JPS61253369A - Surface coating method for sintered hard alloy - Google Patents

Abstract

PURPOSE:To execute the surface coating of a sintered hard alloy which withstands heavy cutting at a low cost by using a high-frequency power source and DC power source in combination for a plasma excitation source, holding a sintered hard alloy base material at negative potential with the DC power source and subjecting the base material to the coating treatment under specific conditions. CONSTITUTION:The high-frequency power source and DC power source are used in combination as the plasma excitation source and the sintered hard alloy base material is maintained at the negative potential in the stage of forming the hard coating film on the surface of the sintered hard alloy by a plasma CVD method. An RF wave power source or microwave power source is adequate as the high-frequency power source. The coating treatment is executed in this state by setting the electric power density of the high-frequency power source in a 0.01-1.0W/cm<3> range, the absolute value of the voltage of the DC power source at <=1,500V and the pressure of the gaseous atmosphere in a 0.05-5Torr range. The surface-coated sintered hard alloy which is adequately improved in the resistance to exfoliation and chipping as a cutting tool is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of surface coating a cemented carbide, and particularly to a method suitable as a surface coating method for a coated cemented carbide tool used as a cutting tool.

<Prior Art> Conventionally, cutting tools having a cemented carbide base material and a hard coating film formed on the surface thereof have been widely used.

The method for forming the above-mentioned coating film includes CVD method and PVD method.
CVD method is adopted, especially for cutting tools.
Law occupies a central position.

<Problems to be solved by the invention> However, according to the CVD method, the strength of the cemented carbide base material decreases after coating treatment, and the cutting edge is likely to break under severe usage conditions such as heavy cutting. Since no significant improvement in service life has been observed, the coating method for heavy cutting tools is as follows:
It is difficult to adopt.

In this regard, according to the PVD method, the strength of the base material does not decrease, chipping is less likely to occur even during heavy cutting, and the tool life can be improved by preventing welding of the rigid material, which is the original function of the coating layer. There are advantages.

However, in addition to high equipment costs, the PVD method requires a special mechanism to rotate the base material due to poor coverage of the coating film, and therefore has significantly lower productivity than the CVD method. However, the disadvantage is that the processing cost is high.

This invention was made in view of the above problems, and
The purpose of the present invention is to provide a surface coating method for cemented carbide that is inexpensive and can sufficiently withstand heavy cutting.

By the way, in view of the decrease in strength after coating treatment of cemented carbide by the CVD method, research was conducted to lower the coating treatment temperature in order to prevent such decrease in strength, and the following findings were obtained.

In other words, (1) lowering the coating treatment temperature reduces the degree of decrease in strength of the cemented carbide base material after coating and improves chipping resistance; (2) the advantages of the CVD method in that the coating film has good coverage; Plasma CV
Method D is preferable; ■ In order to reduce the thermal resistance and form a coating film that can withstand use as a coated cemented carbide, it is necessary to It is necessary to set the plasma intensity and coating treatment temperature within a predetermined range; ■ The strength of the coated cemented carbide depends on the coating temperature, and the lower the coating temperature, the lower the coating film adhesion strength. has been known for a long time, and if we focus only on the strength of the coated cemented carbide, it is preferable to lower the coating temperature as much as possible within the range where a coating film is formed, but if the coating treatment temperature is lowered too much, The adhesion strength of the coating film to the hard metal base material is weak (the coating film peels off easily,
It becomes impossible to use it as a cutting tool, that is, there is a limit to the improvement of cutting characteristics by lowering the coating temperature.

As a result of intensive research based on the above knowledge, we have developed a plasma CVD method suitable for improving the cutting characteristics of coated cemented carbide.

Means for Solving the Problems> The method of coating the surface of cemented carbide according to the present invention uses both a high frequency power source and a DC power source as a plasma excitation source, holds the cemented carbide at a negative potential with the DC power source, and , the power density of the high frequency power source is set in the range of 0.01 to 1.0 W/-,
The coating process is performed by setting the absolute value of the voltage of the DC power supply to 1500 V or less and setting the pressure of the gas atmosphere to a range of 0.05 to 5 Torr.

However, as a high frequency power source, an RF wave power source or a microwave power source is particularly suitable, and when holding the cemented carbide at a negative potential, the cemented carbide base material is in a position insulated from the high frequency power source. , it may be connected to the introduction side pole of the high frequency power supply, or it may be connected to the ground side pole.

According to the surface coating method for cemented carbide mentioned above, ■ By using a high frequency power source as a plasma excitation source, direct current is Chemically active species are more likely to be generated than when excited by a power source, and stable plasma formation and maintenance can be achieved over a wide range of gas atmosphere pressures, power source outputs, and various electrode structures.

■ Due to the above plasma formation, the ionized or activated raw material gas causes a chemical reaction on the surface of the cemented carbide material, forming a hard coating film, but at this time, the cemented carbide base material is negatively affected. By maintaining the potential, positive ions involved in chemical reactions on the surface of the cemented carbide can be preferentially attracted to the surface of the base material.

