Patent Application
20230020010
The present invention relates to an alloy that has resistance to an alloy in a molten state or a plastic state, particularly resistance to an aluminum alloy; and a member that uses the alloy.
For example, JIS SKD61 is used for a die that is used in low-pressure casting, gravity casting and die casting of an aluminum alloy. If the casting is repeated by the same die, damage occurs in the die. One of the main causes of the damage is erosion. It is assumed that the erosion occurs because a portion of the die, which comes into contact with the molten metal of aluminum alloy, is alloyed and the melting point is lowered.
When the erosion becomes severe, the eroded portion is repaired by build-up welding. As the repairing material, the alloy is preferable to have an erosion resistance that has a high melting point, an excellent creep resistance at high temperature. One example of this alloy is disclosed in Patent Literature 1.
While high strength and high corrosion resistance are required, a high entropy alloy (HEA) is attracting attention.
For example, Patent Literature 2 discloses an HEA formed of a multicomponent system that includes at least one selected from the group consisting of molybdenum, hafnium, tungsten, vanadium and chromium, in addition to titanium, zirconium, niobium and tantalum. It is disclosed that the HEA of Patent Literature 2 is used as a metal material for a living body.
However, the alloy disclosed in Patent Literature 2 has insufficient erosion resistance to a molten metal of the aluminum alloy or the like and mechanical strength.
Then, the present invention aims to provide: a multicomponent alloy having a resistance to an aluminum alloy or the like in a molten state, for example, an erosion resistance due to which the alloy resists reacting with the aluminum alloy in a melted state, and having a mechanical strength; and a member using the alloy.
For information, Non Patent Literatures 1 to 6 disclose technical documents which become necessary when the embodiments of the present invention will be described supplementarily. For example, Non Patent Literature 1 describes a method of simulating a process in which an atom moves on the basis of a fundamental equation in quantum mechanics, in other words, a calculation principle in the ab-initio molecular dynamics method. Electrons and atomic nuclei constituting atoms in a material follow the law of the quantum mechanics, and accordingly the properties of the material can be evaluated by this simulation. Non Patent Literature 2 refers to a method for calculating a diffusion coefficient by simulation according to the molecular dynamics method. In addition, Non Patent Literature 3 refers to a method for calculating adsorption energy by the simulation according to the molecular dynamics method. Other Non Patent Literatures 4 to 6 will be referred to in the column of Description of Embodiments, which will be described later.
The present invention relates to an alloy comprising: Nb and Mo as a first element group; and at least two elements selected from Ta, W, Ti, Hf and Zr as a second element group.
When the total of the first element group and the second element group is 100 at. %, a content range of each of the elements contained is 5 to 35 at. %.
In the alloy of the present invention, a lattice mismatch with respect to at least one of Al, Cu and Zn is 13% or more, and the migration barrier energy of dislocation is 310 kJ/mol or more.
In the alloy of the present invention, the adsorption energy with respect to at least one of Al, Cu and Zn is preferably 0.2 J/m2 or smaller.
In the alloy of the present invention, Vickers hardness (HV) is preferably 430 or higher, and thermal conductivity is preferably 25 W/(m·k) or lower.
The alloy of the present invention has a crystal structure preferably of a single type of body-centered cubic lattice structure or a plurality of types of body-centered cubic lattice structures, in the whole or in a portion. In the case of in a portion, the volume ratio is preferably 60% or more.
Furthermore, in the alloy of the present invention, the dendrite structure and the interdendritic region preferably have the body-centered cubic lattice structure.
Furthermore, in the alloy of the present invention, a short-side lattice constant is preferably 0.31 nm or larger and 0.36 nm or smaller.
Furthermore, in addition to the first element group and the second element group, the alloy of the present invention preferably includes at least one of Cr, V and Al as a third element group, and an amount of each of the elements (Cr, V or Al) contained is 5 at. % or more and 35 at. % or less. When the alloy includes the third element group, then the first element group, the second element group and the third element group in total is 100 at. %.
The alloy of the present invention is preferably used for casting of:
a single metal of any one of Al, Cu and Zn;
an alloy mainly containing a single metal of any one of Al, Cu and Zn; or an alloy containing two or more metals of Al, Cu and Zn.
The alloy of the present invention is preferably used for a member having at least one form of a die-casting die, a welding rod, a target material for surface treatment, a film and a powder.
According to the present invention, there are provided: a multicomponent alloy that has resistance to at least one of Al, Cu and Zn in a molten state or in a temperature range of warm working or hot working, including casting of an aluminum alloy, particularly has the erosion resistance and mechanical strength; and a member that uses the multicomponent alloy.
Embodiments of the present invention will be described below with reference to the accompanying drawings.
The present embodiment focuses on the lattice mismatch, which is a relative difference between lattice constants, in order to obtain resistance to an aluminum alloy in a molten state (hereinafter simply referred to as aluminum resistance in some cases). As a result, it has been found that aluminum resistance, particularly excellent erosion resistance can be obtained, by using a material having a large lattice mismatch with respect to aluminum. For information, the lattice mismatch is also referred to as an unconformable lattice, and is obtained by calculation, and the calculation method will be described later. For information, it is preferable that the material is high in a mechanical strength, in the case where a larger structure is produced by die casting, or where high temperature and low temperature are frequently repeated in order to increase productivity, because thermal stress tends to be easily concentrated. Then, as will be described later, the migration barrier energy of dislocation has been also focused on. For information, as will be described later, it is determined that the deformation of a metal material is caused by the migration of the dislocation, and the higher the barrier energy required to move the dislocation is, the more difficult it is for the metal material to be deformed, and the higher the mechanical strength is.
