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

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.

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 (KIC, 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m0.5;
• 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.

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 50 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina, and the substrate further comprising at least one of the following components (a) through (b) wherein the sum of the amounts of components (a) and (b) is equal to an effective amount to achieve full densification and wherein components (a) and (b) comprise:
• (a) a metal component including one or more of aluminum, magnesium and zinc;
• or
• (b) a reduction component containing carbon.

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 50 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina, and the substrate further comprising at least one of the following components (a) and (6) and (c) wherein the sum of the amounts of components (a) and (b) and (c) is equal to an effective amount to achieve full densification and wherein components (a) and (b) and (c) comprise:
• (a) a metal component including one or more of aluminum;
• (b) a reduction component containing carbon;
• or
• (c) an oxide including one or more of zirconium oxide and hafnium oxide.

A method of making a ceramic body comprising the steps of:

• providing a starting powder mixture comprising:
• between about 15 volume percent and about 50 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina, and the substrate further comprising at least one of the following components (a) through (b) wherein the sum of the amounts of components (a) and (b) is equal to an effective amount to achieve full densification and wherein components (a) and (b) comprise:
• (a) a metal component including one or more of aluminum, magnesium and zinc;
• and
• (b) a reduction component containing carbon;
• and
• forming a green compact from the starting powder mixture;
• sintering the green compact to full density so as to form the ceramic body.

A method of making a ceramic body comprising the steps of:

• providing a starting powder mixture comprising:
• between about 15 volume percent and about 50 volume percent of a boron carbide irregular-shaped phase and at least about 50 volume percent alumina, and the substrate further comprising at least one of the following components (a) through (c) wherein the sum of the amounts of components (a) and (b) and (c) is equal to an effective amount to achieve full densification;
• and
• wherein components (a) and (b) and (c) comprise:
• (a) a metal component including one or more of aluminum;
• (b) a reduction component containing carbon;
• or
• (c) an oxide including one or more of zirconium oxide and hafnium oxide;
• and
• forming a green compact from the starting powder mixture:
• sintering the green compact to full density so as to form the ceramic body.