WO2025033302A1 - Tungsten sintered body - Google Patents
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- WO2025033302A1 WO2025033302A1 PCT/JP2024/027447 JP2024027447W WO2025033302A1 WO 2025033302 A1 WO2025033302 A1 WO 2025033302A1 JP 2024027447 W JP2024027447 W JP 2024027447W WO 2025033302 A1 WO2025033302 A1 WO 2025033302A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
Definitions
- the present invention relates to tungsten sintered bodies.
- Tungsten (W) a high melting point metal
- tungsten has better radiation shielding properties than lead (Pb) for the same volume, and is therefore also used in radiation shielding materials and components of X-ray inspection equipment, such as collimators that absorb scattered radiation.
- tungsten has poor machining properties such as cutting and cutting (hereinafter collectively referred to as "cutting")
- cutting since tungsten has poor machining properties such as cutting and cutting (hereinafter collectively referred to as "cutting"), it is known that the above-mentioned components and other complex shaped products are obtained by subjecting a tungsten sintered body (hereinafter also simply referred to as a "sintered body") obtained by a powder sintering method using tungsten powder to machining such as cutting to obtain a product of the final shape.
- a tungsten sintered body hereinafter also simply referred to as a "sintered body”
- Patent Document 1 proposes a method for obtaining tungsten sintered bodies by pressing tungsten powder into a molded body and sintering this molded body.
- This patent document describes a method in which tungsten powder is covered with a material that easily separates from a rubber case, the rubber case is filled with this, and the resultant is loaded into a liner case and pressed to obtain a molded body, which is then sintered in a hydrogen atmosphere.
- This is a useful technology in that it can produce sintered bodies with a high yield by suppressing cracking of the molded body.
- Tungsten is a difficult-to-cut material that is highly susceptible to cracking and chipping during machining such as cutting, and there is a risk that it may cause wear and damage to cutting tools. Furthermore, when attempting to obtain a tungsten sintered body using the method of Patent Document 1, embrittled areas may be present, and there is a risk that handling such as transporting the body to the cutting machine or chucking may cause deformation or cracking of the sintered body itself.
- the object of the present invention is to provide a tungsten sintered body that can suppress not only wear and damage to cutting tools, but also deformation and cracking of the sintered body itself.
- the present invention relates to a tungsten sintered body which is made of tungsten and unavoidable impurities, has a density of 15,000 to 19,000 kg/m 3 , and contains 30 mass ppm or less of hydrogen among the unavoidable impurities.
- the tungsten sintered body of the present invention preferably has an average Vickers hardness of 220 to 320 HV.
- the present invention is a useful technology in that it can provide a sintered body that is less susceptible to deformation and cracking of the sintered body itself, in addition to suppressing wear and damage to cutting tools.
- FIG. 1 is a scanning electron microscope photograph of a sintered body according to an embodiment of the present invention.
- 4 is a scanning electron microscope photograph of a sintered body serving as a comparative example.
- the tungsten sintered body of the present invention is composed of tungsten and unavoidable impurities, and has a density of 15000 to 19000 kg/m 3.
- the density of the tungsten sintered body of the present invention 15000 kg/m 3 or more, it is possible to suppress the deformation of the sintered body body during handling such as transportation to a cutting machine or chucking.
- the density of the tungsten sintered body of the present invention 15000 kg/m 3 or more, it is possible to suppress the coarse pores (voids) present inside the sintered body, and to suppress the tip of the cutting tool from being caught in the pores and being damaged.
- the density of the tungsten sintered body according to the embodiment of the present invention is preferably 15500 kg/m 3 or more, more preferably 17900 kg/m 3 or more, and even more preferably 18000 kg/m 3 or more.
- the tungsten sintered body of the present invention can suppress the wear amount of the tip of the cutting tool by making the density 19000kg/m3 or less. That is, the tungsten sintered body of the present invention is unlikely to cause the cutting depth to gradually decrease with the increase in the wear amount of the tip as machining proceeds, and can suppress the dimensional difference of the sintered body between the cutting start point and the cutting end point in one pass of the cutting process from increasing, and can also suppress the damage of the tip.