As for the difficulty of a reaction with the aluminum alloy in a molten state, which has been regarded most important this time, it is important that aluminum resists adsorption to the alloy (aluminum resists approaching the alloy), and resists intruding into the alloy (aluminum resists diffusing from the surface). The difficulty for aluminum to adsorb to the alloy is expressed by lowness of the adsorption energy (also referred to as detachment energy) which is disclosed in, for example, Non Patent Literature 5. The adsorption energy will be described later in detail. A dominant factor for the adsorption energy is the lattice constant and the lattice mismatch that is a relative difference between the lattice constants, as is shown in Non Patent Literature 6, for example. In other words, it can be said that the lattice constant and the lattice mismatch which is its relative difference are more dominant factors than other factors (surface energy, cohesive energy and electronegativity). Hitherto, in the field of metal materials, it has been attempted to reduce the lattice mismatch and ideally to reduce the lattice mismatch to zero in the case of a bonding strength such as interface strength between a wiring film and a barrier film of an electronic component, as an example in which the lattice mismatch is focused on is described in Non Patent Literature 5, for example. The present invention, on the contrary, is directed at obtaining the aluminum resistance, specifically, a property of resisting a reaction with molten aluminum, by increasing the lattice mismatch; and the idea is opposite to the conventional idea.
In order that the alloy increases the resistance to molten aluminum, in other words, in order that the alloy resists the reaction with aluminum when having come into contact with aluminum in the molten state, it is important to control the alloy to such a state that aluminum resists approaching the alloy and thereby to such a state that aluminum resists adsorption to the alloy. The ease for aluminum in adsorption can be evaluated by the adsorption energy which will be described below, and it can be said that the smaller the adsorption energy is, the more difficult it is for aluminum to adsorb.
In addition, it is important for enhancing the resistance that melted aluminum does not intrude from the surface and react with the alloy; and accordingly, the ease of intrusion of aluminum was evaluated by a diffusion coefficient at the time when aluminum penetrates the inside from the surface. The diffusion coefficient will be described later in detail.
In Table 1, for example, alloys of Nos. 3 to 5 (NbTa, NbTaTi and NbTaTiZrV) shall be compared; and as the number of elements constituting the alloy increases, the lattice mismatch increases, and on the other hand, the adsorption energy and the diffusion coefficient decrease.
Furthermore, a quinary alloy of No. 5 (NbTaTiZrV) formed from five elements shall be compared with a ternary alloy of No. 6 (NbMoTa) formed from three elements, and an alloy of No. 6 has a lattice mismatch equivalent to or higher than that of the alloy of No. 5, though being ternary, meaning containing fewer constituent elements than those of the alloy of No. 5. This can also be seen when an alloy (NbTaTiZrV) of No. 5 is compared with an alloy (NbMoHfZr) of No. 7 formed from four elements. In other words, Nb and Mo are considered to be a combination of constituent elements, which can increase the lattice mismatch.
Furthermore, in Table 1, alloys of No. 6 to No. 21, which contain both Nb and Mo, shall be referred to. When the alloys contain both Nb and Mo, further at least two of Ta, W, Ti, Hf and Zr, and still further at least one of Cr, V and Al, and when the number of constituent elements becomes as large as four or more, the lattice mismatch becomes large, and on the other hand, the adsorption energy and the diffusion coefficient become small.
In addition, it is preferable that an alloy resists being deformed because of resisting being broken, and in general, deformation of metals such as alloys is expressed by the migration of the dislocation, and the difficulty of deformation, in other words, the mechanical strength of the metals, is expressed by the difficulty of the migration of the dislocation. For this reason, as described in, for example, Non Patent Literature 4, the mechanical strength of a metal is represented by the migration barrier energy of dislocation. Details of a method for calculating the migration barrier energy of dislocation and the like will be described later. As for the migration barrier energy in Table 1, when a quaternary alloy of No. 7 and a quinary alloy of No. 5 are compared, the barrier energy of dislocation of the alloy of No. 7, which contains both Nb and Mo, is larger.
Alloys according to the present embodiment based on the findings described above include both Nb and Mo as the first element group, and include at least two of Ta, W, Ti, Hf and Zr as the second element group.
When the total of the first element group and the second element group is 100 at. %, the content range of each of the elements contained shall be 5 at. % or more and 35 at. % or less (hereinafter described simply as 5 to 35 at. %). The alloys including these elements have a high melting point of 1800° C. to 3000° C.
Any element constituting the first element group and the second element group is contained in a range of 5 at % to 35 at %. This range is recognized as a content of elements constituting the high entropy alloy. A preferable range of the content is 5 to 25 at %, and a more preferable range of the content is 5 to 15 at %.
The alloy according to the present embodiment can contain an unavoidable impurity. The alloy can contain the unavoidable impurities of, for example, C, N and O, each in an amount of 500 ppm or less.
