WO2012050271A1

WO2012050271A1 - Alloy of tungsten (w) and copper (cu) having functionally graded material (fgm) layers, metal material having the same and manufacturing method for alloy of w and cu

Info

Publication number: WO2012050271A1
Application number: PCT/KR2011/001471
Authority: WO
Inventors: Seong Lee; Joon Woong Noh
Original assignee: Agency For Defense Development
Priority date: 2010-10-12
Filing date: 2011-03-03
Publication date: 2012-04-19
Also published as: KR101230262B1; KR20120037625A

Abstract

Disclosed are a tungsten-copper alloy, a metal material having the same and a fabrication method for the tungsten-copper alloy, the fabrication method including generating tungsten-copper composite powders such that tungsten is coated on copper powders and the composition ratios of copper and tungsten are different, sequentially laminating the tungsten-copper composite powders to create a plurality of layers, having sequentially increasing or decreasing contents of tungsten, and sintering the plurality of layers under conditions of temperature and time preset for generation of tungsten-copper alloy, whereby the tungsten-copper alloy and high thermal conductivity and fabrication reliability by virtue of precise morphologies can be created.

Description

ALLOY OF TUNGSTEN (W) AND COPPER (CU) HAVING FUNCTIONALLY GRADED MATERIAL (FGM) LAYERS, METAL MATERIAL HAVING THE SAME AND MANUFACTURING METHOD FOR ALLOY OF W AND CU

The present invention relates to an alloy of tungsten and copper capable of reducing anisotropies in functionally graded material (FGM) layers, and a manufacturing method thereof.

A metal material having a tungsten-copper double layer is a structure using the high melting point of the tungsten, which has the highest melting point among every metal type, and physical properties of the copper, which has thermostable properties and excellent thermal conductivities. The structure of the tungsten-copper double layer may be applicable to industrial and munitions fields in the form that the tungsten is placed at the side affected by a load and the copper is present at a heat dissipation side caused due to heat transfer in a system, which generates heat of high temperature. Especially, a tungsten-copper alloy may be applied to a heat sink of IT. In this case, both the properties of the tungsten having thermal expansion characteristics similar to a semiconductor material and properties of the copper having excellent heat transfer characteristics are used together.

Also, the metal material having the tungsten-copper double layer may be applicable to plasma facing materials of a fusion reactor. Here, pure tungsten is present at a side of a plasma area of high temperature, and a component in a copper layer structure having high thermostatic properties is formed at an opposite side to convert heat of high temperature transferred via the plasma side into energy.

Tungsten and copper are remarkably different from each other in thermal expansion coefficients (i.e., tungsten: 4.5ｘ10-6, copper: 16.6ｘ10-6). Hence, the tungsten-copper double layer, which is fabricated by pure bonding of the two metals or applied as a component having a bonded structure of the two metals, may have several problems, such as occurrence of delamination, crack, detachment and the like, those of which are caused due to occurrence of thermal residual stress and heat-induced stress at an interface between the two metals.

In recent time, to overcome such problems, an approach of smoothly continuing extreme interruption of properties by inserting a functionally graded alloy having functionally graded material (FGM) layers between the two metal layers is being studied. Fabrication methods of the functional graded alloy are divided into a fabrication method using infiltration, and a fabrication method for a functionally graded alloy by adjusting a composition ratio of tungsten and copper upon spraying tungsten and copper powders.

The former is a fabrication method using the difference of granularities of tungsten, in which upon mixing and molding different tungsten particles, those particles are controlled such that upper and lower air gaps are inclined with each other and sintered at high temperature to create a tungsten skeletal structure, in which liquid copper is then infiltrated. However, upon exceeding an appropriate thickness, defective infiltration may be caused due to the difference of capillary forces for each portion upon infiltration, which results in difficulties in reproductivity.

