JP5152660B2 - Cutting tool and manufacturing method thereof - Google Patents

Description

  The present invention relates to a cutting tool and a method for manufacturing the cutting tool, and more particularly to a cutting tool capable of increasing the fracture resistance of a coating layer made of ceramics formed on a substrate surface and a method for manufacturing the cutting tool.

  Conventionally, cemented carbide made of a WC-Co alloy or an alloy obtained by adding a carbonitride of Ti, Ta, or Nb to a WC-Co alloy or a WC-Co alloy has been used for cutting of general steel or castings. However, since the cutting edge of the cutting tool has a high temperature of 800 ° C. or higher during the cutting process, cutting tools made of these cemented carbides are easily plastically deformed by heat during the cutting process. As a result, flank wear was likely to be severe.

Therefore, in order to improve the cutting characteristics of the cutting tool at high temperature, carbide, nitride, or carbonitride (TiC, TiN, or TiCN) of group IVa metal of the periodic table is formed on the surface of the cemented carbide base material. Etc.), or a coated cutting tool in which a single layer of hard ceramics such as Al ₂ O ₃ or a coating layer made of a composite layer of these hard ceramics is used. For forming these coating layers, a chemical vapor deposition method such as a CVD (Chemical Vapor Deposition) method or a physical vapor deposition method such as an ion plating method or an ion sputtering method is used.

  Of the coating layers formed by these methods, the coating layer formed by chemical vapor deposition, in particular, has very high adhesion strength with the cemented carbide base material and very excellent wear resistance. In recent years, since the coating layer tends to become thicker due to the demand for higher speed and higher efficiency of cutting, the adhesion strength between the cemented carbide base material and the coating layer is important.

However, on the other hand, in the case of chemical vapor deposition, since the temperature of the coating layer is as high as about 1000 ° C., when the coating layer is formed and cooled to room temperature, the thermal expansion coefficient of the cemented carbide base material and the coating layer is reduced. A tensile stress remains in the coating layer due to the difference. As a result, when a crack occurs starting from the surface of the coating layer during cutting, the crack propagates due to tensile stress, and the coating layer falls off or chipping occurs. Specifically, the thermal expansion coefficient of the cemented carbide base material is about 5.1 × 10 ⁻⁶ K ⁻¹ , whereas the thermal expansion coefficient of the coating layer is about 9.2 × in the case of TiN, for example. 10 ⁻⁶ K ⁻¹ , about 7.6 × 10 ⁻⁶ K ⁻¹ for TiC, and about 8.5 × 10 ⁻⁶ K ⁻¹ for Al ₂ O ₃ . The thickness of the coating layer of cutting tools currently in general use is in the range of about several μm to about several tens of μm. Although the wear resistance increases as the thickness of the coating layer increases, it is thick for the above reasons. This is because the coating layer has a lower fracture resistance.

Therefore, various techniques for improving the characteristics of the coating layer have been proposed. Japanese Patent Application Laid-Open No. 7-216549 (Patent Document 1) describes a technique for improving the cutting life of a cutting tool by eliminating cracks generated during cooling after forming an Al ₂ O ₃ layer.

Further, JP 2005-212047 A (Patent Document 2) describes the occurrence of chipping and delamination by forming a titanium carbonitride layer having a streak structure extending perpendicularly to the substrate surface on the substrate surface. It is described that wear resistance and fracture resistance can be improved.
JP 7-216549 A JP 2005-212047 A

  However, even in the coating layers disclosed in Patent Documents 1 and 2, since tensile stress still remains in the coating layer, when cutting intermittently in high-speed machining and high-efficiency machining, There was a problem that the chipping resistance was still low. In addition, there is a problem that the wear of the coating layer is disturbed and wear resistance is lowered. Although these problems are problems in general cutting tools, they are particularly prominent problems in cutting tools used for cutting such as milling and turning of grooved materials. In the cutting tool of the above-mentioned application, the chipping of the cutting edge is very likely to occur when an intermittent load is applied.