[Lattice Mismatch]
In consideration of the results of erosion tests in Examples, which will be described later, it is preferable that the alloy according to the present embodiment has small adsorption energy and a small diffusion coefficient, in order to suppress that melted aluminum approaches the surface to cause the reaction or intrudes in the surface to cause the reaction; and for this purpose, the lattice mismatch needs to be 13% or more. It is preferable for the lattice mismatch to be 14% or more, and is more preferable to be 15% or more. In Examples which will be described later, the lattice mismatches of 15.5% and further 16% or more are obtained.
[Migration Barrier Energy of Dislocation]
In general, the deformation of metals is expressed by the migration of the dislocation, and the difficulty of deformation, in other words, the mechanical strength of the metals, is expressed by the difficulty of the migration of the dislocation. For this reason, as described in, for example, Non Patent Literature 4, the mechanical strength of a metal is represented by the migration barrier energy of dislocation. If the mechanical strength is large, for example, the hardness which will be described later becomes hard.
In the alloy according to the present embodiment, the migration barrier energy of dislocation is 310 kJ/mol or more.
The migration barrier energy of dislocation is one indicator that represents the mechanical strength of the alloy according to the present embodiment. Accordingly, it is preferable for the migration barrier energy of dislocation in applications requiring the mechanical strength to be 310 kJ/mol or more, is more preferable to be 330 kJ/mol or more, and is further preferable to be 370 kJ/mol or more. In Examples which will be described later, migration barrier energies of the dislocation of exceeding 400 kJ/mol and further exceeding 425 kJ/mol are obtained.
[Adsorption Energy of Aluminum]
In order that the alloy increases the resistance to molten aluminum, in other words, in order that the alloy resists the reaction with aluminum when having come into contact with aluminum in the molten state, it is important to control the alloy to such a state that aluminum resists approaching the alloy and thereby to such a state that aluminum resists adsorption to the alloy. The ease for aluminum in adsorption can be evaluated by the adsorption energy which will be described below, and it can be said that the smaller the adsorption energy is, the more difficult it is for aluminum to adsorb. The details will be described together with a simulation to be described later.
In the alloy according to the present embodiment, an adsorption energy is preferably 0.2 J/m2 or smaller.
The adsorption energy can be said to be one index showing aluminum resistance. Then, in the present embodiment, the adsorption energy is preferably set to 0.2 J/m2 or smaller. The adsorption energy in the present embodiment is more preferably set to 0.15 J/m2 or smaller, is further preferably set to 0.1 J/m2 or smaller, and is further preferably set to 0.083 J/m2 or smaller.
[Diffusion Coefficient of Aluminum]
In order to increase the resistance, it is important that melted aluminum does not intrude from the surface of and react with the alloy, and accordingly, the ease of intrusion of aluminum has been evaluated with the diffusion coefficient at the time when aluminum penetrates the inside from the surface. The diffusion coefficient can be said to be one index that indicates the aluminum resistance. The diffusion coefficient will be described later in detail.
In the alloy according to the present embodiment, the diffusion coefficient of aluminum is preferably 6.4×10−22 m2/s or smaller.
The diffusion coefficient in the present embodiment is more preferably 6.0×10−22 m2/s or smaller, and is further preferably 5.5×10−22 m2/s or smaller.
[Hardness]
Next, in the alloy according to the present embodiment, the hardness is preferably 430 or higher in terms of Vickers hardness (HV). The hardness is one indicator that represents the mechanical strength of the alloy according to the present embodiment. Accordingly, in applications where such harsh use on work is required that heating and cooling are frequently repeated, the hardness in applications where the mechanical strength is required is preferably 450 (HV) or higher, is more preferably 500 (HV) or higher, and is further preferably 550 (HV) or higher. In Examples which will be described later, hardnesses (HV) exceeding 600 (HV) are obtained.
For information, the hardness in Examples (Table 6) which will be described later is an average value of values that are measured at 30 points for one sample with a load set to 200 gf. This load corresponds to a load range in the JIS standard.
[Thermal Conductivity]
As a portion with which the aluminum alloy in the molten state comes into contact, among portions relating to the die-casting die, there is a die-casting sleeve, for example, through which an aluminum alloy in a melted state is poured into the die-casting die. It is desired that the die-casting sleeve has a satisfactory heat retaining property in addition to toughness and erosion resistance, and does not lower the temperature of an aluminum alloy in the molten state. On the contrary, there is a portion where it is better not to keep warm, but here, one object shall be to obtain a material with low thermal conductivity, for such a purpose that the alloy is used in a portion where the heat retaining property is satisfactory.
For this reason, in the alloy according to the present embodiment, the thermal conductivity is preferably 25 W/(m·k) or lower. The lower the thermal conductivity is, the more satisfactory the heat retaining property is; and the alloy is suitable for applications in which heat accumulates, for example, as in a die for low-pressure casting and die casting. Accordingly, in the application in which heat accumulates, the thermal conductivity is preferably 25 W/(m·k) or lower, is more preferably 20 W/(m·k) or lower, and is further preferably 15 W/(m·k) or lower. In Examples which will be described later, thermal conductivities of 20 W/(m·k) or smaller are obtained.
[Observation by X-Ray Diffraction (XRD)]
In any alloy according to the present embodiment, the crystal structure has a structure of a body-centered cubic (bcc) lattice. As for this crystal structure, two types of bcc structures have been observed, which are a first bcc structure indicated by black circles in
For information, the terms “first” and “second” described here are used for the purpose of distinguishing between the two, and do not limit a specific bcc structure.
