JP7733893B2 - Cu-based powder and method for producing the Cu-based powder - Google Patents

Description

The present invention relates to Cu-based powder. Specifically, the Cu-based powder is produced from a molten metal containing P. Because P reacts with oxygen to form gaseous phosphates, reducing the amount of oxygen, the deterioration of the fluidity of the molten metal due to oxygen is suppressed, allowing for production using an atomization method with excellent productivity and safety. Furthermore, the Cu-based powder contains element M, which easily forms phosphides. Therefore, the P contained in the Cu-based powder can form phosphides with element M through heat treatment, which precipitate from the Cu matrix. This Cu-based powder allows for the production of Cu-based alloys with minimal impact of P on thermal and electrical conductivity.

When producing Cu-based powders using the atomization method, fluidity of the molten metal is always required when spraying, for the sake of productivity and work safety.

Oxygen affects the fluidity of molten metal, and if the amount of oxygen is high, the fluidity deteriorates.
Furthermore, if the molten metal contains a large amount of oxygen, the amount of oxygen in the produced powder will increase, causing surface oxidation and internal oxidation, which may cause defects or deterioration in the properties of products produced from such powder.

An established method for reducing oxygen is to add charcoal or flux to the molten metal.

The added charcoal and flux react with the oxygen in the molten metal, forming oxides that reduce the amount of oxygen, thereby improving the fluidity of the molten metal.

However, because the added charcoal and flux float to the top of the molten metal, oxidation cannot be suppressed at the moment the metal is poured, resulting in a sudden deterioration in fluidity. Furthermore, because the charcoal and flux are difficult to remove, there is the problem that the charcoal, flux, or flux oxides may be mixed into the produced Cu-based powder.

One way to solve this problem is to add copper phosphorus, which is made of copper and copper phosphide, to the molten metal.

When phosphorus copper is added to molten metal, phosphorus (P) reacts with oxygen in the molten metal, forming gaseous phosphorus oxide, which reduces the amount of oxygen and prevents the fluidity of the molten metal from deteriorating.

Also, since it is a gas-phase phosphate, there is no need to physically remove it like with charcoal or flux.

However, it is known that when P is present in the Cu matrix of a Cu-based alloy, it significantly reduces the thermal and electrical conductivity, which are excellent features of the Cu-based alloy.

When a Cu-based alloy is produced by heat treating a Cu-based powder that has been produced by adding excess copper phosphorus relative to the amount of oxygen in the molten metal, P remains in the Cu matrix, resulting in reduced thermal and electrical conductivity compared to alloys without the addition of copper phosphorus.

Atmospheric melting allows the fluidity of the molten metal to be maintained without adding phosphorus copper, but since vacuum equipment is required, it is not suitable for mass production and increases manufacturing costs.

P may also be present in Cu-based powders as an unavoidable impurity derived from the raw materials.

In light of the above issues, there is a need to develop Cu-based powder that has minimal impact of P on the thermal and electrical conductivity of Cu-based alloys produced by heat-treating Cu-based powder, even if the Cu-based powder is produced from a molten metal melted using conventional melting methods and to which phosphorus copper or other impurities have been added, or even if the Cu-based powder contains P as an unavoidable impurity.

JP 6-93351

Patent Document 1 discloses a method in which an oxidizing gas is sprayed onto the molten metal to remove P from the molten metal, and then a reducing gas is sprayed onto the molten metal to reduce the amount of oxygen.

However, when the method disclosed in Patent Document 1 is applied to powder production using the atomization method, although it is possible to remove P using an oxidizing gas, there is a problem in that it is not easy to add a reduction step in the event of overoxidation.

The present inventors have set solving the above-mentioned problems as a technical task, and as a result of numerous trial and error trials and experiments, have discovered a Cu-based powder containing element M, P, and Cu, wherein element M is an element whose standard free energy of formation per 1 mol of phosphorus of element M in a temperature range of 298K to 1300K is equal to or less than the standard free energy of formation per 1 mol of phosphorus of Cu ₃ P in the same temperature range, and among the phosphides of element M, the phosphide having the lowest standard free energy of formation in the above temperature range is M _x P _y (where x>0, y>0) and A is expressed as "A=mass % of P×(x/y)×(atomic weight of M/atomic weight of P)," the content of the element M in the Cu-based powder is A×0.3 mass % or more and A×1.2 mass % or less, and the content of P is 0.01 mass % to 1.0 mass %, so that the fluidity of the molten metal is high, and therefore excellent productivity and safety can be ensured even when the Cu-based powder is produced by an atomization method. Furthermore, since the Cu-based powder contains the element M which easily forms phosphide, P and the element M can form phosphide by heat treating the Cu-based powder, and P can be precipitated from the Cu matrix. This is a remarkable finding that has led to the achievement of the above technical object.

