WO2017115987A1 - Hard coating for cutting tool - Google Patents

Abstract

The present invention relates to a hard coating, which is formed on a base material made of a cemented carbide for a cutting tool, comprises a TiCN layer and an α-Al₂O₃ thin film first grown in the (006) plane, and has excellent thin film peeling resistance against the impact occurring at the time of cutting processing, thereby greatly improving the lifetime of the cutting tool. The hard coating according to the present invention is formed with a thickness of 5-30 ㎛ on a base material comprising 7-15 wt% of Co, 0-5 wt% of a carbide or a carbonitride containing a Group 4, 5, or 6 element, and the balance WC and inevitable impurities. The hard coating comprises: a TiC_xN_yO_z (x+y+z=1, x＞0, y＞0, z≥0) layer, which is formed on the base material, has a thickness of 2-15 ㎛ and a residual stress of 0-400 MPa, and is formed of columnar crystals; a Al_1-aTi_aC_xN_yO_z (a≥0, x+y+z=1, x＞0, y＞0, z≥0) layer, which is formed on the TiC_xN_yO_z (x+y+z=1, x＞0, y＞0, z≥0) layer and has a thickness of 1-2 ㎛; and an alpha-phase alumina layer, which is formed on the Al_1-aTi_aC_xN_yO_z (a≥0, x+y+z=1, x＞0, y＞0, z≥0) layer and has a thickness of 1-10 ㎛ and a residual stress of -1,000 to -50 MPa, wherein the residual stress difference (ΔS) between the TiC_xN_yO_z (x+y+z=1, x＞0, y＞0, z≥0) layer and the alpha-phase alumina layer is 500 MPa or less and the TC(006) of the alpha-phase alumina layer is greater than 1.4.

Description

Hard film for cutting tools

The present invention relates to a hard coating formed on a base material for cutting tools, and more particularly, is formed by a chemical vapor deposition method (hereinafter referred to as 'CVD') on the base material for cutting tools made of cemented carbide, and the TiCN layer (006). Α-Al ₂ O ₃ first grown with cotton The present invention relates to a hard coating including a thin film and excellent in peeling resistance of the thin film against impact generated during cutting, thereby greatly improving the life of the cutting tool.

In general, cemented carbide is used as a cutting tool after forming a hard coating layer on its surface to increase abrasion resistance. The hard coating is formed by a CVD method or a physical vapor deposition method (hereinafter referred to as a 'PVD method'). .

On the other hand, the cutting edge of the cutting tool is exposed to a high temperature environment of about 1000 ℃ during high-speed processing of hard materials, not only wear and tear due to friction and oxidation due to contact with the workpiece, but also subjected to mechanical shock such as interruption. Therefore, cutting tools require properties such as proper oxidation resistance, wear resistance and chipping resistance.

To this end, the hard film for cutting tools is generally composed of a single layer or a multi-layered non-oxide thin film, an oxide-based thin film having excellent oxidation resistance or a mixed layer thereof. Examples of the non-oxide thin film include TiN, TiC, TiCN. Carbide, nitride, carbonitride of Group 4, 5 and 6 metal elements on the periodic table such as, and the like is an example of the oxide-based thin film is α-Al ₂ O ₃ .

Of these, α-Al ₂ O ₃ is a material that is widely used in cutting tool coatings because it is a phase stable at high temperatures and thus does not generate phase transformation during cutting and exhibits excellent wear resistance.

Factor influences the wear resistance of such α-Al ₂ O ₃ is known as anisotropy (anisotropy) of the α-Al ₂ O ₃ grain size and the α-Al ₂ O ₃ grains of. In connection with controlling the anisotropy of the α-Al ₂ O ₃ grains, a method of preferentially growing the (110) plane, the (012) plane, the (104) plane, the (006) plane, or the like is known.

Of these, α-Al ₂ O ₃ preferentially grown to (006) plane. In the case of thin films, it suppresses the ductile breakdown of α-Al ₂ O ₃ and improves plastic resistance deformation, thereby reducing the insert wear and K _T wear of the insert during cutting of steel and greatly improving the tool life. In recent years, it is widely applied to cutting tools.

However, the shape of each thin film constituting the hard coating film for the cutting tool differs depending on the base material and the cutting tool used for forming the hard coating, and thus, α-Al ₂ O ₃ preferentially grown to the (006) plane. Even if a thin film is applied, it is necessary to further adapt the state of the base material and other thin films in order to improve the life of the cutting tool.

