JP4676741B2 - Hard coating and hard coating method - Google Patents

Description

  The present invention relates to a hard film and a hard film provided with lubrication characteristics excellent in mechanical characteristics of a hard film such as wear resistance, adhesion and high temperature oxidation resistance coated on cemented carbide, high speed steel, die steel, etc. It is related with the coating method.

With a tool coated with a conventional hard coating, the cutting speed is increased for the purpose of improving the efficiency of metal processing, and the high feed cutting process in which the feed amount per blade exceeds 0.3 mm under cutting conditions. However, satisfactory performance has not been obtained in terms of adhesion and mechanical properties of the hard film, such as oxidation resistance and wear resistance. From such a background, a technique for the purpose of further improving the oxidation resistance and wear resistance of a hard coating has been disclosed. Furthermore, in steel processing for die-casting dies called difficult-to-cut materials, it is common to use cutting fluids that contain components such as Cl, S, and P. There is a growing demand for tools that can be used in the environment. From such a background, research for improving the lubrication characteristics disclosed in Patent Documents 3 and 4 has been conducted.
Patent Documents 1 and 2 disclose a technique for forming a concentration distribution in a hard film and a technique for improving wear resistance by forming a film having a repeated layer of composition change in which the composition continuously changes. ing. However, both are attempts using only the arc discharge ion plating method in the physical vapor deposition method. Moreover, in the processing of steel types where welding is likely to occur at the cutting edge or the like, stable processing is given priority over the discussion of the magnitude of wear generation, and improvement of the welding characteristics is urgent. In the field of cutting, stable, unattended, and inexpensive machining is required. From such a background, it is possible to improve the lubrication characteristics without impairing the adhesion, hardness, and heat resistance characteristics of the hard coating. It is essential.
Patent Document 3 discloses a technique for coating a machining tool with molybdenum disulfide for the purpose of obtaining lubricity, and Patent Document 4 discloses an example of a film in which molybdenum disulfide and TiN are combined. However, the adhesion and hardness of the coating are not sufficient, and there remains a problem in the wear resistance of the cutting tool.

JP 2003-225807 A Japanese Patent No. 3460288 JP-A-5-239618 Japanese National Patent Publication No. 11-509580

  The object of the present invention is to provide a hard film with excellent adhesion, excellent oxidation resistance, wear resistance, and lubrication characteristics, and further, welding resistance at high temperatures and work material elements in the hard film. It is intended to provide a tool coated with a hard coating that suppresses the diffusion of steel and is compatible with dry machining, high speed, and high feed of cutting.

The hard coating of the present invention comprises one or more elements selected from the periodic tables 4a, 5a, 6a, Al and Si, one or more elements selected from C and N, and S and O. The hard coating contains a nitride , carbide, charcoal of a target of one or more elements selected from the periodic table 4a, 5a, 6a group, Al and Si as the first phase. Any one of nitrides, the second phase is one kind of sulfide of WS ₂ , NbS, and CrS, the first phase and the second phase are mixed, and electron spectroscopy analysis It is a hard film characterized by having a peak in the range of 167 to 170 eV indicating the bonding state of S and O in the bonding state analysis by the method.
Next, as a manufacturing method, periodic table 4a, 5a, 6a group, one or more elements selected from Al and Si, one or more elements selected from C and N, and S and O The hard film contains a target of one or more elements selected from the periodic table 4a, 5a, 6a group, Al and Si as the first phase. Using a sulfide target of WS ₂ , NbS, and CrS, the first phase is formed by arc discharge ion plating method, and the second phase is formed by magnetron sputtering method at the same time. the first phase is the periodic table 4a, 5a, 6a, group nitride target of one or more elements selected from Al and Si, carbides, and any of carbonitrides, the second The phase is a sulfide of WS ₂ , NbS, CrS, In addition, the first phase and the second phase are mixed, and, furthermore, in the binding state analysis by electron spectroscopy, it has a peak in the range of 167 to 170 eV indicating the binding state of S and O. It is the coating method of the hard film characterized. By adopting this structure and its production method, it is possible to provide a hard film having excellent adhesion and excellent lubricating properties in addition to oxidation resistance and wear resistance.

  It is preferable that S contained in the hard coating of the present invention is atomic% and is 0.1 or more and 10 or less. Further, the hard coating is to be coated using at least two kinds of evaporation sources by physical vapor deposition having different plasma densities. Here, as evaporation sources having different plasma densities, for example, an arc discharge ion plating method (hereinafter referred to as AIP method) having a relatively high plasma density and a magnetron sputtering method (hereinafter referred to as MS method) having a relatively low plasma density. And the like.