The above technical problems can be solved by the present invention as follows:

The present invention provides a Cu-based powder containing element M, P, and Cu, wherein the element M is an element such that the standard free energy of formation of a phosphide of the element M per 1 mol of phosphorus in a temperature range of 298K to 1300K is equal to or less than the standard free energy of formation of Cu ₃ P per mol of phosphorus in the same temperature range, and when the phosphide of the element M having the lowest standard free energy of formation in the temperature range is represented by M _x P _y (where x > 0, y > 0), and A is represented by the following formula (formula), the content of the element M in the Cu-based powder is equal to or greater than A × 0.3% by mass and equal to or less than A × 1.2% by mass, and the content of P is 0.01% by mass to 1.0% by mass.
(Formula) A = mass % of P × (x/y) × (atomic weight of M/atomic weight of P)

The present invention also relates to the Cu-based powder, which contains 0.1% to 3.0% by mass of Sn.

The present invention also relates to the Cu-based powder, in which the O content is 0.1% by mass or less.

The present invention also relates to the above-mentioned Cu-based powder for use in powder metallurgy or additive manufacturing.

The present invention also relates to the Cu-based powder produced by the atomization method.

The present invention also relates to a Cu-based powder obtained by adding 0.1% to 1.0% by mass of a lubricant to the Cu-based powder.

The Cu-based powder used in this invention can contain P by adding copper phosphorus or other substances with a deoxidizing effect to the molten metal. This allows the P and oxygen to form gaseous phosphate oxides, reducing the amount of oxygen in the molten metal and resulting in a highly fluid molten metal, which can be produced using the atomization method with excellent productivity and safety.

Also, because the phosphorus oxides formed are in the gas phase, they do not need to be physically removed like charcoal or flux.

In addition, the Cu-based powder of the present invention contains element M in an amount excluding unavoidable impurities, at 0.3 to 1.2 times by mass the amount of A represented by the formula (1). Therefore, when the Cu-based powder is heat-treated, any remaining P that does not react with oxygen reacts with element M to form phosphide, which can be precipitated from the Cu matrix. This makes it possible to produce a Cu-based alloy in which P has little effect on thermal conductivity and electrical conductivity.

In addition, Cu-based powder containing 0.1% to 3.0% by mass of tin (Sn) has a lower melting point, which further improves the fluidity of the molten metal during production and also improves the strength of the parent phase of the Cu-based alloy.

Furthermore, if the oxygen (O) content is 0.1% by mass or less, internal oxidation of the powder can be suppressed, resulting in a Cu-based powder that is less likely to cause defects or deterioration in the properties of the Cu-based alloy.

Furthermore, adding 0.1% to 1.0% by mass of lubricant to Cu-based powder improves lubricity, making the Cu-based powder easier to mold into compacts in powder metallurgy.

Therefore, the present invention provides a Cu-based powder that can be used in powder metallurgy applications involving sintering, as well as in additive manufacturing applications, by performing heat treatment that diffuses P and/or element M to form a phosphide between P and element M, thereby obtaining a Cu-based alloy in which the influence of P on thermal conductivity and electrical conductivity is minimal.

The present invention is a Cu-based powder that is subjected to heat treatment to produce a Cu-based alloy.

The heat treatment may be any heat treatment that diffuses the P and/or element M contained in the Cu-based powder and causes the P and element M to form a phosphide. Examples of heat treatment include sintering, aging after sintering, and melting with a laser or electron beam followed by aging.

The heat treatment may be performed once or multiple times.

The Cu-based powder of the present invention can be produced from a molten metal containing P. Because molten metal containing P has excellent fluidity, it can be produced using the atomization method, ensuring excellent productivity and safety.