In addition, in the alloy according to the present embodiment, most preferably, the whole of structure has a body-centered cubic lattice structure, but preferably 60% or more by volume ratio, and more preferably 80% or more by volume ratio of the structure have the body-centered cubic lattice structure.
[Observation by Scanning Electron Microscope (SEM)]
The alloy according to the present embodiment includes a pattern composed of a single-phase structure, and a pattern composed of a dual-phase structure having a dendrite structure.
This dual-phase structure includes a dendrite structure and an interdendritic region. For example, as shown in
As is shown in Examples which will be described later, the dual-phase structure composed of the dendrite structure and the interdendritic region is obtained in an as-melted state. It is understood that the dual-phase structure is formed because a solidification rate after melting is slow, and a single-phase structure can be obtained by the adjustment of the solidification rate. However, as is clear from Examples which will be described later, it is inferred from the peaks of XRD that even in the dual-phase structure of the dendrite structure and the interdendritic region, both of the two types are bcc structures of which lattice mismatches with aluminum are large, as will be described later; and accordingly, the alloy according to the present embodiment can obtain excellent aluminum resistance.
[Regarding Calculation of Evaluation Item]
In order to predict an effect of the present embodiment, a molecular dynamics simulation as is disclosed in Non Patent Literature 1 and the like has been carried out.
[Method for Calculating Lattice Mismatch]
The lattice constant for calculating the lattice mismatch has been defined in the following way, on the basis of Non Patent Literature 5. Specifically, a mismatch between a short-side lattice constant a and a long-side lattice constant b of the face-centered rectangular lattice has been expressed as a percentage, which represents a plane having the highest atomic number density, in other words, a closest-packed crystal plane that will be described below; and a short-side lattice mismatch has been determined as Δa, and a long-side lattice mismatch has been determined as Δb. Here, Δa is more important that has a shorter interatomic distance, and accordingly, in the present embodiment, Δa is defined as the lattice mismatch unless otherwise specified. However, in the case of SKD61 and a nitride thereof that are described in Comparative Examples which will be described later, the short-side lattice mismatch Δa with aluminum is as small as approximately 2% or smaller, but on the other hand, the long-side lattice mismatch Δb is as large as 16% or more; and accordingly, the arithmetic mean of Δa and Δb has been regarded as the lattice mismatch. In the case of the body-centered cubic structure as in the above described embodiment, the closest-packed crystal plane is the (110) plane, and a ratio of the short side a to the long side b is approximately 1:√2. On the other hand, aluminum that is the counterpart material has a face-centered cubic structure, accordingly, the closest-packed crystal plane is the (111) plane, and the ratio of the short side a to the long side b is approximately 1:√3. In addition, the closest-packed crystal plane of a hexagonal close-packed structure such as Ti is the (0001) plane, and the ratio of the short side a to the long side b is approximately 1:√3. For information, it is known from Non Patent Literature 5 and the like that crystal planes other than the closest-packed crystal plane defined here have a weak contribution to the adsorption energy, and accordingly give little influence; and accordingly, the lattice constant is determined on the basis of the closest-packed crystal plane.
The a and b can be calculated by performing relaxation calculation by the molecular dynamics simulation that is described in Non Patent Literature 5 and the like, and determining a stable crystal structure; and accordingly, the lattice mismatch defined above is calculated on the basis of the calculated a and b. The lattice constant and the lattice mismatch have been calculated with the use of self-produced molecular dynamics software, and in parallel, have been calculated with Dmol3 and Forcite of Materials Studio of Dassault Systemes Corp., and it has been confirmed that both results coincide with each other.
[Method for Calculating Migration Barrier Energy of Dislocation]
In general, the deformation of metals is expressed by the migration of the dislocation, and the difficulty of deformation, in other words, the mechanical strength of the metals, is expressed by the difficulty of the migration of the dislocation. For this reason, as described in, for example, Non Patent Literature 4, the mechanical strength of a metal is represented by the migration barrier energy of dislocation. For example, a molten metal of an aluminum alloy is injected into a die-casting die at a considerable pressure, and accordingly, the die-casting die is required to have a mechanical strength. As is shown in
[Method for Calculating Adsorption Energy]
In order that the alloy increases the resistance to molten aluminum, in other words, in order that the alloy resists the reaction with aluminum when having come into contact with aluminum in the molten state, it is important to control the alloy to such a state that aluminum resists approaching the alloy and thereby to such a state that aluminum resists adsorption to the alloy. The ease for aluminum in adsorption can be evaluated by the adsorption energy which will be described below, and it can be said that the smaller the adsorption energy is, the more difficult it is for aluminum to adsorb. The adsorption energy represents energy necessary for changing an adsorption state to a detached state, and is obtained by subtracting the energy of the adsorption state from the energy of the detached state, as shown in Expression (3) of Non Patent Literature 3. The adsorption energy has been calculated with the use of self-produced molecular dynamics software, and in parallel, has been calculated with Dmol3 and Forcite of Materials Studio of Dassault Systemes Corp.; and it has been confirmed that both results coincide with each other. This value means that the larger this value is, the easier the adsorption is.