The latter is a method, such as a thermal spraying, namely, a method of artificially fabricating a functionally graded alloy by differing a fed amount of powders upon laminating the same. However, this method is difficult to precisely laminate powders, and also difficult to spray those powders due to the great difference of melting points (i.e., tungsten: 3410℃, copper: 1083℃). Furthermore, thermal conductivity is lowered because of delamination due to thermal stress upon laminating, cracks hidden inside and the like.

In addition, upon employing those proposed methods, the precision upon laminating the powders is impossible due to the characteristics of the materials without mutual solubilities, thereby lowering reliability of the fabrication. Furthermore, pores may easily be generated inside after fabrication or delamination may be easily caused due to internal stress between layers, generated upon laminating. It has been reported that such pores or inter-layer delamination fatally affect thermal conductivities and upon actual fabrication of the functionally graded alloy, thermal properties are drastically lowered.

Therefore, to address such problems, an aspect of the detailed description is to provide an alloy of tungsten and copper having functionally graded material (FGM) layers with more enhanced reliabilities of fabrication and use, a metal material having the same, and a fabrication method for the tungsten-copper alloy.

Also, another aspect of the detailed description is to provide a tungsten-copper alloy, which can be fabricated using a functionally graded material and have high thermal conductivity.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a tungsten-copper alloy including a plurality of layers made of alloy of tungsten and copper and having different composition ratios of tungsten and copper, respectively, wherein the plurality of layers are disposed such that the content of tungsten sequentially increases or decreases due to tungsten-coated copper powders being sintered in a laminated state according to the content of tungsten.

In accordance with one exemplary embodiment, the plurality of layers may be mixed with a transition element, and the transition element may be nickel, cobalt or iron. The transition element may be mixed with layers containing tungsten whose content is higher than a preset reference value, of the plurality of layers, and sintered to be diffused into layers having tungsten whose content is lower than the preset reference value.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a metal material having a tungsten-copper alloy including a copper layer part made of copper, a tungsten layer part made of tungsten and configured to obscure the copper layer part, and a tungsten-copper alloy disposed between the copper and tungsten layer parts, both surfaces thereof being coupled respectively with the copper and tungsten layer parts, and having a plurality of layers with different composition ratios, laminated such that the content of tungsten sequentially increases toward the tungsten layer part.

In accordance with another exemplary embodiment, a method for fabricating a tungsten-copper alloy may include generating tungsten-copper composite powders such that tungsten is coated on copper powders and the composition ratios of copper and tungsten are different, sequentially laminating the tungsten-copper composite powders to create a plurality of layers, having sequentially increasing or decreasing contents of tungsten, and sintering the plurality of layers under conditions of temperature and time preset for generation of tungsten-copper alloy.

The generating step may include mixing tungsten oxide powders with copper oxide powders, and reducing the mixed tungsten oxide powders and copper oxide powders under a hydrogen atmosphere or a reducing gas atmosphere containing hydrogen such that the tungsten is coated on the copper powders. The generating step may further include mixing a transition element with the tungsten-copper composite powders, and the transition element may be nickel, cobalt or iron. The transition element may be added in the ratio of 0.01wt.% to 10wt.%.

The laminating step may be configured to fill tungsten-copper composite powders in a composition ratio into a mold, perform surface-planarization of the tungsten-copper composite powders using vibration or pressure, and thereafter fill tungsten-copper composite powders in another composition ratio.

The sintering step may include performing solid phase sintering for the plurality of layers for 0.1 to 50 hours at the temperature range of 950 to 1083℃, prior to formation of copper in a liquid state, and performing a liquid phase sintering for the plurality of layers, having undergone the solid phase sintering, for 0.1 to 50 hours at the temperature range of 1100 to 1500℃.

In accordance with the tungsten-copper alloy, the metal material having the same and the fabrication method of the tungsten-copper alloy, the tungsten-copper alloy can be fabricated using tungsten-coated copper powders, so as to reduce residual stress and heat-induced stress at an interface between two layers, generated upon fabrication and use. Also, such formation allows implementation of the tungsten-copper alloy having functionally graded material (FGM) layers with enhanced fabrication and use reliabilities.