- the density of the tungsten sintered body of the present invention 19000 kg/m 3 or less, it is possible to suppress the cracking of the sintered body body during handling such as transportation to a cutting machine or chucking.
- the density of the tungsten sintered body according to the embodiment of the present invention is preferably 18900 kg/m 3 or less, more preferably 18500 kg/m 3 or less, and even more preferably 18200 kg/m 3 or less.
- the tungsten sintered body of the present invention has a hydrogen (H) content of 30 mass ppm or less among unavoidable impurities. This reduces the generation of embrittled parts caused by hydrogen in the tungsten sintered body of the present invention, and can suppress deformation or cracking of the sintered body body during handling such as transportation to a cutting machine or chucking. In addition, the tungsten sintered body of the present invention can suppress deterioration or damage of the molding die, heating device, etc.
- the tungsten sintered body according to the embodiment of the present invention preferably has hydrogen content of 20 mass ppm or less, more preferably has hydrogen content of 10 mass ppm or less, even more preferably has hydrogen content of 5 mass ppm or less, and even more preferably has hydrogen content of 2 mass ppm or less.
- the tungsten sintered body of the present invention preferably has an average Vickers hardness, as specified by JIS Z 2244, of 220 to 320 HV. If soft areas are present in the sintered body, only the low hardness areas may remain or fall off during machining, resulting in a rough surface of the sintered body. For this reason, the tungsten sintered body according to the embodiment of the present invention preferably has an average Vickers hardness of 220 HV or more. For the same reasons as above, the tungsten sintered body according to the embodiment of the present invention more preferably has an average Vickers hardness of 250 HV or more, and even more preferably 280 HV or more.
- the tungsten sintered body according to the embodiment of the present invention preferably has an average Vickers hardness of 320 HV or less in order to prevent the sintered body from cracking during handling such as transport to a cutting machine or chucking, and to reduce the amount of wear on the tip of a cutting tool.
- the Vickers hardness in the present invention refers to an average Vickers hardness measured at any five points on the flat surface of the sintered body in the range of 220 to 320 HV, from the viewpoint of suppressing the above-mentioned deformation or cracking of the sintered body body and wear or breakage of the tip of the cutting tool, as well as smoothing the surface roughness of the sintered body.
- the length of the longest side that can be drawn in the largest pore present in the metal structure is 3.0 ⁇ m or less. And, for the same reasons as above, it is more preferable that the length of the longest side that can be drawn in the largest pore present in the metal structure in the tungsten sintered body according to the embodiment of the present invention is 2.0 ⁇ m or less, and even more preferable that it is 1.0 ⁇ m or less.
- the tungsten sintered body of the present invention can be obtained by the following manufacturing method, and its general form will be described.
- the tungsten sintered body of the present invention is first prepared by preparing tungsten powder with an average particle size (D50) of 1.0 to 4.0 ⁇ m. Then, this tungsten powder is filled into a mold of a predetermined shape, and press-molded at room temperature (20 ⁇ 15°C as specified in JIS Z 8703) with a molding pressure of 0.2 to 5.0 tf/cm 2 (19.6 to 490 MPa) to obtain a molded body. Next, this molded body is sintered in a pressureless state to obtain a sintered body.
- D50 average particle size
- a hydrogen atmosphere is generally used in order to remove the oxide film formed on the surface of the tungsten powder.
- a vacuum atmosphere or an inert gas atmosphere adjusted to the hydrogen content of the air (3 mass ppm) or less is used as the heating atmosphere.
- the preferred sintering conditions are a heating temperature of 1700 to 1900°C and a holding time of 1 to 10 hours. From the standpoint of suppressing pores in the sintered body and reducing the hydrogen content, it is more preferable to set the sintering temperature to 1800°C or higher and the holding time to 5 hours or more.