The produced Cu-based powder contains P that remains in the molten metal without forming gaseous phosphate oxide with oxygen, as well as P that is mixed in as an unavoidable impurity in the raw materials.

The P content is preferably 0.01% to 1.0% by mass, and more preferably 0.05% to 0.5% by mass.

If the P content is less than 0.01% by mass, the deoxidizing effect in the molten metal will be low, and there is a risk that the molten metal will not have high fluidity. Furthermore, if the P content exceeds 1.0% by mass, even if the alloy contains 0.3 to 1.2 times the mass percent of element M represented by formula A, the excess P that does not form a phosphide with element M will remain in the Cu matrix of the Cu-based alloy, which may affect the thermal conductivity and electrical conductivity.

P is preferably added to the molten metal.

The added P can be in any form, such as copper phosphorus or nickel phosphorus, as long as it has a deoxidizing effect, but those with a low melting point are preferable, and between copper phosphorus and nickel phosphorus, copper phosphorus is preferred.

The Cu-based powder in the present invention contains element M, which forms a phosphide having a standard free energy of formation per 1 mol of phosphorus in a temperature range of _{298 K to 1300 K (this temperature range may be referred to as "the same temperature range" or "the temperature range") that is equal to or less than the standard free energy of formation per 1 mol of phosphorus of Cu 3} P in the same temperature range.

The standard free energy of formation of phosphide per mole of phosphorus can be calculated by dividing the literature value for the standard free energy of formation per mole of phosphide by the number of moles of phosphorus.

An element M whose standard free energy of formation per mol of phosphorus is equal to or less than the standard free energy of formation per mol of phosphorus of Cu ₃ P in the above temperature range is an element that easily forms a phosphide.
Therefore, since a phosphide can be formed by heat treatment that diffuses P and/or element M, P is fixed and can be precipitated from the Cu matrix, and therefore a Cu-based alloy can be produced in which P has little effect on thermal conductivity and electrical conductivity.

Examples of element M include nickel (Ni/atomic weight 58.69), cobalt (Co/atomic weight 58.93), manganese (Mn/atomic weight 54.94), and aluminum (Al/atomic weight 26.98).

The content of element M in the Cu-based powder is 0.3 to 1.2 times by mass of A when the phosphide having the lowest standard free energy of formation per 1 mol of phosphorus in the above temperature range among phosphides of element M is represented by M _x P _y (formula), and A is represented by (formula).

(Formula) A = mass % of P × (x/y) × (atomic weight of M / atomic weight of P)

The values for "atomic weight of M" and "atomic weight of P" in the formula can have any number of decimal places as long as the number of decimal places is the same.

A represented by the formula is a value that represents the amount of element M that is neither excessive nor deficient with respect to P contained in M _x P _y .

If the content of element M is less than 0.3 times the mass percent of A, the amount of excess P that does not form phosphides remaining in the Cu matrix will be large, which may significantly affect the thermal and electrical conductivity of the Cu-based alloy.

If the content of element M exceeds 1.2 times the mass percent of A, the influence of the excess element M that does not form phosphide and remains in the Cu matrix becomes significant, and there is a risk that the thermal conductivity and electrical conductivity of the Cu-based alloy will be lower than when element M is not added.

For example, when calculating the range of the content of element M in Example 1 described later, the mass % of P contained in the Cu-based powder is 0.01, the element M is Co, and the phosphide with the lowest literature value for the standard free energy of formation of Co in the above temperature range is Co ₂ P, so x = 2, y = 1, the atomic weight of P is 30.97, and the atomic weight of Co is 58.93. Therefore, when applied to the formula, the value of A is 0.038.
Therefore, the Co content is preferably in the range of 0.011 mass % to 0.046 mass %.

M _x P _y may be determined from the literature value of the standard free energy of formation.

In the present invention, in the case of a special element in which the phosphide with the lowest standard free energy of formation per 1 mol of phosphorus changes within the above temperature range, that is, in the case of an element in which M _x P _y is the phosphide with the lowest standard free energy of formation per 1 mol of phosphorus at 298 K to α K, but M _a P _b is the phosphide with the lowest standard free energy of formation per 1 mol of phosphorus at α K to 1300 K, the value of A is determined by adopting the phosphide with the lowest standard free energy of formation per 1 mol of phosphorus on the low temperature side (M _x P _y in the above case).

