JP4394625B2 - Mold surface protection film - Google Patents

Description

The present invention relates to a protective film formed on the surface of a mold .

  Conventionally, a hard protective film made of a transition metal nitride such as TiN or TiAlN has been formed on the surface of a mold used for die casting or hot extrusion. However, although the above protective film is hard, there is a problem in durability because of insufficient lubricity and good wettability. In other words, the reaction with the molten metal occurs, and a part of the molten metal is deposited, which causes a problem in product accuracy and requires maintenance of the mold, making it difficult to operate continuously for a long time. Further, the protective film and the mold itself were worn out from the welded portion, and the life of the mold was not sufficient.

As another technique, there is a TiBN film that is a mixed phase of TiN and TiB ₂ (Patent Document 1).
JP 2004-1215 A

However, TiN and TiB ₂ are hard films, and increase the hardness by the combination of the hard films. As a protective film for the mold surface, there is a problem in durability like other materials.

As another technique, a voltage is applied between a conductive electrode and a material to be processed in a working fluid having a dielectric strength to generate a discharge, and a treatment layer is formed on the surface of the material to be processed by the thermal action of the discharge. There is a discharge surface treatment method that forms Ti and a constituent material of an electrode and a working fluid that contains TiAlN as a hard material and BN as a lubricating material (Patent Document 2).
JP 2001-279465 A (Claim 7)

  The principle of the electrical discharge surface treatment method is that the electrode for electrical discharge machining is made of a metal (conductor) such as Ti, so that Ti in the electrode reacts with carbon in the oil to become TiC and adheres to the material to be treated. . Therefore, although the discharge surface treatment method described above is described as if a film made of Ti, Al, N, and BN is formed, an electrode of TiAlN that is a material having a large electric resistance is actually manufactured. In addition, it is difficult to disperse BN in TiAlN by this method because the lubricating material such as BN is also an insulator.

  The invention of claim 1 has been developed in consideration of the above circumstances, and its purpose is to improve the durability of the mold, to have a certain degree of high hardness, to improve lubricity, and to improve wettability. It is to form a protective film for the mold surface that reduces the reactivity and weldability.

The invention of claim 1 comprises forming a hard protective film containing Ti, B, and N as essential elements on a metal surface by a vapor phase thin film forming method, and containing one or two elements of Al or Si, The hard protective film consists of a NaCl-type crystal phase containing Ti and N as essential elements and one or two elements of Al or Si, and a BN phase having an amorphous or microcrystalline hexagonal structure. Is a mixed film in which a NaCl-type crystal phase and a BN phase are three-dimensionally mixed, and is a protective film for a mold surface used for an aluminum or magnesium die casting or extrusion mold.

  “A NaCl-type crystal phase containing Ti and N as essential elements and containing one or two elements of Al or Si” refers to a TiAlN phase, a TiAlSiN phase, or a TiSiN phase. The TiAlN phase has a high plastic deformation hardness of about 30 GPa and a high oxidation resistance. The same can be said for the TiAlSiN phase and the TiSiN phase, and the oxidation resistance is improved as compared with the TiAlN phase. In order to maintain high hardness, it is desirable that these NaCl-type crystals have a crystal grain size of approximately 30 nm or less determined by X-ray diffraction.

  The BN phase consists of microcrystals having an amorphous structure or a hexagonal structure, and is very soft with a plastic deformation hardness of 1 GPa or less and has almost no effect of increasing the hardness of the film, but has a solid lubricity, Since the wettability with metal is poor, metal welding can be prevented. In order to achieve the object of the present invention, it is sufficient that both the NaCl-type crystal phase and the BN phase are mixed to the extent that they can perform their respective functions, and it is necessary to completely separate the components of these two phases. Absent. Further, in the film forming process, the NaCl-type crystal phase and the BN phase cross each other at the interface, so that it is impossible to completely separate the two phases. Therefore, it is naturally possible that some components are mixed in between the NaCl-type crystal and the BN phase composed of a microcrystal having an amorphous structure or a hexagonal structure.

  Since the BN phase has solid lubricity and inhibits wetting with metals, these effects can be obtained when the volume ratio of the BN phase is large, but on the other hand, the hardness decreases, so in some cases The hardness may be insufficient for a mold. In order to prevent these, the volume ratio of the BN phase is preferably more than 0% and 50% or less so that a plastic deformation hardness Hpl of 10 GPa or more can be obtained. In order to make the BN phase effect more effective, the proportion of the BN phase is preferably 5% or more, and more preferably 10% or more. On the other hand, the plastic deformation hardness is desirably 10 GPa or more in the portion of the mold to which a greater pressure is applied, and the proportion of the BN phase is desirably 40% or less, and more desirably 35 in order to obtain a harder protective film. % Or less is good.

  Specific examples of the application range related to the die include an aluminum die casting die, a magnesium die casting die (movable die, fixed die, and cast pin), an aluminum extrusion die, and the like.

The NaCl-type crystal phase and BN phase containing Ti and N as essential elements and containing one or two elements of Al or Si are mixed films in which the respective phases are three-dimensionally mixed .