In addition, a plurality of layers can be formed in different composition ratios of copper and tungsten, which allows high thermal conductivity and high functionality in the tungsten-copper alloy having the FGM layers, resulting in creation of the tungsten-copper alloy having precise and uniform fine morphologies in composition.

FIG. 1 is an overview showing a metal material having a tungsten-copper double layer in accordance with one exemplary embodiment;

FIG. 2 is a flowchart showing a method for fabricating a tungsten-copper alloy in accordance with an exemplary embodiment;

FIG. 3 is a photograph showing cross-sectional morphologies of tungsten-coated copper powders;

FIG. 4 is a graph showing sintering properties of various compositions of powders coated with tungsten;

FIG. 5 is a graph showing sintering behaviors of enhanced composite powders;

FIGS. 6 and 7 are photographs showing sintered bodies of a tungsten-copper alloy fabricated without addition of a transition element (Example 1);

FIG. 8 is a photograph showing a sintered body of a tungsten-copper alloy fabricated by addition of 1.0wt.% of Ni (Example 2);

FIG. 9 is a photograph showing a cross-sectional internal morphology of the tungsten-copper alloy of FIG. 8;

FIG. 10 is an enlarged photograph of part A shown in FIG. 9; and

FIG. 11 is a photograph showing a sintered body of a tungsten-copper alloy fabricated by addition of 0.3wt.% of Co, as another example.

Reference will now be made in detail to a tungsten-copper alloy, a metal material having the same, and a fabrication method for the tungsten-copper alloy in accordance with the exemplary embodiments, examples of which are illustrated in the accompanying drawings. This specification employs like/similar reference numerals for like/similar components irrespective of different embodiments, so they all will be understood by the first description. The expression in the singular form in this specification will cover the expression in the plural form unless otherwise indicated obviously from the context.

FIG. 1 shows a metal material having a tungsten-copper double layer in accordance with one exemplary embodiment.

As shown in FIG. 1, the tungsten-copper double layer metal material 100 may include a copper layer part 110, a tungsten layer part 120 and a tungsten-copper alloy 130.

The copper layer part 110 may be made of copper (Cu), and be, for example, a heat sink having high thermostatic properties or a structure having a similar function to the heat sink.

The tungsten layer part 120 may be formed to obscure one surface of the copper layer part 110, and made of tungsten (W). The tungsten layer part 120, for example, may be mounted onto a surface of a semiconductor material or be a plasma facing material of a fusion reactor.

The tungsten-copper alloy 130 may be disposed between the copper and

tungsten layer parts

110 and 120, and both surfaces thereof may be coupled to the copper and

tungsten layer parts

110 and 120, respectively. For instance, tungsten is deposited on one surface of the tungsten-copper alloy 130 so as to be the tungsten layer part 120, while a heat spreader prepared using copper is connected to another surface of the tungsten-copper alloy 130 in a brazing manner so as to be the copper layer part 120.

More concretely, the tungsten-copper alloy 130 may include a plurality of

layers

131, 132 and 133, which have different composition ratios of tungsten and copper. The plurality of

layers

131, 132 and 133 may be laminated such that the content of tungsten thereof sequentially increases toward the tungsten layer part 120. The plurality of

layers

131, 132 and 133 may be mixed with a transition element, such as nickel, cobalt, iron or the like.

Hereinafter, a fabrication method applicable to the tungsten-copper alloy 130 will be described in more detail.

FIG. 2 is a flowchart showing a method for fabricating a tungsten-copper alloy in accordance with an exemplary embodiment, FIG. 3 is a photograph showing cross-sectional morphologies of tungsten-coated copper powders, FIG. 4 is a graph showing sintering properties of various compositions of powders coated with tungsten, and FIG. 5 is a graph showing sintering behaviors of enhanced composite powders.