The Cu-based powder in the present invention may be in any form as long as it contains element M.

It is preferable to add element M in an amount that will convert all of the P remaining in the Cu matrix of the Cu-based alloy into phosphide. Therefore, element M powder or metal may be added in accordance with the expected amount of P remaining in the molten metal, and then pulverized to form a Cu-based alloy powder.

The content (mass%) of P remaining in the produced Cu-based powder can be measured, and the powder can be mixed with a powder of element M according to the P content to produce a Cu-based mixed powder, or it can be mixed with an alloy powder containing element M to produce a Cu-based mixed powder.

The Cu-based powder in the present invention may contain tin (Sn).

Adding Sn to molten metal can lower the melting point of the alloy, further improving the fluidity of the molten metal, and can also improve the strength of the Cu matrix in Cu-based alloys.

The Sn content in the Cu-based powder is preferably 0.1% to 3.0% by mass, and more preferably 0.5% to 2.0% by mass.

If the Sn content is less than 0.1% by mass, the melting point of the alloy will not decrease and the strength of the Cu matrix will not improve. Furthermore, if the Sn content exceeds 3.0% by mass, Sn has a greater effect on thermal and electrical conductivity than P, resulting in a decrease in the thermal and electrical conductivity of the Cu-based alloy compared to when no Sn is added.

It is preferable to add Sn to the molten metal.

The content of the elements M, P, and Sn remaining in the Cu-based powder can be measured by absorptiometry or ICP atomic emission spectrometry.

The Cu-based powder used in this invention inevitably contains oxygen (O), but it is preferable to keep the O content to 0.1% by mass or less.

When the content is 0.1% by mass or less, internal oxidation of the powder is suppressed, making the Cu-based alloy less likely to develop defects or deteriorate in its properties.

The oxygen content of Cu-based powder can be measured using the inert gas fusion infrared absorption method.

The method for producing the Cu-based powder in the present invention is not particularly limited, but it is preferable to produce it using the well-known atomization method.

This results in a highly fluid molten metal, allowing for production that ensures productivity and safety.

Known atomization methods include water atomization, gas atomization, and centrifugal atomization.

A lubricant may be added to the Cu-based powder of the present invention.
Addition of a lubricant improves lubricity, making it easier to form a green compact in powder metallurgy.

The amount of lubricant added is preferably 0.1% to 1.0% by mass, and more preferably 0.2% to 0.8% by mass.

If the amount is less than 0.1% by mass, the lubricity is not significantly improved, and if the amount is more than 1.0% by mass, the sinterability decreases.
Furthermore, if the amount of evaporation of the lubricant is large, there is a risk that the sintering furnace may be soiled.

The lubricant used in the present invention is not particularly limited, but metal soaps such as zinc stearate and EBS waxes are suitable.

The following examples of the present invention are provided, but the present invention is not limited to these.

(Preparation of molten metal)
The Cu-based powders of the examples and comparative examples were prepared by heating raw copper to 1100°C or higher to make it molten, and then adding element M, phosphorus copper, and Sn powder or base metal to produce a molten metal.

(Powder production)
The alloys were produced by a water atomization method in which the molten Cu-based alloy components (molten metal) of the examples and comparative examples were dropped into contact with high-pressure water of about 15 MPa to rapidly cool and solidify them.

Example 15 was prepared by adding 1.14 mass% Co powder to 98.86 mass% Cu-based powder (Cu/P = Bal./0.3 mass%) produced by water atomization.

(Fluidity of molten metal)
The fluidity of the molten metal was evaluated by visual inspection, with samples where the drop of the molten metal did not deteriorate being rated as ◯, samples where the drop of the molten metal began to deteriorate but powder production could be continued being rated as △, and samples where the drop of the molten metal deteriorated so much that powder production had to be interrupted being rated x.

(Measurement of each element in powder)
The contents of the elements M, Sn, P, and O shown in Table 1 were obtained by measuring the respective powders produced.

Elemental values of M and Sn were measured using an ICP optical emission spectrometer iCAP7600 (manufactured by Thermo Fisher Scientific Inc.), P was measured using a spectrophotometer UV-1850 (manufactured by Shimadzu Corporation), and O was measured using an EMGA-920 (manufactured by Horiba Ltd.) using the inert gas fusion infrared absorption method.

