Ceramic-metal composite bodies are disclosed, which are each formed by joining a projection on a ceramic member to a recess or a through hole formed in a metallic member together. A groove portion is provided substantially all around the outer periphery of the metallic member such that a fitting end of the metallic member is located in a position corresponding to the groove portion. A difference between a diameter of a bottom of the groove portion and an outer diameter of the projection of the ceramic member is 0.05 to 0.8 times as large as a difference between an outer diameter of the metallic member and the outer diameter of the projection of the ceramic member.

Background of the Invention 
(1) Field of the Invention 
The present invention relates to ceramic-metal composite bodies. 
(2) Related Art Statement 
In ceramic-metal composite bodies as shown partially in section in FIG. 7, 
it has been a common practice that a recess 52 is formed at a joint end 
face of a metallic member 51 and a projection 54 of a ceramic member 53 to 
be joined to the metallic member is fitted into the recess 52 to join the 
ceramic and metallic members together. 
In the conventional ceramic-metal composite bodies having the 
above-mentioned construction, a large stress concentration occurs in the 
ceramic member at a fitting end due to a compression force for the fitting 
when the ceramic member is fitted into the metallic member. As a result, 
the ceramic-metal composite bodies are weak against bending or twisting so 
that the composite bodies are liable to be broken. Thus, there is a 
problem that the ceramic-metal composite bodies having high reliability 
cannot be obtained. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to solve the 
above-mentioned problems and to provide high reliability ceramic-metal 
composite bodies in which a stress concentration upon a ceramic member 
when joined to a metallic member is low to make the ceramic-metal 
composite bodies less liable to be broken. 
According to the present invention, there is a provision of ceramic-metal 
composite bodies comprising a ceramic member and a metallic member, the 
ceramic member and the metallic member being joined together by fitting a 
projection formed on the ceramic member into a recess or a through hole 
formed in the metallic member, wherein a groove portion is provided 
substantially all around the outer periphery of the metallic member, a 
fitting end of the metallic member is located on the inside of the recess 
or the through hole of the metallic member in a position corresponding to 
the groove portion, and a difference between a diameter of a bottom of the 
groove portion and the outer diameter of the projection of the ceramic 
member is 0.05 to 0.8 times as large as a difference between an outer 
diameter of the metallic member and the outer diameter of the projection 
of the ceramic member. 
According to the ceramic-metal composite bodies thus constructed, since the 
groove portion is provided substantially entirely around the outer 
periphery of the metallic member and the fitting end is located at a 
position corresponding to the groove portion while the difference between 
the outer diameter of the bottom of the groove portion and the outer 
diameter of the ceramic member is 0.05 to 0.8 times as large as the 
difference between the outer diameter of the metallic member and the outer 
diameter of the projection of the ceramic member, a stress concentrated 
upon the ceramic member at the fitting end is mitigated so that high 
reliability ceramic-metal composite bodies which are resistant to being 
broken against bending or twisting can be obtained. 
These and other objects, features and advantages of the invention will be 
appreciated upon reading of the following description of the invention 
when taken in connection with the attached drawings, with the 
understanding that some modifications, variations and changes of the same 
could be made by the skilled person in the art to which the invention 
pertains without departing from the spirit of the invention or the scope 
of claims appended hereto.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained in more detail with reference to 
the attached drawings below. 
In FIG. 1 is shown a partial sectional view illustrating the ceramic-metal 
composite body according to the present invention. In FIG. 1, a projection 
1a is provided at an end portion of a ceramic member 1. This projection 1a 
is fitted into a recess 2a formed at one end of a metallic member 2 
through press fitting, etc. A groove portion 3 is provided entirely around 
the outer periphery of a recessed portion 2b of the metallic member 2, and 
a fitting end 4 is provided at the inner periphery of the recess 2a of the 
metallic member 2 at a position corresponding to the groove portion 3. 
Although the shape of the groove portion 3 is semicircular, in section in 
the embodiment of FIG. 1, this shape is not restrictive. A groove portion 
having any shape may be employed so long as it essentially functions as a 
groove. 
FIG. 1 shows an example of a shaft structure in which the outer diameter of 
the ceramic member 1 is equal to that of the metallic member 2, but the 
present invention is not limited to embodiments in which the outer 
diameter of the shaft is uniform. 
