Boron carbide based sintered compact and method for preparation thereof

Abstract

A boron carbide based sintered body having a four-point flexural strength of at least 400 MPa and a fracture toughness of at least 2.8 MPa·m 1/2 , which has the following two preferred embodiments. (1) A boron carbide-titanium diboride sintered body obtained by sintering a mixed powder of a B 4 C powder, a TiO 2 powder and a C powder while reacting them under a pressurized condition and comprising from 95 to 70 mol % of boron carbide and from 5 to 30 mol % of titanium diboride, wherein the boron carbide has a maximum particle diameter of at most 5 μm. (2) A boron carbide-chromium diboride sintered body containing from 10 to 25 mol % of CrB 2 in B 4 C, wherein the sintered body has a relative density of at least 90%, boron carbide particles in the sintered body have a maximum particle diameter of at most 100 μm, and the abundance ratio (area ratio) of boron carbide particles of from 10 to 100 μm to boron carbide particles having a particle diameter of at most 5 μm, is from 0.02 to 0.6.

1 . A boron carbide based sintered body characterized by having a four point flexural strength of at least 400 MPa as measured in accordance with JIS R1601 and a fracture toughness of at least 2.8 MPa·m 1/2  as measured in accordance with JIS R1607-SEPB method.  
     
     
         2 . The boron carbide based sintered body according to  claim 1 , which is a boron carbide-titanium diboride sintered body obtained by sintering a mixed powder of boron carbide (B 4 C) powder, titanium dioxide (TiO 2 ) powder and carbon (C) powder while reacting them under a pressurized condition and which comprises from 95 to 70 mol % of boron carbide and from 5 to 30 mol % of titanium diboride, wherein the boron carbide has a maximum particle diameter of at most 5 μm.  
     
     
         3 . The boron carbide based sintered body according to  claim 1  or  2 , wherein the four point flexural strength is at least 700 MPa.  
     
     
         4 . The boron carbide based sintered body according to  claim 1 ,  2  or  3 , wherein the four point flexural strength is at least 800 MPa, and the fracture toughness is at least 3.0 MPa·m 1/2 .  
     
     
         5 . A boron carbide based sintered body which is a boron carbide-chromium diboride sintered body containing from 10 to 25 mol % of chromium diboride (CrB 2 ) in boron carbide (B 4 C), characterized in that the sintered body has a relative density of at least 90%, boron carbide particles in the sintered body have a maximum particle diameter of at most 100 μm, and the abundance ratio (area ratio) of boron carbide particles of from 10 to 100 μm to boron carbide particles having a particle diameter of at most 5 μm, is from 0.02 to 0.6.  
     
     
         6 . The boron carbide based sintered body according to  claim 5 , which has an electric conductivity of at least 5×10 2  S/m.  
     
     
         7 . The boron carbide based sintered body according to  claim 6 , which has a four point flexural strength of at least 400 MPa and a fracture toughness of at least 3.0 MPa·m 1/2 .  
     
     
         8 . A process for producing a boron carbide based sintered body, characterized by mixing a titanium dioxide powder having an average particle diameter of less than 1 μm and a carbon powder having an average particle diameter of less than 1 μm to a boron carbide powder having a maximum particle diameter of at most 5 μm, an average particle diameter of at most 1 μm and a specific surface area of at least 10 m 2 /g, and sintering the mixture within a temperature range of from 1900 to 2100° C. while reacting them under a pressurized condition.  
     
     
         9 . The process for producing a boron carbide based sintered body according to  claim 8 , wherein the specific surface area of the boron carbide powder is at least 16 m 2 /g, and the average particle diameter of each of the titanium dioxide powder and the carbon powder is less than 0.1 μm.  
     
     
         10 . A process for producing a boron carbide based sintered body, characterized by molding a raw material powder having from 10 to 25 mol % of a chromium diboride powder added and mixed to a boron carbide powder having an average particle diameter (D 50 ) of at most 2 μm and a specific surface area of at least 10 m 2 /g, followed by heating from 1950 to 2100° C. in a non-oxidizing atmosphere under a non-pressurized condition.  
     
     
         11 . A shock absorber made of the boron carbide based sintered body as defined in any one of  claims 1  to  7 .  
     
     
         12 . The shock absorber according to  claim 11 , wherein the shock absorber is for a high velocity missile.  
     
     
         13 . An abrasion resistant component made of the boron carbide based sintered body as defined in any one of  claims 1  to  7 .