[Method for calculating diffusion coefficient]
The diffusion coefficient has been obtained from the following expressions (A) and (B) which are Einstein's relational expressions and are shown in Expression (2) of Non Patent Literature 2.
D=limt→∞D(t) Expression (A)
D(t)=<[ri(t+t0)−ri(t0)]2>/6t Expression (B)
Expression (B) is obtained by dividing the mean-square displacement from t0 which is the reference time set after sufficient alleviation to t+t0, by 6t, and actually converges in a finite time step, and accordingly the diffusion coefficient can be calculated without being calculated up to infinity. For information, ri(t+t0)−ri(t0) can be calculated from the equation of motion. In addition, when the diffusion coefficient at which a metal intrudes in the direction perpendicular to the interface is obtained, the diffusion coefficient is calculated from the mean-square displacement of the displacement in the direction. It means that the larger the diffusion coefficient is, the easier the intrusion is. Specifically, it means, the easier it is for the molten aluminum to intrude from the surface and to react, in other words, the easier it is to erode.
The alloy according to the present invention will be described below on the basis of specific Examples.
Samples of 10 types of alloys were prepared which were described in Table 2. Alloys Nos. 34 to 40 according to Examples were produced by arc melting under the following conditions. In addition, a sample (No. 31) composed of JIS SKD61, a sample (No. 32) in which the surface of JIS SKD61 was nitrided, and a NbTaTi alloy (No. 33) were prepared as Comparative Examples. The JIS SKD61 was produced by the composition and production method according to JIS G4404, and the NbTaTi alloy (No. 33) was produced in the same manner as in Examples.
Among the alloys according to Examples in Table 2, in Nos. 34 to 36, the contents of constituent elements are equal; and in No. 40, the contents of four constituent elements (Nb, Mo, Ta, and W) are equal, and the other element is twice as much as the equal amount. In addition, alloys Nos. 37 to 39 have a composition that is obtained by simulating a combination of elements which satisfy a plurality of physical properties such as adsorption energy and thermal conductivity, although details are omitted. In the alloys Nos. 37 to 39, the contents of the constituent elements are not equal, but the sample names are described as listing the constituent elements, in order to match with others.
[Arc Melting Condition of Sample]
Each element was weighed so that the total mass became 50 g, and an ingot material was produced with the use of an automatic arc melting furnace (manufactured by DIAVAC LIMITED). In order to melt the aggregation of metal pieces, the melting was carried out through stages so as to prevent the pieces from flying up due to a sudden increase in the power of the arc. The melting was carried out for 6 cycles in total (each cycle composed of 3 steps) under an Ar gas atmosphere under the conditions shown in Table 3. In order to enhance the homogeneity of the ingot material, a mechanism was provided that turned the top and rear bottom surfaces of a sample (lump of alloy) by 180° at the end of each cycle.
The obtained samples were each subjected to an erosion test in which the sample was immersed in aluminum molten metal.
An erosion test piece having a dimension and shape of φ4.8×20 mm was cut out from the as-cast sample after arc melting, this test piece was attached to a holder, the position of the furnace body was adjusted so that the test piece was immersed in the aluminum molten metal by 10 mm, and the test was started. In addition, the test piece was attached to the outer peripheral end of a disk having a diameter of 140 mm, and was rotated and moved along an arc; and the moving speed of the test piece was set to 5 m/min, and the immersion time was set to 5 minutes. An Al—Si—Mg-based JIS AC4CH was used as the Al molten metal, and the molten metal temperature was set to 993 K.
The results are shown in Table 2.
It is understood that the alloys according to Examples have a smaller erosion rate than the alloys according to Comparative Examples and have excellent erosion resistance. For information, the erosion rate is obtained by the following expression.
erosion rate [%]=(pre-test mass−post-test mass)/pre-test mass×100
[Observation by X-Ray Diffraction (XRD)]
Crystal structures of the alloys according to Examples and Comparative Examples were observed by XRD. The outline of the result is as described above, but the following will be additionally described.
As shown in
In addition, from the XRD observation result described above, a phase other than the two bcc structures, for example, a chemical compound is not specified.
[Observation by Scanning Electron Microscope (SEM)]
Next, a composition image of the alloys according to Examples and Comparative Examples were observed by SEM. The outline of the result is as described above, but the following will be additionally described.
In Examples, respective chemical compositions of dendrites (dendritic structures) that are shown by light colors and interdendritic regions that are shown by dark colors, respective lattice mismatches with aluminum thereof, and respective area ratios thereof were specified on the basis of
For information, the interdendritic region is also referred to as an inter-dendritic structure, an inter-dendrite structure, an interpillar structure, or the like.
As is shown in Table 4, in all the samples (Nos. 34 to 40), there is a slight difference in composition between the dendrite structure and the interdendritic structure. However, in all the samples, the elements constituting the dendrite structure and the elements constituting the interdendritic structure coincide with each other. For example, in the alloy of No. 34, the constituent elements of the interdendritic structure are Mo, Nb, Ta, Ti, Zr and Hf, and the constituent elements of the dendrite structure are also Mo, Nb, Ta, Ti, Zr and Hf.