  The hard film of the present invention is a hard film having excellent adhesion between the hard film and the substrate, and excellent lubricating properties in addition to oxidation resistance and wear resistance. For example, when the hard coating of the present invention is applied to a cutting tool or the like, it is stable and stable even under intermittent cutting conditions at the time of die processing, including dry high-efficiency cutting of die casting steel for severe welding. It has a long life and is extremely effective in improving productivity in cutting.

It can be confirmed by analysis by electron spectroscopy (hereinafter referred to as ESCA) that the hard coating of the present invention has a peak indicating a bonded state of S and O. In the present invention, the ESCA analysis was confirmed by X-ray photoelectron spectroscopy analysis (hereinafter referred to as XPS analysis) by X-ray irradiation. The XPS analysis was performed under the conditions of X-ray source: Al, Kα ray, analysis region: 100 μmφ, and electron neutralizing gun. Under these conditions, a peak indicating a state of bonding between S and O (hereinafter referred to as S—O bonding) in a range of 167 to 170 eV can be confirmed.
It was confirmed that lubrication characteristics can be remarkably improved by incorporating S into the hard coating of the present invention by sulfide and S—O bond . The evaluation method used a ball-on-disk friction and wear tester, and measured the coefficient of friction at a high temperature of 600 ° C. in the atmosphere. S contained in the hard film of the present invention is oxidized at a relatively low temperature of about 200 ° C. on the surface of the hard film. This oxidation phenomenon functions as a protective film on the surface of the hard film, and exhibits excellent lubrication characteristics by suppressing welding of the workpiece. As a result, inward diffusion of the workpiece into the hard film under high temperature in an oxidizing atmosphere such as cutting heat can be prevented and stable machining can be performed. In order to form an S—O bond at the time of coating, it can be obtained by incorporating oxygen into a reaction gas which is a main component for obtaining a hard film. The important point here is to obtain a hard film having excellent lubrication characteristics by containing S in the hard film and forming an S—O bond.

  S contained in the hard film of the present invention is preferably at least 0.1 and no more than 10 in atomic%. If the content is lower than 0.1%, it is difficult to detect using a general-purpose analytical instrument, and it is difficult to specify it as a management item at the time of mass production. did. On the other hand, when the S content exceeds 10%, the crystal structure of the hard coating changes from a columnar crystal form to an amorphous microstructure. As a result, since the residual compressive stress that greatly affects the hardness reduction of the hard coating and the securing of adhesion increases, the hard coating peels off due to a strong external impact. For these reasons, the S content is specified to be 0.1 or more and 10 or less. More preferably, the S content is not less than 0.1% and not more than 7%.

Production method of the present invention, the first, is because to obtain the hard film rich in toughness and, secondly, because it is possible to effectively adding S into the hard film.
First, by simultaneously using two or more types of film formation methods having different plasma densities, ions having different valences simultaneously reach the substrate surface from the generated plasma discharges. At this time, in the vicinity of the evaporation source having a relatively high plasma density, a hard crystal mainly forms a phase. This is the first phase. On the other hand, in the vicinity of an evaporation source having a relatively low plasma density, a soft crystal is the main phase. This is the second phase. Since the evaporation sources having different plasma densities coexist in the same vacuum apparatus, the coating is deposited on the substrate in a mixture of the first phase and the second phase. When the second phase is present between the crystals of the first phase, the soft crystal exhibits a cushioning effect, and as a result, a hard film rich in toughness is obtained as the entire hard film, and the impact resistance characteristics of the covering member are improved. is there. That is, a hard film having toughness and high lubricating properties can be obtained. Specifically, the evaporation source with a relatively high plasma density is the AIP method, the evaporation source with a relatively low plasma density is the MS method, and both are discharged simultaneously to form an interface with respect to the crystal growth direction of the hard coating. It is possible to obtain a hard film in which crystals are continuously grown without any problems. However, if both of them are operated sequentially or intermittently in the formation of the hard film, there arises an inconvenience that an interface is formed in the hard film and bonding at the interface becomes weak. When the hard film of the present invention is coated on the surface of a wear-resistant member or heat-resistant member that requires high hardness, such as a cutting tool, the adhesion of the hard film is improved, and the oxidation resistance and wear resistance are remarkably improved. To do. In particular, since the lubrication characteristics are remarkably improved, it is possible to suppress welding resistance at a high temperature in cutting and diffusion of the work material element into the hard coating. Furthermore, it is possible to provide a hard film coated tool that can cope with dry cutting, high speed, and high feed of cutting. Here, the high feed processing is defined as a cutting condition in which the feed amount per blade under the cutting condition exceeds 0.3 mm / tooth.
Second, in order to effectively contain S in the hard film by physical vapor deposition, it is an evaporation source having a relatively high plasma density, and further, an AIP vapor deposition source capable of obtaining strong adhesion. By this, when coating a hard film mainly composed of one or more elements selected from the groups 4a, 5a, 6a, Al and Si, the MS evaporation source having a relatively low plasma density is discharged at the same time. It is preferable to add S from a target material containing sulfide such as WS, CrS, or NbS. It is preferable to use a sulfide having excellent heat resistance such as WS, CrS, or NbS as a target material, and coat using the MS method having a relatively low plasma density. Here, the reason why the physical vapor deposition method is used is that it is preferable to use a metal target installed in the evaporation source and containing S in advance. On the other hand, when chemical vapor deposition or the like is employed and H ₂ S or the like is used as a reaction gas, it is not preferable from the viewpoint of handling such as environmental problems and safety. When WS, CrS, NbS or the like is used as a target material for an evaporation source having a relatively high plasma density, it is difficult to stabilize the discharge phenomenon. It is also possible to select using a target material in which sulfides such as WS, CrS, NbS are added to a matrix composed of one or more elements selected from the periodic table 4a, 5a, 6a group, Al and Si. However, when the plasma density during discharge is relatively high, it becomes difficult to contain S in the hard coating. Therefore, it is preferable to add S using the MS method with a relatively low plasma density.

