Fire-resistant and thermal shock-resistant composite ceramic material and method of making same

The invention provides a ceramic composite material which includes 60-85% silicon carbide, 4-15% titanium carbide, 4-20% titanium boride, 4-13% aluminum oxide, and 1-8% titanium oxide. All constituents are in powder form, and have a particle size of between 1 and 40 microns, and a purity of at least 97%. The powdered constituents are blended and consolidated by sintering, although either hot isostatic pressing (HIPing) or by hot pressing can be used to improve certain properties such as impact resistance.

FIELD OF THE INVENTION 
The invention pertains to inorganic materials and can be used in different 
types of fire-resistant products and applications and in metallurgy. For 
example, the present invention can be used for fire-proof safes and other 
similar products as it can resist temperatures higher than 2000.degree. C. 
in corrosive oxygen-rich environments, and has excellent insulation 
properties. By using production methods such as hot press and hot 
isostatic press (HIP), the material of the present invention has high 
fracture toughness and can be used in anti-ballistic applications as well. 
BACKGROUND OF THE INVENTION 
There is a significant demand for ceramic materials made from carbide 
compounds, because these materials have a very high melting/decomposition 
temperature and have several advantages over ceramic oxides. They are less 
brittle than the oxide-based ceramics and are harder materials than the 
oxides. 
Silicon carbide is one of the least expensive and widely used carbides 
which can be used in fire and oxidation resistant applications if certain 
disadvantages of this material could be avoided. By itself, silicon 
carbide has disadvantages in fire-resistant and high temperature 
applications, in that it is quite brittle, has low thermal-shock 
resistance, and also exhibits low high-temperature strength and low 
heat-resistance especially in oxygen-rich environments at high 
temperatures (over 1600.degree. C.). 
Russian author-certificate No. 666152 MKI C04B 35/36, 1977, describes a 
ceramic composite material containing silicon carbide, aluminum oxide, and 
aluminum-chromium-phosphate binder. However, this material has relatively 
low fire-resistance, very low high-temperature strength, and very low 
impact-resistance. 
Thus, a continuing need exists for an improved ceramic composite material 
capable of achieving improved physical properties and performance 
characteristics for fire-resistance, heat-resistance, thermal 
shock-resistance, and impact-resistance. 
SUMMARY OF THE INVENTION 
The present invention provides a ceramic composite material using silicon 
carbide as a base, that has significantly better physical properties and 
performance characteristics than silicon carbide and known silicon carbide 
based composites, and does not have the high-temperature disadvantages of 
these materials. 
An object of the present invention is to provide a ceramic composite 
material having myriad uses and diverse applications. 
Another object of the present invention is to provide a ceramic composite 
material that maintains good high temperature strength and impact 
resistance, while exhibiting excellent fire-resistance, heat resistance 
and thermal shock resistance. 
Still another object of the present invention is to provide a ceramic 
composite material which is composed of relatively inexpensive 
non-metallic constituents, and is capable of being manufactured relatively 
inexpensively. 
Another object of the present invention is to provide a ceramic composite 
material in which its physical properties can be tailored for different 
end uses by adjusting one or more of the following aspects of its 
composition and/or production method: (a) variations in material 
granularity and quality; (b) variations in selection of production method; 
(c) variations in composite ratios; (d) relatively minor additions of new 
constituents; (e) variations in specific process steps in each production 
process; and (f) introduction of certain fibers to reinforce the invented 
material. 
These and other objects of the invention are met by providing a ceramic 
composite material which includes 60-85% silicon carbide, 4-15% titanium 
carbide, 4-20% titanium boride, 4-13% aluminum oxide, and 1-8% titanium 
oxide. All constituents are in powder form, and have a particle size of 
between 1 and 40 microns, and a purity of at least 97%. The powdered 
constituents are blended and consolidated by sintering, although blanks 
with different properties such as higher impact-resistance can be produced 
by either hot isostatic pressing (HIPing) or by hot pressing. 
Properties are optimized with the constituent materials provided in the 
mass ratios of 70-80% silicon carbide, 5-10% titanium carbide, 6-10% 
titanium boride, 5-10% aluminum oxide, and 2-5% titanium oxide. 
Other objects, advantages and salient features of the invention will become 
apparent from the following detailed description, which discloses 
preferred but non-limiting embodiments of the invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention includes a ceramic composite material which contains 
silicon carbide, titanium carbide, titanium boride, aluminum oxide, and 
titanium oxide, all of which are, prior to consolidation, in powder form 
and of powder particle size between 1 and 40 microns, with the range of 3 
to 10 microns being preferred, and purity of 97 percent and higher. 
The cost-quality optimal is at or about 98 percent. 
The preferred mass ratios are as follows: 
______________________________________ 
Optimal properties range 
General Range 
______________________________________ 
Silicon carbide: 
70-80% 60-85% 
Titanium carbide: 
5-10% 4-15% 
Titanium boride: 
6-10% 4-20% 
Aluminum oxide: 
5-10% 4-13% 
Titanium oxide: 
2-5% 1-8% 
______________________________________ 
The general range is used as a trade-off where certain properties and 
qualities can be traded for cost and simplification of production, whereas 
the optimal properties range provides the best overall physical 
properties. 
While ranges outside the optimal ranges provide acceptable trade-offs, 
ranges outside the general ranges are considered to have unacceptable 
results. 
The ceramic composite material of the present invention is produced by 
sintering, hot press or by HIP. Sintering is the least expensive and 
simplest but results in lower impact-resistance. Hot-press and HIPing are 
preferred for achieving better impact-resistance properties. 
Methodology 
The ceramic material of the present invention is produced pursuant to the 
following steps. First, the powders of the above mentioned components with 
the particle size of, preferably, 3-10 micrometers are mixed in the 
desired proportions in a vibration ball mill to obtain homogeneous 
distribution of components in the resultant composite mixture and a 
uniform distribution of particle sizes. Mixing time depends on the 
specific ratios, particle sizes, and mixing techniques. In one example, 
using the ball mill, mixing took 4-5 hours. The blended composite mixture 
thus obtained is pressed into raw product form that is finally processed 
by sintering or hot press or high temperature isostatic pressure (HIP). To 
obtain products of adequate quality it is necessary to strictly follow the 
production procedure, since this material is very sensitive to variations 
of temperature and pressure, and pressure and duration of the exposure to 
heat and pressure after achieving the initial densification.