As described above, all the samples according to Examples have the two phase structure of the dendrite structure and the interdendritic structure, but as shown in the X-ray diffraction measurement result of
In the above description, when values X of the peak angles of the first bcc structure and the second bcc structure observed between 30° and 40° was converted into the short-side lattice constant a, a conversion expression of a=0.10902/sin(X/2) was used. This expression is derived by substituting a wavelength of 0.15418 nm of the CuKα ray (characteristic X-ray) which has been used for measurement, for example, into 2d sin θ=λ, which is a known Bragg's expression, substituting X/2 to θ, and using that √2 times of the interplanar spacing λ becomes the short-side lattice constant a of the bcc structure; and then a≈0000.10902/sin(X/2) can be derived.
As described above, both the two phases of the bcc structures have large lattice mismatches with respect to aluminum, accordingly, the adsorption energy of aluminum and the diffusion coefficient of intrusion of aluminum are small, and the alloys resist reacting with the aluminum in the molten state. In other words, these alloys have high erosion resistances to the aluminum in the molten state. Note that the sample of No. 33 also has a lattice mismatch of 13% or more, and accordingly has a high erosion resistance, but as shown in Table 6, is low in the migration barrier energy of dislocation and is weak in the strength.
In addition, when the lattice mismatches are compared among the samples, the lattice mismatch is higher in the dendrite structure than in the interdendritic structure.
The samples described above were subjected to the erosion test, the actual measurement of characteristics and various calculations; and the values are collectively shown in Table 6.
The alloys of Nos. 34 to 40 according to Examples are significantly excellent in an erosion rate, compared to the alloys of Nos. 31 to 33 according to Comparative Examples. The alloys of Nos. 34 to 40 according to Examples had properties that the lattice mismatch was 13% or more and the migration barrier energy was 310 kJ/mol or more; and it is understood that the alloys according to Examples had both of these two properties higher than those of the alloys according to Comparative Examples, and thereby could realize a low erosion rate. By the way, in low-pressure casting and gravity casting or the like of an aluminum alloy, a moving speed of the molten metal is kept low so as to produce castings with few defects. At this time, it is effective for keeping the flowability of the molten metal that the thermal conductivity of the portion in contact with the molten metal is low. For example, it is considered that stable casting becomes possible if the thermal conductivity is 25 W/m·K or lower, and the thermal conductivity is preferably lower. At the time of casting, the molten metal and the die surface are in contact with each other over a long period of time, and the die surface needs to have erosion resistance to aluminum; and it can be said that the alloys of Nos. 34 to 40 according to Examples were low in the erosion resistance and the thermal conductivity, and accordingly could achieve the lower erosion rate.
In the above, the present invention has been described on the basis of the embodiments and Examples, but other than the above description, the constitutions described in the embodiments can be selected or appropriately changed to other constitutions, as long as the main purpose of the present invention is not deviated from.
Although not specifically shown in Examples, it is implied that alloys containing the first element group (Nb and Mo) and the second element group (at least two of Ta, W, Ti, Hf and Zr), and alloys further containing the third element group (at least one of Cr, V and Al) listed in Table 1 are also excellent in resistance to aluminum alloy in a molten state, for example, in erosion resistance.
The alloy according to the present invention is suitably used in, for example, an application in contact with an aluminum alloy which is in a molten state. As one example thereof, there is a welding rod which is prepared when the die of the low-pressure casting has been eroded and the eroded part is repaired by welding. In addition, there is an application as a target material for surface treatment of forming a protective film composed of the alloy of the present invention, on a portion in contact with an aluminum alloy in a molten state. In addition, there is an application as a powder of the case where a repairing and protecting film is formed by powder build-up. Furthermore, it is preferable to use the alloy in, for example, an injection sleeve (die-casting sleeve), an injection plunger or the like, which pours the aluminum alloy in the molten state into the die-casting die, as a portion with which the aluminum alloy in the molten state comes into contact, among the portions relating to the die-casting die, because the alloy is excellent in the heat retaining property.
In the die for the low-pressure casting, a moving speed of the molten metal is lower than that in die casting, and a time period required for the molten metal to spread into the details of the die is longer. In such a die, the lower the thermal conductivity of the die is, the more stably the viscosity of the molten metal is kept and the melt flow is kept from the sprue to the details of the die, which are preferable.
When an aluminum alloy is plastically worked, the forming speed becomes high due to an enhancement of a cycle time, and seizure occurs in some cases due to frictional heat that is generated between a workpiece and the die during the forming process. In order to prevent such a phenomenon that the aluminum alloy is softened by the frictional heat and causes the seizure, it is useful to form a layer of a composition on the surface of the die, of which the reactivity with aluminum is low and the hardness is high. For example, it is difficult to plastically work a high-tensile steel sheet in a cold state, and accordingly, a hot stamping (hot pressing) method is used. The hot stamping method is a method of plastically working the steel sheet heated to a high temperature, and accordingly, needs to prevent oxidation of the steel sheet; and the steel sheet is subjected to aluminum plating. This aluminum-plated steel sheet is heated to 700° C. or higher and is press-formed, and accordingly the die surface is required to have low reactivity with aluminum. The alloy according to the present invention has the low reactivity with aluminum, and accordingly it is preferable that at least the layer of the die surface is formed from the alloy according to the present invention.
In the above description, the lattice constants of aluminum, the alloy and the like, and the lattice mismatch were calculated in a room temperature state, but the values in a high temperature state are only influenced by contribution due to thermal expansion, and accordingly also become almost equal values, while the value of the lattice mismatch shows a difference of only about 1% at maximum. Specifically, the error level is about 1% in the mismatch at 1000° C. The reason will be described below why the phenomenon associated with melted aluminum relates to the lattice constant of aluminum in an unmelted state.
