WO1992016039A1 - Heavily alloyed refractory alloy electrode and pressure wave generating device using said electrode - Google Patents

Abstract

The invention discloses a refractory alloy electrode characterized in that the refractory alloy is a heavily alloyed refractory alloy comprising at least 5 % by weight of at least one elment selected from the group consisting of tungsten, molybdenum, chromium, cobalt and vanadium. Said electrode may be used to produce an electrical discharge between two electrodes immersed in a discharge liquid as in the case of pressure wave generating devices.

Description

Highly alloyed refractory alloy electrode and pressure wave generating apparatus comprising the same.

The present invention essentially relates to a highly alloyed refractory alloy electrode and to a pressure wave generating apparatus having application thereof.

It is known from document EP-B-0098944 to use, in the context of pressure wave generation apparatuses, electrodes made of refractory material produced from a heterogeneous alloy powder which essentially contains tungsten and a binding phase consisting, in addition to tungsten, of two or more of the following metals: nickel, copper, silver, iron, cobalt, molybdenum or rare earths. Parts, such as electrodes, are obtained by sintering the powder. It is therefore a complicated procedure for preparing the electrodes. Also, these electrodes being essentially made of tungsten, their cost is very high. It will be observed that these electrodes do not contain carbon.

Also, document EP-A-0 204909 relates to the use of a multi-phase tungsten alloy, sintered, having a high content of tungsten for producing electrodes of pressure wave generating apparatuses. The tungsten being initially present in the form of very fine particles having a diameter of less than 5 μm, surrounded by an envelope of a thin binder. As an example of tungsten powder with a high tungsten content, an alloy is cited comprising 90% tungsten, 6% nickel, 2% cobalt and 2% iron. Also, this alloy does not contain carbon.

It has now been discovered in a completely surprising way that a highly alloyed refractory alloy could constitute a remarkable electrode material, especially when it is a question of carrying out electric discharges between two electrodes immersed in a discharging liquid. . Indeed, in the context of submerged electrical discharges, there is the problem of rapid wear of the electrodes due to successive electrical discharges. in the discharge liquid. The lifetime of the electrodes is therefore generally relatively short, which implies high maintenance costs.

The solutions proposed by the prior art cited above are not satisfactory because very refractory materials with a very high tungsten content (at least 90% by weight) are very brittle and resist poorly the pressure wave or shock resulting from electrical discharge between the electrodes.

The present invention therefore aims to provide a new type of electrode which can be used to perform an electrical discharge between two electrodes immersed in a discharge liquid and which has improved resistance to wear, shock and friction, in thus significantly increasing its lifespan. The present invention also aims to solve the new technical problem stated above, with the further obtaining of an electrode having very good ductility.

The present invention also aims to solve the new technical problems stated above, with the further provision of an electrode having a high melting point.

The present invention also aims to solve the new technical problems stated above, by further providing an electrode which has good resistance to corrosion. This solution must also be simple, reliable and inexpensive.

The present invention makes it possible to solve the new technical problems described above for the first time, in a simple, reliable, inexpensive manner, usable on an industrial scale.

Thus, according to a first aspect, the present invention provides an electrode in particular usable for carrying out an electrical discharge between at least two said electrodes immersed in a discharge liquid, comprising a refractory alloy, characterized in that said refractory alloy is an alloy highly alloyed refractory, comprising at least 5% by weight, and preferably between 5 and 40% of at least one element combining noble refractory metal, in particular chosen from tungsten, molybdenum, cobalt, vanadium and chromium. Preferably, this alloy has a high melting point greater than 1,300 ° C., in particular between 1,300 and 1,400 ° C.

According to an advantageous embodiment, the highly alloyed refractory alloy comprises carbon, preferably from 0.4% to 1.60% by weight of carbon. Preferably, this percentage by weight of carbon is between 0.6% and 1.60%.

According to a particular characteristic, the tungsten content is between 0.5 and 8% by weight.

According to another alternative embodiment, the molybdenum content is between 0.5 and 8% by weight. According to another particular variant embodiment, the above-mentioned refractory alloy comprises up to 8% chromium, preferably from 2 to 6% by weight of chromium.

According to another variant, the alloy comprises from 0.5 to 8% by weight of vanadium. According to another alternative particular embodiment, the refractory alloy comprises up to 8% cobalt, ^'preferably from 2 to 8% by weight of cobalt.

According to a preferred embodiment, the total weight content of the aforementioned noble alloying elements is between 5 and 30%, in particular between 5 and 25%.

