Ceramic-metal structure

Abstract

A ceramic-metal structure in which a metallic body (2) is inserted into or disposed above a through hole (4h) of a ceramic substrate (4) and which includes an annular pad layer (6) disposed around the through hole; an annular ring member (8) joined to the pad layer via a first brazing filler portion (10) and having a coefficient of thermal expansion smaller than that of the metallic body; a second brazing filler portion (12) intervening between the ring member and metallic body; and brazing filler flow prevention layers (7a, 7b) covering an outer surface of the pad layer so as to expose a central region (6c) of the outer surface of the pad layer facing the first brazing filler portion. The first brazing filler portion joins the central region and the ring member without projecting to a radially inner or outer side of the flow prevention layers.

Claims

1. A ceramic-metal structure in which a pipe-shaped or rod-shaped metallic body is inserted into a through hole extending through a ceramic substrate from a surface of the ceramic substrate in a thickness direction thereof or is coaxially disposed just above the through hole, the ceramic-metal structure comprising: an annular pad layer made of a metal and disposed on the surface of the ceramic substrate to be located around the through hole; an annular ring member joined to the pad layer via a first brazing filler portion and having a coefficient of thermal expansion smaller than that of the metallic body; a second brazing filler portion intervening between the ring member and the metallic body and joining the ring member and the metallic body together; and a brazing filler flow prevention layer which covers an outer surface of the pad layer in such a manner as to expose a central region of an upper surface of the outer surface of the pad layer, the upper surface facing the first brazing filler portion, wherein the first brazing filler portion joins the central region and the ring member together without projecting to a radially inner side and a radially outer side of the brazing filler flow prevention layer.

2. A ceramic-metal structure according to claim 1, wherein the ring member has an outer diameter smaller than that of the pad layer, and the first brazing filler portion has a portion which is in contact with a peripheral surface of the ring member and forms a fillet shape.

3. A ceramic-metal structure according to claim 1, wherein the first brazing filler portion has a portion which extends toward a radially inner side of the ring member and forms a fillet shape.

4. A ceramic-metal structure according to claim 1, wherein the ceramic substrate and the brazing filler flow prevention layer contain the same material as their main components.

5. A ceramic-metal structure according to claim 1, wherein the ceramic substrate has a flow channel formed therein which is connected to the through hole and through which gas flows, the metallic body is pipe-shaped, and exchange of gas can be performed between the flow channel and the outside of the ceramic substrate through an internal space of the metallic body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 Exploded perspective view of a ceramic-metal structure according to an embodiment of the present invention.

(2) FIG. 2 Sectional view taken along line of FIG. 1.

(3) FIG. 3 Sectional view showing a modification of the ceramic-metal structure according to the embodiment of the present invention.

(4) FIG. 4 Sectional view showing another modification of the ceramic-metal structure according to the embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

(5) The present invention will next be described in detail with reference to the drawings. FIG. 1 is an exploded perspective view of a ceramic-metal structure 100 according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line of FIG. 1.

(6) In FIG. 1, the ceramic-metal structure 100 includes a pipe-shaped metallic body 2, a generally quadrate ceramic substrate 4 having a through hole 4h, a pad layer 6 disposed on a surface of the ceramic substrate 4 around the through hole 4h, brazing filler flow prevention layers 7a and 7b to be described in detail later, an annular ring member 8, a first brazing filler portion 10 joining the pad layer 6 and the ring member 8 together, and a second brazing filler portion 12 joining the ring member 8 and the metallic body 2 together.

(7) The ceramic substrate 4 is a ceramic sintered body which predominantly contains alumina, and the metallic body 2 is formed of stainless steel. The annular pad layer 6 is made of a metal, enhances adhesion between the ceramic substrate 4 and the first brazing filler portion 10, and prevents direct brazing of the first brazing filler portion 10 to the ceramic substrate 4. The pad layer 6 can be formed as follows: a paste which contains, for example, at least one of tungsten and molybdenum as a main component is printed onto a surface of a green body of the ceramic substrate 4, followed by firing and subsequent Ni plating onto the surface of the fired paste.

(8) The brazing filler flow prevention layers 7a and 7b can be formed as follows: a paste of, for example, a material whose main component (alumina in the present embodiment) is the same as that of the ceramic substrate 4 is printed annularly in a bridging manner (to extend) between green bodies of the ceramic substrate 4 and the pad layer 6, followed by simultaneous firing together with the green bodies of the ceramic substrate 4 and the pad layer 6.

(9) The ring member 8 is formed of, for example, Kovar having a coefficient of thermal expansion smaller than that of the metallic body 2.

(10) Examples of a brazing filler metal which is to form the first brazing filler portion 10 and the second brazing filler portion 12 include an AuCu alloy, an AgCu alloy, and various conductive materials (e.g., Cu (copper) and Ag (silver)).

(11) The ceramic substrate 4 has a flow channel 4c (see FIG. 2) formed therein and communicating with the through hole 4h, whereby exchange of gas G can be performed between the flow channel 4c and the outside of the ceramic substrate 4 through an internal space of the metallic body 2. Notably, in an internal space of the ceramic substrate 4, a predetermined processing (e.g., heating) can be performed on the gas G, or the concentration of the gas G can be detected.

(12) As shown in FIG. 2, the metallic body 2 is inserted into the through hole 4h extending through the ceramic substrate 4 in a thickness direction thereof and is disposed coaxially with an axis AX of the through hole 4h.