In aluminum in the following three states, aluminum atoms having thermal energy are in a state of moving around on the alloy surface.
State 1: aluminum that is melted in a state of higher temperature than the melting point (approximately 660° C.)
State 2: aluminum that is in a high temperature (approximately 300° C. to approximately 660° C.) as a whole, though the temperature is lower than the melting point
State 3: the case where aluminum in a state of being locally heated due to frictional heat or the like, though being at a room temperature level as a whole, is in contact with the surface of the alloy
As described above, although the aluminum atoms move around, an atomic force acts on each of the aluminum atoms; and such a force as to attempt to become an interatomic spacing of the short-side lattice constant (0.286 nm) acts on the aluminum atoms to each other. On the other hand, in the NbMo-based alloys shown in Examples of the present invention, the stable interatomic spacings are 0.32 nm to 0.35 nm as shown in the short-side lattice constants of Table 5. Because of this, from the surface of these alloys, an atomic force acts on the aluminum atoms, which attempts to control the interatomic spacing between aluminum atoms to a value of 0.32 nm to 0.35 nm. In other words, an atomic force acts which attempts to widen the interatomic spacing by 12 to 22%, compared to the original interatomic spacing (0.286 nm) of aluminum. In this way, the interatomic spacing (0.286 nm) at which aluminum itself is going to become stable and the interatomic spacing (0.32 nm to 0.35 nm) of aluminum, at which the alloy surface of the present invention is going to become stable, are relatively different from each other even by 12 to 22%; and as a result, such interatomic spacing does not exist as to stabilize aluminum atoms, and consequently, it becomes difficult for aluminum atoms to be in a stable state. Because of this, the aluminum atoms remain in a state of moving around, and aluminum becomes a state of resisting adsorption to the alloy surface and resisting reacting with the alloy surface (besides, being weak in diffusion to the inside).
In contrast to this, for example, from the surface of titanium (short-side lattice constant: 0.295 nm) of which the lattice mismatch with aluminum is as small as approximately 3%, such atomic force acts on the aluminum atoms as to attempt to control the interatomic spacing of the aluminum atoms to 0.295 nm. This distance is close to the interatomic spacing of aluminum (0.286 nm), at which aluminum itself is going to become stable, and accordingly when the interatomic spacing of moving aluminum atoms becomes about this distance (0.286 nm to 0.295 nm), such a phenomenon occurs that the aluminum atom is stabilized on the titanium surface and the movement becomes slow. Thereby, aluminum is in a state of staying on the titanium surface for a long period of time, being settled thereon, and adsorbed onto the titanium surface, and the diffusion into the inside also tends to easily occur. Because of this, the reaction can easily occur. This state is a state in which the adsorption energy is large and the diffusion coefficient is also large. In this way, when the aluminum atoms moving around reach the interatomic spacing (0.286 nm to 0.295 nm), the aluminum atoms are settled in a stable state, and consequently tend to easily react with the alloy. For this reason, in order to ensure the resistance to aluminum, it is important for the die to have an alloy having a large lattice mismatch on the surface so that such interatomic spacing does not exist thereon at which aluminum atom tends to be easily stabilized.
The phenomenon as described above is a phenomenon that occurs in the vicinity of the surface of the alloy, even in the case where the whole aluminum is not at a high temperature, but the aluminum in the vicinity of the surface of the alloy is in a state of locally generating heat or in a state of easily causing plastic deformation, due to frictional heat or the like.
It should be noted that the alloy according to the present invention can be used also for applications in which an alloy comes in contact with metals and alloys with which the alloy has a larger mismatch than that with the aluminum alloy. Specific examples thereof include: copper (where short-side lattice constant is 0.256 nm) and zinc (where short-side lattice constant is 0.266 nm), which have short-side lattice constants smaller than the short-side lattice constant (0.286 nm) of aluminum; and alloys thereof.
Similarly to aluminum in Table 6 described above, the lattice mismatch, the migration barrier energy of dislocation, and the adsorption energy of the alloys according to Examples with respect to copper or zinc were calculated; and the results are respectively shown in Table 7 and Table 8.
Here, aluminum, copper and zinc have about the same level (0.255 to 0.290 nm) of short-side lattice constants (which are the same as the atomic diameters in closest-packed crystal materials), have the melting points of 1400K or lower, and have a commonality as a material which is industrially used through a forming process of a shaped material which uses a die in a casting and semi-molten state.
From Table 7, it has been found that the alloys according to Examples satisfy that the lattice mismatch with respect to copper is 13% or more as compared with conventional examples (SKD61 and nitrided material of SKD61), and that the migration barrier energy of dislocation is 310 kJ/mol or more. Here, the lattice mismatch of 25% or more, further 30% or more is obtained. At the same time, the migration barrier energy of dislocation of 330 kJ/mol or more, further 370 kJ/mol or more is obtained. The use of a material in which the lattice mismatch and the migration barrier energy of dislocation are thus large at the same time indicates that the resistance to copper or copper alloys, in particular, excellent erosion resistance, can be obtained.
