DE202013004704U1 - Tungsten alloy and electrode comprising a tungsten alloy - Google Patents

Abstract

Tungsten alloy, characterized in that it contains 0.05 to 4.0 wt .-% terbium oxide.

Description

The present invention relates to a tungsten alloy, in particular for the production of tungsten electrodes.

Tungsten electrodes are needed in the industry in numerous applications, such as for a variety of thermal spraying processes for surface treatment or coating such. As plasma spraying, welding and cutting processes such. As inert gas welding, in particular tungsten inert gas welding (TIG), and z. B. as lamp components such. B. electrodes in high-pressure gas discharge lamps (HID lamps).

To improve the emission properties and resulting better ignition properties, greater arc stability and higher current carrying capacity or higher life such electrodes are for a long time usually not made of pure tungsten (W) but of tungsten with a slight addition of cerium oxide (CeO ₂ ), lanthanum oxide (La ₂ O ₃ ), thorium oxide (ThO ₂ ) or zirconium oxide (ZrO ₂ ), cf. z. B. the Standard ISO 6848 , 2004 edition.

Sintered tungsten electrodes with an addition of thorium oxide (ThO ₂ ), z. B. are currently widespread for the above-mentioned welding or coating methods and as lamp components. B. with a proportion of 2.0 wt .-% (classification symbol "WTh 20"). Disadvantageously, the integration of thorium in the material of the electrodes causes a corresponding radioactive load, so that efforts have already been made to replace the thorium oxide in tungsten alloys by another environmentally friendlier addition, without focusing on the particular advantages thoriated tungsten alloys in industrial use (and in the production ) to refrain. However, these efforts, especially when used in thermal spraying, have so far not given a satisfactory result, ie the specific properties of thoriated tungsten have not yet been achieved by the available alternative products.

It is therefore an object of the present invention to provide a suitable in particular as an electrode material novel tungsten alloy, which makes no addition of ThO ₂ unnecessary without significant loss of performance characteristics.

The tungsten alloy according to the invention is characterized in that it contains 0.05 to 4.0 wt .-% terbium oxide. It has been found that with such a proportion of terbium oxide, in particular Tb ₄ O ₇ , a good manufacturability can be achieved with simultaneously excellent performance characteristics of an electrode produced therewith.

In a preferred embodiment, the proportion of terbium oxide in the alloy is in the range of 0.2 to 2.0 wt .-%, in particular 0.5 to 1.5 wt .-%.

The term "tungsten alloy" as used herein is intended to mean that the alloy contains at least 90% by weight of tungsten, preferably even at least 95% by weight or at least 97% by weight.

In a preferred embodiment, it is a sintered tungsten alloy. In order to produce such a sintered tungsten alloy or an electrode which consists at least partially thereof, it is advantageously possible to make use of the general state of the art for the production of sintered tungsten products (cf. DE 38 35 328 C1 ). In such known production processes, powdered tungsten is usually mixed with the corresponding pulverulent additive, pressed and sintered, with preferably subsequent mechanical refinement and / or recrystallization treatment also being carried out below. The grain size of the alloying components used in this case, ie tungsten and / or additive, z. B. in the range of 0.5 to 100 microns.

According to such a known pressing and sintering method, the tungsten alloy (or electrode) according to the invention can also be produced.

In one development of the invention, the tungsten alloy further contains 0.05 to 2.0 wt .-%, in particular 0.3 to 0.7 wt .-% of a rare earth oxide and / or zirconium oxide (in particular, for example, ZrO ₂ ). It has been found that with such an additive, the performance characteristics and the lifetime of an electrode made therefrom can be further improved.

In an advantageous embodiment, the rare earth oxide is lanthanum oxide, in particular La ₂ O ₃ , yttrium oxide, in particular Y ₂ O ₃ , or cerium oxide, in particular Ce ₂ O ₃ , or a combination thereof.