  Therefore, this invention is providing the cutting tool excellent in both abrasion resistance and fracture resistance, and its manufacturing method.

  The cutting tool of this invention is equipped with the base | substrate and the coating layer. The substrate has a plurality of hard phases made of a hard compound and a binder phase that bonds the hard phases together. The coating layer is made of ceramics formed on the substrate surface. The coating layer has a crack. The crack has a width of 50 nm or more and 200 nm or less, a distance of 30 μm or more and 100 μm or less, and a width of the constituent region of 5.0 μm or more and 10.0 μm or less in a cross section along the normal line of the substrate surface. .

  According to the cutting tool of the present invention, the tensile stress in the coating layer can be released by forcibly generating a crack of a predetermined size in the coating layer in advance. Further, even if a new crack is generated from the surface of the coating layer during cutting, propagation of the newly generated crack is suppressed by the anchor effect of the crack that originally exists. As a result, while the wear resistance is improved by the coating layer, the coating layer can be prevented from falling off and chipping, and a cutting tool excellent in both wear resistance and fracture resistance can be obtained.

  According to the cutting tool of this invention, the anchor effect by a crack can be acquired by making the width | variety of a crack into 50 nm or more and 200 nm or less. When the width of the crack exceeds 200 nm, the anchor effect of the crack itself is reduced, and chipping is likely to occur in the coating layer. Moreover, the wear resistance by a crack can be reduced by making the space | interval of a crack into 30 micrometers or more, and the tensile stress of a coating layer can fully be open | released by making the space | interval of a crack into 100 micrometers or less. Furthermore, the anchor effect by a crack can be acquired by making the width | variety of the structure area | region of a crack into 5.0 or more and 10.0 micrometers or less. When the width of the crack constituent area exceeds 10.0 μm, the newly generated crack propagates in parallel to the surface of the coating layer during cutting, and causes the coating layer to drop off and chipping together with the newly generated crack. There is a fear.

  Preferably, in the cutting tool of the present invention, the hard phase is selected from the group consisting of tungsten carbide, carbides of elements of Group IVa, Va, or VIa, nitrides of these elements, and carbonitrides of these elements. It consists of at least one material selected.

In the cutting tool of the present invention, preferably, the hard phase is made of tungsten carbide.
The hard phase made of these materials is hard and has excellent wear resistance. In addition, the decrease in hardness at high temperatures is small. For this reason, it is suitable as a material for cutting tools.

  In the cutting tool of the present invention, preferably, the binder phase is made of at least one element selected from the group consisting of iron, cobalt, and nickel.

  Since these materials have the property of strengthening the bonds between the hard phases made of metal carbide, they are suitable as the binder phase.

  Preferably, in the cutting tool of the present invention, the coating layer is composed of a carbide of element IVa, Va, VIa, aluminum, or silicon, a nitride of the element, a carbonitride of the element, an oxide of the element, It consists of at least one substance selected from the group consisting of the above-mentioned elemental carbonates, the above-mentioned element carbonitrides, the above-mentioned elemental boronitrides, and the above-mentioned elemental borocarbonitrides.

  Thereby, since the base | substrate surface is comprised with a hard ceramic film | membrane, abrasion resistance can be improved.

In the cutting tool of the present invention, preferably, the tensile stress of the coating layer is released.
Thereby, the propagation of the crack which generate | occur | produces at the time of a cutting process is suppressed, and wear resistance can be improved.

  In the cutting tool of the present invention, preferably, the coating layer has a thickness of 3 μm or more and 20 μm or less.

  By setting the thickness of the coating layer to 3 μm or more, the effect of improving the wear resistance of the coating layer can be obtained. The thicker the coating layer, the better the wear resistance, but the thickness of the coating layer should be 20 μm or less. Thus, the fracture resistance of the coating layer can be ensured.