The invention of claim 1 has good lubricity while maintaining a certain degree of high hardness by combining the advantages of the TiAlN phase, TiAlSiN phase or TiSiN phase and the advantages of both the BN phase on the film surface . Poor wettability is exhibited, welding of molten metal to the mold is suppressed, the durability of the mold is improved, and maintenance of the mold becomes unnecessary for a long time.

The invention of claim 2 can further improve the good lubricity and the poor wettability while achieving a plastic deformation hardness of 10 GPa or more.

  Using a Ti-Al (Ti51.0% -Al49.5% residual impurity) target and a 99.0% h-BN target, two-way simultaneous sputtering is performed, and the substrate facing the target is continuously rotated at a rotation speed of 30 rpm. This produced a protective film on the substrate surface. Flow a mixed gas of argon and nitrogen (mixing ratio 10:25), connect a DC power source to the Ti-Al target and a high-frequency power source to the h-BN target at a gas pressure range of 0.1 to 0.5 Pa. A power of 1 kW was applied, and a TiAlBN mixed film having a thickness of 3 microns was formed on the surface of the substrate using a steel tool (casting pin). The mixing ratio estimated from the film formation rate of TiAlN and h-BN was TiAlN: h-BN = 7: 1.

＊：窒化処理材は2300回で使用不能になる程度に溶湯が付着した。○：良、△：可（使用可能）、×：不可（使用不能）。 Table 1 below compares the protective film of Example 1 described above with other protective films. As a comparative example, the same substrate as in Example 1 was used, and each protective film of CrN, TiN, and TiAlN with a thickness of 3 microns was attached by sputtering, or by the discharge surface treatment method (EDC method) described in the background art. The one with a TiC protective film and one with only nitriding applied to the substrate were used. The substrates with the protective films of Example 1 and the comparative example were compared after casting 3000 times as cast pins for aluminum die casting. In comparison, the state in which aluminum and oxides thereof were adhered was visually determined, and the weight of the deposit was measured.

*: The molten material adhered to the extent that the nitriding material could not be used after 2300 times. ○: Good, Δ: Acceptable (usable), ×: Impossible (unusable).

  By using the Ti-Al (Ti51.0% -Al49.5% remaining impurity) target and the 99.0% h-BN target to carry out dual simultaneous sputtering and rotating the substrate intermittently at a fixed angle, A laminated protective film in which TiAlN films and h-BN films were alternately stacked on the substrate surface was formed. Flow a mixed gas of argon and nitrogen (mixing ratio 10:25), connect a DC power source to the TiAl target, a high-frequency power source to the h-BN target, and a high frequency power source to the DC power source. About 1.2 kW, about 700 W of power is applied to the high frequency power supply, a steel tool (cylindrical cast pin with a diameter of 10φ) is used for the substrate, and a 3 micron thick TiAlN / h-BN laminated film on the substrate surface The film was formed. The thickness of each layer of TiAlN and h-BN was 5 nm and 1 nm, respectively, and this was repeated 500 times (1000 layers).

Table 2 below compares the protective film of Example 2 described above with other protective films. As a comparative example, the same substrate as in Example 2 was used, and a protective film of CrN, TiN, TiAlN with a thickness of 3 microns was attached by sputtering, and a protective film of TiN with a thickness of 3 microns was attached by the PCVD method. Used. After the substrate with the protective film of Example 2 and the comparative example was used 3000 times as a casting pin for magnesium die casting, the central portion of the contact portion with the molten metal was cut, and the circumferential portion of the cross section was scanned with an electron microscope Was observed, and the number and length of defect portions were measured, and the results were compared.

  Simultaneous sputtering with Ti-Al (Ti51.0% -Al49.5% remaining impurities) target and 99.0% purity h-BN target and mixing by rotating the substrate continuously at a rotation speed of 30 rpm A membrane was formed. Flow a mixed gas of argon and nitrogen (mixing ratio 10:25), connect a DC power source to the TiAl target, a high frequency power source to the h-BN target, and a high frequency power source to the DC power source in a gas pressure range of 0.1 to 0.5 Pa. A power of 1.0 kW and 800 W was applied to the high-frequency power source, and a steel tool (core pin) was used for the substrate, and a 3 micron thick TiAlBN mixed film was formed on the substrate surface. The mixing ratio estimated from the film formation rate of TiAlN and h-BN was TiAlN: h-BN = 9: 1.

Table 3 below compares the protective film of Example 3 described above with other protective films. As a comparative example, the same substrate as in Example 3 was used, and a protective film of CrN, TiN, TiAlN having a thickness of 3 microns was attached by sputtering. Using the substrate with the protective film of Example 3 and the comparative example as a core pin for zinc (ZDC1) die casting, after casting 40,000 times, the cross section of the cavity part of the substrate was examined with a scanning electron microscope. The total length of the parts was compared.

