Technology of soldering of ZrO 2 ceramics with solders of the Ag-Cu-O system in air
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TECHNOLOGY OF SOLDERING OF ZrO2 CERAMICS WITH SOLDERS OF THE Ag – Cu – O SYSTEM IN AIR O. V. Durov
UDC 621.791.3
We have developed a technique for obtaining soldered joints of ZrO2 ceramics in air with the help of solders of the copper–silver–oxygen system. We used different methods of the preliminary application of a layer of copper-oxide onto the surface of ZrO2 ceramics (with burn-in and without it) with subsequent soldering in a mixture of silver and CuO powders and also with the help of Ag-22Cu alloy. The bending strength of these joints is about 300 MPa. Soldered joints possess a high corrosion resistance and can be used for operation in air at a temperature up to 700°C.
Since customary solders do not wet the surface of oxide ceramic materials, it is customary to apply active solders, which contain components with an affinity for oxygen (chromium, titanium, etc.). They favor the formation of a transition layer between the metal and oxide (e.g., metal-like TiO oxide), which provides adhesion of the solder to ceramics. However, one can solder with active solders only in vacuum or inert gas, which requires special equipment. As is well known, oxygen in a metal melt improves the wetting of the surface of solid oxide with this melt [1]. In particular, copper oxides (CuO, Cu2 O) demonstrate high adhesion to other oxides owing to the similarity of their composition to metals [2, 3]. This feature opens the possibility to solder oxide ceramics with such melts. One can also apply a layer of copper oxide onto the surface of an oxide material and afterwards solder with a metallic solder. In order to have a sufficient amount of copper oxide, this process is realized in an oxidizing medium (most simply in air). At the same time, excessive oxidation of the solder is undesirable, and, hence, as its base, one usually applies silver, which does not oxidize and dissolves a sufficient amount of oxygen in the liquid state. In addition, silver is inexpensive and has a melting point about 980°C, which is quite acceptable for soldering (a fairly low heating temperature) and for the operating parameters of soldered joints that are used within the range 600 – 700°C. This method is called metal-oxygen soldering. The aim of the present work is to study the possibility of using the technology of metal-oxygen soldering for joining ZrO2 ceramics. Materials and Procedure We investigated ceramics of zirconium dioxide, partially stabilized by Y2 O3 and Ce2 O3 , with a bending strength of 460 MPa. Wetting was studied on disks 15 mm in diameter and 3 – 4 mm in thickness, the surface of which was polished by diamond paste. Beam blanks of size 5 × 4.1 × 25 mm were joined by butt soldering. We manufactured the solders of powders of copper oxide and commercially pure silver, highly-clean silver and Ag-22Cu alloy in the form of a wire from which tape of thickness 0.2 mm was rolled. Soldering and tests after wetting in air were carried out at the melting point of the solder (780°C in the case of using Ag-22Cu alloy and 980°C in all other experimen
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