JP2023138104A - Coated member, method for manufacturing the same, and product using coated member - Google Patents

Abstract

To provide: a coated member including a hard film excellent in Al, Zn, Fe erosion resistance, fusion resistance and galling damage resistance; a method for manufacturing the same; and a product using the coated member.SOLUTION: A coated member includes a hard film in the surface layer part of an alloy base material. The hard film includes at least one kind element of a first element group consisting of Nb and Mo and at least two kind elements of a second element group consisting of Ta, W, Ti, Hf and Zr; when setting the total elements of the first element group and the second element group to 100 atom%, the content of each element is 5-35 atom%; the crystal structure of the hard film is a face centered cubic structure; and when setting the total content of all elements in the hard film to 100 atom%, the total of O, N and C is 30 atom% or more and less than 50 atom%.SELECTED DRAWING: Figure 7

Description

The present invention provides a hard coating (hereinafter referred to as "hard coating") having excellent resistance to Al, Zn or Fe melting and adhesion to the surface of an existing alloy base material (hereinafter sometimes simply referred to as "base material"). The present invention relates to a coated member formed with a coating (sometimes simply referred to as a film), a method for manufacturing the coated member, and a product using the coated member.

Wear of molds causes variations in product quality and is directly linked to reduced productivity. In particular, in applications where there is severe wear and direct contact with molten or semi-molten metals such as Al, Zn, and Fe, molds must be replaced frequently, so molds should be replaced in consideration of cost and effective use of resources. There has been a demand for longer life of special steel components.

One method to extend the life of special steel components is to apply a coating with high hardness and excellent wear resistance to the product surface, which is subject to severe wear. Conventionally, coatings have been used and developed that have a basic composition of nitrides of Cr, Ti, and V, to which other elements are added.

Here, Patent Document 1 discloses a casting member having a coating layer on at least the working surface, the base material being hot die steel or high speed steel, the outermost layer of the coating layer being mainly composed of V. Casting in which a coating layer consisting of one or more types of nitrides, oxynitrides, and carbonitrides, and further consisting of one or more types of nitrides, oxynitrides, and carbonitrides mainly composed of Cr, is formed as a layer directly above the base material. A member for use is disclosed.

Further, according to Patent Document 2, there is provided a die-casting coated mold in which the surface of a die-casting mold made of tool steel is coated with a film, and the coated die-casting mold is an oxide film having a corundum structure. It is said that molds can be provided.

Patent Document 1: Japanese Patent Application Publication No. 2006-51510
Patent Document 2: Japanese Patent Application Publication No. 2010-58135

However, conventional nitride films of Cr, Ti, and V as described in Patent Document 1 are insufficient in countermeasures against erosion, welding, and galling caused by Al, Zn, and Fe. For example, in a hot stamping process for steel plates, in order to prevent the formation of iron scale when heating non-plated steel plates, a method is used in which the plates are plated with Al or Zn and then heated and pressurized. Therefore, the mold comes into direct contact with Al and Zn on the surface of the steel plate. Therefore, there is a need for a hard coating that has excellent resistance to Al or Zn erosion and can withstand high temperatures and high surface pressures. Furthermore, in addition to direct contact with Al and Zn, the surface of the mold during molding may also come into contact with Fe of the steel plate, and in this case, resistance to reaction with Fe and resistance to fusion are required.

Furthermore, in the coated mold for die casting as described in Patent Document 2, countermeasures against melting damage and seizure (galling) caused by Al and Zn are insufficient. In the process of manufacturing Al or Zn castings, molten Al or Zn is poured into a mold, solidified, and then the casting adhered to the surface of the mold is peeled off to obtain a casting. The surface of the mold comes into direct contact with the high-temperature molten metal, and surface components may melt into the molten metal, or the mold surface may become uneven and the casting may stick. In order to suppress these problems and continue stable production, a hard coating is required that has excellent Al or Zn erosion resistance and can withstand galling damage.

In other words, the composition of conventional hard coatings lacks reaction resistance and adhesion resistance to Al, Zn, and Fe, and also has poor resistance to mechanical loads applied to the mold surface during solidification and demolding of molten metal. In order to endure, it is necessary to improve wear resistance. The compositions that have been studied so far are nitride-based hard coatings mainly composed of Cr, Ti, and V, and there remains room to study coating compositions for improving the above characteristics.