According to a particularly advantageous embodiment, the above-mentioned alloy has the following composition:

- carbon at least 0.4% - tungsten 0.5 - 6%

- molybdenum 0.5 - 6%

- chromium 2 - 6%

- vanadium 1 - 3%

- cobalt 2 - 6% An even more preferred embodiment of the above-mentioned electrode consists in that the electrode comprises a refractory alloy having the following composition:

- carbon approximately 0.85%

- tungsten around 6%

- molybdenum about 6%

- cobalt about 5%

- vanadium about 2% - chrome ..... about 4%

- iron: balance.

In all of the above embodiments, the above-mentioned highly alloyed refractory alloy is advantageously based on iron, that is to say that iron constitutes the balance of the alloy.

According to an advantageous alternative embodiment, the above-mentioned electrode is characterized in that the surface of the electrode is covered with a layer of a metal favoring the welding of a refractory alloy, for example chosen by the group consisting of copper, gold, silver.

Preferably, the thickness of the layer of the metal favorite¬ health The weld is between 0.5 μm and 50 μm, preferably between 1 μm and 40 μm.

According to another advantageous characteristic of the invention, the above-mentioned electrode is obtained from a refractory alloy which has undergone at least one heat treatment at a temperature at least equal to 1000 ° C., preferably at least equal to 1,100 C, followed by at least one stepped quenching at a temperature between 500 and 600 C, for example about 550 C. According to an advantageous characteristic, after quenching, the alloy is cooled to room temperature and carried out at at least one tempering operation and preferably at least two tempering operations, at a temperature of between 500 and 600 ° C., preferably around 550 ° C. for a sufficient period of time, for example around 1 hour. According to another particular characteristic of the invention, the above-mentioned electrode is obtained by machining a casting from the above-mentioned refractory alloy.

The invention also relates to the use of the aforementioned electrode for carrying out an electrical discharge between at least two said electrodes immersed in a discharge liquid. This discharge liquid can be any, and advantageously be electrically conductive.

According to a second aspect, the present invention also covers an apparatus for generating a pressure wave by electrical discharge between two electrodes immersed in a liquid medium, characterized in that at least one of said two electrodes is as defined above.

Preferably, this device is also characterized in that the aforementioned electrodes are mounted at least partly inside a truncated ellipsoidal reflector comprising an internal focal point and an external focal point where the pressure waves must be focused, in the vicinity of the internal hearth, and in particular on either side of the internal hearth. This device is in particular used for the extracorporeal destruction of tissues, lithiasis or concretions, for osteotritis or bone treatment, in particular within the framework of accelerated healing of fractures. Such applications are well known to those skilled in the art. Reference may be made, for example, to the RIEBER patent US-A-2,559,227 or US-A-3,942,531 or US-A-4,730,614 or WO-A-88/09190.

The invention will now be described in detail with a particularly preferred embodiment of an electrode according to the invention particularly suitable for use as an electrode in the context of an electric discharge between two electrodes immersed in a discharge liquid, this discharge electric being produced under high voltage, in particular at least 10,000 V, as described in the above applications. Example

A refractory alloy casting with the following basic chemical composition is produced:

- carbon about 0.85%

- tungsten around 6%

- molybdenum about 6%

- cobalt about 5%

- vanadium about 2% - chromium about 4%

- iron: balance.

according to a conventional metallurgical manufacturing method. This alloy has a high melting point of approximately 1,400 C. From this casting, at least two electrodes are produced by machining.

These machined electrodes are subjected to a heat treatment at a temperature at least equal to 1000 C, preferably at least equal to 1100 C, for example 1180 C, followed by at least one quenching at a temperature between 500 and 600 C. For example, quenching is carried out at approximately 550 C in a stepped manner. Then, air cooling is carried out and at least one tempering operation is carried out and preferably at least two tempering operations are carried out at a temperature of between 500 and 600 ° C., preferably around 550 ° C. for a sufficient period. , for example about 1 hour.

Advantageously, a surface treatment of the electrode is carried out by covering it with a layer of a metal promoting the welding of a refractory alloy, for example chosen from the group consisting of copper, gold, silver. Copper is particularly preferred.

This surface treatment makes it possible in part to make a silver solder on the electrode to fix it in an electrode holder part. Thanks to this processing, the soldering is carried out correctly. On the other hand, this surface treatment made it possible to avoid corrosion of the electrode in storage.

The thickness of the layer of the metal favoring the welding is advantageously between 0.5 μm and 50 μm, preferably between 1 μm and 40 μm.

It is also possible, according to another alternative embodiment, to prevent corrosion on storage by coating the surface of the electrode with a varnish, or another insulator, or even by making a suitable surface treatment such as phosphating on all metal parts which are then intended to be brought into contact with the discharge liquid.