■ Adjust the power density of the high frequency power source to 0.01 to 1. OWW2O
By setting within this range, the coating film can be reliably formed at low cost. That is, if the power density is less than 0.01 W/-, it is impossible to form a coating film;
, 014/cj, ion sputtering phenomenon occurs, which adversely affects the coating process, and
It requires a high-output power source and is expensive.

(2) By setting the pressure of the gas atmosphere in the range of 0.05 to 5 Torr, a uniform coating film can be formed and the plasma can be maintained in a stable state. That is, if the pressure of the gas atmosphere is less than 0.05 Torr, the mean free path becomes long and the vapor deposition becomes directional, which is undesirable from the viewpoint of uniform coating.If the pressure is higher than 5 Torr, the plasma becomes stable. It becomes difficult to maintain the

■ If the absolute value of the negative potential applied to the cemented carbide base material by a DC power source is larger than 1500V, abnormal discharge will occur locally, but by keeping it below 1soov, no abnormal discharge will occur and stable discharge will occur. condition can be maintained.

As a result of the above, the peeling resistance and chipping resistance of the coated cemented carbide tool can be significantly improved.

<Comparative Example 1> Commercially available ISOP-30 (model number 5P) was used as the cemented carbide base material.
CH42TR) was used for coating according to the present invention under various conditions shown in Table 1. However, as a coating film, T i C? It is a lIl coating film, and its formation thickness is set to 2p. Further, as the excitation Hgl, a 13.56 MHz RF wave was used.

As is clear from Table 1, TiC coating films were obtained in samples NO2 to NO7 and sample NO9, and in sample NO1.
No film was formed on samples No. 8 and No. 9, and it was difficult to maintain stable plasma, and good coating could not be achieved on samples No. 8 and No. 9.

Next, the coated chip obtained above was attached to a cutter and a cutting test was conducted under the conditions shown in Table 2. At this time, for comparison, a commercially available PVD2I-Ting tip (product name AC330: Sumitomo Electric Industries, Ltd.) was used.
A cutting test was also conducted under the same conditions for 1).

As a result of the above cutting test, at the time of cutting for 12 minutes,
No chipping occurred on the cutting edge of any of the chips. Also, 12
The flank wear width after cutting for 1 minute is 0.070 mm for the PVD coated tip, 0.131 mm for sample NO2, and 0.103 mm for sample NO3.
mm.

Sample No. 4 is 0.111 mm 1 Sample No. 5 is 0.093 mm
mm.

Sample No. 6 is 0.074 mm, sample No. 7 is 0.065 mm.
mm.

Sample No.9 is 0.146mm Met.

Comparative Example 2 shown in Table 1 and Table 2> Commercially available ISOP-30 (model number 5N) was used as the cemented carbide base material.
HN432) was used for coating according to the present invention under various conditions shown in Table 3. However, the coating film is a TiN or Ti (CN) coating film, and its formation thickness is set to 2p. Further, as an excitation power source, an RF wave of 13.56 M l-I Z was used.

As is clear from Table 3, coating films were obtained under all conditions. Then, the coated chips obtained above were attached to a cutter and a cutting test was conducted under the conditions shown in Table 4. At this time, for comparison, a cutting test was also conducted on a commercially available PVD coated chip (trade name AC330; manufactured by Sumitomo Electric Industries, Ltd.) under the same conditions.

As a result of the above cutting test, at the time of cutting for 20 minutes,
No chipping occurred on the cutting edge of any of the chips. Also, 20
The flank wear width after cutting for one minute is 0.095 mm for the PVD coated tip, 0.138 mm for sample No. 11, and 0.1 mm for sample No. 12.
32mm.

Sample N013 is 0.126 mm, sample N014 is 0.1
16mm.

Sample N015 is 0.102 mm, sample N016 is 0.1
12mm.

Sample N017 is 0.100mm, sample N018 is 0.0mm
93mm.

Sample N019 is 0.116 mm, sample NO2O is 0.0
It was 90mm.

From the above comparative examples, the surface liquid NF1 of the present invention is PVD
It is clear that a coating film that is approximately four times better than the method can be obtained.

Table 3 Table 4 <Effects of the Invention> As described above, according to the cemented carbide surface coating method of the present invention, the peeling resistance and chipping resistance of the coated cemented carbide tool by plasma CVD method are significantly improved. The cutting performance is comparable to that of a coated cemented carbide tool made by the PVD method, and the coating process cost is low.

Claims (1)

[Claims] 1. In a method of forming a hard coating film on the surface of a cemented carbide using a plasma CVD method, a high frequency power source and a DC power source are used together as a plasma excitation source, and the DC power source is used to form a hard coating film on a cemented carbide base material. A method for coating the surface of a cemented carbide, characterized in that the surface of the cemented carbide is maintained at a negative potential and the coating treatment is carried out under the following conditions (1) to (3). (1) The power density of the high frequency power supply is in the range of 0.01 to 1.0W/cm^3, (2) The absolute value of the voltage of the DC power supply is 1500V or less, (3) The gas atmosphere pressure is Must be in the range of 0.05 to 5 Torr.