Here, in WO2021/193529, the applicant has proposed an alloy that is resistant to molten aluminum alloy and the like. WO2021/193529 contains Nb and Mo as the first element group, at least one of Ta, W, Ti, Hf, and Zr as the second element group, and the total of the elements in the first element group and the second element group is When taken as 100 at.%, the content range of the included elements is 5 to 35 at.%, the lattice mismatch with respect to at least one of Al, Cu, and Zn is 13% or more, and the dislocation migration barrier energy is 310 kJ. /mol or more are disclosed. However, it is difficult to form a film using an alloy composition with a high melting point, and there has been no study to date of forming a hard film using the alloy described in WO2021/193529, which has a high melting point. .

From the above, an object of the present invention is to provide a coated member having a hard coating having a composition excellent in Al, Zn or Fe erosion resistance, fusion resistance, and galling resistance on the surface of an alloy base material, and a method for manufacturing the coated member. , and a product using the covered member.

The present invention is a coated member having a hard coating on the surface layer of an alloy base material, and the hard coating is made of at least one of the first element group consisting of Nb and Mo, and Ta, W, Ti, Hf, and Zr. When the total of the elements of the first element group and the second element group is 100 atomic %, the content of each element is 5 to 35 atomic %. and the crystal structure of the hard coating is a Menbayashi cubic structure, and when the total content of all elements in the hard coating is 100 atomic %, the total of O, N, and C is The coated member is characterized by containing 30 at % or more and less than 50 at %.

Further, the hard coating preferably includes an A phase containing at least one type of Ti or Zr, and a B phase containing at least one type of Mo, Ta, Hf, and W.

Further, in the hard coating, it is preferable that the nitrogen content in the B phase is higher than that in the A phase.

Further, in the hard coating, it is preferable that the A phase and the B phase are arranged alternately, and the composition of each phase changes continuously.

Further, the covering member has an intermediate layer containing at least three elements selected from Nb, Mo, Ta, W, Ti, Hf, and Zr between the alloy base material surface and the hard coating. is preferred.

Moreover, it is preferable that the coating hardness of the coating member is 20 GPa or more.

Moreover, in the hard coating, it is preferable that the number of droplets is 600 or less.

The method for manufacturing a coated member of the present invention includes at least one element from the first element group consisting of Nb and Mo and at least two elements from the second element group consisting of Ta, W, Ti, Hf and Zr, A step of producing a target alloy in which the content of each element is 5 to 35 at%, when the total of the elements of the first element group and the second element group is 100 at%, and using the target alloy. The method for manufacturing the coated member is characterized by comprising the step of forming the hard coating on the surface of the alloy base material.

Further, in the method for manufacturing the covered member, it is preferable to use a PVD method as a method for forming the hard coating.

Further, in the method for manufacturing the covering member, when the melting point of the target alloy is 2000° C. or higher, it is preferable that the current value applied to the target alloy of the cathode evaporation source is 100 A or higher.

Further, the present invention is a product using the covering member.

According to the present invention, it is possible to form a hard film on the surface of an alloy base material, which has a composition excellent in resistance to Al, Zn or Fe erosion, fusion resistance, and galling resistance. It is possible to provide a coated member with excellent Zn or Fe melting resistance, fusion resistance, and galling resistance, a method for manufacturing the coated member, and a product using the coated member.

FIG. 3 is a diagram showing the relationship between the melting point and arc voltage value of target alloys of Examples and Comparative Examples of the present invention. It is a figure showing the relationship between the arc voltage value and the film-forming rate of the Example of this invention, and a comparative example. It is a figure showing the relationship between the arc voltage value and the number of droplets in Examples and Comparative Examples of the present invention. It is a figure which shows the surface observation photograph and droplet analysis image of the Example of this invention, and a comparative example. It is a figure showing film hardness and Young's modulus of an example of the present invention and a comparative example. FIG. 3 is a diagram showing the relationship between residual compressive stress and film hardness in Examples and Comparative Examples of the present invention. It is a figure which shows the observation result of the hard coating fracture surface of the Example of this invention. It is a figure showing the quantitative analysis result of the hard coating composition of the Example of this invention. It is a figure which shows the XRD evaluation result of the hard coating of the Example of this invention. FIG. 3 is a diagram showing the relationship between the crystal grain size and film hardness of a hard coating according to an example of the present invention. FIG. 7 is a diagram showing a TEM image of a cross section of the film of Example 5. FIG. 7 is a diagram showing electron beam diffraction results including each phase in a cross section of the film of Example 5.

Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments mentioned here, and combinations and improvements can be made as appropriate without departing from the technical idea of the invention.
The covering member of the present invention can be applied to various mechanical parts, molds, tools, etc. Preferably, molds for hot stamping are required to have low reactivity, corrosion resistance, adhesion resistance, and galling resistance because they come into direct contact with Al, Zn, and Fe alloys, and molds that do not cause corrosion damage due to contact with molten metal. It can be applied to easy-to-use low-pressure casting molds, die-casting molds, and friction stir welding tools that require friction and wear resistance at high temperatures.

[Coated member]
First, an embodiment of the covering member of the present invention will be described. The coated member of this embodiment is a coated member in which a hard coating (hereinafter sometimes simply referred to as a coating) is formed on the surface layer of an alloy base material (hereinafter sometimes simply referred to as a base material), and includes Nb and Containing at least one element from the first element group consisting of Mo and at least two elements from the second element group consisting of Ta, W, Ti, Hf and Zr, the first element group and the second element group When the total of the elements is 100 at%, the content of each element is 5 to 35 at%, and the crystal structure of the hard coating is a face-centered cubic structure, and the content of O, N, and C in the hard coating is 5 to 35 at%. It is characterized in that the total content is 30 atomic % or more and less than 50 atomic %.

(Composition of hard film)
The hard coating is made of Nb and Mo as the first element group, as an alloy with a high lattice mismatch, which is a relative difference in lattice constants, in order to obtain resistance to erosion, welding, and galling damage caused by Al and Zn in the molten state. Containing at least one kind and at least two of Ta, W, Ti, Hf and Zr as a second element group, when the total of the elements of the first element group and the second element group is 100 atomic %, The amount of each element contained is 5 atomic % or more and 35 atomic % or less.

Here, it is preferable that the ratio of each element selected from the first element group and the second element group in the hard coating is equimolar. When the ratio of each element approaches an equimolar ratio, the properties of a high entropy alloy (HEA), which is attracting attention as having high strength and high corrosion resistance, are more likely to be exhibited. That is, the present alloy system has increased resistance to melting loss and galling damage caused by Al and Zn in a molten state. In addition to these, resistance to galling damage due to Fe fusion resistance and adhesion resistance increases. When a film is formed, these metal components react with light elements such as O, N, and C to form a film as an oxide, nitride, carbide, oxynitride, or carbonitride.

Here, when all the elements in the hard coating are 100 atomic%, the total content of O, N, and C should be less than 50 atomic%, since the hard coating has metallic properties, the toughness can be improved. can be increased. Furthermore, if the total content of O, N, and C in the hard coating is less than 30 atomic percent, it will have mainly metallic properties, so it will be difficult to obtain resistance to Al and Zn in the molten state, and hardness will not be obtained. Hard to get caught. Therefore, the total content of O, N, and C in the hard coating is 30 atomic % or more and less than 50 atomic %.

Further, the hard coating of this embodiment may contain inevitable impurities. The hard coating may contain metal elements and light elements on the order of ppm as inevitable impurities.

The alloy composition can be analyzed using an Electron Probe Micro Analyzer (EPMA). In particular, when analyzing hard coatings containing light elements such as O, N, and C, quantitative analysis can be performed using a wavelength dispersive X-ray spectrometer (WDX).

(Hard film structure)
The hard coating may include an A phase containing at least one of Ti or Zr, and a B phase containing at least one of Mo, Ta, Hf, and W. At this time, it is preferable that the A phase and the B phase are alternately formed in the film growth direction. By repeating the two types of phases, when an excessive load is applied to the film surface, a phenomenon occurs in which destruction progresses between the phases, so it is possible to suppress destruction of the entire film. Here, by setting each phase to an appropriate layer thickness, resistance to destruction can be increased. When the layer thickness is small, the effects of the boundaries between each phase are less likely to occur, which tends to lead to large fractures. On the other hand, if the layer thickness is large, the fracture size is large to begin with, making it difficult to obtain the effect of improving wear resistance. Therefore, the thickness of each phase in the growth direction is preferably repeated every 10 to 100 nm, more preferably every 20 to 60 nm. The thickness of these layers can be confirmed, for example, by observation using an electron microscope.