FIGS. 2(a) and 2(b) are partial sectional views illustrating embodiments in 
which the ceramic-metal composite body according to the present invention 
is applied to a composite body such as a ceramic turbocharger rotor or a 
ceramic gas turbine rotor which is provided with a seal ring groove and/or 
an oil slinger groove all around the outer periphery of a recessed portion 
of a metallic member from the constructual necessity. In FIGS. 2(a) and 
2(b), a projection 12 is provided on a ceramic rotor 11, and the 
projection 12 is fitted into a recess 14a formed in a metallic member 13 
through press fitting, shrinkage fitting, expansion fitting, combinations, 
thereof or the like. A seal ring groove 15 and an oil slinger groove 16 
are formed all around the outer periphery of the recessed portion 14b of 
the metallic member 13 such that in FIG. 2(a), a fitting end 17 is 
positioned at a location corresponding to the seal ring groove 15 and in 
FIG. 2(b), a fitting end 17 is positioned at a location corresponding to 
the oil slinger groove 16. Accordingly, when the present invention is to 
be applied to composite bodies such as ceramic turbocharger rotors and 
ceramic gas turbine rotors in which a seal ring groove and/or an oil 
slinger groove is provided around the outer periphery of the recessed 
portion of the metallic member from the constructual necessity, the seal 
ring or the oil slinger groove can be used as a groove portion in the 
present invention. Therefore, the object of the present invention can be 
advantageously attained by a simple structure. 
Next, specific embodiments of the present invention will be explained. 
These embodiments are merely given in illustration of the present 
invention, but should never be interpreted to limit the scope thereof. 
EXAMPLE 1 
A ceramic-metal composite body having a shape shown partially in section in 
FIG. 3 was prepared by joining a projection 22 of a ceramic member 21 made 
of Si.sub.3 N.sub.4 to a recess 24a of a metallic member 23 made of 
nickel-chrome-molybdenum steel (JIS-SNCM439). In the illustrated 
embodiment, the joining was performed by press fitting. The press fitting 
was carried out after the outer diameter D.sub.c of the projection 22 of 
the ceramic member 21 and the inner diameter d.sub.m of the recess 24a of 
the metallic member 23 were processed to be 13 mm and 12.9 mm, 
respectively. After the press fitting, the metallic member was finished to 
have the outer diameter D.sub.m of 18 mm at the recessed portion 24b and 
then a rectangular section groove portion 26 of a width b=2.5 mm was 
formed all around the outer periphery of the recessed portion 24b of the 
metallic member at a location corresponding to the fitting end 25. 
In order to examine the influence of the depth of the groove portion 26, 
samples having varied values of D being the diameter of the bottom of the 
groove portion 26 were prepared, and a tensile test was carried out at 
room temperature. Results are shown in Table 1 and FIG. 4. In Table 1 and 
FIG. 4, a tensile load is a load P under which the ceramic member 21 was 
broken from the fitting end 25. The influence of the depth of the groove 
portion 26 was evaluated based on X which is defined in the following 
equation (1): 
##EQU1## 
Thus, X=1.0 corresponds to a case where no groove portion 26 is provided 
around the outer periphery of the recessed portion 24b of the metallic 
member. 
TABLE 1 
______________________________________ 
Tensile load 
Average value 
X (kgf) (kgf) 
______________________________________ 
0.03 1200 1050 
900 
0.05 1480 1300 
1250 
1160 
0.1 1530 1470 
1480 
1410 
0.2 1560 1490 
1480 
1420 
0.4 1570 1500 
1510 
1420 
0.6 1440 1350 
1360 
1260 
0.8 1170 1150 
1030 
950 
1.0 1210 1000 
970 
750 
1080 
1010 
______________________________________ 
As evident from Table 1 and FIG. 4, the tensile strength was larger when 
X=0.05 to 0.8 corresponding to the cases where the groove portion 26 is 
provided at a location corresponding to the fitting end 25 according to 
the present invention, as compared with the conventional case 
corresponding to X=1.0 in which no groove portion was provided. 
