Alumina/zirconia ceramics and method of producing the same

Abstract

Composite ceramics having a high strength, a high toughness and an excellent abrasion resistance, and a method of producing the same. The composite ceramics comprises 10 to 30 mass % of a zirconia crystal phase containing 9 to 12 mol % of CeO 2 and 2.8 to 4.5 mol % of Y 2 O 3 ; and 70 to 90 mass % of an alumina crystal phase, the zirconia crystal phase having an average crystal particle size of not larger than 1 μm.

1 . Alumina/zirconia ceramics comprising: 
 10 to 30 mass % of a zirconia crystal phase containing 9 to 12 mol % of CeO 2  and 2.8 to 4.5 mol % of Y 2 O 3 ; and    70 to 90 mass % of an alumina crystal phase;    the zirconia crystal phase having an average crystal particle size of not larger than 1 μm.    
     
     
         2 . Alumina/zirconia ceramics according to  claim 1 , wherein the alumina crystal phase has an average crystal particle size of not larger than 2 μm.  
     
     
         3 . Alumina/zirconia ceramics according to  claim 1 , wherein Zn is contained in an amount of not larger than 3 mass % calculated as an oxide thereof per 100 mass % of the total amount of the zirconia crystal phase and the alumina crystal phase, and needle-like crystals of a composite oxide including Ce and Al as constituent elements are further contained.  
     
     
         4 . Alumina/zirconia ceramics according to  claim 3 , wherein the composite oxide has a magnetoplumbite structure expressed by the formula ZnCeAl 11 O 19 .  
     
     
         5 . Alumina/zirconia ceramics according to  claim 1 , wherein a Vickers' hardness is not smaller than 1600, a fracture toughness is not smaller than 4.5, and a flexural strength after hydrothermal aging testing is not smaller than 1000 MPa.  
     
     
         6 . A method of producing alumina/zirconia ceramics comprising the steps of: 
 preparing a Ce-stabilized zirconia powder having an average particle size of not larger than 1 μm and in which CeO 2  is dissolved as a solid solution, a Y-stabilized zirconia powder having an average particle size of not larger than 1 μm and in which Y 2 O 3  is dissolved as a solid solution, and an alumina powder having an average particle size of not larger than 2 μm;    preparing a mixed powder for molding by mixing the Ce-stabilized zirconia powder, the Y-stabilized zirconia powder and the alumina powder so as to satisfy the following conditions (a) to (c):    (a) the mass ratio of the Ce-stabilized zirconia powder to the Y-stabilized zirconia powder is 65/35 to 85/15;    (b) the CeO 2  concentration is 9 to 12 mol % and the Y 2 O 3  concentration is 2.8 to 4.5 mol % per the total amount of the Ce-stabilized zirconia powder and the Y-stabilized zirconia powder; and    (c) the mass ratio of the total amount of the Ce-stabilized zirconia powder and the Y-stabilized zirconia power to the alumina powder is 10/90 to 30/70;    molding the mixed powder for molding into a predetermined shape; and    firing the obtained molded article in an oxidizing atmosphere of not higher than 1600° C.    
     
     
         7 . A method of producing alumina/zirconia ceramics according to  claim 6 , wherein the mixed powder for molding contains a zinc oxide powder in an amount of not larger than 3 parts by mass per 100 parts by mass of the total amount of the Ce-stabilized zirconia powder, Y-stabilized zirconia powder and alumina powder.  
     
     
         8 . A method of producing alumina/zirconia ceramics according to  claim 6 , wherein after the firing step, a hot isostatic pressure firing is further conducted at not higher than 1500° C.