Example I 
100 gm of silicon carbide powder (73% mass) with the average particle 
diameter 3-10 mkm, 10 gm of titanium carbide powder (7.3% mass) with the 
average particle diameter of 3-7 mkm, 12 gm of titanium boride powder 
(8.8% mass) with the average particle diameter of 7-15 mkm, 10 gm of 
aluminum oxide powder (7.3% mass) with the average particle diameter of 
7-10 mkm, and 5 gm (3.6% mass) of titanium oxide with the average particle 
diameter of 5-10 mkm are blended as stated above. The resultant blend is 
then pressed into raw product forms which are then sintered at high 
temperature of about 1,900.degree. C. for about one hour. 
Test Results 
Samples made according to Example I were tested for fire resistance, heat 
resistance, thermal-shock resistance, bending strength, and compression 
strength. 
Samples 4.times.4.times.27 mm were mounted in a device for 4-point bending 
tests at room temperature and stress was applied until the sample snapped. 
The load at breaking point was measured and the maximum resistance to 
bending was calculated. 
Samples 4.times.4.times.12 mm were subjected to compression at room 
temperature by applying stress until the sample broke. The load at 
breaking point was measured and the maximum resistance to compression was 
calculated. 
The heat resistance of similar samples was measured. The change in the mass 
of the sample was measured after oxidation in air at 1,200.degree. C. 
during 10 hours. 
Thermal-shock resistance of the samples was measured using cylindrical 
samples 10 mm in diameter and 10 mm high. The number of thermal shocks 
(1,200.degree. C. to water at 10.degree. C.) necessary to destroy the 
sample was determined. 
The fire resistance of the samples was tested using samples 50 mm in 
diameter and 5-8 mm thick. The samples were placed 30-40 mm away from the 
nozzle of a propane-oxygen burner having a flame temperature of about 
2000.degree. C. The samples were held under the flame for 30-60 minutes, 
after which they were allowed to cool and were inspected for damage. 
All tests were conducted using several samples for each test. The following 
properties of the present material were observed: 
______________________________________ 
Density (g/cm.sup.3) 
2.4-3.52 
Porosity (%) 32-0 (test samples: 28%) 
Bending Strength (MPa) 
82-85 (porosity 28%) 
Compression Strength (MPa) 
323-330 (porosity 28%) 
Thermal Shock 30-35 cycles 
Heat Resistance (mg/cm.sup.2) 
&lt;0.5 
Fire Resistance (at 2000.degree. C.) 
&gt;60 minutes 
______________________________________ 
The heat resistance measure is the change in mass due to oxidation in air 
at 1,200.degree. C. after 10 hour exposure. 
The fire resistance measure is the time the material has been tested to 
successfully withstand a propane-oxygen flame at 2,000.degree. C. 
One aspect of the present invention is that the material properties can be 
traded off for other advantages. For example, the optimum amount of 
silicon carbide is in the range of 70 to 80 percent. If the percentage 
ratio of silicon carbide is less than 70 percent, the fire-resistance 
capability is degraded. On the other hand, increasing the amount of 
silicon carbide more than 80 percent results in significant degradation of 
impact resistance and heat-strength. 
The optimum amount of titanium carbide is in the range of 5 to 10 percent. 
Reducing titanium carbide to less than 5 percent degrades the heat 
strength, thermal-shock resistance, and impact resistance properties of 
the material. Increasing titanium carbide to more than 10 percent will 
degrade the fire resistance and heat resistance of the material. 
The introduction of 6 to 10 percent of titanium boride in the composite 
mixture improves the fire resistance, heat resistance, and impact 
resistance of the material. 
The introduction of 5 to 10 percent of aluminum oxide in the composite 
mixture makes it possible to process the material at lower temperatures 
without negatively affecting the properties of the material. 
The introduction of 2 to 5 percent of titanium oxide in the composite 
mixture significantly improves the thermal-shock resistance and impact 
resistance of the material. 
Sintering, as opposed to HIPing or hot pressing, can be used where certain 
uses are envisioned where high strength and impact resistance are not as 
critical. 
While advantageous embodiments have been chosen to illustrate the subject 
invention, it will be understood by those skilled in the art that various 
changes and modifications can be made therein without departing from the 
scope of the invention as defined by the appended claims.