Film formation was performed using a device in which an AIP evaporation source and an MS evaporation source were provided in a small vacuum apparatus. The substrate was a cemented carbide insert. The reaction gas was selected from N ₂ gas, CH ₄ gas, and Ar / O ₂ mixed gas, from which the desired film was obtained. The reaction pressure was selected so that both film forming methods can generate plasma simultaneously in a vacuum apparatus. The substrate temperature was 400 ° C., and the bias voltage was a voltage in the range of −40V to −150V. Various alloy targets can be selected as the evaporation source. In the embodiment, an alloy target having a predetermined composition is used as the evaporation source for the AIP method, WS ₂ , NbS, CrS, etc. are used as the evaporation source for the MS method, and S is used for the hard film. For the addition, the AIP evaporation source and the MS evaporation source were simultaneously discharged. At this time, the reaction pressure was set to 3 Pa in order to discharge the two evaporation sources simultaneously. Evaluation of the obtained hard film performed the cutting test on the cutting conditions shown below. The work material used under these cutting conditions is SKD61 used as a steel type for die casting molds, and the hardness is HRC45. In this steel type, a welding phenomenon occurs at the cutting edge portion in the early stage of cutting, and the hard coating is severely damaged at the coated insert cutting edge portion. By cutting the surface of the work material under high-efficiency machining conditions, wear and heat cracks caused by welding generated in the insert at the initial stage of cutting were evaluated. In the evaluation method, processing was performed until the tool became uncut due to chipping or wear of the blade edge, and the cutting length at that time was defined as the tool life. Table 1 shows the details of the hard coating and the results of the cutting test for the inventive examples, comparative examples, and conventional examples.
(Cutting conditions)
Tool: Face mill Insert shape: SDE53 type special shape Cutting method: Center cut method Workpiece shape: width 100mm x length 250mm
Work material: SKD61, hardness, HRC45
Cutting depth: 1.5mm
Cutting speed: 100 m / min
1-blade feed amount: 0.6 mm / blade Cutting oil: None