(13) The brazing filler flow prevention layers 7a and 7b cover an outer surface of the pad layer 6 in such a manner as to expose a central region 6c of an upper surface of the outer surface of the pad layer 6, the upper surface facing the first brazing filler portion 10. Specifically, the annular inner brazing filler flow prevention layer 7a is formed in a bridging manner between the ceramic substrate 4 and a radially inner circumferential edge of the pad layer 6 such that the annular inner brazing filler flow prevention layer 7a rises above an upper surface 6f of the pad layer 6. The inner brazing filler flow prevention layer 7a is formed in contact with the surface of the ceramic substrate 4 while covering the inner circumferential surface of the pad layer 6.

(14) Similarly, the annular outer brazing filler flow prevention layer 7b is formed in a bridging manner between the ceramic substrate 4 and a radially outer circumferential edge of the pad layer 6 such that the annular outer brazing filler flow prevention layer 7b rises above the upper surface 6f of the pad layer 6. The outer brazing filler flow prevention layer 7b is formed in contact with the surface of the ceramic substrate 4 while covering the outer circumferential surface of the pad layer 6.

(15) The first brazing filler portion 10 intervenes between and brazes together the central region 6c of the pad layer 6 and the ring member 8 without projecting to the radially inner side of the inner brazing filler flow prevention layer 7a and to the radially outer side of the outer brazing filler flow prevention layer 7b.

(16) Meanwhile, the second brazing filler portion 12 intervenes between and brazes together the ring member 8 and the metallic body 2.

(17) Since the first brazing filler portion 10 does not project to the radially inner side and the radially outer side of the brazing filler flow prevention layers 7a and 7b, respectively, direct contact of the first brazing filler portion 10 with the ceramic substrate 4 can be prevented. Also, as a result of the brazing filler flow prevention layers 7a and 7b being disposed above the interface between the ceramic substrate 4 and the metal pad layer 6 on which stress is imposed most intensively, the strength of the ceramic substrate is improved. Further, as a result of an end portion of the first brazing filler portion 10 being located internally of the interface, stress imposed on the interface is mitigated. As a result, there can be restrained separation of the first brazing filler portion 10 and occurrence of cracking in the ceramic substrate 4 which could otherwise result from concentration of stress at the first brazing filler portion 10 during cooling due to a difference in coefficient of thermal expansion between the ceramic substrate 4 and the first brazing filler portion 10, whereby reliable brazing can be ensured.

(18) According to the present embodiment, an outer diameter D1 of the ring member 8 is smaller than an outer diameter D2 of the pad layer 6, and the first brazing filler portion 10 has a portion 10a which forms a fillet shape and is in contact with the outer circumferential surface of the ring member 8. In the case of the first brazing filler portion 10 having the portion 10a in a fillet shape (a concave shape), the fillet shape indicates that a molten brazing filler metal has penetrated into a space between the ring member 8 and the pad layer 6 with sufficient wettability to thereby improve brazing strength.

(19) Similarly, according to the present embodiment, the first brazing filler portion 10 has a portion 10b which extends toward the radially inner side of the ring member 8 and forms a fillet shape. As a result of the portion 10b also forming a fillet shape, brazing strength is improved.

(20) According to the present embodiment, since the ceramic substrate 4 and the brazing filler flow prevention layers 7a and 7b contain the same material as their main components, adhesion between the ceramic substrate 4 and the brazing filler flow prevention layers 7a and 7b is excellent.

(21) The ceramic-metal structure 100 of the present embodiment can be manufactured, for example, as follows.

(22) First, a first brazing filler metal which is to become the first brazing filler portion 10 is disposed on the pad layer 6 of the ceramic substrate 4, and the ring member 8 is disposed on the first brazing filler metal. Next, in a state in which the metallic body 2 is inserted into the ring member 8 and the through hole 4h of the ceramic substrate 4, the metallic body 2 is held with a jig or the like. Further, a second brazing filler metal which is to become the second brazing filler portion 12 is disposed between the metallic body 2 and the ring member 8.

(23) Then, the resultant assembly is heated so as to melt the first brazing filler metal and the second brazing filler metal at a time for brazing.

(24) The present invention is not limited to the above embodiment, but extends into various modifications and equivalents encompassed by the ideas and scope of the invention.

(25) For example, as shown in FIG. 3, the metallic body 2 may be disposed coaxially with the through hole 4h such that an end 2f of the metallic body 2 butts against the surface of the ceramic substrate 4 around the through hole 4h. In the example of FIG. 3, the first brazing filler portion 10 and the second brazing filler portion 12 merge together in a region R located on the radially inner side of the ring member 8. In this case, the first brazing filler portion 10 is a portion joining the pad layer 6 and the ring member 8 together, and the second brazing filler portion 12 is a portion joining the ring member 8 and the metallic body 2; however, in the case where the material of the first brazing filler portion 10 is identical with the material of the second brazing filler portion 12, the boundary therebetween may not necessarily be clear.

(26) Also, as shown in FIG. 4, an outer diameter D3 of the metallic body 2 may be greater than a diameter D4 of the through hole 4h; thus, the metallic body 2 may be disposed coaxially with the axis AX just above the through hole 4h.

(27) In the above embodiment, the metallic body 2 is pipe-shaped; however, the metallic body 2 may be rod-shaped.

DESCRIPTION OF REFERENCE NUMERALS

(28) 2: metallic body 4: ceramic substrate 4c: flow channel 4h: through hole 6: pad layer 6c: central region of pad layer 7a, 7b: brazing filler flow prevention layer 8: ring member 10: first brazing filler portion 10a, 10b: portion in fillet shape 12: second brazing filler portion 100: ceramic-metal structure AX: axis of through hole D1: outer diameter of ring member D2: outer diameter of pad layer G: gas