Oxide film formed on surface of base material that is iron-based sintered body, sliding member on which oxide film is formed, and apparatus including sliding member

Abstract

An oxide film ( 170 ) is formed on a surface of a base material ( 175 ) that is a sintered body constituted by an iron-based material. The oxide film ( 170 ) includes a first layer ( 171 ), a second layer ( 172 ), and a third layer ( 173 ). The first layer ( 171 ) is located on an outermost surface and is constituted by at least fine crystals. The second layer ( 172 ) is located under the first layer ( 171 ) and contains columnar structures. The third layer ( 173 ) contains columnar structures and is provided on the second layer ( 172 ) through an interface ( 174 ) so as to be located close to the base material ( 175 ). The first layer ( 171 ) includes a dense layer ( 171 a ). The oxide film ( 170 ) can exhibit satisfactory abrasion resistance.

1 . An oxide film formed on a surface of a base material that is a sintered body constituted by an iron-based material,
 the oxide film comprising:   a first layer constituted by at least fine crystals;   a second layer located under the first layer and containing columnar structures; and   a third layer containing columnar structures and provided on the second layer through an interface so as to be located close to the base material.   
     
     
         2 . The oxide film according to  claim 1 , wherein the first layer includes a dense layer containing the fine crystals that exist more densely than the fine crystals of the other part of the first layer. 
     
     
         3 . The oxide film according to  claim 1 , wherein the first to third layers are constituted by at least diiron trioxide (Fe 2 O 3 ) and triiron tetroxide (Fe 3 O 4 ). 
     
     
         4 . The oxide film according to  claim 3 , wherein:
 a component contained most in the first layer is diiron trioxide (Fe 2 O 3 );   a component contained most in the second layer is triiron tetroxide (Fe 3 O 4 ); and   a component contained most in the third layer is triiron tetroxide (Fe 3 O 4 ).   
     
     
         5 . The oxide film according to  claim 1 , wherein:
 a crystal grain diameter of the first layer falls within a range of 0.001 to 1 μm; and   the crystal grain diameter of the first layer is smaller than a crystal grain diameter of the second layer.   
     
     
         6 . The oxide film according to  claim 1 , wherein the columnar structures contained in the second layer are vertically long crystal structures each having an aspect ratio that falls within a range of 1 to 20. 
     
     
         7 . The oxide film according to  claim 1 , wherein the columnar structures contained in the third layer are vertically long crystal structures each having an aspect ratio that falls within a range of 1 to 15. 
     
     
         8 . The oxide film according to  claim 1 , wherein a film thickness of the oxide film falls within a range of 1 to 5 μm. 
     
     
         9 . A sliding member comprising the oxide film according to  claim 1 , the oxide film being formed on a sliding surface of the base material that is the sintered body constituted by the iron-based material. 
     
     
         10 . The sliding member according to  claim 9 , wherein the sintered body contains iron at 90 mass % or more. 
     
     
         11 . The sliding member according to  claim 10 , wherein the sintered body contains at least one of sulfur and molybdenum. 
     
     
         12 . An apparatus comprising the sliding member according to  claim 9 .