From Table 1, the cutting performance was greatly different depending on the presence or absence of S—O bond in the vicinity of the hard coating surface. In addition, the difference in the cutting performance was clearly shown by the amount of S content when S was added to the hard film using two or more kinds of physical evaporation sources.
As shown in Examples 1 to 14 of the present invention, by applying the hard coating of the present invention, high-efficiency machining that has been difficult to realize until now can be realized. For example, as shown in Example 5 of the present invention, the hard film to which S was added by WS2 showed the best results during the evaluation of the examples. As a result of investigating the hard film of Invention Example 5 in detail, the S content was 6.8%, and further, as shown in FIG. 1, S—O bonds were confirmed in the range of 167 to 170 eV in the XPS analysis. It was. Also in the cutting test, it was confirmed that intense welding at the initial stage of cutting was suppressed. This suppression effect is considered to be due to the presence of the S—O bond. In FIG. 1, in addition to the S—O bond, it is confirmed that a sulfide with a metal element exists at 161 to 164 eV, and that a W—O bond exists at 33 to 36 eV as shown in FIG. It was. As described above, sulfides and oxides having excellent lubrication characteristics are formed in the vicinity of the hard coating surface of Example 5 of the present invention, so that it is considered that a remarkable effect was exerted in the processing of a metal in which welding is severely generated. . As shown in FIG. 3, as a result of observing the cross-sectional structure of the hard coating, it was a columnar structure. As a result, it was confirmed that the mechanical strength in the shearing direction was also obtained in cutting with a high impact such as high feed machining.
Further, with respect to Invention Example 5, Invention Example 11, Conventional Example 32, and Conventional Example 33, the friction coefficient at high temperature of 600 ° C. in the atmosphere was measured using a ball-on-disk type frictional wear tester. The result is shown in FIG. From FIG. 4, Invention Example 5 and Invention Example 11 showed a coefficient of friction of 0.4 or less, and it was confirmed that the lubrication characteristics were greatly improved. As in Example 11 of the present invention, it was confirmed that the form of sulfide such as Cr was also excellent in lubrication characteristics.
Using Example 5 of the present invention, an attempt was made to process intermittent parts such as a fixing hole seen in a mold in the cutting process. However, stable cutting could be performed without loss. This is because the simultaneous use of two or more types of film formation methods with different plasma densities has an S—O bond near the surface of the hard film, and the film as a whole is rich in toughness. It is thought that it was connected to. As a result, a hard coating having excellent adhesion, which is the subject of the present invention, having excellent lubrication characteristics in addition to oxidation resistance and wear resistance, and excellent chipping resistance was obtained. In order to exhibit stable and excellent cutting performance, WS2 tends to be suitable as a target material used as an addition source of S element. Even when CrS or NbS is used, it has been confirmed that cutting characteristics are remarkably improved by showing unprecedented lubrication characteristics.
In Comparative Examples 15 to 20, 24 to 26, and 28, it was confirmed that the S content exceeded 10%. For example, in Comparative Example 17, no S—O bond was confirmed, and the amount of S contained in the hard coating was 14.1%, exceeding 10%. As a result, it was confirmed that the crystal structure of the hard coating was an amorphous microstructure as shown in FIG. The hardness of the hard coating also had a tendency to soften with about 26 in HV.
In Comparative Example 23, the S content in the hard film was 7%, but the S—O bond was not formed on the surface of the hard film because it was coated without adding oxygen to the reaction gas used during film formation. It was. Although a certain amount of cutting distance could be processed by the effect of addition of S, it was insufficient for suppressing welding that occurred in the early stage of cutting.
In Comparative Examples 21 and 22, WS2 and NbS target materials were used for coating, respectively, but the discharge output was set low. As a result, the S content of the obtained hard coating was so small that S could not be detected using an XPS analyzer. In the cutting test, welding at the initial stage of cutting occurred vigorously. In particular, in Comparative Example 22, sparks were generated, and the evaluation was stopped midway. The addition of S to the hard coating must control the chemical state of the hard coating, such as S—O bonds, as well as the S content.
Conventional examples 29 to 31 show a case where the cutting tool surface is coated with MoS2. Although MoS2 has excellent lubrication characteristics, when it comes into contact with the workpiece, MoS2 has low hardness and low heat resistance, so abnormal wear occurs, and the lubrication characteristics of MoS2 cannot be fully exhibited. Therefore, it has been difficult to ensure heat resistance, hardness, and adhesion enough to cope with the severe conditions under the cutting environment in recent years.

FIG. 1 shows the XPS analysis result of Example 5 of the present invention. FIG. 2 shows the XPS analysis result of Example 5 of the present invention. FIG. 3 shows a hard film cross-sectional structure of Example 5 of the present invention. FIG. 4 shows the results of the friction coefficient measurement. FIG. 5 shows a hard film cross-sectional structure of Comparative Example 17.

Claims (3)

Periodic table 4a, 5a, 6a, a hard film containing one or more elements selected from Al and Si, one or more elements selected from C, N, and S and O, hard coating is to the first phase, the periodic table 4a, 5a, 6a, group nitride target of one or more elements selected from Al and Si, carbides, and any of carbonitrides, The second phase is a sulfide of WS ₂ , NbS, CrS, and the first phase and the second phase are mixed, and further, in the binding state analysis by electron spectroscopy, A hard film characterized by having a peak in a range of 167 to 170 eV indicating a bonding state of S and O.   The hard film according to claim 1, wherein S contained in the hard film is atomic% and is 0.1 or more and 10 or less. Periodic table 4a, 5a, 6a, a hard film containing one or more elements selected from Al and Si, one or more elements selected from C, N, and S and O, The hard film uses a target of one or more elements selected from the periodic table 4a, 5a, 6a group, Al and Si as the first phase, and WS ₂ , NbS, Using a sulfide target of one kind of CrS, the first phase is simultaneously formed by an arc discharge ion plating method, and the second phase is formed by a magnetron sputtering method. The target of one or more elements selected from the periodic table 4a, 5a, 6a group, Al and Si is any one of nitride , carbide, carbonitride, and the second phase is WS ₂ , NbS and CrS, one kind of sulfide, and the first phase and the first phase A hard film coating method characterized by having a peak in the range of 167 to 170 eV, which shows a binding state of S and O in a binding state analysis by electron spectroscopy analysis.