Designer's Guide Results
The following is a list of materials, selected and ranked per your specification.

MaterialFracture Toughness
Zirconia-PSZ12 MPa m½
Zirconia-TZP7 - 13 MPa m½
Zirconia Toughened Alumina (ZTA)5 - 7 MPa m½
Silicon Nitride4 - 6 MPa m½
Alumina 94%4 - 5 MPa m½
Alumina 99.9%4 - 5 MPa m½
Sialon4 - 5 MPa m½
Silicon3 - 6 MPa m½
Silicon Carbide Reaction Bonded4 - 5 MPa m½
Alumina 99.5%4.3 MPa m½
Reference Materials
Tool Steel50 - 80 MPa m½
Diamondn/a
Stainless Steeln/a

All properties values are at room temperature unless otherwise noted. Engineering data are representative, and are not intended as absolute nor warrantable. Data shown is blended from multiple sources and therefore illustrates the marketplace. The relative rankings are approximate and are based on representative values if the particular material has a range of values for a given property.

Wikipedia Definition(s) :  Fracture Toughness;

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Please Note:  This Designers guide is compiled of materials currently machined by Insaco and a few others included for reference.