- Tungsten powder with an average particle size (D50) of 1.9 to 2.3 ⁇ m was filled into a mold, and press molding was performed at room temperature with a molding pressure of 0.7 to 2.5 tf/cm 2 (49 to 245 MPa) to obtain a molded body. Then, this molded body was sintered in a vacuum atmosphere without pressure under the sintering conditions shown in Table 1 to obtain a tungsten sintered body.
- the density, hydrogen content, Vickers hardness, and length of the long side that can be drawn at the maximum pore were evaluated for each of the tungsten sintered bodies obtained above.
- the density was measured using an electronic specific gravity meter SD-120L manufactured by Kensei Kogyo Co., Ltd.
- the Vickers hardness was measured at five arbitrary points on the flat surface of the sintered body at a load of 9.8 N using an MVK-E manufactured by Akashi Seisakusho Co., Ltd. in accordance with JIS Z 2244, and the average value was calculated.
- the pores were observed with a scanning electron microscope (SEM), and the largest pore in the SEM image area of 497 ⁇ m2 was extracted, and the length of the longest side that could be drawn in the pore was measured. Scanning electron microscope photographs of the sintered bodies of the present invention and comparative examples are shown in Figures 1 and 2 .
- the tungsten sintered body of Sample No. 1 to 4 which is an example of the present invention, has a density in the range of 15,000 to 19,000 kg/ m3 , and by suppressing the hydrogen content to 30 mass ppm or less, it was confirmed that there was no wear or damage to the tip during machining, and no cracks or chips in the appearance of the sintered body after machining. In addition, the sintered body was not deformed or damaged by handling such as transportation to the cutting machine or chucking. In addition, it was confirmed that the tungsten sintered body of Sample No. 1, which is an example of the present invention, does not have coarse pores with a maximum long side length exceeding 3.0 ⁇ m, as shown in FIG. 1. On the other hand, the tungsten sintered body of sample No.
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Abstract
Description
本発明は、タングステン焼結体に関するものである。 The present invention relates to tungsten sintered bodies.
高融点金属であるタングステン（Ｗ）は、熱膨張率が低く、熱伝導率が高いことから、電子機器等の電極や高温炉の発熱体や反射板等に用いられている。また、タングステンは、同体積における放射線の遮蔽特性が鉛（Ｐｂ）よりも優れていることから、放射線遮蔽材や、散乱した放射線を吸収するコリメータといったＸ線検査機器の構成部品等にも用いられている。
そして、タングステンは、切削や切断等（以下、総称して「切削」という。）の機械加工性が悪いため、上記構成部品等の複雑形状品は、タングステン粉末を用いた粉末焼結法で得たタングステン焼結体（以下、単に「焼結体」ともいう。）に切削等の機械加工を施して最終形状の製品を得ることが知られている。
Tungsten (W), a high melting point metal, has a low thermal expansion coefficient and high thermal conductivity, and is therefore used in electrodes of electronic devices, heating elements of high-temperature furnaces, reflectors, etc. In addition, tungsten has better radiation shielding properties than lead (Pb) for the same volume, and is therefore also used in radiation shielding materials and components of X-ray inspection equipment, such as collimators that absorb scattered radiation.
And, since tungsten has poor machining properties such as cutting and cutting (hereinafter collectively referred to as "cutting"), it is known that the above-mentioned components and other complex shaped products are obtained by subjecting a tungsten sintered body (hereinafter also simply referred to as a "sintered body") obtained by a powder sintering method using tungsten powder to machining such as cutting to obtain a product of the final shape.