In addition, similarly, from Table 8, it has been found that the alloys according to Examples satisfy that the lattice mismatch with respect to zinc is 13% or more as compared to the conventional examples and that the migration barrier energy of dislocation is 310 kJ/mol or more. Here, the lattice mismatch of 20% or more, further 25% or more is obtained. At the same time, the migration barrier energy of dislocation of 330 kJ/mol or more, further 370 kJ/mol or more is obtained. Thus, the alloys according to Examples show that the excellent erosion resistance can be obtained even with respect to zinc or zinc alloys.
Methods of pouring molten metal into a die and molding the metal as in low-pressure casting, gravity casting and die casting can be used for the purpose of molding each of aluminum, copper and zinc or alloys mainly containing these metals. Alternatively, there is also a case where each of aluminum, copper and zinc or alloys of these metals are formed by plastically working such as pressing, forging, extrusion forming or wire drawing. For any die, when molding is repeated in the same die, damage occurs in the die. There are erosion and galling as main causes of the damage. These damages occur because a part of the die is alloyed, which comes in contact with copper or a copper alloy, or zinc or a zinc alloy, and becomes fixed. These damages can be suppressed by using an alloy in which the lattice mismatch and the migration barrier energy of dislocation become large as in the present invention, as a material of the die for die casting or the like.
Examples of the alloy mainly containing each of aluminum, copper and zinc are as follows.
[Examples of Aluminum Alloy]
Al—Cu system, Al—Mn system, Al—Si system, Al—Mg system, and Al—Zn system
[Examples of Copper Alloy]
Cu—Zn system, Cu—Zn—Pb system, Cu—Zn—Sn system, Cu—Sn system, Cu—Sn—Pb system, Cu—Al system, Cu—Si system, Cu—Ni system, Cu—Zn—Si system, Cu—Al—Fe system, Cu—Al—Fe—Ni system, Cu—Ni—Fe system, Cu—Ni—Zn system, Cu—Be system, Corson copper, Cu—Ni—Si—Mg system, Cu—Ni—Si—Sn—Zn system, Cu—Ni—Si—Mg—Mn system, Cu—Ni—Si system, and Cu—Co—Si system
[Examples of Zinc Alloy]
Zn—Al—Cu—Mg system, Zn—Al—Cu—Ti—Cr—Mn—Be system, and Zn—Al—Cu—Mg—Ti—Be system
According to Table 6 to Table 8 shown above, the alloys according to Nos. 34 to 40 of Examples satisfy that the lattice mismatches with respect to the three types (first aspect) of aluminum, copper and zinc are each 13% or more, and the migration barrier energies of dislocation are each 310 kJ/mol or more. However, the present invention is not limited to these, and includes the following second aspect and third aspect.
A second aspect: the lattice mismatch with respect to any one type of aluminum, copper and zinc is 13% or more, and the migration barrier energy of dislocation is 310 kJ/mol or more.
A third aspect: the lattice mismatches with respect to any two types of aluminum, copper and zinc are each 13% or more, and the migration barrier energies of dislocation are each 310 kJ/mol or more.
Hereinafter, Application Examples of the alloy of the present invention will be specifically described. It should be noted that the member of the present invention is not limited to the applications of these Examples.
<Production of Raw Material Powder>
A plurality of raw material powders shown in Table 9 were prepared. All the raw material powders are pure metal powders that were obtained by a chemical reduction method. These raw material powders were weighed so as to become samples of Nos. 41 to 44 shown in Table 10, and a plurality of powder raw materials having different specific gravities in each raw material powder were uniformly mixed, by mixing by a V mixer for 30 minutes. The compositions in Table 10 are in at %.
<Production of Target Material for Surface Treatment>
A method for manufacturing a target material for surface treatment will be shown, which is used for physical vapor deposition (PVD).
Sintered bodies for alloy target materials were produced with the use of powders of sample Nos. 41 to 44 shown in Table 10, according to the following procedure. Each of sample Nos. 41 to 44 was charged into a die made from carbon and subjected to uniaxial pressure molding with the use of a punch made from carbon. The die was set at φ110 mm. After that, the pressure-molded body was placed in a hot press apparatus, was heated in vacuum, and was pressed and sintered under conditions of being pressurized at 11 MPa and kept for 5 hours. The sintering temperature was set at 1430° C. for Nos. 41, 42 and 43, and 1510° C. for No. 44.
The sintered body was taken out from the die made from carbon, and was machined into a molded body of φ100×10 mm thick; and thereby an alloy target material 10 shown in
For information, the target material was manufactured with the use of the sintering method in the above Example, but a manufacturing method can be adopted that forms an alloy in which segregation is reduced, for example, by using a hot-pressed cylindrical ingot as a consumable electrode, and remelting and solidifying the ingot little by little by ESR (electroslag remelting) or VAR (vacuum arc remelting). In addition, a manufacturing method can also be employed that uses a hot-pressed cylindrical ingot as an electrode, pulverizes the ingot through an EIGA (electrode induction melting gas atomization) furnace which directly melts and atomizes the ingot by induction heating, and forms an alloy by subjecting the powder to hot pressing again. In addition, in order to further densify the obtained alloy, the alloy may be subjected to hot isostatic pressing.
A coating film is formed on a die surface by a PVD method, with the use of the above described alloy target material 10 for surface treatment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-056014 | Mar 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/011706 | 3/22/2021 | WO |
