Alumina-boron carbide ceramics and methods of making and using the same

Abstract

A ceramic body that contains between about 15 volume percent and about 35 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent of alumina. The substrate has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 .

1 . A ceramic metalcutting insert for chip forming machining made from a starting powder mixture, the ceramic insert body comprising: 
 a substrate having a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a cutting edge;    the substrate comprising between about 15 volume percent and about 35 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina; and    the substrate having a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 .    
     
     
         2 . The ceramic metalcutting insert according to  claim 1  wherein the substrate has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 5.5 MPa·m 0.5 .  
     
     
         3 . The ceramic metalcutting insert according to  claim 1  wherein the substrate has a Young's Modulus equal to or greater than about 300 GPa.  
     
     
         4 . The ceramic metalcutting insert according to  claim 1  wherein the substrate has a Vicker's micro-hardness equal to or greater than about 17 GPa.  
     
     
         5 . The ceramic metalcutting insert according to  claim 1  wherein the substrate comprises between about 15 volume percent and about 35 volume percent of the boron carbide irregular-shaped phase and between about 65 volume percent and about 85 volume percent alumina.  
     
     
         6 . The ceramic metalcutting insert according to  claim 1  wherein the substrate comprises between about 20 volume percent and about 30 volume percent of the boron carbide irregular-shaped phase and between about 70 volume percent and about 80 volume percent alumina.  
     
     
         7 . The ceramic metalcutting insert according to  claim 1  wherein the substrate comprises about 25 volume percent of the boron carbide irregular-shaped phase and about 75 volume percent alumina.  
     
     
         8 . The ceramic metalcutting insert according to  claim 1  wherein the substrate further comprises residue from a sintering aid in the starting powder mixture and the sintering aid is selected from the group comprising yttrium oxide, ytterbium oxide, yttrium aluminum garnet, lanthanum oxide, and chromium oxide.  
     
     
         9 . The ceramic metalcutting insert according to  claim 1  wherein the substrate further includes the constituents from one or more of the following additives in the starting powder mixture: the oxides of hafnium and/or zirconium, and silicon carbide whiskers.  
     
     
         10 . The ceramic metalcutting insert according to  claim 1  further including a refractory coating on the substrate.  
     
     
         11 . A process for making a ceramic body comprising the steps of: 
 providing a starting powder mixture,    the starting powder mixture comprises between about 15 volume percent and about 35 volume percent boron carbide powder and at least about 50 volume percent alumina powder and no more than about 5 volume percent of a sintering aid; and    consolidating the powder mixture at a temperature equal to between about 1400 degrees Centigrade and 1850 degrees Centigrade to achieve a ceramic with a density equal to greater than 99 percent of theoretical density.    
     
     
         12 . The process according to  claim 11  wherein the consolidating conditions further comprise a hot pressing pressure equal to between about 30 MPa and about 40 MPa.  
     
     
         13 . The process according to  claim 11  wherein the consolidating conditions further comprise a hot pressing duration equal to between about 30 minutes and about 90 minutes.  
     
     
         14 . The process according to  claim 11  wherein the ceramic body has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 .  
     
     
         15 . The process according to  claim 11  wherein the ceramic body has a Young's Modulus greater than or equal to about 300 GPa.  
     
     
         16 . The process according to  claim 11  wherein: 
 the starting powder mixture comprises between about 20 volume percent and about 30 volume percent of the boron carbide powder and between about 70 volume percent and about 80 volume percent of the alumina powder.    
     
     
         17 . The process according to  claim 11  further including the step of applying a coating to the ceramic body.  
     
     
         18 . A ceramic body comprising: 
 between about 15 volume percent and about 35 volume percent of a boron carbide irregular-shaped phase, and at least about 50 volume percent alumina, and    the ceramic body has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 .    
     
     
         19 . The ceramic body according to  claim 18  wherein the body further includes the residue from a sintering aid.  
     
     
         20 . A method of machining a workpiece comprising the steps of: 
 providing a workpiece;    providing a ceramic cutting insert having a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a cutting edge and the ceramic cutting insert having a substrate that comprises between about 15 volume percent and about 35 volume percent of a boron carbide phase and at least about 50 volume percent alumina and has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 ;    causing relative rotational movement between the workpiece and the ceramic cutting insert wherein the surface speed of the relative rotational movement is equal to or greater than about 457 surface meters per minute; and    bringing the ceramic cutting insert and the workpiece into contact with each other so as to remove material from the workpiece.    
     
     
         21 . The method of  claim 20  wherein the surface speed of the relative rotational movement is equal to or greater than about 610 surface meters per minute.  
     
     
         22 . The method of  claim 20  wherein the workpiece material is cast iron.  
     
     
         23 . The method of  claim 20  wherein the workpiece material is ductile cast iron.