Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-09-08
2001-10-30
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C051S295000, C051S307000, C051S309000, C407S119000, C428S212000, C428S336000, C428S697000, C428S698000, C428S699000
Reexamination Certificate
active
06309738
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to a hard multilayer coated tool which includes a substrate made of a high-speed tool steel, cemented carbide, cermet or CBN sintered body, and a hard multilayer coating covering the substrate.
BACKGROUND ART
Conventionally, for the purpose of increasing the wear resistance of a tool which is made of high-speed tool steel, cemented carbide, cermet or CBN sintered body, the tool is covered with a hard coating formed of a nitride, carbide or carbon-nitride of Ti, Cr, Hf or Zr, by a physical vapor deposition method (PVD method), a chemical vapor deposition method (CVD method), or other suitable method, such that the hard coating has the average thickness of 0.50-10.0 &mgr;m. In recent years, for the purpose of increasing the rust or oxidation resistance of the hard coating so as to satisfy the requirement for increased cutting velocity, there has been widely used a tool which is formed by covering the substrate or base material made of a cemented carbide with a hard coating of AlTiN or AlTiCN by the PVD method. For example, JP-B2-4-53642 discloses a hard coating which has a thickness of 0.50-10.0 &mgr;m and which is formed of a composite solid solution of carbide, nitride or carbon nitride of Al and Ti. Further, JP-B2-5-67705 discloses a hard coating which has a thickness of 0.80-10.0 &mgr;m and which is formed of a wear resistant coating having a chemical composition wherein the content of aluminum is in a range of 56-75%, in an attempt to further increase the heat resistance of the hard coating. Still further, JP-A-7-97679 discloses a hard multilayer coating which has a total thickness of 0.50-10.0 &mgr;m and a stoichiometrically aluminum-rich bulk composition, wherein titanium-rich ultra thin AlTiN layers and aluminum-rich ultra thin AlTiN layers are alternately superposed on each other such that the pitch or spacing interval between the adjacent tanium-rich ultra thin AlTiN layers, or between the adjacent aluminum-rich ultra thin AlTiN layers is in a range of 0.50-20.0 nm (nanometer).
In recent years, the required cutting velocity has been further increased while the work material to be cut has become harder. Where the conventional coated tool is used for cutting the harder work material at a required high cutting velocity, the coating of the tool tends to be slightly broken or chipped instead of being worn. Particularly, the aluminum-rich AlTiN coating is easily chipped due to its high hardness of 2600 Hv or more. Thus, the conventional coated tool does not exhibit the desired degree of wear resistance, irrespective of whether the tool is covered by a coating constituted by a single layer, a coating constituted by a plurality of layers, or a coating constituted by layers each having a considerably small thickness. The coating of the tool tends to be chipped more easily when the hardness of the coating is relatively high, so that the tool with the hard coating is not capable of exhibiting an expected or satisfactory degree of wear resistance.
DISCLOSURE OF INVENTION
The present invention was developed under the above-described background situation and has an object of providing a hard multilayer coated tool which has an outstandingly improved toughness (the opposite condition to brittleness) while assuring a high heat resistance without deteriorating the wear resistance.
The above object may be achieved by the principle of the present invention which is a hard multilayer coated tool comprising: (a) a substrate; and (b) a multilayer coating covering the substrate, the multilayer coating comprising first and second coating layers which are alternately laminated on the substrate, each of the first coating layers having an average thickness of 0.01-0.50 &mgr;m and containing titanium therein, each of the second coating layers having an average thickness of 0.01-0.50 &mgr;m and containing aluminum therein, the multilayer coating having an average thickness of 0.50-10.0 &mgr;m.
The hard multilayer coating according to the present invention is formed through ion plating method, sputtering method or other physical vapor deposition method (PVD method), or alternatively, plasma CVD, heat CVD or other chemical vapor deposition method (CVD method). Where the hard multilayer coating of the present invention is formed through the ion plating method, the ionized metal component is reacted in a furnace under N
2
atmosphere or CH
4
atmosphere. The hard multilayer coating is obtained by using a target made of an alloy including titanium and a target made of an alloy including aluminum. The two targets are alternately activated to serve as the cathode, so that the first and second coating layers are alternately laminated on the substrate, namely, whereby the first and second coating layers are alternately superposed on each other. The compositions of the two targets correspond to those of the first and second coating layers.
The material of the substrate may be any one of various tool materials such as high speed tool steel, cemented carbide, cermet and CBN sintered body. It is preferable that one of the first coating layers constitute an innermost layer of the multilayer coating, and that one of the coating layers other than the first coating layers constitute an outermost layer of the multilayer coating which is remote from the substrate.
If the first coating layer, which has a relatively low degree of hardness due to the absence of aluminum in the first coating layer or due to the lower percentage content of aluminum in the first coating layer than in the second coating layer, has a thickness of less than 0.01 &mgr;m, the multilayer coating is not capable of absorbing an impact applied thereto when the tool is in process of machining or cutting the work material. If the first coating layer has a thickness of more than 0.50 &mgr;m, on the other hand, the wear resistance and the heat resistance of the entirety of the multilayer are undesirably reduced. Further, if the second coating layer, which has a relatively high degree of hardness due to the content of aluminum in the second coating layer or due to the higher percentage content of aluminum in the second coating layer than in the first coating layer, has a thickness of less than 0.01 &mgr;m, the multilayer coating is not capable of exhibiting a sufficient wear resistance. If the second coating layer has a thickness of more than 0.50 &mgr;m, on the other hand, the second coating layer is inevitably broken or chipped even where the second coating layer is interposed between the first coating layers which absorb the impact applied to the multilayer coating. Therefore, the thickness of each coating layer is limited to range from 0.01 to 0.50 &mgr;m.
According to a first aspect of the present invention, the each of the first coating layers has a composition represented by (Al
X
Ti
1−X
) (N
Y
C
1−Y
) wherein 0.05≦X≦0.50, 0.50≦Y≦1.00, while the each of the second coating layers has a composition represented by (Al
Z
Ti
1−Z
)(N
T
C
1−T
) wherein 0.50<Z≦0.80, 0.50≦T≦1.00.
According to a first preferred form of the first aspect of the present invention, the multilayer coating has a stoichiometrically aluminum-rich bulk composition.
The aluminum-rich stoichiometric composition in the entirety of the multilayer coating leads to satisfaction in the following expression (1), wherein X, Z represent the mixing ratio of aluminum in the respective first and second coating layers; l
1
represents the average thickness of the first coating layer; and l
2
represents the average thickness of the second coating layer.
(Xl
1
+Zl
2
)/(l
1
+l
2
)>0.5 (1)
According to a second aspect of the present invention, the each of the first coating layers has a composition represented by Ti(N
x
C
1−x
) wherein 0.50≦x≦1.00, while the each of the second coating layers has a composition represented by (Al
y
Ti
1−y
)(N
z
C
1−z
) wherein 0.20≦y≦0.80, 0.50≦z≦1.00.
If the second coating layer has an aluminum co
Oliff & Berridg,e PLC
OSG Corporation
Turner Archene
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