ここで、タングステン焼結体は、タングステン粉末を加圧して成形体とし、この成形体を焼結して得る方法が特許文献１で提案されている。この特許文献１は、タングステン粉末をゴムケースとの剥離性のよい材料で覆い、ゴムケースに充填したものをライナー用ケースに装入して加圧して成形体を得た後、この成形体を水素雰囲気中で焼結する方法が記載されており、成形体の割れを抑制することにより、高い歩留で焼結体を生産することができるという点で有用な技術である。 Patent Document 1 proposes a method for obtaining tungsten sintered bodies by pressing tungsten powder into a molded body and sintering this molded body. This patent document describes a method in which tungsten powder is covered with a material that easily separates from a rubber case, the rubber case is filled with this, and the resultant is loaded into a liner case and pressed to obtain a molded body, which is then sintered in a hydrogen atmosphere. This is a useful technology in that it can produce sintered bodies with a high yield by suppressing cracking of the molded body.
タングステンは、切削等の機械加工時に、割れや欠けが発生する可能性の高い、いわゆる難削材であり、切削工具の摩耗や破損を誘発する虞がある。また、特許文献１の手法によりタングステン焼結体を得ようとすると、脆化部が存在してしまう場合があり、切削機械への搬送やチャッキングといったハンドリング等で焼結体本体の変形や割れを誘発する虞がある。 Tungsten is a difficult-to-cut material that is highly susceptible to cracking and chipping during machining such as cutting, and there is a risk that it may cause wear and damage to cutting tools. Furthermore, when attempting to obtain a tungsten sintered body using the method of Patent Document 1, embrittled areas may be present, and there is a risk that handling such as transporting the body to the cutting machine or chucking may cause deformation or cracking of the sintered body itself.
本発明の目的は切削工具の摩耗や破損を抑制することに加え、焼結体そのものの変形や割れも抑制できるタングステン焼結体を提供することである。 The object of the present invention is to provide a tungsten sintered body that can suppress not only wear and damage to cutting tools, but also deformation and cracking of the sintered body itself.
本発明は、タングステンおよび不可避的不純物からなり、密度が１５０００～１９０００ｋｇ／ｍ３、前記不可避的不純物のうち水素が３０質量ｐｐｍ以下であるタングステン焼結体の発明である。 The present invention relates to a tungsten sintered body which is made of tungsten and unavoidable impurities, has a density of 15,000 to 19,000 kg/m 3 , and contains 30 mass ppm or less of hydrogen among the unavoidable impurities.
本発明のタングステン焼結体は、ビッカース硬さの平均値が２２０～３２０ＨＶであることが好ましい。 The tungsten sintered body of the present invention preferably has an average Vickers hardness of 220 to 320 HV.
本発明は、切削工具の摩耗や破損を抑制することに加えて、焼結体そのものの変形や割れが抑制された焼結体を提供できる点で有用な技術である。 The present invention is a useful technology in that it can provide a sintered body that is less susceptible to deformation and cracking of the sintered body itself, in addition to suppressing wear and damage to cutting tools.
本発明のタングステン焼結体は、タングステンおよび不可避的不純物からなり、密度が１５０００～１９０００ｋｇ／ｍ３である。本発明のタングステン焼結体は、密度を１５０００ｋｇ／ｍ３以上にすることで、切削機械への搬送やチャッキングといったハンドリング等で焼結体本体が変形することを抑制できる。また、本発明のタングステン焼結体は、密度を１５０００ｋｇ／ｍ３以上にすることで、焼結体内部に存在する粗大なポア（空孔）が抑制され、切削工具のチップ先端がポアに引っ掛かることにより損傷してしまうことを抑制できる。そして、上記と同様の理由から、本発明の実施形態にかかるタングステン焼結体は、密度が１５５００ｋｇ／ｍ３以上であることが好ましく、１７９００ｋｇ／ｍ３以上であることがより好ましく、１８０００ｋｇ／ｍ３以上がさらに好ましい。 The tungsten sintered body of the present invention is composed of tungsten and unavoidable impurities, and has a density of 15000 to 19000 kg/m 3. By making the density of the tungsten sintered body of the present invention 15000 kg/m 3 or more, it is possible to suppress the deformation of the sintered body body during handling such as transportation to a cutting machine or chucking. In addition, by making the density of the tungsten sintered body of the present invention 15000 kg/m 3 or more, it is possible to suppress the coarse pores (voids) present inside the sintered body, and to suppress the tip of the cutting tool from being caught in the pores and being damaged. And, for the same reason as above, the density of the tungsten sintered body according to the embodiment of the present invention is preferably 15500 kg/m 3 or more, more preferably 17900 kg/m 3 or more, and even more preferably 18000 kg/m 3 or more.