In accordance with the fabrication method for the tungsten-copper alloy, first, tungsten-copper composite powders with different composition ratios of copper and tungsten are generated (S100). The tungsten-copper composite powders may be composed such that tungsten is coated on copper powders. For example, the tungsten may be used in various composition ratios, such as 45W(i.e., the content of tungsten is 45 % by weight (45wt.%)) , 55W, 65W, 75W, 85W, 90W and the like.

Referring to FIG. 2, the generation step S100 may include a mixing step (S110) and a thermal treatment step (S120).

The mixing step S110 may be a step of mixing tungsten oxide powders with copper oxide powders. For example, tungsten oxide (WO3 or WO2.9) powders and copper oxide (CUO or CU2O) powders are mixed and milled using tubular mixing or ball milling.

The thermal treatment step S120 may be performed to reduce and thermally treat the tungsten oxide powders and the copper oxide powders, which are mixed such that the tungsten is coated on the copper powders, under a hydrogen atmosphere or a reducing gas atmosphere containing hydrogen. More particularly, the powders mixed and milled by the tubular mixing or ball milling are reduced under the hydrogen atmosphere or the reducing gas atmosphere containing hydrogen. The reducing gas atmosphere may be created by the mixed gas of hydrogen and nitrogen, and such gas may be acquired from decomposition of ammonia gas (NH3).

Also, as one example of the thermal treatment, a method may be employed in which mixed and milled powders are left sequentially for 1 minute to 5 hours at the temperature range of 200℃ to 400℃, for 1 minute to 5 hours at higher temperature range of 500℃ to 700℃, for 1 minute to 5 hours at much higher temperature range of 750℃ to 1080℃, and finally cooled.

During the generation step S100, the tungsten is coated on the copper powders. Referring to FIG. 3, it can be found that the tungsten-copper composite powders have a structure that copper in a dark color is surrounded by tungsten in a bright white color.

Referring to FIG. 2, the tungsten-copper composite powders are sequentially laminated so as to create a plurality of layers having sequentially increasing or decreasing contents of tungsten (S200).

At the lamination step S200, tungsten-copper composite powders in a certain composition ratio are introduced (filled) in a mold and vibrated or pressed to planarize surfaces of the tungsten-copper composite powders in the certain composition ratio, and thereafter tungsten-copper powders in another composition ratio are filled.

For example, tungsten-copper powders having different composition ratios may be filled in the mold by a specific amount, respectively. The filling of the composite powders may be achieved by a method, in which of composite powders in one composition ratio are filled to be surface-planarized using vibration and composite powders in another composition ratio are filled, or by a method, in which composite powders in one composition ratio are pressed (tramped) using pressure other than vibration to be surface-planarized and composite powders in another composition ratio are laid thereon to create the plurality of layers.

Finally, the plurality of layers are sintered at conditions of temperature and time, which are preset to generate the tungsten-copper alloy (S300).

The sintering step S300 may include solid phase sintering and liquid phase sintering.

The solid phase sintering may be a step of performing the solid phase sintering for the plurality of layers for 0.1 to 50 hours at the temperature range of 950℃ to 1083℃, which is a temperature before copper is turned to a liquid state. The liquid phase sintering may be a step of performing the liquid phase sintering for the plurality of layers, which have experienced the solid phase sintering, for 0.1 to 50 hours at the temperature range of 1100℃ to 1500℃.

FIG. 4 is a graph showing sintering properties according to various compositions of the tungsten-copper composite powders, which shows that similar sintering behaviors are observed in the composition ratio below 65W. Therefore, even if various compositions of composite powders are simultaneously molded and sintered in the composition ratio below 65W, the tungsten-copper alloy with a precise morphology can be obtained. Here, examining the graph, as the composition ratio increases to 75W and 85W, higher temperature range is needed for perfect precision.