In this regard, Patent Document 1 (US Patent Publication No. 2011-0045283) discloses a technique for improving the life of a cutting tool by applying a compressive residual stress to a hard film through post-treatment such as blasting. Α-Al ₂ O ₃ First Grows Technology to (006) Plane When applied to a hard film for cutting tools including a thin film as it is, there is a side that the improvement in life improvement is not enough.

The present invention aims to solve the problem of providing a hard film for a cutting tool that can improve the life of the cutting tool compared to the conventional one by suppressing the peeling of the hard film formed on the cutting tool against the impact generated during cutting. .

The present invention is to solve the above problems, Co 7 ~ 15% by weight, Carbide or carbonitrides 0 to 5% by weight containing elements of Group 4, Group 5 or 6, and the remaining WC and inevitable impurities the hard coating having a thickness of 5 ~ 30㎛ formed on a base material, wherein the hard coating is formed on the base material, and a thickness of 2 ~ 15㎛, a residual stress is 0 ~ 400MPa, TiC _x N formed in a columnar _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer and the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0 , z≥0) formed on the layer and having a thickness of 1 to 2 μm, Al _{1 -a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0 , z≥0) and the Al _{1 - a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer And an alpha phase alumina layer having a thickness of 1 to 10 µm and a residual stress of -1,000 MPa to -50 MPa, wherein TiC _x N _y O _z (x + y + z = 1, x> 0, y> The residual stress difference (ΔS) between 0, z≥0) layer and alpha phase alumina layer is 500 MPa or less, Provides a hard coating film for the cutting tool, characterized in that TC (006) is greater than 1.4, calculated by the group on the alpha-alumina, the following [Expression 1].

[Equation 1]

TC (hkl) = I (hkl ) / Io (hkl) {1 / nΣI (hkl) / Io (hkl)} -1

Where I (hkl) = (hkl) reflectivity, Io (hkl) = standard intensity according to JCPDS card 46-1212, n = number of reflections used in the calculation, (hkl) reflections are (012), (104 ), Using (110), (006), (113) and (116))

In the present invention, in the hard coating formed on the surface of the insert base material for milling, the residual stress of the alumina layer is in the compressive stress state, the stress difference between the alumina layer and the TiCN layer is 500 MPa or less, and TC (006) of the alumina is By making it exceed 1.4, the effect which remarkably improves cutting tool life compared with the conventional cutting tool can be acquired.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention illustrated below may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

MEANS TO SOLVE THE PROBLEM The present inventors can suppress the peeling of a hard film with respect to the impact which arises at the time of cutting when it is applied to the cutting insert for milling with the hard film containing the alpha-phase alumina layer which was first grown to the (006) plane. As a result, the coefficient of thermal expansion of the cemented carbide base material for milling containing 7 to 15% by weight of Co is about 6.0 to 6.5 × 10 ^-6 / K, and the coefficient of thermal expansion of the c-axis of alumina having HCP crystal structure is about 7.0 × 10, and the ^-6 / degree K, and the thermal expansion coefficient of TiN about 9.35 × 10 ^-6 / K, and the thermal expansion coefficient of the TiC consider about 7.4 × 10 ^-6 / K around a point, constituting the base material and the hard coating In order to minimize the difference in coefficient of thermal expansion between the thin films, the alumina layer is grown first in the (006) orientation, and the TiCN layer formed as the lower layer forms a carbon-rich layer as much as possible, and forms a hard film. Alpha phase grown preferentially to (006) plane When the residual stress state of the alumina layer is maintained in the compressive stress state and the stress difference between the TiCN layer and the alpha phase alumina layer is controlled, the peeling between the thin films or the base material and the thin film constituting the hard coating by external impact is reduced, The present invention has been found to suppress the breakdown at and to obtain an improved service life compared to the prior art.

