Composite Body and Method of Manufacturing the Same

1. Field of the Invention

The present invention relates to a composite body obtained by combining and bonding a sintered metal body and a sintered ceramic body and a method of manufacturing the same.

2. Description of the Prior Art

The use of composite bodies obtained by bonding sintered ceramic bodies with metal bodies as mechanical parts providing high wear-resistance has been the subject of recent study. In the manufacture of such composite bodies, the ceramic and metal bodies must be firmly bonded. Conventional methods of bonding ceramic and metal bodies include thermal insertion, diffusion bonding, and soldering. Since the bonding between the ceramic and metal bodies is weak in these conventional methods, the finished composite bodies have low reliability. In addition, these processes are complex and expensive in terms of production.

Ishida et al. describe a bonding method in Japanese Patent Disclosure No. 59-205406. In this method, a metal ring-shaped body is obtained after pre-forming a metal powder. A sintered ceramic body is fitted in the metal body and the assembly is sintered. In the cooling step after sintering, the sintered metal body contracts and compresses the ceramic body. This method is an example of manufacturing a composite body by thermal insertion and therefore features the problems discussed above.

It is an object of the present invention to provide a composite body with improved reliability wherein sintered ceramic and metal bodies are firmly bonded, and to provide a method of manufacturing such a composite body.

It is another object of the present invention to provide a method of manufacturing a composite body which has high productivity and a composite body manufactured by this method.

In order to achieve the above objects of the present invention, a bonding portion is formed in a ceramic body. A sintered metal body locks with the bonding portion of the ceramic body provided, if necessary, with an infiltrator, and thus, physically bonds the ceramic and metal bodies together.

FIG. 1 is a sectional view showing an example of a composite body according to the present invention;

FIGS. 2 and 3 are sectional views showing different embodiments of a method of manufacturing a composite body according to the present invention;

FIGS. 4 to 10 are sectional views showing different embodiments of composite bodies according to the present invention;

FIG. 11 is a sectional view of a composite body sample according to the present invention;

FIG. 12 is a sectional view of a control sample;

FIG. 13 is a sectional view of a method of manufacturing respective samples; and

FIG. 14 is a view showing a method of performing a bonding strength test on respective samples.

In a composite body according to the present invention, a bonding portion is formed in a sintered ceramic body. A sintered metal body is fitted to the bonding portion or an infiltrator is filled in a space which the bonds portion and the sintered metal body, which bonds the ceramic and metal bodies.

The shapes and sizes of the composite body and the ceramic and metal bodies constituting it, and the method of bonding the ceramic and metal bodies can be changed freely. However, the bonding portion must be able to withstand forces applied to the composite body. Therefore, the bonding portion can be an annular groove or have a step-like profile in a cross-section. Different combinations of ceramic and metal bodies include:

(a) A bonding portion formed in the outer circumferential surface of a ceramic body with a metal body fitted around the outer circumferential surface of the ceramic body with the bonding portion. In this case, the thermal expansion coefficient of the ceramic body is set to be larger than that of the metal body. Combinations of materials satisfying this requirement are Al.sub.2 O.sub.3, Si.sub.3 N.sub.4, SiC, ZrO.sub.2, and the like for the ceramic body, and invar (36 wt% Ni-Fe alloy) and the like for the metal body.

(b) A bonding portion formed in the inner circumferential surface of a ceramic body, and a metal body is fitted in the inner surface having the bonding portion. In this case, the thermal expansion coefficient of the metal body is selected to be larger than that of the ceramic body. Combinations of materials satisfying this requirement are Al.sub.2 O.sub.3, Si.sub.3 N.sub.4, SiC, ZrO.sub.2, or the like for the ceramic body, and Fe-based, stainless steel, or Cu-based alloy for the metal body.

Composite bodies consisting of ceramic and metal bodies having different thermal expansion coefficients are effectively manufactured by sintering the bodies in a heated atmosphere. When such a difference in thermal expansion coefficient is present, the ceramic and metal bodies are bonded more firmly.

(c) A bonding portion is formed in the outer circumferential surface of a ceramic body. A metal body is fitted to the outer circumferential surface of the ceramic body. A matrix body consisting of ceramic or metal is fitted around the outer circumferential surface of the metal body. In this case, the thermal expansion coefficients of the materials of the respective bodies are selected such that (ceramic body)<(matrix body)<(metal body). In this combination, a bonding portion can also be formed in the matrix body.