Electrodes thus produced from the above-mentioned high-alloy refractory alloy are particularly suitable for serving as a discharge electrode immersed in a discharge liquid.

A particularly preferred application consists in use in the context of devices for generating a pressure wave by electrical discharge in two electrodes immersed in a liquid medium and preferably comprising a truncated ellip- soldai reflector where the electrodes are mounted at the less partially inside said reflector in the vicinity of the internal focal point and in particular on either side of the internal focal point, as is known from the abovementioned applications cited in the abovementioned documents. Thanks to the invention, the electrode has very good resistance to shocks generated by discharges, in particular thanks to the fact that the above-mentioned highly alloyed refractory alloy has excellent ductility, as well as a high melting point. It also has lower wear and therefore a much longer lifespan. Also, it can be used advantageously when the discharge liquid is an electrically conductive liquid as described in application FR-A-2 649 252 which is incorporated by reference, and in particular has a linear resistivity not greater than about 20 ohms.cm. A resistivity ^preferred linear is between a few ohms. m and enviro- 20 ohms.cm. It is naturally understood that various alternative embodiments of the invention are possible. The invention therefore includes all the technical means constituting technical equivalents of the means described as well as their various combinations.

Claims

1. An electrode which can be used in particular to produce an electrical discharge between two said electrodes immersed in a discharge liquid, comprising a refractory alloy, characterized in that said refractory alloy is a highly alloyed refractory alloy, comprising at least 5% by weight, preferably between 5 and 40% by weight, of at least one element combining noble refractory metal, in particular chosen from tungsten, molybdenum, cobalt, vanadium and chromium. 2. Electrode according to claim 1, characterized in that the alloy comprises carbon, preferably from 0.4% to 1.60% by weight of carbon. 3. An electrode according to claim 2, characterized in that the alloy comprises from 0.5 to 8% by weight of tungsten. 4. Electrode according to claim 2 or 3, characterized in that the alloy comprises from 0.5 to 8% by weight of molybdenum. 5. Electrode according to one of claims 2 to 4, characterized in that the alloy comprises up to 8% by weight of chromium, preferably from 2 to 6% by weight of chromium. 6. Electrode according to one of claims 2 to 5, characterized in that the alloy comprises up to 8% of cobalt, preferably from 2 to 8% by weight of cobalt. 7. Electrode according to one of claims 2 to 6, characterized in that the alloy comprises from 0.5 to 8% by weight of vanadium. 8. Electrode according to one of claims 2 to 7, charac¬ terized in that the alloy has the following composition: - carbon at least 0.4% - tungsten 0.5 - 6% - molybdenum 0.5 - 6% - chromium 2 - 6% - vanadium 1 - 3% - cobalt 2 - 6%. 9. An electrode according to claim 8, characterized in that the alloy has the following composition: - carbon around 0.85% - tungsten around 67, - molybdenum about 6% - cobalt about 5% - vanadium about 2% - chromium about 4% - iron: balance. 10. Electrode according to one of the preceding claims, characterized in that the surface of the electrode is covered with a layer of a metal promoting the welding of a refractory alloy, for example chosen from the group consisting of copper, gold, silver. 11. An electrode according to claim 10, characterized in that the thickness of the layer of the metal promoting the weld is between 0.5 μm and 50 μm, preferably between 1 μm and 40 μm. 12. Electrode according to one of the preceding claims, characterized in that the aforementioned refractory alloy has undergone at least one heat treatment at a temperature at least equal to 1000 ° C, preferably at least equal to 1100 C, followed at least one stepped quench at a temperature between 500 and 600 C, for example around 550 C. 13. An electrode according to claim 12, characterized in that after quenching, the alloy is cooled to ambient temperature and at least one tempering operation and preferably at least two tempering operations are carried out at a temperature ¬ taken between 500 and 600 C, preferably about 550 C for a sufficient period of time, for example about 1 h. 14. Electrode according to one of the preceding claims, characterized in that said electrode is obtained by machining a casting piece of the above-mentioned refractory alloy. 15. Apparatus for generating a pressure wave by electrical discharge between two electrodes immersed in a liquid medium, characterized in that at least one of said two electrodes is as defined in any one of the preceding claims, preferably the aforementioned liquid medium is electrically conductive, in particular by having a linear resistivity not greater than about 20 ohms.cm. 16. Apparatus according to claim 15, characterized in that said aforementioned electrodes are mounted at least partially inside a truncated ellipsoidal reflector in the vicinity of the internal focal point, and in particular on either side of the internal focal point. 17. Apparatus according to claim 15 or 16, characterized in that it is an apparatus for the extracorporrelation destruction of tissues, lithiasis or concretions, for osteotripsy or bone treatment, for accelerated healing of fractures.