Tungsten based sintered compact and method for production thereof

Abstract

The present invention is directed to provide a tungsten-based sintered body having a relative density of 99.5% or more (a porosity of 0.5 volume % or less) and a uniform and isotropic structure, which has not been able to be achieved by conventional techniques. In particular, the tungsten-based sintered body is intended for use as a discharge lamp electrode, a sputtering target, a crucible, a radiation shielding member or a resistance welding electrode. The intended tungsten-based sintered body is produced by subjecting a tungsten-based powder to a CIP process at a pressure of 350 MPa or more to form a powder compact, sintering the powder compact in a hydrogen gas atmosphere at a sintering temperature of 1600° C. or more for a holding time of 5 hours or more to form a sintered compact, and subjecting the sintered compact to a HIP process in an argon gas atmosphere under conditions of 150 MPa or more and 1900° C. or more. The tungsten-based sintered body of the present invention is suitably used, for example, as a discharge lamp electrode, a sputtering target, a crucible, a radiation shielding member, an electric discharge machining electrode, a semiconductor element mounting substrate and a structural member.

Description

TECHNICAL FIELD [0001] The present invention relates to a tungsten-based sintered body and a production method therefor. [0002] The present invention also relates to a product of the tungsten-based sintered body, such as a discharge lamp electrode, a sputtering target, a crucible, a radiation shielding member, a resistance welding electrode, a semiconductor element mounting substrate, a structural member, a switch contact, a member for semiconductor manufacturing equipment, a member for an ion-implantation apparatus or an internal member for a nuclear fusion reactor. BACKGROUND ART [0003] Typically, a tungsten-based sintered body has been produced by use of a “electric current-aided sintering process” which is designed to apply a high-voltage pulsed current to a rod-shaped tungsten-based powder compact through a pair of electrodes attached, respectively, to opposite ends of the powder compact, so as to sinter the powder compact. [0004] The electric current-aided sintering process ha...

AI Technical Summary

Benefits of technology

[0021] The sintered body of the present invention has a relative density of 99.5% or more. This makes it possible to significantly reduce gas and / or impurities mainly intruding into pores of the sintered body so as to eliminate adverse effects thereof in the surrounding atmosphere.

[0088] 2. As compared with the conventional tungsten-based sintered body production method based on a electric current-aided sintering process and a forging process, the production method of the present invention makes it possible to provide increased flexibility in shape of a sintered body. Further, the production method of the present invention has no need for increasing density based on deformation in a forging process. Thus, the production method of the present invention is suitable for production of a large member which is difficult to be subjected to a forging process. In addition, such a large member can be produced at a relatively low cost.

Problems solved by technology

The first disadvantage is that the sintered body has an extremely poor flexibility in shape due to the need for sintering the rod-shaped powder compact in a given gas atmosphere while applying a pulsed current to the powder compact through the electrodes connected to the respective ends thereof.

This leads to a considerable increase in production cost.

The second disadvantage is that a sufficient density cannot be obtained without an additional process after the sintering.

While the sintered compact may be subjected to a forging process, such as a swaging process, to provide enhanced density, the restriction in shape will become more severe.

Further, if it is attempted to obtain a relatively large sintered body with a sufficient density through a plastic working process, such as a forging process, it is necessary to allow the sintered compact before the forging process to have a larger size causing the need for a single-purpose facility requiring a large cost.

This also leads to a large increase in production cost.

The third disadvantage is that a crystal structure of the sintered compact is distorted or deformed due to the forging process.

Thus, an obtained sintered body will deteriorate in uniformity.

The fourth disadvantage is that, due to a dislocation introduced in the crystal structure during the forging process, a recrystallization phenomenon occurs in the forged compact when it is heated up to a given temperature or more.

The recrystallization is likely to cause a significant change in properties of a sintered body to be obtained, and adversely affect an intended performance thereof.

This density is not sufficient when the sintered body is used in a large electrode for a light source based on a vacuum system, such as a discharge lamp.

Specifically, gas and / or impurities are accumulated in pores of the sintered body, and released therefrom during lighting to cause various negative effects.

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