To address such problem, the fabrication method may include a mixing step (S130). In more detail, the mixing step (S130) may be performed to mix a transition element, such as nickel, cobalt, iron or the like, with the tungsten-copper composite powders. The transition element may be added in the ratio of 0.01wt.% to 10wt.%.

The transition element may be mixed with the tungsten-copper composite powders during the generation step (S100). For example, the mixing step (S130) may be performed to mix a small amount of the transition element, such as nickel, cobalt, iron or the like, in the forms of powder and salt. The transition element may be added prior to or after reducing the tungsten-copper composite powders.

As such, the sintering behaviors of the composite powders containing the transition element may change as shown in FIG. 5, and be shown similar to the sintering behaviors in the composition ratio below 65W even if the content of tungsten is 85W.

Hereinafter, the tungsten-copper alloy fabricated by the tungsten-copper alloy fabrication method will be described in more detail with reference to FIGS. 6 to 11.

FIGS. 6 and 7 are photographs showing sintered bodies of a tungsten-copper alloy fabricated without addition of a transition element (Example 1), FIG. 8 is a photograph showing a sintered body of a tungsten-copper alloy fabricated by addition of 1.0wt.% of Ni (Example 2), FIG. 9 is a photograph showing a cross-sectional internal morphology of the tungsten-copper alloy of FIG. 8, and FIG. 10 is an enlarged photograph of part A shown in FIG. 9.

[Example 1]

Tungsten-copper composite powders of 45W, 55W, 65W, 75W, 85W and 90W are sequentially introduced in Φ15㎜ mold by about 0.4g, respectively. A surface planarization of each layer is performed by vibration or pressure. A solid phase sintering is performed under a condition of 1 hour at 1000℃, and a liquid phase sintering is performed under a condition of 1 hour at 1350℃ by increasing the temperature after the solid phase sintering.

FIG. 6 shows a case where vibration is used and molding pressure is lowered, and FIG. 7 shows results of increasing the molding pressure to 5 ton with tramping. As shown in FIGS. 6 and 7, the difference of sintering properties is caused by composite powders containing more tungsten, and accordingly, a bending phenomenon (see FIG. 6) or delamination (see FIG. 7) are caused.

[Example 2]

Tungsten-copper composite powders of 45W, 65W and 85W (1Ni) are sequentially filled and molded in Φ15㎜ mold by about 3g, respectively. The filling of the composite powders is performed in the manner of filling powders in one composition ratio, performing surface planarization of the powders using vibration, and filling powders in another composition ratio. The solid phase sintering is performed under a condition of 10 hours at 1050℃, and the liquid phase sintering is performed under a condition of 1 hour at 1250℃ by increasing the temperature after the solid phase sintering.

A transition element is mixed with layers containing tungsten, whose content is higher than a preset reference value, of a plurality of layers 231, 232 and 233, and sintered to be diffused to layers containing tungsten, whose content is lower than the preset reference value. For example, 1wt.% of nickel is added to the third layer 233 corresponding to 85W (1Ni), and then sintered to be diffused to the first and second layers 231 and 232 corresponding to 45W and 65W. Accordingly, the entire weight ratio of the nickel may be decreased.

Referring to FIG. 8, it can be noticed that no bending phenomenon or delamination of the tungsten-copper alloy is visibly found.

Referring to FIGS. 9 and 10, the plurality of layers 231, 232 and 233 having different composition ratios of tungsten and copper are arranged such that the content of tungsten thereof increases or decreases in a sequential manner, and ensure minute morphologies with a uniform and precise structure. It can be obvious in the enlarged part of FIG. 10 that the tungsten-copper alloy has the precise and uniform minute morphology. This can be implemented by sintering the tungsten-coated copper powders in the state of being laminated to form the plurality of layers 231, 232 and 233 according to the content of tungsten.

[Example 3]

FIG. 11 is a photograph showing a sintered body of a tungsten-copper alloy fabricated by addition of 0.3wt.% of Co, as another example (Example 3).