  Preferably, in the cutting tool of the present invention, the coating layer has a width of 50 nm or more and 200 nm or less, an interval of 30 μm or more and 100 μm or less, and a width of the constituent region in the cross section after being polished by ion milling. It has a crack of 0 μm or more and 10.0 μm or less.

  When observing cracks in the coating layer, the cross section is polished by ion milling, whereby damage to the coating layer during polishing can be reduced, and cracks during film formation can be observed as they are.

  The manufacturing method of the cutting tool of the present invention is the above-described manufacturing method of the cutting tool, and preferably forms the coating layer at a temperature of 800 ° C. or higher and 1100 ° C. or lower by a vapor phase synthesis method.

  By forming the film at 800 ° C. or higher, the coating layer can be easily formed on the substrate, and by forming the film at 1100 ° C. or lower, the tensile stress generated in the coating layer during cooling can be reduced.

  The manufacturing method of the cutting tool of the present invention is the above-described manufacturing method of the cutting tool, and preferably, after the step of forming the coating layer in the chamber and the step of forming the coating layer, the inside of the chamber is zeroed. A step of cooling the coating layer at a rate of 10.0 ° C./min to 15.0 ° C./min in a state maintained in a pressurized atmosphere of 1 MPa.

  Thereby, in the cross section along the normal line of the substrate surface, a crack having a width of 50 nm or more and 200 nm or less, an interval of 30 μm or more and 100 μm or less, and a width of a constituent region of 5.0 μm or more and 10.0 μm or less. Can be easily generated in the coating layer.

  According to the cutting tool and the manufacturing method thereof of the present invention, it is possible to obtain a cutting tool excellent in both wear resistance and fracture resistance.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an essential part schematically showing a configuration of a cutting tool according to an embodiment of the present invention. FIG. 1 is a cross-sectional view taken along the normal line of the coating layer surface. Referring to FIG. 1, the cutting tool (coated cutting tool) in the present embodiment includes a base 1 and a coating layer 2. The coating layer 2 is formed on the surface 1 a of the substrate 1. The covering layer 2 has a number of meandering cracks 11 and 12.

  The substrate 1 has a plurality of hard phases as a matrix and a binder phase that bonds the hard phases together. The substrate 1 is preferably a cemented carbide made by sintering a hard metal carbide powder.

The hard phase is made of a hard compound, for example, selected from the group consisting of tungsten carbide and carbides of elements of group IVa, Va or VIa, nitrides of these elements, and carbonitrides of these elements It consists of at least one substance. Specific examples include TiC, TiN, TaC, NbC, ZrCN, Cr ₃ C ₂ , ZrC, ZrN, or TiCN. The hard phase may be made of cermet or tungsten carbide alone instead of the above-mentioned material.

  The binder phase plays a role of bonding the hard phases to each other, and is made of, for example, at least one element selected from the group consisting of iron-based metals, in other words, iron, cobalt, and nickel. When the hard phase is made of cermet, the binder phase is particularly preferably cobalt, nickel, or an alloy of cobalt and nickel.

The covering layer 2 is made of ceramics (hard ceramic), for example, carbides of elements of group IVa, Va, VIa, aluminum or silicon, nitrides of these elements, carbonitrides of these elements, Oxides of elements, carbonates of these elements, carbonitrides of these elements, boronitrides of these elements, and at least one substance selected from the group consisting of borocarbonitrides of these elements ing. Specifically, TiC, TiN, TiCN, or the like Al ₂ O _3. The covering layer 2 may be a single layer or a composite layer. Moreover, the coating layer 2 has a thickness of 3 μm or more and 20 μm or less, for example.

  In the present embodiment, the coating layer 2 has a width of 50 nm or more and 200 nm or less, a distance of 30 μm or more and 100 μm or less, and a width of the constituent region in the cross section along the normal line of the surface 2a. It has the cracks 11 and 12 which are 0 micrometer or more and 10.0 micrometers or less. By generating such a crack, the tensile stress of the coating layer is released.