本発明のタングステン焼結体は、密度を１９０００ｋｇ／ｍ３以下にすることで、切削工具のチップの摩耗量を抑えることができる。すなわち、本発明のタングステン焼結体は、機械加工を進めるに連れてチップの摩耗量が増大することに伴い、切り込み量が次第に小さくなることが生じにくく、切削工程の１パスにおける切削開始点と切削終了点とで焼結体の寸法差が大きくなることを抑制できることに加え、チップの破損を抑制することもできる。
また、本発明のタングステン焼結体は、密度を１９０００ｋｇ／ｍ３以下にすることで、切削機械への搬送やチャッキングといったハンドリング等で焼結体本体が割れることを抑制できる。そして、上記と同様の理由から、本発明の実施形態にかかるタングステン焼結体は、密度が１８９００ｋｇ／ｍ３以下であることが好ましく、１８５００ｋｇ／ｍ３以下であることがより好ましく、１８２００ｋｇ／ｍ３以下であることがさらに好ましい。
The tungsten sintered body of the present invention can suppress the wear amount of the tip of the cutting tool by making the density 19000kg/m3 or less. That is, the tungsten sintered body of the present invention is unlikely to cause the cutting depth to gradually decrease with the increase in the wear amount of the tip as machining proceeds, and can suppress the dimensional difference of the sintered body between the cutting start point and the cutting end point in one pass of the cutting process from increasing, and can also suppress the damage of the tip.
In addition, by making the density of the tungsten sintered body of the present invention 19000 kg/m 3 or less, it is possible to suppress the cracking of the sintered body body during handling such as transportation to a cutting machine or chucking. And, for the same reason as above, the density of the tungsten sintered body according to the embodiment of the present invention is preferably 18900 kg/m 3 or less, more preferably 18500 kg/m 3 or less, and even more preferably 18200 kg/m 3 or less.
本発明のタングステン焼結体は、不可避的不純物のうち水素（Ｈ）の含有量を３０質量ｐｐｍ以下とする。これにより、本発明のタングステン焼結体は、水素に起因した脆化部の生成が低減され、切削機械への搬送やチャッキングといったハンドリング等で焼結体本体が変形したり割れたりすることを抑制できる。
また、本発明のタングステン焼結体は、水素の含有量を３０質量ｐｐｍ以下にすることで、焼結体を得る焼結工程において、成形型や加熱装置等が水素脆化によって劣化したり損傷したりすることを抑制できる。上記と同様の理由から、本発明の実施形態にかかるタングステン焼結体は、水素を２０質量ｐｐｍ以下にすることが好ましく、１０質量ｐｐｍ以下にすることがより好ましく、５質量ｐｐｍ以下にすることがさらに好ましく、２質量ｐｐｍ以下にすることがよりさらに好ましい。
なお、タングステン焼結体中の水素を０質量ｐｐｍにすることは困難である。このため、本発明の実施形態にかかるタングステン焼結体は、工業的生産性を考慮して、水素を０．０１質量ｐｐｍ以上にすることが好ましく、０．０３質量ｐｐｍ以上にすることがより好ましい。
The tungsten sintered body of the present invention has a hydrogen (H) content of 30 mass ppm or less among unavoidable impurities. This reduces the generation of embrittled parts caused by hydrogen in the tungsten sintered body of the present invention, and can suppress deformation or cracking of the sintered body body during handling such as transportation to a cutting machine or chucking.