(d) A bonding portion is formed in the inner circumferential surface of a ceramic body. A metal body is fitted in the inner circumferential surface of the ceramic body. A matrix body consisting of a ceramic or metal is fitted around the outer circumferential surface of the ceramic body. In this case, the thermal expansion coefficients of the materials of the respective bodies are selected such that (metal body)<(matrix body)<(ceramic body).

Composite bodies of combinations (c) and (d) are also suitable for manufacture in a heated atmosphere. The reason for this can be surmised as follows. In the case of combination (c), since the matrix body regulates thermal expansion of the metal body, a thermal expansion reaction is generated in the metal body. This reaction force serves to securely bond the ceramic and metal bodies, thereby providing an integral composite body.

In the case of combination (d), since the matrix body regulates thermal expansion of the ceramic body, a thermal expansion reaction is generated in the ceramic body. This reaction force serves to firmly bond the metal and ceramic bodies, again providing an integral composite body.

In order to obtain a metal body with a desired thermal expansion coefficient, the materials can be selected as described above or a ceramic powder such as glass can be mixed with a metal powder.

A composite body of the present invention is manufactured in the following manner:

(a) A sintered ceramic body having a bonding portion is prepared. The shape, size, and material of the ceramic body, and the shape of the bonding portion are selected as described above;

(b) A metal body of a powder consisting mainly of a metal powder is combined with the ceramic body. The metal body can be selected from a metal body having the powder arranged around a ceramic body (M1), a metal body obtained by compressing the powder into a predetermined shape (M2), a metal body obtained by compressing the powder and presintering the compressed powder into a predetermined shape (M3), and a metal body obtained by compressing the powder and sintering the compressed powder into a predetermined shape (M4). When metal body M1 is used, it need not be formed before it is combined with the ceramic body. Therefore, the total number of steps required is reduced. When metal body M2 or M3 is used, since the metal body is very soft, it can be formed easily in a later step. Metal body M4 is used when the selected material has a high tendency to deform;

(c) The metal body combined with the ceramic body is pressed so that part of it is fitted inside the bonding portion of the ceramic body. Each of metal bodies M1 to M4 has a number of pores and can easily deform even if the metal itself cannot be easily deformed. Therefore, the fitting step can be easily performed; and

(d) The pressed metal body is sintered with the ceramic body to provide a composite body in which the ceramic and metal bodies are securely locked and bonded with each other.

In sintering step (d) or in a later step, if the metal body is infiltrated with an infiltrator such as copper, the strength of the metal body is increased. In addition, the infiltrator bonds with the ceramic body, thereby improving the bonding strength between the two sintered bodies.

As another method of manufacturing a composite body according to the present invention, in step (b) described above, one of metal bodies M2 to M4 (excluding metal body M1) is combined with a ceramic body. A space is formed enclosed by the bonding portion of the ceramic body and the metal body, step (c) is omitted, and step (d) follows directly. At the same time, an infiltrator such as copper is infiltrated into the bonding portion, thereby manufacturing a composite body. In the obtained composite body, the ceramic and metal bodies are securely bonded with each other and with the infiltrator infiltrated into the bonding portion.

According to still another method of manufacturing a composite body according to the present invention, if no space is formed between the bonding portion of a ceramic body and a metal body (one of M2 to M4), after the metal body is fitted with the ceramic body, sintering step (d) is performed without performing step (c). During or after sintering step (d), the above-mentioned infiltration step can be performed.

Some examples of the shape of composite bodies and manufacturing methods thereof according to the present invention will be described below with reference to the accompanying drawings.

Ceramic body 11 has rod-like portion 11a at the center of a plate. Annular groove 11b is formed in a part of the outer circumferential surface of rod-like portion 11a, and serves as a bonding portion. Metal body 12 has hole 12a for fitting over portion 11a of ceramic body 11. Projection 12b locks with annular groove 11b after the composite body is compressed.

In order to manufacture this composite body, ceramic body 11 is placed inside die 13. A metal powder filled on ceramic body 11 is pressed by upper and lower punches 14 and 15 to produce green compact metal body 12'. With this method, the metal powder flows and enters groove 11b of ceramic body 11. Formed metal body 12' is sintered to provide the composite body shown in FIG. 2.