  Here, the width of the crack is obtained by the following method. Focusing on an arbitrary crack 11, the length l in the thickness direction (vertical direction in the figure) is divided into four equal parts, and three imaginary lines 20a to 20c are parallel to the surface 1a of the substrate 1 at a position of l / 4. pull. Next, at each intersection of the virtual lines 20a to 20c and the crack 11, the widths W1a to W1c of the grooves of the crack 11 are measured, and the average value W1 of the widths W1a to W1c is calculated. This average value W1 is the width of one crack 11. Similarly, the widths W1 to W50 of each of the fifty cracks are measured and calculated, and the average value W of the widths W1 to W50 of the fifty cracks is calculated. This average value W is taken as the crack width.

  In addition, the crack interval is calculated by counting the number of cracks included in a region in the range of 1.5 mm along the surface 1a of the substrate 1 (lateral direction in the figure), and the width of the region (the number of cracks existing in the region ( 1.5mm).

  Furthermore, the width of the constituent region of the crack is obtained by the following method. Focusing on an arbitrary crack 12, the region of the coating layer 2 where the crack 12 propagates is specified. Then, the width R1 along the surface 1a of the substrate 1 in that region is measured. Similarly, the widths R1 to R50 in each of the fifty crack constituent areas are measured, and the average value R of the widths R1 to R50 in the fifty crack constituent areas is calculated. This average value R is the width of the constituent region of the crack.

  The method for observing cracks in the coating layer 2 is arbitrary, but it is preferable to observe after the cross section is polished by ion milling. Ion milling is a technique of mirror polishing by irradiating an ion beam to a cross section.

Then, the manufacturing method of the cutting tool in this Embodiment is demonstrated.
First, a substrate 1 having a plurality of hard phases made of a hard compound and a binder phase for bonding the hard phases is prepared. Subsequently, the coating layer 2 is formed on the surface 1 a of the substrate 1. The covering layer 2 is formed on the substrate 1 at a temperature of 800 ° C. or higher and 1100 ° C. or lower using a vapor phase synthesis method such as a CVD method by arranging the substrate 1 in a chamber, for example. In particular, the coating layer 2 formed by the CVD method has very high adhesion strength with the substrate 1. As a result, the coating layer 2 can be thickened and the wear resistance can be improved. Further, a physical vapor deposition method such as an ion plating method or an ion sputtering method may be used instead of the CVD method.

  Next, the coating layer 2 is cooled in the chamber. The coating layer 2 is cooled at a rate of 10.0 ° C./min or more and 15.0 ° C./min or less in a state where the inside of the chamber is kept in a pressurized atmosphere of 0.1 MPa, for example. In particular, when the hard ceramic coating layer 2 is formed by CVD or the like, it is known that tensile stress is generated in the coating layer 2. By cooling the coating layer 2 under the above conditions, a crack of a desired size can be generated in the coating layer 2 and the tensile stress generated in the coating layer 2 can be released.

  Here, when a coating layer having a thickness of several μm to several tens of μm is formed and the natural cooling is performed without controlling the cooling rate within the above range after the film formation, the tensile stress generated in the coating layer during cooling Exceeds the breaking strength of the coating layer, and the coating layer spontaneously cracks at an average interval of 100 to 400 μm. Thereby, a part of tensile stress is released. However, in this case, an elastic strain of about 0.5 to 1.0 GPa remains in the coating layer. As a result, the fracture resistance cannot be improved. The residual stress in the coating layer can be measured by, for example, the sin2Ψ method.

  Even if a method other than cooling the coating layer 2 under the above conditions is used, a desired crack can be generated in the coating layer 2. For example, a method in which fine particles collide with the coating layer 2 using shot peening may be used. By the above method, the cutting tool in the present embodiment is obtained.

  The cutting tool in the present embodiment includes a base 1 and a coating layer 2. The substrate 1 has a plurality of hard phases made of a hard compound and a binder phase that bonds the hard phases together. The covering layer 2 is made of ceramics formed on the surface 1 a of the base 1. The covering layer 2 has a width W of 50 nm or more and 200 nm or less, a spacing of 30 μm or more and 100 μm or less, and a constituent region width R of 5.0 μm or more in a cross section along the normal line of the surface 1a of the substrate 1. It has the cracks 11 and 12 which are 10.0 micrometers or less.

