. The further recognition of the merits of a narrow particle size distribution B4C powder and the use of sintering soak temperatures at the threshold of close porosity which achieve post-HIPed microstructures with average grain sizes approaching the original median particle size. The combination of interdependent factors has led to B4C-based articles of higher hardness than previously reported.

What is claimed is: 
     
         1 . A process for preparation of a powder comprising:
 preparing a slurry with boron carbide particles and a solution that contains a titanium compound capable of adhering to the exterior surfaces of the boron carbide particles; and   drying the slurry to obtain a powder composition that includes boron carbide particles coated with a titanium compound.   
     
     
         2 . The process of  claim 1 , wherein the solution is an aqueous solution and the titanium compound is an organometallic compound. 
     
     
         3 . The process of  claim 2 , wherein the titanium compound is ammonium lactato titanium (IV). 
     
     
         4 . The process of  claim 1 , wherein the step for preparing a slurry further includes adding a carbon containing compound to the slurry. 
     
     
         5 . The process of  claim 4 , wherein the carbon containing compound is phenolic resin. 
     
     
         6 . The process of  claim 4 , wherein the amount of titanium compound is selected to result in an amount of titanium in the range 0.081-5 wt % and the amount of phenolic resin is selected to yield a carbon content in the range 0-3.7 wt %. 
     
     
         7 . A boron carbide based powder composition comprising:
 boron carbide particles coated with a coating comprising a titanium compound.   
     
     
         8 . The boron carbide based powder of  claim 7 , wherein the titanium compound is an organometallic titanium compound. 
     
     
         9 . The boron carbide based powder of  claim 8 , wherein the organometallic titanium compound is ammonium lactato titanium (IV). 
     
     
         10 . The boron carbide based powder of  claim 7 , wherein the coating further comprises a carbon containing compound. 
     
     
         11 . The boron carbide based powder of  claim 10 , wherein the carbon containing compound is phenolic resin. 
     
     
         12 . A process for fabricating a ceramic article, comprising:
 selecting a boron carbide powder having boron carbide particles with a median particle diameter;   selecting a carbon source in a first amount;   selecting a titanium source in a second amount based on the first amount;   preparing a body from the boron carbide powder, the titanium source and the carbon source; and   pressureless sintering the body at a pressureless sintering temperature which is low enough to produce a sintered body at a threshold of closed porosity, wherein said first amount and the second amount are selected so that the median grain size of phases in said body are no more than 100% larger than the median particle diameter.   
     
     
         13 . The method of  claim 12 , wherein said boron carbide particles have a narrow particle size distribution of d 10 −d 90 =0.2−1.5 μm with a d 50 =0.6 μm.