A metal powder is pressed into green compact metal body 12' with pores. After presintering, metal body 12' is combined with ceramic body 11. Presintered metal body 12' is pressed to partially crease it, such that the creased portion extends into groove 11b of ceramic body 11. Metal and ceramic bodies 12' and 11 are sintered to obtain the composite body shown in FIG. 3. In the sintering step or in a later step, the infiltration step can also be performed.

Presintered metal body 12' is combined with ceramic body 11. When bodies 12' and 11 are combined, a space is formed between groove 11b of body 11 and body 12'. The assembly is sintered without pressing metal body 12', and at the same time or in a later step, an infiltrator such as copper is infiltrated into the bonding portion. In the obtained composite body, the two bodies are bonded at the bonding portion with infiltrator 16.

The composite bodies shown in these figures have different shapes or combinations of ceramic and metal bodies and bonding portions. These shapes and combinations are selected in accordance with the possible forces expected to be applied uses of the composite bodies and possible applications thereof.

Ceramic body 21 is inserted in a central hole of metal matrix body 23 with a predetermined gap left therebetween. Annular presintered metal body 22, indicated by the dotted line, is fitted in the gap. Metal body 22 is pressed so that it locks with both bonding portion 23a of the matrix body and with bonding portion 21a of ceramic body 21. The assembly is sintered to obtain the composite body.

Metal matrix body 33 has a recess having a tapered sectional shape. Ceramic body 31 has a shape obtained by placing a small disk at the center of a large disk. Ceramic body 31 is placed in the recess of matrix body 33 with a predetermined gap left therebetween. Annular presintered metal body 32, indicated by the dotted line, is fitted in the gap. The space enclosed by metal body 32 and matrix body 33 is bonding portion 33a of matrix body 33. Metal body 32 is pressed to extend into bonding portion 33a and lock therewith. Thereafter, the assembly is sintered to complete the composite body.

Ceramic body 31 and metal body 32 of the same shapes as those in FIG. 9 are fitted in a recess of matrix body 33. Infiltrator 34 is infiltrated in bonding portion 33a of the matrix body through metal body 32 during or after sintering, thereby completing the composite body.

Composite body samples having the shape shown in FIG. 11 and control composite body samples having the shape shown in FIG. 12 were prepared. Ceramic bodies 41 of the respective samples were obtained by sintering Si.sub.3 N.sub.4 -5 wt%Y.sub.2 O.sub.3 -4 wt%Al.sub.2 O.sub.3 -3 wt%AlN-1.5 wt%TiO.sub.2 at ambient temperature. SUS 304 stainless steel was used as a metal powder for metal bodies 42. SK-3 carbon tool steel was used for matrix bodies 43. The respective samples had the following dimensions: lengths l1=40 mm, l2=18 mm, and l3=30 mm; and diameters d1=10 mm, d2=18 mm, d3=30 mm, and d4=10.5 mm.

The respective samples were manufactured in the following manner. As shown in FIG. 13, ceramic body 41 was placed in die 44. After filling the metal powder on lower punch 45 in a space defined by matrix body 43 and ceramic body 41, pressing was performed by upper punch 46 at a pressure of 6 ton/cm.sup.2. The assembly was sintered at 1,200.degree. C. to obtain metal body 42, which was contracted by 1.1%. After forming a composite body by combining ceramic body 41 and metal body 42, it was pressed into matrix body 43 by a press machine to obtain the sample shown in FIGS. 11 and 12. In some samples, a copper mass was placed on sintered metal body 42 and heated to allow infiltration.

Each sample prepared in this manner was mounted on a press testing jig, shown in FIG. 14, and was subjected to a press test by a 10 ton universal testing machine, available from Instron Inc., at a crosshead speed of 0.5 mm/min. The obtained results are shown in Table 1. Note that in FIG. 14 reference numeral 51 denotes a load cell; 52, a press rod; and 53, a support ring.

It is seen from the above Table that when bonding portions comprising steps were formed, the bonding strength was 7.8 to 8.3 kg/mm.sup.2. This bonding strength is about 15% higher than Control samples. In the samples of the Example in which copper was infiltrated, the bonding strength was 12.6 to 14.8 kg/mm.sup.2. This bonding strength is about 65% higher than the samples in which copper was not infiltrated.