  According to the cutting tool in the present embodiment, the tensile stress in the coating layer 2 can be released by forcibly generating cracks 11 and 12 of a predetermined size in the coating layer 2 in advance. Further, even if a new crack starting from the surface 2a of the coating layer 2 is generated during the cutting process, propagation of the newly generated crack is suppressed by the anchor effect of the cracks 11 and 12 that are originally present. As a result, while the wear resistance is improved by the coating layer 2, it is possible to prevent the coating layer 2 from dropping off and chipping, and it is possible to obtain a cutting tool that is excellent in both wear resistance and fracture resistance.

A cemented carbide base material (substrate) having a cutting tool shape of JIS B 4120 (1998) CNMG120408 defined in JIS (Japanese Industrial Standard) was prepared. Three cemented carbide base materials were prepared for each of the samples A1 to A4. This base material is composed of 87.0 wt% WC, 7.0 wt% CO, 3.0 wt% TiC, and 3.0 wt% NbC. Then, on the surface of the base material, MT (moderate temperature) -TiCN having a thickness of 7 μm and Al ₂ O ₃ having a thickness of 4 μm are formed in this order by CVD, thereby forming a coating layer. Formed. At the time of cooling after the coating layer is formed, hydrogen gas is fed into the chamber at a rate of 50 liters / min to make the chamber a pressurized atmosphere of 0.1 MPa, and the cooling rate is set to 5.0 for each sample. The temperature was controlled to ° C./min (sample A1), 10.0 ° C./min (sample A2), 15.0 ° C./min (sample A3), and 20.0 ° C./min (sample A4). This forced a crack into the coating layer, thereby releasing the tensile stress of the coating layer. Of the three samples A1 to A4 thus obtained, one sample A1 to A4 was cut along a cross section along the normal of the surface of the coating layer and mirror-polished by ion milling. Then, this cross section was observed using an electron microscope, and the width of the crack, the interval between the cracks, and the width of the constituent region of the crack were measured. In addition, wear resistance was evaluated using another one of the three samples A1 to A4. Further, chipping resistance was evaluated using the remaining one of the three samples A1 to A4. The evaluation methods of wear resistance and chipping resistance are shown in Tables 1 and 2 below, respectively, and the evaluation results of wear resistance and chipping resistance are shown in Table 3. Moreover, the microscope picture of the cross section of sample A3 is shown in FIG.

  Referring to FIG. 2 and Tables 1 to 3, samples A2 and A3, which are cutting tools according to the present invention, have the same flank wear results as sample A1, while samples A1 and A4 have the same results. Even the impact time has been dramatically increased.

  From the results of this example, according to the cutting tool of the present invention, it is possible to obtain a cutting tool excellent in both wear resistance and fracture resistance.

The same material as that of Example 1 was prepared, and a coating layer was formed by depositing MT-TiCN having a thickness of 7 μm and Al ₂ O ₃ having a thickness of 4 μm in this order by a CVD method. At the time of cooling after the coating layer is formed, the pressure in the chamber is set to 0 (<0.05 MPa, sample B1), 0.05 MPa (sample B2), and 0.1 MPa in each sample by feeding hydrogen gas into the chamber. After setting to (Sample B3), the cooling rate was controlled to 15.0 ° C./min. This forced a crack into the coating layer, thereby releasing the tensile stress of the coating layer. Using one sample B1 to B3 among the three samples B1 to B3 thus obtained, the width of the crack, the interval between the cracks, and the width of the constituent region of the crack were measured in the same manner as in Example 1. did. Further, the remaining two of the three samples B1 to B3 were used to evaluate the wear resistance and chipping resistance in the same manner as in Example 1. Table 4 shows the evaluation results of wear resistance and chipping resistance.