The hard coating according to the present invention comprises a base material phase comprising Co 7 to 15 wt%, carbides or carbonitrides containing elements of Group 4, 5 or 6 and 0 to 5 wt%, and the remaining WC and unavoidable impurities. It is formed in the thickness of 5 ~ 30㎛, is formed on the base material, the thickness is 2 ~ 15㎛, the residual stress is 0 ~ 400MPa, TiC _x N _y O _z (x + y + formed in columnar top in the z = 1, x> 0, y> 0, z≥0) layer and the _{TiC x N y O z (x} + y + z = 1, x> 0, y> 0, z≥0) layer Formed, and having an Al _{1 - a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer having _a thickness of 1 to 2 µm, It is formed on the Al _{1 - a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer, the thickness is 1 ~ 10㎛ And an alpha phase alumina layer having a residual stress of -1,000 MPa to -50 MPa, wherein the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer and The residual stress difference (ΔS) between the alumina layers of the alpha phase is 500 MPa or less, and the alumina of the alpha phase is 1 characterized in that TC (006) is greater than 1.4, calculated by the.

[Equation 1]

TC (hkl) = I (hkl ) / Io (hkl) {1 / nΣI (hkl) / Io (hkl)} -1

Where I (hkl) = (hkl) reflectivity, Io (hkl) = standard intensity according to JCPDS card 46-1212, n = number of reflections used in the calculation, (hkl) reflections are (012), (104 ), Using (110), (006), (113) and (116))

The base material is brittle increases when the content of Co is less than 7% by weight, wear resistance is reduced when the content of more than 15% by weight, it is preferable to add in the range of 7 to 15% by weight.

Carbide or carbonitride containing the elements of the Group 4, 5 or 6 group is more than 5% by weight since the occurrence of thermal cracks due to repeated thermal shock increases when the content exceeds 5% by weight, Do.

The TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer and the TiC _x N _y O _z (x + y + z = 1, x> 0 , y > 0, z > 0) layer has a slight improvement in mechanical wear when the thickness is less than 2 mu m, and the brittleness of the thin film increases when the thickness is more than 15 mu m, so that the thickness is preferably 2 to 15 mu m. The residual stress is preferably a compressive stress, but when it is in a compressive stress state, it is difficult to maintain the residual stress difference between the alumina layers located above 500 MPa or less, or because the damage of the alumina layer becomes large, a tensile stress of more than 400 MPa is preferable. In the state, since the thin film loss easily occurs due to external impact, the range of 0 to 400 MPa is preferable.

Further, in the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer, when x is 0.5 or less, the difference in thermal expansion coefficient with the base material becomes large, which is not preferable. , If it is more than 0.9, since the thin film is easily oxidized in a high temperature oxidation atmosphere, it is preferable to maintain the range of more than 0.5 and 0.9 or less, and x is more preferably 0.6 or more.

The Al _{1 - a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer has a thickness of less than 1 µm. If the upper layer and the lower layer does not function, and if it exceeds 2㎛ brittle strong and easily cracks, 1 ~ 2㎛ range is preferred.

In addition, since the alpha phase alumina layer does not exhibit abrasion resistance and oxidation resistance when the thickness is less than 1 μm, and becomes brittle strong ceramic layer when it exceeds 10 μm, the range of 1 to 10 μm is preferable. .

In addition, the residual stress of the alumina layer in the alpha phase is in a compressive stress state, and when the absolute value is less than 50 MPa, the thin film toughness does not function. Since it is highly likely to occur, it is preferable to maintain the range of -1,000 MPa to -50 MPa.

In addition, it is preferable that the alpha phase alumina layer is preferentially grown to the (006) plane, and the TC (006) calculated by the above formula (1) is more than 1.4, more preferably more than 3.0, and most preferably more than 4.0.

In addition, the residual stress difference (ΔS) between the alumina layer of the alpha phase and the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer is greater than 500 MPa. The possibility of peeling increases due to stress nonuniformity, and it is preferable to maintain it at 500 MPa or less, and more preferably 400 MPa or less.

EXAMPLE

As an example of the present invention, a hard coating having a structure shown in Table 1 was formed on a cemented carbide base material having the composition shown in Table 1 below. In addition, the hard film according to Comparative Example 1 to Comparative Example 4 was formed for comparison with the embodiment of the present invention.

Specifically, the cemented carbide base material is an insert prepared by pressing and sintering a powder composed of 10 wt% Co and 1.5 wt% of carbide with TaC and the remaining WC with SPCN1203EDR (Korean metallurgy model number), and then grinding the upper and lower surfaces and honing the edges. Was used.