(Crystal structure of hard coating)
The crystal structure of the hard coating formed is mainly a face-centered cubic structure. Since the face-centered cubic structure has a larger number of slip planes than other crystal structures, it has high toughness when used as a structural material and is less prone to large wear due to fracture. The crystal structure can be evaluated by X-ray diffraction (XRD). Here, "mainly having a face-centered cubic structure" means that as a result of XRD evaluation, when comparing the sum of the three strong lines of the spectra showing each crystal structure, the spectrum showing the face-centered cubic structure accounts for 50% or more of the whole. It means that. Preferably it is 80% or more, more preferably 95% or more.

(Hardness of hard film)
The hardness of hard coatings can be measured with a nanoindenter. In order to improve galling resistance, it is preferably 20 GPa or more. More preferably it is 25 GPa or more, and still more preferably 30 GPa or more. If the hardness becomes too high, the toughness of the film will decrease and wear in the form of destruction will occur, so it is preferably 50 GPa or less.

(Hard film droplet)
Droplets are molten particles that inevitably get mixed into hard coatings, and can be confirmed by surface observation. Since droplets cause deterioration of surface roughness, the number of droplets observed on the hard coating surface can be 600 or less in a field of view of approximately 200 μm x 280 μm observed at 500 times magnification. Preferably it is 500 or less, more preferably 450 or less.

(Type of alloy base material)
The alloy base material that forms the hard film is not particularly limited, but if the hardness of the base material is high, the film formed on the surface may be deformed and destroyed when a load is applied to the film formed on the surface. It is preferable that the HRC is 40 HRC or more in order to suppress the occurrence of damage. For example, mold steels, cutter steels, and alloys that provide high hardness such as SKD61, SKD11, SKH51, and cemented carbide are preferable. It is also effective to increase the surface hardness by subjecting the base material to nitriding, carburizing, or the like.

[Production method]
Next, a method for manufacturing a covering member according to an embodiment of the present invention will be described.
(solidification of alloy)
First, a composition containing at least one of Nb and Mo as a first element group and at least two of Ta, W, Ti, Hf, and Zr as a second element group is determined, and the desired composition is determined. Blend raw material powder. As a method for melting and solidifying the raw material powder, for example, a method may be used in which the powder raw materials are mixed, press-molded, and then sintered and solidified by hot pressing, discharge plasma sintering, or the like.

Alternatively, a method may be used in which the raw material powder is filled in a crucible and melted and solidified by an arc method, a high frequency heating method, etc., or a cylindrical ingot hot-pressed after mixing the powder materials is used as a consumable electrode, It is also possible to pulverize the material through an EIGA (electrode induction melting gas atomization) furnace that directly melts and atomizes it by induction heating, and then alloys it again by hot pressing.

Furthermore, after mixing the raw material powders, a hot-pressed cylindrical ingot is used as a consumable electrode, and by ESR (electroslag remelting) or VAR (vacuum arc remelting), they are gradually remelted and solidified to form an alloy. You can also use methods. When this method is adopted, it is preferable to re-melt and solidify the material little by little because segregation during alloying can be reduced.

The thus solidified alloy can be machined and used as a target alloy for physical vapor deposition (PVD) methods. Here, before machining the solidified alloy, a step of densifying the alloy by hot isostatic pressing (HIP) may be performed. Alternatively, the raw material powder may be sealed in a can and directly solidified by hot isostatic pressing.

(Film forming method)
A PVD method can be used as a method for forming the hard film. The PVD method is a method in which a target alloy is vaporized by electrical discharge or sputtering, and is adhered to a target base material at the atomic level. In particular, the cathode arc method is preferable for uniformly forming a multi-element hard coating because the target alloy is melted in a vacuum and turned into plasma to form a film. On the other hand, when forming a film using other methods of PVD, a hard film is obtained by evaporating a multi-element target alloy and depositing it on the surface of the alloy base material. Due to the difference, the target alloy does not evaporate uniformly, making it difficult to form a uniform hard film. That is, by forming a film using the PVD method, particularly the cathode arc method, even if the structure of the target alloy is not homogeneous, it is possible to form a film more uniformly than with other coating methods, which is preferable. Since the variation of each element with respect to the target composition can be adjusted to within 20%, preferably within 10%, this method is more suitable for synthesizing a high entropy composition such as the present coated member.