  Referring to Table 4, samples B2 and B3, which are cutting tools of the present invention, have the same flank wear amount results as sample B1, while the impact time is significantly longer than sample B1. It has become.

  In the sample B1, since the pressure in the chamber at the time of cooling was set to 0 MPa, the width of the crack constituent area was narrow, that is, the crack was close to a straight line, so the chipping resistance of the coating layer was deteriorated. On the other hand, in Samples B2 and B3, since the constituent area of the crack is wide, that is, a meandering crack, the chipping resistance is greatly improved while maintaining excellent flank wear resistance.

  In addition, the reason that the meandering crack can be formed by setting the pressure inside the chamber to 0.1 MPa is that the pressure inside the chamber is increased due to the pressure inside the chamber (the inside of the chamber). This is presumed to be because the resultant force of the pressure and the tensile stress remaining in the coating layer does not act parallel to the surface of the coating layer, but acts in an oblique direction.

  From the results of this example, according to the cutting tool of the present invention, it is possible to obtain a cutting tool excellent in both wear resistance and fracture resistance.

  The embodiments and examples disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

  The cutting tool of the present invention is particularly suitable for cutting that is subjected to an intermittent load, such as milling and turning of a grooved material.

It is principal part sectional drawing which shows typically the structure of the cutting tool in one embodiment of this invention. It is a microscope picture of sample A3 in Example 1 of the present invention.

Explanation of symbols

  1 substrate, 1a substrate surface, 2 coating layer, 2a coating layer surface, 11, 12 crack, 20a-20c imaginary line.

Claims (10)

A substrate having a plurality of hard phases made of a hard compound and a binder phase for bonding the hard phases;
A coating layer made of ceramics formed on the substrate surface,
The covering layer has a width of 50 nm or more and 200 nm or less, a distance of 30 μm or more and 100 μm or less, and a width of a constituent region of 5.0 μm or more and 10.0 μm in a cross section along the normal line of the surface of the coating layer A cutting tool having a crack that is:   The hard phase is composed of tungsten carbide and at least one substance selected from the group consisting of carbides of group IVa, Va, or VIa elements, nitrides of the elements, and carbonitrides of the elements. The cutting tool according to claim 1.   The cutting tool according to claim 1, wherein the hard phase is made of tungsten carbide.   The cutting tool according to any one of claims 1 to 3, wherein the binder phase is made of at least one element selected from the group consisting of iron, cobalt, and nickel.   The covering layer is composed of a carbide of element IVa, Va, VIa, aluminum or silicon, a nitride of the element, a carbonitride of the element, an oxide of the element, a carbonate of the element, the element The cutting tool of any one of Claims 1-4 which consists of at least 1 sort (s) of material chosen from the group which consists of carbonitride of the above, the boron nitride of the said element, and the boron boron nitride of the said element.   The cutting tool according to any one of claims 1 to 5, wherein a tensile stress of the coating layer is released.   The cutting tool according to claim 1, wherein the coating layer has a thickness of 3 μm to 20 μm.   In the cross section after polishing by ion milling, the coating layer has a width of 50 nm or more and 200 nm or less, an interval of 30 μm or more and 100 μm or less, and a width of a constituent region of 5.0 μm or more and 10.0 μm or less. The cutting tool according to claim 1, wherein the cutting tool has a certain crack. It is a manufacturing method of the cutting tool according to any one of claims 1 to 8,
The manufacturing method of a cutting tool provided with the process of forming the said coating layer into a film at the temperature of 800 degreeC or more and 1100 degrees C or less by a gaseous-phase synthesis method. It is a manufacturing method of the cutting tool according to any one of claims 1 to 8,
Depositing the coating layer in a chamber;
After the step of forming the coating layer, the coating layer is cooled at a speed of 10.0 ° C./min or more and 15.0 ° C./min or less while the inside of the chamber is maintained in a pressurized atmosphere of 0.1 MPa. And a cutting tool manufacturing method.