Bimodal silicon nitride BAS ceramic composites

Details Bimodal silicon nitride BAS ceramic composites Bimodal silicon nitride BAS ceramic composites

2000-10-19

2001-09-18

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S095300, C501S097300, C501S097400, C264S676000, C264S662000

Reexamination Certificate

active

06291376

ABSTRACT:

TECHNICAL FIELD
This invention relates to the field of high temperature strength ceramics, and, more particularly, to pressureless sintered silicon nitride (Si
3
N
4
)-barium aluminosilicate (BAS) ceramic composites.
BACKGROUND OF THE INVENTION
Silicon nitride ceramics are particularly useful for applications that require high temperature strength and thermal shock resistance. Previously, high pressure methods were used to fabricate these ceramics. However, the use of high pressures often increased manufacturing costs and limited the geometric shape of the formed component. In order to overcome these barriers, researchers developed the technique of pressureless sintering.
Using pressureless sintering techniques, researchers have been able to fabricate Si
3
N
4
-BAS ceramic composites with high strength and some levels of damage tolerance. However, the industry needs further improvements in fracture toughness and flexural strength before pressureless sintered Si
3
N
4
-BAS ceramic composites can rival Si
3
N
4
-BAS composites fabricated using high pressure techniques.
At present time, researchers have been unable to fabricate pressureless sintered Si
3
N
4
-BAS composites that exhibit both increased flexural strength and fracture toughness. Experimentation has shown that Si
3
N
4
-BAS composites with relatively uniform microstructures, consisting of &bgr; whiskers of several microns in length, usually exhibit high flexural strength and little or no R-curve behavior. Further, experimentation has also shown that Si
3
N
4
-BAS composites with microstructures consisting of &bgr; whiskers with increased diameters usually exhibit high fracture toughness and rising R-curves. Based on these observations, researchers hypothesized that a Si
3
N
4
-BAS composite with optimum distributions of coarse &bgr;-Si
3
N
4
whiskers, surrounded by a matrix of short &bgr;-Si
3
N
4
whiskers and fine BAS grains, or a bimodal microstructure, would provide an ideal compromise between toughness and strength.
Therefore, what is needed is a composition and a method to fabricate pressureless sintered Si
3
N
4
-BAS ceramic composites, with optimum distributions of coarse &bgr;-Si
3
N
4
whiskers, surrounded by a matrix of short &bgr;-Si
3
N
4
whiskers and fine BAS grain and flexural strength.
SUMMARY OF THE INVENTION
The present invention provides for a composition and method of fabricating pressureless sintered 70 volume % Si
3
N
4
—30 volume % BAS ceramic composites. The composites are made from 70 volume % Si
3
N
4
, containing varying amounts and size distributions of initial Si3N
4
, and 30 volume % BAS. The resulting ceramic composites contain microstructures with coarse &bgr;-Si
3
N
4
whiskers, as well as narrow distributions of short &bgr;-Si
3
N
4
whiskers, surrounded by fine BAS grains.
An advantage is achieved with the present invention in that it enables the fabrication of 70 volume % Si
3
N
4
—30 volume % BAS ceramic composites with bimodal microstructures. Another advantage achieved with the present invention is that the composites exhibit improved fracture toughness and flexural strength.


REFERENCES:
patent: 5358912 (1994-10-01), Freitag et al.
patent: 5538925 (1996-07-01), Talmy et al.
patent: 5578534 (1996-11-01), Talmy et al.
patent: 5585314 (1996-12-01), Ezis et al.
patent: 5723392 (1998-03-01), Ezis et al.
Drummond, C.H., III, “Glass-Formation and Crystallization in High-Temperature Glass Ceramics and Si3N4”, Journal of Non-Crystalline Solids, vol. 123, 114-128 (1990).
Pickup, H. and Brook, R.J., “Barium Oxide as a Sintering Aid for Silicon Nitride”, British Ceramic Society Proceedings, vol. 39, 69-76 (1987).
Richardson, Kerry K., Freitag and Doug W., Hunn, David L., “Barium Aluminosilicate Reinforced In Situ with Silicon Nitride”, Journal of American Ceramic Society, vol. 78[10], 2662-68 (1995).
Hwang, C.J. and Newman, R.A., “Silicon Nitride Ceramics With Celsian as an Additive”, Journal of Materials Science, vol. 31, 150-156 (1996).

Affiliated with

Also associated with

Rating

Bimodal silicon nitride BAS ceramic composites does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bimodal silicon nitride BAS ceramic composites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bimodal silicon nitride BAS ceramic composites will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2474594