In addition, the surface of the insert is a hydrocarbon gas such as TiCl ₄ gas, CH ₃ CN, N ₂ , H ₂ , C ₂ H ₄ , C ₂ H ₆ , at a process partial pressure of 60 to 80 mbar and a process temperature of 750 to 900 ° C. Chemical vapor deposition (CVD) using HCl gas to form a columnar titanium carbon nitride (TiCN) layer. At this time, the carbon content of the titanium carbon nitride (TiC _x N _1-x ) layer ( _x ≧ 0.6) was higher than the nitrogen content to form a carbon rich phase.

Next, as the interfacial layer on the titanium carbonitride layer, using a gas such as TiCl ₄ and CO or CO ₂ , CH ₄ , N ₂ , H _{2 at a} process partial pressure of 100 ~ 150 mbar, a process temperature of 900 ~ 1010 ℃ Titanium carbonaceous oxide (TiC _x N _y O _z , x + y + z = 1, x> 0, y> 0, z> 0) layer was formed by chemical vapor deposition (CVD).

And on the titanium carbon oxide layer, TC (006) by using a gas of AlCl ₃ and gas such as CO ₂ or CO, HCl, H ₂ S, H _{2 at a} process partial pressure of 50 ~ 80 mbar, a process temperature of 1000 ~ 1050 ℃. Α-Al ₂ O ₃ with preferential orientation so that) A layer was formed. Α-Al ₂ O ₃ with a preferred orientation of (006) The layer was formed through the control of the flow rate of H ₂ S gas in the range of 100 ~ 600ml and the flow rate of HCl gas in the range of 1-3L.

In addition, for the stress control of the α-Al ₂ O ₃ layer, a blasting treatment was performed.

In addition, as the outermost layer, a titanium nitride (TiN) layer was formed by chemical vapor deposition (CVD) using TiCl ₄ gas and N ₂ and H ₂ gas at a process partial pressure of 100 to 200 mbar and a process temperature of 850 to 1000 ° C. It was formed by a method of depositing less than 탆.

In the present invention, the outermost TiN layer is intended for wear identification and is a layer that can be selectively formed.

On the other hand, in the hard film according to Comparative Examples 1 to 4, the formation of the TiCN layer, the interfacial layer, the TiN layer is the same as the embodiment of the present invention, and through the flow rate control of the reaction gas when forming the alumina of the alpha phase (006) Residual stresses were controlled in such a way that they did not preferentially grow into cotton or do not undergo post-treatment.

The structure of the hard film according to Examples and Comparative Examples 1 to 4 of the present invention formed as described above is shown in Table 1 below.

	Base material composition (% by weight)			Film thickness (㎛)
	Co	TaC	WC	MT-TiCN layer	TiAlCNO layer	Alpha-alumina layer	TiN layer
Comparative Example 1	10	1.5	bal.	4.1	1.1	5	One
Comparative Example 2	10	1.5	bal.	4.5	1.1	5.1	1.2
Comparative Example 3	10	1.5	bal.	5	One	4.7	1.3
Comparative Example 4	10	1.5	bal.	4.3	1.5	4.8	1.2
Example	10	1.5	bal.	4.7	1.2	4.5	One

As shown in Table 1, the composition of the hard base material according to the Examples and Comparative Examples 1 to 4 is the same, and the thickness of the MT-TiCN layer, TiAlCNO layer, alpha-phase alumina layer and TiN layer is almost similar. Formed.

However, as shown in Table 2 below, the preferred growth direction of the alpha-phase alumina layer and the residual stress through the post-treatment were adjusted differently.

The cutting tool insert thus prepared was evaluated for cutting life as follows.

-Processing type: Shouldering processing

-Workpiece: SKD11 (Dimension 100mm × 200 × 300mm)

-Vc (cutting speed): 250mm / min

fz: 0.2mm / min

-ap (depth of cut): 2mm

ae: 10mm, wet

The results of evaluating the cutting life under the above conditions are shown in Table 2 below.

	TC (006)	Residual stress (MPa)		Stress difference (ΔS) (MPa)	life span
		TiCN layer	Alumina layer
Comparative Example 1	0	323	450	120	701
Comparative Example 2	0	247	-315	562	813
Comparative Example 3	3.4	213	-451	664	961
Comparative Example 4	4.8	342	421	79	892
Example	5.1	270	-97	367	1153

In Table 2, TC (006) shows the preferential growth tendency toward the (006) plane of the alpha phase alumina, '-' in the residual stress means a compressive stress, the tensile stress in the absence of '-' The stress difference ΔS means an absolute value of the stress difference between the TiCN layer and the alumina layer, and the lifespan means the amount of chip removal per unit area (cm 2) per unit minute (min).