(Film forming conditions)
The cathode arc method of the PVD method is a technology in which arc discharge is generated in a cathode evaporation source with a target alloy installed in the cathode part, and the target alloy is ionized and formed into a film. It consists of arc spots. When using an alloy containing high melting point elements such as Ta, W, Ti, Hf, and Zr as the target alloy, it is difficult to stably maintain the arc spot on the target alloy during film formation because the alloy itself has a high melting point. becomes important. In order to stably generate and maintain an arc spot in a high-melting point material, high electrical energy is required for the arc spot, and for this purpose, the average magnetic flux density on the target alloy must be controlled by a low magnetic field of 5 mT or less. Preferably, a cathode evaporation source is used. The current value applied to the high melting point target material of the cathode evaporation source is preferably 100 A or more, more preferably 150 A or more. During film formation, gases such as nitrogen and argon are also introduced into the furnace. On the other hand, if the furnace pressure is increased excessively, it becomes difficult for metal ions generated from the cathode evaporation source to sufficiently reach the surface of the alloy member, so it is desirable that the furnace pressure is 2 to 15 Pa. More preferably, the pressure inside the furnace is 5 to 8 Pa. In this way, by using the PVD method and selecting appropriate conditions, it is possible to form a film of a high-melting point, high-entropy alloy with a homogeneous composition on a base material.

[Applications/Products]
There are no particular limitations on the uses or products using the coated member of the present invention. By appropriately selecting the manufacturing method, it is possible to obtain mechanical properties, wear resistance, and erosion resistance depending on the application.

Examples of applications include mold parts that have sufficient corrosion resistance, adhesion resistance, and mechanical strength against molten metals such as aluminum alloys and zinc alloys, and have excellent galling resistance, as well as mold parts that have excellent wear resistance and galling resistance. Press dies, forging dies, mandrels used for extrusion molding, drawing dies used for wire drawing, rotary tools used for friction stir welding of aluminum alloys and aluminum and steel plates, etc.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Note that the present invention is not limited to these examples.

[Experiment 1]
(Preparation of target alloy)
Raw material powders of Nb, Mo, Ta, W, Ti, Hf, and Zr were prepared. All of these raw material powders are pure metal powders obtained by chemical reduction methods. These raw materials were weighed so as to have the target alloy composition listed in Table 1, and mixed for 30 minutes using a V-mixer to uniformly mix a plurality of powder raw materials with different specific gravities within each raw material powder.
Next, sintered bodies of alloys having the compositions of the respective examples were produced in the following procedure. The mixed raw material powder was filled into a carbon die and uniaxially press-molded using a carbon punch. The die had a diameter of 110 mm. Thereafter, it was placed in a hot press apparatus, heated in vacuum, pressurized at 11 MPa, and subjected to pressure sintering under conditions of holding for 5 hours. The sintering temperature was 1430°C.
The sintered body was taken out from the carbon die and machined into a molded body having a diameter of 100 mm and a thickness of 10 mm to obtain a target alloy. Thereafter, a target alloy was bonded onto a backing plate of oxygen-free copper using a brazing material (In), and this was used as a target for PVD film formation.

(PVD film formation process)
First, 45HRC DAC (manufactured by Hitachi Metals, Ltd., DAC is a registered trademark), which is a material equivalent to SKD, was prepared as an alloy base material. The film forming apparatus used was an arc ion plating apparatus (AIP-S20, manufactured by Kobe Steel Corporation), and Cr was used as a target for film forming and metal ion bombardment, and the above-mentioned PVD film forming target was prepared as a target for hard components. . Before forming a hard film on the base material, the surface of the base material was polished to an average roughness of Ra=0.05 μm and Rz=0.1 μm, and then degreased and cleaned, and then fixed to a base material holder.

Then, the base material was heated to around 500° C. using a heating heater installed in the chamber and held for 50 minutes. Next, Ar gas was introduced, a bias voltage of -200V was applied to the substrate, and plasma cleaning treatment (Ar ion etching) was performed for 20 minutes. Subsequently, the bias voltage applied to the base material was changed to -800V, and Ar ion etching was performed for about 20 minutes.

