Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Utilizing chemically reactive atmosphere other than air – per...
Reexamination Certificate
1999-04-30
2001-06-26
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Utilizing chemically reactive atmosphere other than air, per...
C264S658000, C501S127000
Reexamination Certificate
active
06251335
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the fabrication of textured ceramics and, more particularly, to an improved method for such fabrication
BACKGROUND OR THE INVENTION
Textured microstructures in ceramic materials represent a significant departure from the traditional ceramics which have equiaxed grains. Many ceramic materials exhibit anisotropic characteristics in electronic and structural properties. Since traditional microstructures have random structure, traditional microstructures meet the requirements of most applications by averaging the anisotropic property characteristic of many ceramic crystal structures.
However, improved electronic and structural properties can be obtained if polycrystalline ceramics can be made to exhibit the anisotropic characteristics that are typical of single crystals. Such properties can be obtained if the polycrystalline body is textured.
Textured ceramics can be produced by a number of techniques including sinter forging and eutectic solidification. Another more general approach for producing textured ceramics is templated or seeded grain growth. Templated grain growth (TGG) is a technique for developing crystallographic texture in polycrystalline ceramic bodies via the grain growth of aligned template particles. In TGG, large, anisotropic particles are dispersed in a dense, fine-grained matrix. During heat treatment, the immediate environment of the template particle favors its growth. The template particles should grow until they impinge on one another or the matrix grain has coarsened enough to halt the template growth. If the template particles are oriented and grown, a textured microstructure should evolve.
Recent experiments in SiC (N. P. Padture et al., J. Am. Ceram. Soc., 77 [2] 519-23 (1994)), Si
3
N
4
(K. Hirao et al., J. Am. Ceram. Soc., 77 [7] 1857-62 (1994)), mullite (S. H. Hong et al., J. Eur. Ceram. Soc., 16 133-41 (1996)), and Al
2
O
3
(M. M. Seabaugh et al., J. Am. Ceram. Soc., 80 [5] 1181-88 (1997)) have shown oriented template particles initiate textured microstructure development.
Templates can be oriented by a variety of techniques, including tape casting, slip casting, centrifugal casting, and extrusion. In initial studies, dry forming techniques have not been used because orientation is difficult to induce during pressing of ceramic particles. Therefore, most attempts have relied on the use of colloidal processing.
Textured &agr;-Al
2
O
3
-based ceramics have been made by a number of techniques. Since dielectric constant anisotropy is deleterious for alumina substrates used in the microelectronics industry, texture development in commercial tape cast alumina substrates was studied extensively in the early 1970s and means were developed to avoid it (F. V. DiMarcello, J. Am. Ceram. Soc., 55 [10] 509-14 (1972)). In 1995, Brandon et al. (Mater. Sci. Eng., A195, 189-96 (1995)) oriented &agr;-Al
2
O
3
platelet particles in an &agr;-Al
2
O
3
matrix in an effort to reinforce the matrix with the platelet particles. The samples demonstrated improved thermal shock resistance and inhibited crack propagation in the through-thickness direction.
Belmonte et al. (J. Mater. Sci., 29 [1] 179-83 (1994)) investigated the sintering behavior of alumina 10 powder compacts containing alumina platelet particles. The &agr;-Al
2
O
3
platelet particles were shown to inhibit densification. Recently, L. An et al. (J. Mater. Res., 12 [12] 3300-3306 (1997)) combined the reaction bonding of aluminum oxide process and water-based gel casting to obtain textured alumina-platelet reinforced composites. They used tape casting as the forming process with an extended doctor blade arrangement to align template particles, and hence to produce textured specimens. Their initial composition was 45 vol. % Al, 35 vol. % &agr;-Al
2
O
3
, and 20 vol. % ZrO
2
. They sintered samples for 5 h at 1550° C.
The processing of textured ceramic components by approaches described in the literature are limited by high temperature (>1600° C.), colloidal-based processes and subsequent part size limitations, and limited texture.
Accordingly, it is an object of the invention to provide an improved method for the manufacture of textured ceramics.
SUMMARY OF THE INVENTION
The process incorporating the invention enables fabrication of dense, highly textured (fraction of 5 oriented grains >20 vol. %) alumina. The method uses a mixture of aluminum metal powder, alumina powder, tabular alumina grains and a liquid phase former. A dry powder mixture of these components is compacted by dry forming techniques such as roll compaction, uniaxial pressing, forging and/or double action pressing. The formed part is then heated at 0.5-10° C./min. to a temperature between 450 and 500° C. and is held for 2-15 h, and is then heated at 1-10° C./min. to 900-1070° C. and is held for 2-10 hours to convert the aluminum particles into alumina. The part is then heated to a higher temperature (>1400° C.) to form a liquid phase which assists densification and promotes the growth of the tabular alumina grains. The aspect ratio range of the textured alumina grains is from 2-14.
REFERENCES:
patent: 4670320 (1987-06-01), Yamaguchi et al.
patent: 5158916 (1992-10-01), Nils Claussen
“In Situ-Toughened Silicon Carbide” by Nitin P. Padture as appeared in J. Am. Ceram. Soc. 77(2), pp. 519-523 (1994).
“Microstructure Control of Silicon Nitride by Seeding with Rodlike &bgr;-Silicon Nitride Particles”; by Hirao et al.as appeared in J. Am. Ceram. Soc. 77 (7); pp. 1857-1862 (1994).
“Anisotropic Grain Growth in Seeded and B2O3-doped Diphasic Mullite Gels” by Hong et al. As appeared in J. Euro. Ceram Soc. 16 (1996), pp. 133-141.
“Texture Development by Templated Grain Growth in Liquid Phase Sintered &agr;-Alumina”; by Seabaugh et al. As appeared in J. Am. Ceram. Soc. 80 (5); pp. 1181-1188 (1997).
“Preferred Orientation in Al2O3Substrates”, by DiMarcello et al.as appeared in J. Am. Ceram Soc. vol. 55 No. 10 pp. 509-514, Oct., 1972.
“Control of Texture in Monolithic Alumina”, by Brandon et al. as appeared in Mat. Science & Engin. A195 (1995); pp. 189-196.
“Obtention of Highly Dispersed Platelet-Reinforced AL2O3Composites” by Belmonte et al. as appeared in J. of Mat. Science 29 (1994); pp. 179-183.
“Alumina Platelet Reinforced Reaction Bonded Aluminum Oxide Composites: Textured and Random” by An et al. as appeared in J. Mater. Res., vol. 12, No. 12, Dec. 1997; pp. 3300-3306.
Messing Gary L.
Suvaci Ender
Fiorilla Christopher A.
Ohlandt Greeley Ruggiero & Perle L.L.P.
The Penn State Research Foundation
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