In addition, the tungsten sintered body of the present invention can suppress deterioration or damage of the molding die, heating device, etc. due to hydrogen embrittlement during the sintering process of obtaining the sintered body by making the
In addition, it is difficult to make the hydrogen in the tungsten sintered body 0 mass ppm. Therefore, in the tungsten sintered body according to the embodiment of the present invention, in consideration of industrial productivity, it is preferable to make the hydrogen be 0.01 mass ppm or more, and more preferably to make it be 0.03 mass ppm or more.
本発明のタングステン焼結体は、ＪＩＳ Ｚ ２２４４で規定されるビッカース硬さの平均値を２２０～３２０ＨＶにすることが好ましい。焼結体に軟らかい部位が存在してしまうと、機械加工時に低硬度の部位のみが残存したり脱落したりすることで焼結体の表面粗さが粗くなる場合がある。このため、本発明の実施形態にかかるタングステン焼結体は、ビッカース硬さの平均値を２２０ＨＶ以上にすることが好ましい。また、上記と同様の理由から、本発明の実施形態にかかるタングステン焼結体は、ビッカース硬さの平均値を２５０ＨＶ以上にすることがより好ましく、２８０ＨＶ以上がさらに好ましい。 The tungsten sintered body of the present invention preferably has an average Vickers hardness, as specified by JIS Z 2244, of 220 to 320 HV. If soft areas are present in the sintered body, only the low hardness areas may remain or fall off during machining, resulting in a rough surface of the sintered body. For this reason, the tungsten sintered body according to the embodiment of the present invention preferably has an average Vickers hardness of 220 HV or more. For the same reasons as above, the tungsten sintered body according to the embodiment of the present invention more preferably has an average Vickers hardness of 250 HV or more, and even more preferably 280 HV or more.
また、本発明の実施形態にかかるタングステン焼結体は、切削機械への搬送やチャッキングといったハンドリング等で焼結体本体が割れることを抑制する観点や、切削工具のチップの摩耗量を抑える観点から、ビッカース硬さの平均値を３２０ＨＶ以下にすることが好ましい。
本発明でいうビッカース硬さは、上述した焼結体本体の変形や割れ、切削工具のチップの摩耗や破損を抑制することに加え、焼結体の表面粗さを平滑にする観点から、焼結体の平面部における任意の５箇所で測定されるビッカース硬さの平均値が２２０～３２０ＨＶの範囲にあることをいう。
In addition, the tungsten sintered body according to the embodiment of the present invention preferably has an average Vickers hardness of 320 HV or less in order to prevent the sintered body from cracking during handling such as transport to a cutting machine or chucking, and to reduce the amount of wear on the tip of a cutting tool.
The Vickers hardness in the present invention refers to an average Vickers hardness measured at any five points on the flat surface of the sintered body in the range of 220 to 320 HV, from the viewpoint of suppressing the above-mentioned deformation or cracking of the sintered body body and wear or breakage of the tip of the cutting tool, as well as smoothing the surface roughness of the sintered body.
本発明の実施形態にかかるタングステン焼結体は、焼結体本体の変形や割れを抑制する観点から、金属組織中に存在する最も大きいポアに描ける最大長辺の長さが３．０μｍ以下であることが好ましい。そして、上記と同様の理由から、本発明の実施形態にかかるタングステン焼結体は、金属組織中に存在する最も大きいポアに描ける最大長辺の長さは２．０μｍ以下であることがより好ましく、１．０μｍ以下であることがさらに好ましい。 In the tungsten sintered body according to the embodiment of the present invention, from the viewpoint of suppressing deformation or cracking of the sintered body body, it is preferable that the length of the longest side that can be drawn in the largest pore present in the metal structure is 3.0 μm or less. And, for the same reasons as above, it is more preferable that the length of the longest side that can be drawn in the largest pore present in the metal structure in the tungsten sintered body according to the embodiment of the present invention is 2.0 μm or less, and even more preferable that it is 1.0 μm or less.