Subsequently, film forming conditions, ion etching conditions, etc. were adjusted to produce an example of the present invention. The PVD film forming target was placed on a cathode (normal cathode) on which an electromagnetic coil was arranged.
Among the film forming conditions, the substrate temperature was set at 500°C, the reaction gas was nitrogen, the substrate bias voltage was set at -100V, the pressure was set in the range of 5.0 to 10.0 Pa, and the discharge current was in the range of 100 to 160 A. A value suitable for the film was selected, and the film was formed on the surface of the substrate for 30 minutes, aiming for a film thickness of about 3 to 4 μm.

Table 1 shows the film-forming conditions of Examples and Comparative Examples and the situation when applying a discharge to the cathode evaporation source. Furthermore, as a reference example, film formation conditions when film formation could not be performed are also shown. Details of each item in Table 1 are shown below.
Target alloy composition: Indicates the composition of the target alloy used.
Melting point: Melting point calculated from a calculated phase diagram using Thermo-Calc.
Pressure: Indicates the pressure inside the device during film formation.
Arc current: Indicates the arc current value during film formation.
Arc voltage: Indicates the arc voltage value applied to the cathode evaporation source under each film forming condition.
Work temperature: Indicates the actual temperature of the coated substrate itself, which rises in temperature due to reaction heat during film formation. Regarding the control parameters, the heater heating temperature is controlled at 450°C.
Possibility of film formation: Indicates whether film formation is possible. Examples and comparative examples are conditions under which film formation was successful, and conditions under which film formation was not possible are used as reference examples.
Discharge status: Indicates the status of arc discharge during film formation.

From Table 1, it can be seen that all of the Examples had melting points of 2000° C. or higher, which were higher melting points than comparative examples with conventional material compositions. Further, in Examples 2, 4, and 6, although film formation was successful, arc discharge was unstable. Therefore, the workpiece temperatures that could be measured are listed.

Figure 1 shows the relationship between the melting point of the target material and the arc voltage applied to the cathode evaporation source during arc discharge. In both Examples and Comparative Examples, as the melting point of the target alloy increases, the arc voltage value required to maintain stable arc discharge at the cathode evaporation source increases. All of the examples are high melting point target alloys with melting points of 2000°C or higher, and if the arc current value to be controlled is low, the electrical energy required to maintain the arc spot will be insufficient, resulting in unstable or unstable arc discharge. There was a tendency for discharge to become impossible. Therefore, application of a high current value is stable for arc discharge to the high melting point target material. Specifically, 150A or more is preferable.

(Measurement of various properties of hard coating)
Various physical properties were measured for the hard coating coated under each of the above film forming conditions. Table 2 shows each physical property value. Here, in Examples 2, 4, and 6, the arc discharge was unstable as described above. Therefore, what was able to be measured for each physical property is described.

(film formation rate)
The film-forming rate is the film-forming thickness per unit time, and a higher film-forming rate is preferable because the time required to obtain the desired hard coating can be shortened.
The film thickness was measured using a CALOTESTER (manufactured by CSM) for the film produced by discharging for 30 minutes under each film-forming condition, and calculated as a film-forming rate (μm/min).
FIG. 2 shows a diagram of the relationship between film formation rate and arc voltage. The nitride film formed using the high melting point target alloy of the example has a faster film formation rate than that of CrN, TiN, and AlCrN of the comparative example. Furthermore, from FIG. 2, it can be seen that the film formation rate increases in proportion to the increase in arc voltage value. That is, since the target alloy of the example has a higher melting point than that of the comparative example, the arc voltage required for arc discharge is also higher, and the film formation rate is also higher accordingly. Therefore, it is presumed that the present invention using a target alloy with a high melting point is effective in improving the film formation rate.

(Droplet area ratio and quantity)
Droplets are molten particles generated from the cathode evaporation source and inevitably mixed into the hard coating, and since they deteriorate the surface roughness, it is preferable that the area ratio and number of droplets are low.
The surface of the film coated under each film formation condition was observed at 500x magnification using a laser microscope, and the spherical shape of the droplets within the field of view was detected using image analysis software. The droplet area ratio divided by the area (210.93 μm×281.33 μm) and the number of droplets within the visual field were calculated.
Figure 3 shows a diagram of the relationship between arc voltage and the number of droplets. In the Examples, it was found that the number of droplets remaining on the film surface after film formation tended to be smaller than in the Comparative Examples, and in particular, a large improvement was observed in terms of the number of droplets compared to the Comparative Examples. Moreover, from FIG. 3, it can be seen that the number of droplets decreases in proportion to the increase in the arc voltage value. That is, since the target alloy of the example has a higher melting point than that of the comparative example, the arc voltage required for arc discharge is also higher, and the number of droplets is accordingly smaller. Therefore, the present invention using a target alloy with a high melting point can be expected to improve the number of droplets.

