Whisker reinforced ceramic and a method of clad/hot isostatic pressing same

A method of achieving a density greater than 95% of theoretical in a ceramic cutting tool insert incorporating a ceramic whisker phase therein by hot isostatic pressing comprising the steps of

• (a) forming a compact substrate of sinterable ceramic composition having at least 5 volume percent ceramic whiskers therein substantially in the desired shape of the cutting tool,
• (b) applying a coating to the compact substrate by vapor deposition of a ceramic composition that does not become vitreous before or during the subsequent isostatic pressing step, and
• (c) heating and isostatically pressing the coated compacts in an atmosphere that reacts with the coating and/or the compact substrate at temperatures and pressures to cause the compact to approach theoretical density, and
• (d) grinding away the coating adhering to the isostatically pressed compact and further shaping the compact in the shape of a cutting tool insert if required.

A method of achieving a density greater than 95% of theoretical in a shaped ceramic article incorporating a carbide whisker phase therein by hot isostatic pressing comprising the steps of

• (a) forming a compact of sinterable alumina based ceramic composition having at least 20 volume percent carbide whiskers selected from the group consisting of titanium carbide and silicon carbide therein,
• (b) heating the compact at near atmospheric pressures to presinter the compact in argon atmosphere,
• (c) applying a titanium nitride coating to the presintered compact by chemical vapor deposition at about 1000.degree. C. which coating does not become vitreous before or during the subsequent isostatic pressing step, and
• (d) heating and isostatically pressing the coated compacts in a nitrogen atmosphere that reacts with the compact substrate at temperatures and pressures in excess of 1500.degree. C. and 10,000 psi respectively to cause the compact to approach theoretical density.

A cutting tool comprising:

• a fired ceramic composition having a matrix phase, a ceramic whisker phase and a nitrogen containing phase formed as a reaction product of said ceramic whisker phase with nitrogen;
• said ceramic whisker phase forming 25 to 40 volume percent of said fired ceramic composition;
• and wherein the x-ray parameter of whisker orientation being within the range of 0.66 to 1.5;
• the density of said fired ceramic composition exceeding 95 percent theoretical;
• and said fired ceramic composition having a cutting edge at a juncture of a rake face and a flank face.