US4866014A — Method of making a stress resistant, partially st…

Claim 1

Independent Claim 141 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide of at least one mol percent but less than 7.3 mol percent of the mixture, comprising: (a) sintering said article at a temperature and for a period of time of less than 10 hours to produce a densified partially stabilized zirconia product having essentially no monoclinic crystal phase when cooled to room temperature; (b) subjecting the sintered article to an operation that results in the formation of monoclinic crystal phase at the surface of the article; and (c) heat treating said article to a temperature range below sintering of step (a) and within the range of 1800°-1950° F. (982°-1065° C.) for 4-30 hours to substantially transform all monoclinic crystal structure to tetragonal crystal and/or remove substantially all seeds for monoclinic phase growth.

Claim 2

Independent Claim 141 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide of at least one mol percent but less than 7.3 mol percent of the mixture, comprising: (a) sintering said article at a temperature and for a period of time of less than 10 hours to produce a densified partially stabilized zirconia product having essentially no monoclinic crystal phase when cooled to room temperature; (b) subjecting the sintered article to an operation that results in the formation of monoclinic crystal phase at the surface of the article; and (c) heat treating said article to a temperature range below sintering of step (a) and within the range of 1800°-1950° F. (982°-1065° C.) for 4-30 hours to substantially transform all monoclinic crystal structure to tetragonal crystal and/or remove substantially all seeds for monoclinic phase growth.

Claim 3

Dependent Claim 15 words

The method as in claim 1, in which the operation of step (b) is machining.

Claim 4

Dependent Claim 21 words

The method as in claim 1, in which step (b) may additionally permit the existence of seeds for monoclinic crystal growth.

Claim 5

Dependent Claim 32 words

The method as in claim 1, in which said step (a) is carried out in the temperature range of 2550°-2650° F. (1399°-1454° C.) and for a period of time of 0.5-4 hours.

Claim 6

Dependent Claim 18 words

The method as in claim 1, in which said steps (a) and (c) are carried out in air.

Claim 7

Dependent Claim 18 words

The method of claim 1, in which the operation of step (b) is cracking of the article surface.

Claim 8

Dependent Claim 25 words

The method as in claim 1, in which the article is fabricated from a powder mix having an average particle size of about 250 angstroms.

Claim 9

Dependent Claim 38 words

The method as in claim 1, in which said article is by compacting a reactive powder of said zirconium oxide an yttrium compound, said compaction being carried out at a pressure in the range of about 105-315 MPa.

Claim 10

Dependent Claim 47 words

A sintered, machined, and heat treated article comprised of zirconium oxide and 1-7.3 mol percent yttrium oxide, said article being comprised of a substantially tetragonal crystalline structure with surface zones of re-transformed monoclinic to tetragonal crystals resulting from post-sintering heat treatment at 1800°-1950° F. for 4-30 hours.

Claim 11

Dependent Claim 47 words

A sintered, machined, and heat treated article comprised of zirconium oxide and 1-7.3 mol percent yttrium oxide, said article being comprised of a substantially tetragonal crystalline structure with surface zones of re-transformed monoclinic to tetragonal crystals resulting from post-sintering heat treatment at 1800°-1950° F. for 4-30 hours.

Claim 12

Dependent Claim 18 words

The article in claim 9, in which the crystal structure has an average particle size of 0.5-2 microns.

Claim 13

Independent Claim 148 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide of at least one mol percent and less than 7.3 mol percent of the mixture, comprising: (a) sintering said fabricated article at temperature of about 2550°-2650° F. (1399°-1454° C.) and for a period of time of less than 10 hours to produce a sintered transformation-toughened yttria partially stabilized densified product having little or no monoclinic crystal phase when cooled to room temperature; (b) heat treating said product to the temperature range of 1800°-1950° F. (982°-1065° C.) for 4-30 hours to remove substantially all seeds for monoclinic phase growth and/or transform substantially all monoclinic crystal structure to tetragonal crystal; and (c) following step (a) and prior to or subsequent to step (b), subjecting the product to a machining operation or cracking that would be capable of stimulating monoclinic crystal growth.

Claim 14

Independent Claim 148 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide of at least one mol percent and less than 7.3 mol percent of the mixture, comprising: (a) sintering said fabricated article at temperature of about 2550°-2650° F. (1399°-1454° C.) and for a period of time of less than 10 hours to produce a sintered transformation-toughened yttria partially stabilized densified product having little or no monoclinic crystal phase when cooled to room temperature; (b) heat treating said product to the temperature range of 1800°-1950° F. (982°-1065° C.) for 4-30 hours to remove substantially all seeds for monoclinic phase growth and/or transform substantially all monoclinic crystal structure to tetragonal crystal; and (c) following step (a) and prior to or subsequent to step (b), subjecting the product to a machining operation or cracking that would be capable of stimulating monoclinic crystal growth.

Claim 15

Independent Claim 149 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide present in an amount of at least one mol percent and less than 7.3 mol percent of the mixture, comprising: (a) sintering said fabricated article at a temperature in the range of 2550°-2650° F. (1399°-1454° C.) and for a period of time of about 0.5-4 hours to produce a densified product having substantially no monoclinic crystal phase when cooled to room temperature; (b) heating said product to substantially the temperature range of 1800°-1950° F. (982°-1065° C.) for about 4-30 hours to substantially transform all monoclinic crystal structure to tetragonal crystal and/or remove substantially all seeds for monoclinic phase growth; and (c) following step (a) and prior to or subsequent to step (b), subjecting the product to a machining operation or cracking that would be capable of stimulating monoclinic crystal growth.

Claim 16

Independent Claim 149 words

A method of imparting aging resistance to an article fabricated of a mixture of zirconium oxide and yttrium oxide present in an amount of at least one mol percent and less than 7.3 mol percent of the mixture, comprising: (a) sintering said fabricated article at a temperature in the range of 2550°-2650° F. (1399°-1454° C.) and for a period of time of about 0.5-4 hours to produce a densified product having substantially no monoclinic crystal phase when cooled to room temperature; (b) heating said product to substantially the temperature range of 1800°-1950° F. (982°-1065° C.) for about 4-30 hours to substantially transform all monoclinic crystal structure to tetragonal crystal and/or remove substantially all seeds for monoclinic phase growth; and (c) following step (a) and prior to or subsequent to step (b), subjecting the product to a machining operation or cracking that would be capable of stimulating monoclinic crystal growth.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1992-09-11	1993-03-13	1993-09-12	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1996-09-11	1997-03-13	1997-09-12	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2000-09-11	2001-03-13	2001-09-12	$7700.00	Window Closed / Lapsed

Method of making a stress resistant, partially stabilized zirconia ceramic

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