(Heat treatment)
Each Cu-based powder in the examples and comparative examples was added with 0.3% by mass of zinc stearate as a lubricant, and then molded to a ^green density of 8.0 g/cm3. The powder was sintered by heat treatment at 1000°C for 120 minutes in a hydrogen atmosphere, then water-cooled, and then aged by again holding at 550°C for 120 minutes in a hydrogen atmosphere. After that, each sintered body was obtained by water-cooling.

(Evaluation of electrical conductivity)
The electrical conductivity (thermal conductivity) was evaluated by measuring the electrical conductivity (% IACS) converted into true density.

Each sintered body was cut into a size of 5 mm x 30 mm x 1 mm, and the volume resistance value at a terminal distance of 20 mm was measured using a resistance meter 3541 (manufactured by Hioki E.E. Corporation) to determine the conductivity converted to true density (% IACS).

The electrical conductivity (% IACS) of each Cu-based alloy was measured for examples containing element M and comparative examples not containing element M. Cu-based alloys with the same P content and containing element M whose electrical conductivity was higher than that of Cu-based alloys not containing element M were evaluated as "improved," while those whose electrical conductivity was the same or lower were evaluated as "not improved."

The Vickers hardness of the sintered bodies of Examples 5 to 8 was measured using a microhardness tester HMV-G (manufactured by Shimadzu Corporation) under a load of 25 gf.

The results are shown in Tables 1 and 2.
In Tables 1 and 2, A was calculated from the mass % of P and the phosphide listed in "M _x P _y ", and the minimum value of element M was A × 0.3 mass % and the maximum value was A × 1.2 mass %. If the content of element M in each Cu-based powder was within the range between the minimum and maximum values, a circle was indicated in the compatibility column, and if it was outside the range, an × was indicated.

As shown in Examples 1 to 15, it was confirmed that all of the Cu-based alloys produced from the Cu-based powder of the present invention had higher electrical conductivity than the Cu-based alloys produced from Cu-based powders with the same P content but without the addition of element M, as shown in Comparative Examples 2 to 4.

It was also confirmed that the addition of Sn improves the strength of the matrix.
It was observed that the molten metals of the examples to which Sn was added had improved fluidity compared to the molten metals of the examples to which Sn was not added.

In the present invention, since the alloy is produced from a molten metal containing P, the P reacts with oxygen to form a gaseous phosphate, thereby reducing the amount of oxygen, and thus preventing the deterioration of the fluidity of the molten metal due to oxygen. Therefore, the alloy can be produced by the atomization method while ensuring excellent productivity and safety.
Furthermore, since the Cu-based powder contains element M, which easily forms phosphides, heat treatment can be performed to cause the P contained in the Cu-based powder and element M to form phosphides that precipitate from the Cu matrix, thereby enabling the production of a Cu-based alloy in which P has little effect on thermal conductivity and electrical conductivity.
Therefore, the present invention has high industrial applicability.

Claims (5)

A Cu-based powder containing elements M, P, and Cu,
the element M is an element whose standard free energy of formation of a phosphide of the element M per 1 mol of phosphorus in a temperature range of 298 K to 1300 K is equal to or less than the standard free energy of formation of Cu ₃ P per 1 mol of phosphorus in the same temperature range;
Among the phosphides of the element M, the phosphide having the lowest standard free energy of formation in the temperature range is represented by M _x P _y (where x>0, y>0), and A is represented by the following formula (formula), the content of each element M in the Cu-based powder is A x 0.3% by mass or more and A x 1.2% by mass or less, the content of P is 0.01% by mass to 1.0% by mass, and the Cu-based powder contains 3.0% by mass or less (including 0) of Sn .
(Formula) A = mass % of P × (x/y) × (atomic weight of M/atomic weight of P) 2. The Cu-based powder according to claim 1 , wherein the O content is 0.1 mass % or less. The Cu-based powder according to claim 1 or 2 , which is for powder metallurgy or additive manufacturing. 4. A Cu-based powder obtained by adding 0.1% by mass to 1.0% by mass of a lubricant to the Cu-based powder according to claim 1 . 4. The method for producing a Cu-based powder according to claim 1, wherein the powder is produced by an atomization method.