Highly toughened, sintered mass of zirconia

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In Japanese Patent Application Nos.
56-127004 and 56-127005 as well as Japanese Patent Application No.
56-132934, the applicant presented as highly-toughened, sintered masses of zirconia some of the results obtained due to an effort to attain the above-mentioned objects.
In other words, the applicant discovered that the temperature at which tetragonal zirconia transforms into monoclinic zirconia can be lowered by allowing Al.
sub.
2 O.
sub.
3 or TiN to form a solid solution with, and disperse in, a ZrO.
sub.
2 matrix, whereby the grain growth of zirconia is so restrained that the content of tetragonal zirconia increases with resulting increases in slip resistance at the grain interfaces of zirconia resulting in increase in strength, which will double at higher temperatures.
However, although the sintered masses referred to in the foregoing applications had their density reaching nearly the theoretically possible value, there were still a slight number of micropores.
Besides, what was allowed for dispersion in the zirconia matrix, was limited to those materials having strong ionic bond, such as Al.
sub.
2 O.
sub.
3 or TiN that could be sintered under the normal pressure.
To obtain further improved zirconia-base ceramic sintered masses on the basis of the aforesaid findings, sintering testing has been carried out with a variety of materials dispersed in zirconia, using hot-pressing.
As a result, it has been found that a sintered mass is obtained, which is substantially free from any micropore, and has a strength of as high as about 160 kg/mm.
sup.
2 that has not been possibly attained with the conventional ceramic materials.
Such findings underlie the present invention.
In what follows, % is given by weight unless otherwise specified.
The component B (dispersant material) such as Al.
sub.
2 O.
sub.
3 is poorly effective when applied in an amount of below 0.
5%.
When it is applied in an amount exceeding 70%, the content of zirconia taking part in toughness is so reduced that both toughness and strength become unsatisfactory