Figure 4 shows surface observation photographs and droplet analysis images of each film. The cause of droplets is that when metal ions are generated by arc discharge from a cathode evaporation source, particles generated as molten metal particles without being ionized are contained in the coating. For example, in the field of Al die casting, when a coated mold is immersed in molten Al, it is known that droplets in this film preferentially react with Al, causing Al melt loss of the coated mold. In addition, the droplets themselves are a defect in the film, and since the film density decreases, it is thought that this also leads to Al melt loss. Compared to the comparative example, the example has fewer droplets, and since a high melting point target material is used as a starting material, the melting point of the droplets themselves generated in the film is also high. Therefore, the examples can be expected to be nitride films with excellent resistance to Al, Zn, or Fe erosion and reaction resistance.

(hardness and Young's modulus)
The hard coating in the present invention preferably has high hardness and Young's modulus in order to obtain wear resistance.
The hardness and Young's modulus were measured using an ultra-microhardness meter (nanoindentation) on the surface of the coated member of each example under a load of 10 mN, and were calculated from the average of 15 measurements.
Figure 5 shows the nanoindentation measurements of each film. From FIG. 5, the hardness of the present invention is 33.30 to 39.60 GPa, which is significantly higher than that of general nitride films such as TiN and AlCrN. Furthermore, it can be seen that the Young's modulus tends to increase accordingly. Under the usage environment of Al die-casting, wear of the film upon contact with molten Al is also a concern, so a high hardness film like the one in the example is an effective measure in terms of wear resistance.

(Residual compressive stress)
Since the presence of residual compressive stress improves fatigue resistance and wear resistance, it is preferable that the residual compressive stress is large.
A 10 mm x 24 mm x 1 mm carbide plate-like substrate (EW07) was coated under each film formation condition, and the residual compressive stress of the film was calculated from the amount of deflection and other physical properties of the plate-like substrate based on the Stoney-Hoffman formula. was calculated.
FIG. 6 shows a diagram of the relationship between residual compressive stress and film hardness for each film. All of the examples have high residual compressive stress, and this value is also correlated with the hardness of the coating, so residual compressive stress is one of the factors contributing to the high hardness of the coating of the examples. It is thought that there are.

FIG. 7 shows the observation results of the fractured surface of each film of the present invention using a scanning electron microscope (SEM) (left: SEM image, right: backscattered electron image). The relatively smooth fracture surface morphology suggests that the structure within the film is homogeneous and that the influence of grain boundaries, which have brittle characteristics, is small. This contributes to stable wear.

(Measurement of film composition)
In order to confirm the chemical composition of the formed hard film, the chemical composition of the hard film was measured by EPMA.
FIG. 8 shows the results of quantitative analysis of the film composition of each example by EPMA. For quantitative analysis, a wavelength dispersive X-ray spectrometer (WDS) was used as a detector. It was confirmed that each metal component was the same as the target composition, and was contained in approximately equimolar amounts. Further, it can be seen that the N content is about 40 at%, and the proportion of metal components is high.
Regarding the film hardness mentioned above, it was found that the hardness of the example was significantly higher than that of the conventional material, but this was because the hard film of the example had metallic properties and that each metal element was It is presumed that one of the reasons is that it has a high entropy composition containing approximately equimolar amounts.

(Crystal structure of hard coating)
XRD measurement was performed to confirm the crystal structure of the formed hard film. FIG. 9 shows the XRD evaluation results of each example. All of them were confirmed to have only a face-centered cubic structure, and were mainly oriented in the (111) plane. Table 3 also shows the (111) and (200) planes calculated from the XRD diffraction peaks. Information on crystal grains oriented in In Table 3, 2θ is the peak position in FIG. 9, d is the lattice spacing, a is the lattice constant, FWHM is the half width of the peak at 2θ, and the crystal grain size is the crystal grain size and orientation calculated from FWHM based on the Scherrer formula. The ratio indicates the proportion of crystal grains oriented in the (111) plane or the (200) plane.
From Table 3, the crystal grain size is 6.27 nm to 8.95 nm for crystal grains oriented in the (200) plane, and it can be judged that the crystal grains are finer than those of the conventional material.
Further, FIG. 10 shows a relationship diagram between crystal grain size and film hardness. As shown in Figure 10, there is a correlation between the crystal grain size and film hardness, and it is thought that grain refinement, in addition to the residual compressive stress mentioned above, also contributes to the high hardness of the film of the present invention. It will be done.