本発明のタングステン焼結体は、以下の製造方法で得ることができ、その一般的形態を説明する。本発明のタングステン焼結体は、先ず、平均粒径（Ｄ５０）が１．０～４．０μｍであるタングステン粉末を準備する。そして、このタングステン粉末を所定形状の型内に充填し、常温（ＪＩＳ Ｚ ８７０３で規定された２０±１５℃）で、０．２～５．０ｔｆ／ｃｍ２（１９．６～４９０ＭＰａ）の成形圧力でプレス成形を施して成形体を得る。次いで、この成形体を無加圧の状態で焼結して焼結体を得る。
なお、タングステン焼結体を得るための焼結時の加熱雰囲気については、タングステン粉末の表面に形成された酸化被膜を除去することを目的として水素雰囲気を用いることが一般的である。しかしながら、本発明では、焼結体の水素含有量を低減する観点から、大気中の水素含有量（３質量ｐｐｍ）以下に調整された真空雰囲気または不活性ガス雰囲気を加熱雰囲気とする。
The tungsten sintered body of the present invention can be obtained by the following manufacturing method, and its general form will be described. The tungsten sintered body of the present invention is first prepared by preparing tungsten powder with an average particle size (D50) of 1.0 to 4.0 μm. Then, this tungsten powder is filled into a mold of a predetermined shape, and press-molded at room temperature (20±15°C as specified in JIS Z 8703) with a molding pressure of 0.2 to 5.0 tf/cm 2 (19.6 to 490 MPa) to obtain a molded body. Next, this molded body is sintered in a pressureless state to obtain a sintered body.
In addition, as for the heating atmosphere during sintering to obtain a tungsten sintered body, a hydrogen atmosphere is generally used in order to remove the oxide film formed on the surface of the tungsten powder. However, in the present invention, in order to reduce the hydrogen content of the sintered body, a vacuum atmosphere or an inert gas atmosphere adjusted to the hydrogen content of the air (3 mass ppm) or less is used as the heating atmosphere.
焼結条件は、加熱温度を１７００～１９００℃、保持時間を１～１０時間とすることが好ましい。ここで、焼結体のポアを抑制することに加え、水素含有量を低減する観点から、焼結温度は１８００℃以上、保持時間は５時間以上にすることがより好ましい。 The preferred sintering conditions are a heating temperature of 1700 to 1900°C and a holding time of 1 to 10 hours. From the standpoint of suppressing pores in the sintered body and reducing the hydrogen content, it is more preferable to set the sintering temperature to 1800°C or higher and the holding time to 5 hours or more.
平均粒径（Ｄ５０）が１．９～２．３μｍのタングステン粉末を成形型内に充填し、常温で、０．７～２．５ｔｆ／ｃｍ２（４９～２４５ＭＰａ）の成形圧力でプレス成形を行ない、成形体を得た。そして、この成形体を表１に記載した焼結条件で、真空雰囲気中にて無加圧の状態で焼結を行ない、タングステン焼結体をそれぞれ得た。 Tungsten powder with an average particle size (D50) of 1.9 to 2.3 μm was filled into a mold, and press molding was performed at room temperature with a molding pressure of 0.7 to 2.5 tf/cm 2 (49 to 245 MPa) to obtain a molded body. Then, this molded body was sintered in a vacuum atmosphere without pressure under the sintering conditions shown in Table 1 to obtain a tungsten sintered body.
上記で得た各タングステン焼結体について、密度、水素含有量、ビッカース硬さおよび最大ポアに描ける長辺の長さを評価した。
なお、密度は、研精工業株式会社製の電子比重計ＳＤ－１２０Ｌを使用して測定した。ビッカース硬さは、ＪＩＳ Ｚ ２２４４に準じ、株式会社明石製作所社製のＭＶＫ－Ｅを用いて、荷重９．８Ｎのときの値を、焼結体の平面部における任意の５箇所を測定し、その平均値を算出した。ポアにおいては、走査型電子顕微鏡（ＳＥＭ）で観察し、ＳＥＭ像の面積が４９７μｍ２の中で最も大きいポアを抽出し、そのポアに描ける最大となる長辺の長さを測定した。本発明例および比較例となる焼結体の走査型電子顕微鏡観察写真を図１および図２に示す。
The density, hydrogen content, Vickers hardness, and length of the long side that can be drawn at the maximum pore were evaluated for each of the tungsten sintered bodies obtained above.
