Tungsten based sintered compact and method for production thereof

Abstract

The present invention is directed to provide a tungsten-based sintered body having a relative density of 99.5% or more (a porosity of 0.5 volume % or less) and a uniform and isotropic structure, which has not been able to be achieved by conventional techniques. In particular, the tungsten-based sintered body is intended for use as a discharge lamp electrode, a sputtering target, a crucible, a radiation shielding member or a resistance welding electrode. The intended tungsten-based sintered body is produced by subjecting a tungsten-based powder to a CIP process at a pressure of 350 MPa or more to form a powder compact, sintering the powder compact in a hydrogen gas atmosphere at a sintering temperature of 1600° C. or more for a holding time of 5 hours or more to form a sintered compact, and subjecting the sintered compact to a HIP process in an argon gas atmosphere under conditions of 150 MPa or more and 1900° C. or more. The tungsten-based sintered body of the present invention is suitably used, for example, as a discharge lamp electrode, a sputtering target, a crucible, a radiation shielding member, an electric discharge machining electrode, a semiconductor element mounting substrate and a structural member.

1 . A tungsten-based sintered body consisting of at least either one selected from the group consisting of tungsten, doped tungsten, a tungsten-based material and a tungsten-molybdenum alloy, wherein said doped tungsten comprises tungsten doped with 100 ppm or less (except for zero ppm) of alkali metal, and said tungsten-based material comprises tungsten containing 4 weight % or less (except for zero weight %) of at least one additive selected from the group consisting of oxides of cerium, thorium, lanthanum, yttrium, strontium, calcium, zirconium and hafnium, wherein said tungsten-based sintered body has an isotropic crystal structure, a relative density of 99.5% or more, and an average crystal grain size of 30 μm or less.  
   
   
       2 . The tungsten-based sintered body as defined in  claim 1 , which includes pores each having a major axis of 1 μm or more, wherein the number of the pores is 10000 or less per 1 mm 2  of unit cross-sectional area thereof.  
   
   
       3 . The tungsten-based sintered body as defined in  claim 1  or  2 , which has a hardness difference of 1.0 or less in terms of HRA between a surface portion and an inside portion thereof.  
   
   
       4 . The tungsten-based sintered body as defined in  claim 1  or  2 , which has a recrystallization temperature of at least 1600° C. or more.  
   
   
       5 . The tungsten-based sintered body as defined in  claim 1  or  2 , which has a ratio of a minimum value to a maximum value of an electric resistivity of 1.1 or less between any two points therein.  
   
   
       6 . The tungsten-based sintered body as defined in  claim 1  or  2 , which has a ratio of a minimum value to a maximum value of a thermal conductivity of 1.1 or less between any two points therein.  
   
   
       7 . A discharge lamp electrode formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       8 . A sputtering target formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       9 . A crucible formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       10 . A radiation shielding member formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       11 . A resistance welding electrode formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       12 . A semiconductor element mounting substrate formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       13 . A structural member formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       14 . A switch contact formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       15 . A member for semiconductor manufacturing equipment, which is formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       16 . A member for an ion-implantation apparatus, which is formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       17 . An internal member for a nuclear fusion reactor, which is formed of the tungsten-based sintered body as defined in  claim 1  or  2 .  
   
   
       18 . A method for producing a tungsten-based sintered body, comprising: 
 subjecting a raw powder having an average particle size of 0.5 to 4 μm to a CIP process at a pressure of 350 MPa or more to form a powder compact, wherein said raw material consists of at least either one selected from the group consisting of: tungsten; doped tungsten comprising tungsten doped with 100 ppm or less of alkali metal; a material of comprising tungsten containing up to 4 weight % of at least one additive selected from the group consisting of oxides of cerium, thorium, lanthanum, yttrium, strontium, calcium, zirconium and hafnium; and a tungsten-molybdenum alloy;    sintering said powder compact in a hydrogen gas atmosphere at a sintering temperature of 1600° C. or more for a holding time of 5 hours or more to form a sintered compact; and    subjecting said sintered compact to a HIP process in an argon gas atmosphere under conditions of 150 MPa or more and 1900° C. or more.