(Surface condition of hard coating)
FIG. 11 shows a high-magnification observation result (TEM image) of a cross section of the film of Example 5 using a transmission electron microscope (TEM). It was confirmed that the black phase present at analysis position 1 was phase A, and the white phase present at analysis position 2 was phase B, and that each phase was formed with a thickness of about 20 μm while alternating compositional gradients.
Further, Table 4 shows the composition analysis results at analysis positions 1 and 2 in FIG. For the compositional analysis, an energy dispersive X-ray spectroscopy (EDS) detector attached to the TEM was used. From Table 4, the A phase at analysis position 1 contains many elements such as Nb, Ti, and Zr, which have smaller atomic weights than other metal elements in the film. On the other hand, it was found that the B phase at analysis position 2 contains many elements with larger atomic weights than other metal elements in the film, such as Ta and Hf.
Further, FIG. 12 shows the electron beam diffraction results including each phase within the same field of view as in FIG. 11. Since multiple diffraction spots appeared, it was confirmed that the material was composed of microcrystals and exhibited a uniform structure from the base material to the vicinity of the surface.

Although the reason why the hard coating of Example 5 exhibits the surface structure shown in FIG. 11 is not clear, it is presumed that it is due to the film forming conditions. The target alloy in the example is a high-entropy alloy, and in order to form a film so that the non-equilibrium composition does not undergo phase separation, it is possible to form a film by attaching gas plasma to the surface of the alloy base material, such as the cathode arc method. is valid. However, since the film forming conditions were very severe, it is presumed that Example 5 had a surface structure as shown in FIG. 11 as a result of phase separation of the non-equilibrium structure.

Claims (9)

A coated member having a hard coating on the surface layer of an alloy base material,
The hard coating contains at least one element from the first element group consisting of Nb and Mo and at least two elements from the second element group consisting of Ta, W, Ti, Hf and Zr, and and when the total of the elements of the second element group is 100 atomic %, the content of each element is 5 to 35 atomic %,
The crystal structure of the hard coating is a face-centered cubic structure;
When the total content of all elements in the hard coating is 100 at%, the total content of O, N, and C is 30 at% or more and less than 50 at%;
A covering member characterized by: The hard coating according to claim 1, characterized in that the hard coating comprises an A phase containing at least one type of Ti or Zr, and a B phase containing at least one type of Mo, Ta, Hf, and W. Covering member. The coated member according to claim 2, wherein in the hard coating, the nitrogen content is higher in the B phase than in the A phase. 4. The coated member according to claim 2, wherein in the hard coating, the A phase and the B phase are arranged alternately, and the composition of each phase changes continuously. Claim characterized in that an intermediate layer containing at least three elements selected from Nb, Mo, Ta, W, Ti, Hf, and Zr is provided between the surface of the alloy base material and the hard coating. The covering member according to any one of items 1 to 4. The coated member according to any one of claims 1 to 5, wherein the hard coating has a hardness of 20 GPa or more. A method for manufacturing a coated member having a hard coating on the surface layer of an alloy base material, the method comprising:
At least one element from the first element group consisting of Nb and Mo and at least two elements from the second element group consisting of Ta, W, Ti, Hf and Zr, the first element group and the second element A step of producing a target alloy in which the content of each element is 5 to 35 at% when the total of the group elements is 100 at%;
forming the hard coating on the surface of the alloy base material using the target alloy;
A method for manufacturing a covered member, comprising: 8. The method for manufacturing a coated member according to claim 7, wherein a PVD method is used for forming the hard coating. The method for manufacturing a coated member according to claim 7 or 8, characterized in that when the melting point of the target alloy is 2000° C. or higher, a current value applied to the target alloy of the cathode evaporation source is set to 100 A or higher.