In a particularly advantageous specific embodiment, the tungsten alloy contains 0.9 to 1.1 wt% Tb ₄ O ₇ , 0.4 to 0.6 wt% La ₂ O ₃ , optionally one or more further additives or impurities of at most (maximum) 1% by weight, and the remainder tungsten.

In another particularly advantageous specific embodiment, the Tungsten alloy 0.7 to 0.9 wt .-% Tb ₄ O ₇ , 0.4 to 0.6 wt .-% Y ₂ O ₃ , optionally one or more further additives or impurities of at most 1 wt .-%, and Remainder tungsten.

According to another aspect of the present invention, there is provided an electrode (eg, as a cathode or an anode) comprising a tungsten alloy of the type described above, in particular an electrode for use in a welding, separating or coating process, for example for use in a the aforementioned method.

In the simplest case, the electrode according to the invention consists overall of a tungsten alloy of the type proposed here. B. in the form of cylindrical rods as "TIG electrodes" use and in this case preferably have in the Standard ISO 6848 Table 2, standard diameter specified and / or a length defined in this standard, Table 3, as standard. Such electrodes may also z. B. in the form of rods or coils in the lamp industry application. In particular for Hg high-pressure discharge lamps electrodes of a tungsten alloy with the addition of ThO _{2 are} known.

In another embodiment, the electrode comprises a first electrode section of a tungsten alloy of the type described here and at least one further electrode section made of a different material, in particular an electrode section provided for heat dissipation and / or electrical connection of the electrode, which is made of a different material (eg. As copper or copper alloy) is formed. At such an electrode composed of different material sections, the first electrode section (tungsten alloy) may be fixedly connected to the at least one further electrode section (eg electrical connection section).

This embodiment of the electrode is particularly suitable as a cathode or anode for a thermal spraying process such. As plasma spraying or arc spraying plasma generating device, in particular nozzle device for generating a plasma jet. Such nozzle devices are as such z. B. as part of spray guns for plasma spraying of the prior art. A typical nozzle device, for example, provides a pin-shaped cathode which is arranged inside a sleeve-shaped (and a nozzle-forming) anode in order to generate the relevant plasma by means of an arc burning between the cathode and the anode. The nozzle (anode) can be z. B. be charged with a gas mixture of argon and hydrogen or argon and helium.

The invention will be further described by means of embodiments with reference to the accompanying drawings. They show:

1 a side sectional view of a plasma-assisted metal powder coating nozzle provided with a pin-shaped negative electrode (cathode) in a sleeve-shaped positive electrode (anode), and

2 a side view of an intended for tungsten inert gas welding (TIG) electrode.

With reference to the 1 and 2 Two embodiments of the invention will be explained below. In each of these examples, a tungsten alloy containing a minor addition of terbium oxide is used to form portions of electrodes (example of 1 ) or an electrode as such (example according to 2 ) train.

1 shows a nozzle device 10 for a coating spray gun, with a pin-shaped negative electrode (cathode) 12 and a sleeve-shaped positive electrode (anode) 14 into which the cathode 12 protruding coaxially from one side.

During operation of the nozzle device 10 becomes like through the arrows in 1 2 illustrates a plasma gas (eg, mixture of argon and hydrogen) through the anode 14 passed through, passing through an arc between the cathode 12 and anode 14 an ionization and heating of the plasma gas takes place, which the nozzle device 10 thus leaves with very high temperature (typically several 1000 ° C). This "plasma jet" can be such z. B. be used for coating. In the case of plasma powder build-up welding provided in the example, a metal powder is supplied to the plasma jet as the application material (not shown in the figure). This powder is heated in the plasma jet and applied to the relevant workpiece surface.

In the example shown, the cathode 12 and the anode 14 shaped substantially rotationally symmetrical. Except in the example shown, only a screw connection is excluded 16 the cathode 12 , which with a thread, and possibly a flattening for tool engagement, for fastening and electrical contacting of the cathode 12 is provided, and a cooling fin section 18 the anode 14 , The anode 14 is provided in this area with a plurality of radially projecting, distributed over the anode circumference arranged cooling fins.