  Simultaneous sputtering with Ti-Al-Si (Ti51.1at% -Al38.1at% -Si10.3at% balance impurity) target and 99.0% purity h-BN target, and substrate intermittently at a constant angle The laminated film was formed by rotating the film. Flow a mixed gas of argon and nitrogen (mixing ratio 10:25), connect a DC power source to the TiAl target, a high-frequency power source to the h-BN target, and a high frequency power source to the DC power source. About 1.2 kW, about 700 W of power is applied to the high-frequency power supply, and a steel tool (casting pin) is used for the substrate, and a 3 micron thick TiAlN / h-BN multilayer film is formed on the substrate surface. It was. The thickness of each layer of TiAlSiN and h-BN was 5 nm and 1 nm, respectively, and this was repeated 500 times (1000 layers).

○：１ｍｍ未満、△：１ｍｍ以上 Table 4 below compares the protective film of Example 4 described above with other protective films. As a comparative example, the same substrate as in Example 4 was used, and a protective film of CrN, TiN, TiAlSiN having a thickness of 3 microns was attached by sputtering. The substrates with protective films of Example 3 and Comparative Example were used as casting pins for magnesium die casting, and the number of castings until the thickness of deposits (magnesium and oxides thereof) on the substrate exceeded 1 mm was compared. Although all the comparative examples are about 20,000 to 80,000 times and are 1 mm or more, Example 4 is still less than 1 mm even if it exceeds 100,000 times.

○: Less than 1mm, △: 1mm or more

  The present invention is suitable as a protective film for the mold surface by obtaining good results in any of the four examples described above by comparative experiments, and improved lubricity and deterioration of wettability are obtained. Can be judged. The protective film of the present invention obtained in the above example was analyzed by the X-ray diffraction method, and calculated from the half width of the X-ray diffraction peak using the Scherrer equation. The average of the TiAlN phase, TiAlSiN phase, or TiSiN phase The crystal grain size was determined to be 20 nm or less. In addition, since an error appears in the crystal grain size depending on the measurement method, if such an error is taken into consideration, the average crystal grain size of the TiAlN phase, TiAlSiN phase, or TiSiN phase is 30 nm or less. It is thought that it is necessary to obtain, and it is desirable that it is 20 nm or less.

Mold surface protective film of the present invention as shown in the above embodiment, Ti, Al, B, and to N may be a mixed layer composed mainly of, Although not shown in the examples, Ti, Al, Si, B, and to N may be a mixed layer composed mainly of, Ti, Si, B, and N may be a mixed film composed mainly of. In addition, there is an experimental result by the present inventors about the excellent oxidation resistance of TiAlSiN itself, and since it can be expected that the characteristics of the protective film composited with BN are excellent, Ti, Si, Even with a mixed film containing B and N as main components, the same effect can be expected .

As mentioned above, since BN was very soft, it was thought that there was almost no increase in hardness. However, when the volume ratio of BN was changed, the plastic hardness of the protective film for the mold surface was investigated. An unexpected fact was found. As shown in the graph of FIG. 1, the number of samples is 6, but when the volume ratio of the BN phase is changed around 0 to 30%, the volume ratio of the BN phase is 0% (TiAlN monolayer). There was a range that became harder than the plastic hardness of 30 GPa. Depending on how the curve is drawn between the BN phase 17% volume sample and the 28% sample, if it is at least 17% or less, a plastic hardness equivalent to or higher than that of a TiAlN single layer can be obtained. It has been shown. From Table 3 of Example 3 described above, it can be said that the wettability, adhesion, reactivity, and lubricity are improved when the volume ratio of the BN phase is 10%. Therefore, if the volume ratio of the BN phase is increased to 10% or more, it can be estimated that the lubricity is further improved from the wettability as a characteristic of the BN phase itself. When the results of Examples 3 and 4 are summarized, when the volume ratio of the BN phase is 10% to 17%, not only wettability, adhesion, reactivity, and lubricity, but also the same as the case of a single layer of TiAlN. The above plastic hardness is obtained. Note that it can be seen from the graph of FIG. 1 that even if the same sample is measured twice immediately after production and half a year after production, the characteristics are hardly deteriorated.

The protective film for the mold surface of the present invention is manufactured by the vapor-phase thin film forming method, and the PVD method is used in the above-described embodiments. However, the CVD method may be used if the conditions are adjusted. Is possible.

It is a graph which shows the change of the plastic hardness of the protective film for metal mold | die surfaces by BN mixing ratio.

Claims (2)

A hard protective film containing Ti, B, and N as essential elements and containing one or two elements of Al or Si is formed on the metal surface by a vapor phase thin film forming method, and the hard protective film is made of Ti. And N is an essential element, and consists of a NaCl-type crystal phase containing one or two elements of Al or Si and a BN phase having an amorphous structure or a microcrystalline hexagonal structure. A protective film for a mold surface, which is a mixed film in which a crystal phase and a BN phase are mixed three-dimensionally, and is used for an aluminum or magnesium die casting or extrusion mold.
The protective film for a mold surface according to claim 1, wherein the ratio of the BN phase is in the range of 5 to 50% by volume.

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