Example 3 is a fabrication example having enhanced sintering properties. Tungsten-copper composite powders of 45W, 65W and 85W (0.3Co) are sequentially filled and molded in Φ20㎜ mold by about 3g, respectively. The filling of the composite powders is performed in the manner of filling powders in one composition ratio, performing surface planarization of the powders using vibration, and filling powders in another composition ratio. The solid phase sintering is performed under a condition of 10 hours at 1050℃, and the liquid phase sintering is performed under a condition of 1 hour at 1250℃ by increasing the temperature after the solid phase sintering.

Referring to FIG. 11, it can be noticed that a tungsten-copper alloy without delamination or pores and with a precise morphology is fabricated.

The foregoing embodiments and advantages of the tungsten-copper alloy, the metal material having the same and the fabrication method for the tungsten-copper alloy may not be limitedly applied, but such embodiments may be configured by a selective combination of all or part of each embodiment so as to derive many variations.

The tungsten-copper alloy having functionally graded material (FGM) layers, the metal material having the same and the fabrication method for the tungsten-copper alloy may be industrially applicable.

Claims

A tungsten-copper alloy comprising a plurality of layers made of alloy of tungsten and copper and having different composition ratios of tungsten and copper, respectively,

wherein the plurality of layers are disposed such that the content of tungsten sequentially increases or decreases due to tungsten-coated copper powders being sintered in a laminated state according to the content of tungsten.
The alloy of claim 1, wherein the plurality of layers are mixed with a transition element, the transition element comprising nickel, cobalt or iron.
The alloy of claim 2, wherein the transition element is mixed with layers containing tungsten whose content is higher than a preset reference value, of the plurality of layers, and sintered to be diffused into layers having tungsten whose content is lower than the preset reference value.
A metal material having a tungsten-copper alloy comprising:

a copper layer part made of copper;

a tungsten layer part made of tungsten and configured to obscure the copper layer part; and

a tungsten-copper alloy disposed between the copper and tungsten layer parts, both surfaces thereof being coupled respectively with the copper and tungsten layer parts, and having a plurality of layers with different composition ratios, laminated such that the content of tungsten sequentially increases toward the tungsten layer part.
The material of claim 4, wherein the plurality of layers are mixed with a transition element, the transition element comprising nickel, cobalt or iron.
A method for fabricating a tungsten-copper alloy comprising:

generating tungsten-copper composite powders such that tungsten is coated on copper powders and the composition ratios of copper and tungsten are different;

sequentially laminating the tungsten-copper composite powders to create a plurality of layers, having sequentially increasing or decreasing contents of tungsten; and

sintering the plurality of layers under conditions of temperature and time preset for generation of tungsten-copper alloy.
The method of claim 6, wherein the generating step comprises:

mixing tungsten oxide powders with copper oxide powders; and

reducing the mixed tungsten oxide powders and copper oxide powders under a hydrogen atmosphere or a reducing gas atmosphere containing hydrogen such that the tungsten is coated on the copper powders.
The method of claim 7, wherein the generating step further comprises mixing a transition element with the tungsten-copper composite powders, the transition element comprising nickel, cobalt or iron.
The method of claim 8, wherein the transition element is added in the ratio of 0.01wt.% to 10wt.%.
The method of claim 6, wherein the laminating step is configured to fill tungsten-copper composite powders in a composition ratio into a mold, perform surface-planarization of the tungsten-copper composite powders using vibration or pressure, and thereafter fill tungsten-copper composite powders in another composition ratio.
The method of claim 6, wherein the sintering step comprises:

performing solid phase sintering for the plurality of layers for 0.1 to 50 hours at the temperature range of 950 to 1083℃, prior to formation of copper in a liquid state; and

performing a liquid phase sintering for the plurality of layers, having undergone the solid phase sintering, for 0.1 to 50 hours at the temperature range of 1100 to 1500℃.