The density was measured using an electronic specific gravity meter SD-120L manufactured by Kensei Kogyo Co., Ltd. The Vickers hardness was measured at five arbitrary points on the flat surface of the sintered body at a load of 9.8 N using an MVK-E manufactured by Akashi Seisakusho Co., Ltd. in accordance with JIS Z 2244, and the average value was calculated. The pores were observed with a scanning electron microscope (SEM), and the largest pore in the SEM image area of 497 μm2 was extracted, and the length of the longest side that could be drawn in the pore was measured. Scanning electron microscope photographs of the sintered bodies of the present invention and comparative examples are shown in Figures 1 and 2 .
本発明例となる試料Ｎｏ．１～４のタングステン焼結体は、いずれも、密度が１５０００～１９０００ｋｇ／ｍ３の範囲にあり、水素含有量を３０質量ｐｐｍ以下に抑えることで、機械加工時にチップの摩耗や破損がなく、機械加工後の焼結体外観に割れや欠けがないことを確認できた。また、切削機械への搬送やチャッキングといったハンドリング等で焼結体が変形や破損することもなかった。また、本発明例となる試料Ｎｏ．１のタングステン焼結体は、図１に示すように、最大長辺の長さが３．０μｍを超える粗大なポアがないことも確認できた。
一方、比較例となる試料Ｎｏ．５のタングステン焼結体は、密度が１５０００ｋｇ／ｍ３を下回っており、水素含有量が３０質量ｐｐｍを超えたことにより、機械加工時に割れが発生し、図２に示すような最大長辺の長さが６．１μｍのポアも確認された。
また、比較例となる試料Ｎｏ．６のタングステン焼結体は、密度が１００００ｋｇ／ｍ３を下回ったことにより、ビッカース硬さおよびポアの測定をすることができなかった。
The tungsten sintered body of Sample No. 1 to 4, which is an example of the present invention, has a density in the range of 15,000 to 19,000 kg/ m3 , and by suppressing the hydrogen content to 30 mass ppm or less, it was confirmed that there was no wear or damage to the tip during machining, and no cracks or chips in the appearance of the sintered body after machining. In addition, the sintered body was not deformed or damaged by handling such as transportation to the cutting machine or chucking. In addition, it was confirmed that the tungsten sintered body of Sample No. 1, which is an example of the present invention, does not have coarse pores with a maximum long side length exceeding 3.0 μm, as shown in FIG. 1.
On the other hand, the tungsten sintered body of sample No. 5, which is a comparative example, had a density below 15,000 kg/ m3 and a hydrogen content exceeding 30 mass ppm, so that cracks occurred during machining, and pores with a maximum long side length of 6.1 μm as shown in FIG.
In addition, the tungsten sintered body of sample No. 6, which is a comparative example, had a density below 10,000 kg/ m3 , so it was not possible to measure the Vickers hardness and pores.
Claims (2)
The tungsten sintered body according to claim 1, having an average Vickers hardness of 220 to 320 HV.
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| JP2003171760A (en) * | 2001-12-04 | 2003-06-20 | Toshiba Corp | Tungsten sputtering target |
| WO2014148588A1 (en) * | 2013-03-22 | 2014-09-25 | Jx日鉱日石金属株式会社 | Tungsten-sintered-body sputtering target and method for producing same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2003171760A (en) * | 2001-12-04 | 2003-06-20 | Toshiba Corp | Tungsten sputtering target |
| WO2014148588A1 (en) * | 2013-03-22 | 2014-09-25 | Jx日鉱日石金属株式会社 | Tungsten-sintered-body sputtering target and method for producing same |
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