In the results of Table 2, in comparison with Comparative Example 1 and Comparative Example 2, it can be seen that when the stress of the alpha-phase alumina layer in the compressive stress state, the life of the cutting tool is improved compared to the tensile stress state.

In comparison with Comparative Example 2 and Comparative Example 3, when the stress of the alpha-phase alumina layer is a compressive stress and the TC (006) is preferentially grown to be greater than 3, the life of the cutting tool is remarkable compared to Comparative Example 2. It can be seen that increases.

In addition, in comparison with Comparative Example 3 and Comparative Example 4, the TC (006) of the alpha phase alumina layer of Comparative Example 4 is 4.8, compared with 3.4 of the TC (006) of the alpha phase alumina layer of Comparative Example 3 Although the preferential growth tendency of was higher, the stress state of the alpha-phase alumina layer was in the tensile stress state, and the life of the cutting tool was lower than in Comparative Example 3.

In addition, in comparison with Example 3 and Comparative Example 3, both hard coatings had a TC (006) of more than 3 alpha-alumina layers, and the alumina had a compressive stress state or a comparative stress in the stress difference between the alumina and TiCN layers. 3 exceeds 500 MPa, but the embodiment has a difference of 500 MPa or less, and in the residual stress of the alpha-phase alumina layer, there is a difference in that the comparative compressive stress is present in Comparative Example 3, which is significantly higher than that of Comparative Example 3. Improved cutting tool life.

That is, the conditions that the residual stress of the alpha-phase alumina layer is in a compressive stress state, the residual stress difference between the alpha-phase alumina layer and the TiCN layer is 500 MPa or less, and the TC (006) of the alpha-phase alumina layer are more than 3 are all satisfied. Only then, it can be seen that an excellent effect of improving the life of a cutting tool as in the embodiment of the present invention can be obtained.

The difference in residual stress between the alumina layer and the TiCN layer is preferably 500 MPa or less, and more preferably 400 MPa or less.

Claims (4)

1. 5-15 micrometers in thickness formed on the base material containing 7-15 weight% of Co, 0-5 weight% of carbides or carbonitrides containing the elements of group 4, 5, or 6, and the remaining WC and unavoidable impurities As a hard coating of,

   The hard coating is formed on the base material, the thickness is 2 ~ 15㎛, the residual stress is 0 ~ 400MPa, formed in columnar top TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer,

   The _{TiC x N y O z (x} + y + z = 1, x> 0, y> 0, z≥0) is formed on the layer, the _{Al 1-a Ti a C x} N having a thickness of 1 ~ 2㎛ _{a y} O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer,

   It is formed on the Al _{1 - a} Ti _a C _x N _y O _z (a≥0, x + y + z = 1, x> 0, y> 0, z≥0) layer, the thickness is 1 ~ 10㎛ It comprises an alpha phase alumina layer having a residual stress of -1,000 MPa to -50 MPa,

   The residual stress difference ΔS between the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z≥0) layer and the alumina layer of the alpha phase is 500 MPa or less,

   The alumina layer of the alpha phase is a hard film for a cutting tool, characterized in that the TC (006) calculated by the following [Formula 1] is more than 1.4.

   [Equation 1]

   TC (hkl) = I (hkl ) / Io (hkl) {1 / nΣI (hkl) / Io (hkl)} -1

   Where I (hkl) = (hkl) reflectivity, Io (hkl) = standard intensity according to JCPDS card 46-1212, n = number of reflections used in the calculation, (hkl) reflections are (012), (104 ), Using (110), (006), (113) and (116))
2. The method of claim 1,

   The residual stress difference (ΔS) is 400MPa or less, hard film for cutting tools.
3. The method of claim 1,

   TC (006) of the alumina layer of the alpha phase is more than 3, hard coating for cutting tools.
4. The method of claim 1,

   Hard film for a cutting tool, in the TiC _x N _y O _z (x + y + z = 1, x> 0, y> 0, z ≧ 0) layer, wherein x is greater than 0.5 and 0.9 or less.