Brazeable Zirconia Ceramics, Methods Of Brazing Zirconia Ceramics, And Brazed Zirconia Ceramics

Abstract

A method of brazing a sintered zirconia ceramic body, comprises: providing a sintered zirconia ceramic body having a surface; chemically reducing the sintered zirconia ceramic body in whole or in part to form a reduced surface to the sintered zirconia ceramic body; applying a brazing material to at least part of the reduced surface to form an assembly comprising said brazing material and sintered zirconia ceramic body; heating said assembly to a temperature sufficient to at least partially melt the brazing material such that the brazing material wets the reduced surface; and cooling the assembly to solidify the brazing material.

Claims

1. A method of brazing a sintered zirconia ceramic body, comprising: providing a sintered zirconia ceramic body having a surface; chemically reducing the sintered zirconia ceramic body in whole or in part to form a reduced surface to the sintered zirconia ceramic body; applying a brazing material to at least part of the reduced surface to form an assembly comprising said brazing material and sintered zirconia ceramic body; heating said assembly to a temperature sufficient to at least partially melt the brazing material such that the brazing material wets the reduced surface; and cooling the assembly to solidify the brazing material.

2. A method of preparing a sintered zirconia ceramic body for brazing, comprising: providing a sintered zirconia ceramic body having a surface comprising at least in part a region adapted to be brazed; and chemically reducing the sintered zirconia ceramic body in whole or in part to form a reduced surface to the sintered zirconia ceramic body.

3. The method of claim 1, wherein chemically reducing the sintered zirconia ceramic body comprises exposing the sintered zirconia ceramic body to a reducing atmosphere.

4. The method of claim 3, wherein the reducing atmosphere comprises hydrogen.

5. The method of claim 1, wherein in which the sintered zirconia ceramic body comprises greater than 50 wt % zirconia.

6. The method of claim 5, wherein the sintered zirconia ceramic body is a tetragonal zirconia polycrystal ceramic.

7. A brazed article comprising a sintered zirconia ceramic body comprising a chemically reduced surface.

Description

EXAMPLES

The Zirconia Ceramic

[0029] The following examples illustrate but do not limit the invention and each use an injection moulded and sintered dense (>90% dense) material made from yttria stabilised TZP (YTZP) [made from TZ-3YSE-E grade zirconia powder supplied by Tosoh Corporation which had an analysed composition in weight percent:Y.sub.2O.sub.3 5.23%, Al.sub.2O.sub.3 0.252%, SiO.sub.2 at most 0.002%, Fe.sub.2O.sub.3 at most 0.002%, Na.sub.2O 0.007%, ignition loss of 0.45%, balance zirconia].

[0030] The material, prior to brazing, had been fired in dry hydrogen (dew point 60 C. or better) at 1500 C. for 30 min and then cooled in dry hydrogen to 150 C.

[0031] This heat treatment turned the YTZP dark (material changing from white to black). The YTZP did not become electrically conductive.

[0032] Heat treatment temperatures that may be used include (without limitation)>1350 C., >1400 C., >1500 C., >1550 C.

Example 1

[0033] The inventors have brazed articles to titanium, using a 50 m (2 thousandth of an inch) thick foil of Ticuni active brazing alloy (15 Cu, 15 Ni, 70 Ti) placed between the YTZP and the titanium. Brazing took place at 980 C. in vacuum.

[0034] A good joint resulted that did not pull apart with significant force and that was hermetic.

[0035] FIG. 2 shows an SEM micrograph of the braze, with the dense ceramic 1 joined to titanium 2 at joint 3

Example 2

[0036] The heat treated YTZP of example 1 was brazed to titanium using a 50 m (2 thousandth of an inch) thick pure gold foil as brazing material.

[0037] A good joint resulted that did not pull apart with significant force and that was hermetic.

Example 3

[0038] The heat treated YTZP of example 1 was brazed to stainless steel using a 50 m (2 thousandth of an inch) thick foil of copper-gold brazing alloy.

[0039] A good joint resulted showing good wetting of the YTZP.

Example 4

[0040] The heat treated YTZP of example 1 was brazed to another piece of the heat treated YTZP of example 1 using a copper-silver alloy as brazing material.

[0041] A good joint resulted showing good wetting of the YTZP.

Prospective Examples

[0042] Although exemplified with respect to TZP, improved wetting properties resulting from reduction of zirconia are predicted to apply to other zirconia containing ceramics such as PSZ and ZTC.

[0043] In light of the zirconia content, the improved strength is expected to apply at least to PSZ.

[0044] Optionally the zirconia ceramic may comprise other oxides that darken when exposed to reducing conditions (for example, and without limitation, one or more of: iron oxide, titanium oxide, cerium oxide, chromium oxide, nickel oxide, cobalt oxide) to enhance the uniformity and darkness of colour. Such elements need not be present in high quantities to provide such effect [e.g. <1%; <0.5%; <0.1%; <0.05%; <0.01%; or <0.005%] although if appropriate may be at higher levels.

Typical Processing Steps

[0045] FIG. 1 shows typical processing steps in brazing according to the present invention.

INDUSTRIAL APPLICABILITY

[0046] The invention is not limited to any particular brazing materials (other than that they are compatible both with the zirconia ceramic and any other article to which the ceramic is brazed), nor to any particular form of brazing material, and encompasses, for example, foils, pastes, powders, wires.

[0047] Brazed zirconia ceramics will have a variety of uses including (without limitation) in: medical implants, electrical feedthroughs, surgical equipment, analytical equipment, aerospace applications, oxygen sensors, fuel cell components.

[0048] The above description is illustrative only and the person skilled in the art will recognise that many variants may fall within the scope of the appended claims.