EXAMPLE 2 
A ceramic turbocharger rotor having a shape shown partially in section in 
FIG. 5 was prepared by joining a projection 32 of a ceramic rotor 31 made 
of Si.sub.3 N.sub.4 to a recess 34a of a cup-like metallic member 34 made 
of an Fe-Ni alloy which was joined to one end of a metallic shaft 33 made 
of nickel-chrome-molybdenum steel (JIS-SNCM439) through a friction 
welding. In this embodiment, the projection 32 (13 mm in outer diameter) 
of the ceramic rotor 31 was fitted, through press fitting, into a recess 
34a of the low expansion cup-like metallic member 34 having an inner 
diameter of 12.9 mm and an outer diameter of 18 mm before the press 
fitting. A seal ring groove 35 and an oil slinger groove 36 were formed 
all around the outer periphery of the metallic member 34 such that a 
fitting end may be positioned at a location corresponding to the seal ring 
groove 35 and a diameter of the bottom of the seal ring groove 35 may be 
15 mm. The hardness of the metallic shaft 33 made of 
nickel-chrome-molybdenum steel (JIS-SNCM439) was adjusted by induction 
hardening and tempering treatment. 
Although the thus obtained ceramic turbocharger rotor was assembled into a 
high temperature rotation tester and was subjected to a rotation test at a 
number of revolutions of 150,000 rpm for 50 hours by using a combustion 
gas of 800.degree. C., no abnormality was observed. When the same test was 
performed with respect to a ceramic turbocharger rotor in which the 
fitting end 37 was not provided at a location corresponding to a seal ring 
groove 35 and an oil slinger groove 36, the ceramic member was broken from 
the fitting end 37 in 38 hours. 
EXAMPLE 3 
FIG. 6 is a partial sectional view illustrating an embodiment in which the 
present invention is applied to a piston. A piston cap 41 having a 
cylindrical projection 42 of an outer diameter of 20 mm and a length of 20 
mm was prepared from Si.sub.3 N.sub.4. In the meanwhile, a metallic member 
44 having an outer diameter of 30 mm, an inner diameter of 19.7 mm and an 
entire length of 15 mm was prepared from stainless steel. Then, the 
cylindrical projection 42 of the piston cap 41 was press fitted into a 
through hole 47 of the metallic member 44 while both the members were 
maintained at 500.degree. C. Thereby, a ceramic-metal composite body 
having a trapezoidal section groove portion 46 of a diameter of 25 mm 
formed all around the outer periphery of the metallic member 44 
corresponding to a fitting end 45 was prepared. 
On the other hand, a recess 49 into which the ceramic-metal composite body 
thus obtained was to be inserted was formed in a crown portion 48 of a 
piston body 43 made of a spheroidal graphite cast iron having an outer 
diameter of 70 mm. Then, a male screw thread provided at the outer 
periphery of the metallic member 44 of the ceramic-metal composite body 
was screwed to a female screw thread formed in the recess 49 to obtain a 
heat insulating engine piston having a shape shown partially in section in 
FIG. 6. Even when the thus obtained piston was tested in a diesel engine 
having a cylinder bore of 70 mm and a stroke of 75 mm at an engine speed 
of 2200 rpm for 100 hours, no abnormality was observed. When the same test 
was performed with respect to a piston in which no groove portion was 
provided around the outer periphery of a metallic member 44 at a location 
corresponding to the fitting end 45, the ceramic was broken from the 
fitting end 45 in 87 hours. 
The present invention is not limited to the above-mentioned embodiments, 
but various modifications and variations may be made. For instance, in the 
above embodiments, Si.sub.3 N.sub.4 was used as the ceramic material, but 
the present invention is not limited thereto. Silicon carbide, sialon, 
zirconia, mullite, alumina, beryllia, etc. may be used. Further, the 
metallic member is not limited to the above-mentioned materials, but 
needless to say, other metallic materials can be used. 
As evident from the aforementioned, according to the ceramic-metal 
composite bodies of the present invention, the fitting end is provided at 
a location corresponding to the groove portion formed substantially all 
around the outer periphery of the metallic member, and the difference 
between the diameter of the bottom of the groove portion and the outer 
diameter of the projection of the ceramic member is 0.05 to 0.8 times as 
large as the difference between the outer diameter of the metallic member 
and the outer diameter of the projection of the ceramic member, so that 
the stress concentration upon the ceramic member at the fitting end is 
mitigated to give ceramic-metal composite bodies having high reliability.