In the example shown, both electrodes 12 . 14 each two-piece (composed of different material sections) composed: the cathode 12 has a first cathode portion 20 from said tungsten alloy and a second cathode section fixedly connected thereto 22 made of electrically and thermally good conductive material (here, for example, a copper alloy). The anode 14 also has a first anode section 24 from said tungsten alloy and a second anode section 26 from electrically and thermally good conductive material such. Eg copper (alloy). A reliable connection between copper alloy) and tungsten alloy can be used in the production of anode 12 and cathode 14 in a simple way z. B. each by back-casting the previously sintered tungsten alloy sections 20 respectively. 24 be realized with the copper material.

How out 1 The cathode protrudes clearly 12 with the tapered first cathode portion 20 in the interior of the sleeve-shaped anode 14 into it, so that the arc provided for the plasma generation between this first cathode section 20 and the one inner jacket of the anode 14 forming the first anode section 24 is trained.

Due to the special composition of the first electrode sections 20 and 24 excellent performance characteristics (eg ignitability, arc stability, service life) result for the nozzle device 10 ,

In a special and particularly advantageous embodiment, the electrode sections contain 20 and 24 the electrodes 12 respectively. 14 in each case 1.0% by weight of Tb ₄ O ₇ , 0.5% by weight of La ₂ O ₃ , optionally one or more further additives or impurities of at most 1% by weight, and the remainder tungsten. In one variant, the electrode section contains 20 and / or the electrode section 24 0.8% by weight of Tb ₄ O ₇ , 0.5% by weight of Y ₂ O ₃ , optionally one or more further additives or impurities of at most 1% by weight, and the remainder tungsten.

2 shows a TIG electrode 30 , which was sintered in one piece in the form of a cylindrical rod made of a tungsten alloy with a slight addition of terbium oxide. As in the previous example, the tungsten alloy used here also advantageously a further addition of z. For example, lanthanum oxide or yttrium oxide (and / or of, for example, another rare earth oxide). With the reference number 32 is a (color) marking of the TIG electrode 30 characterized.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3835328 C1 [0009]

Cited non-patent literature

• Standard ISO 6848 [0003]
• Standard ISO 6848 [0016]

Claims (8)

Tungsten alloy, characterized in that it contains 0.05 to 4.0 wt .-% terbium oxide. Tungsten alloy according to claim 1, characterized in that the proportion of terbium oxide in the range of 0.2 to 2.0 wt .-%, in particular 0.5 to 1.5 wt .-% is. Tungsten alloy according to one of the preceding claims, characterized in that it further contains 0.05 to 2.0 wt .-%, in particular 0.3 to 0.7 wt .-%, of a rare earth oxide and / or zirconium oxide. Tungsten alloy according to claim 3, characterized in that the rare earth oxide is lanthanum oxide, yttrium oxide or cerium oxide, or a combination thereof. Tungsten alloy according to one of claims 1 to 4, characterized in that it contains 0.9 to 1.1 wt .-% Tb ₄ O ₇ , 0.4 to 0.6 wt .-% La ₂ O ₃ , optionally one or more further additives or impurities of at most 1 wt .-%, and remainder tungsten. Tungsten alloy according to one of claims 1 to 4, characterized in that it contains 0.7 to 0.9 wt.% Tb ₄ O ₇ , 0.4 to 0.6 wt.% Y ₂ O ₃ , optionally one or more further additives or impurities of at most 1 wt .-%, and remainder tungsten. Electrode ( 12 . 14 . 30 ), in particular in the form of a pin or in the form of a sleeve, comprising a tungsten alloy according to one of the preceding claims. Electrode ( 12 . 14 ) according to claim 7, composed of a first electrode section ( 20 . 24 ) consisting of the tungsten alloy and at least one further electrode section connected thereto ( 22 . 26 ) consisting of another material, in particular metallic material, in particular copper or copper alloy.

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