Surface coated cutting tools
In one aspect, cutting tools are described herein comprising wear resistant coatings employing one or more refractory layers of polycrystalline α-Al 2 O 3 . Briefly, a coated cutting tool described herein comprises a substrate, and a coating adhered to the substrate, the coating comprising a layer of polycrystalline α-Al 2 O 3 deposited by chemical vapor deposition (CVD), wherein at least 5% of all grain boundaries in the polycrystalline α-Al 2 O 3 layer have a misorientation angle less than 15 degrees as determined using a field-emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector.
1 . A coated cutting tool comprising:
a substrate; and
a coating adhered to the substrate, the coating comprising a layer of polycrystalline α-Al 2 O 3 deposited by chemical vapor deposition (CVD), wherein 5% to 15% of all grain boundaries in the polycrystalline α-Al 2 O 3 layer have a misorientation of 2-5 degrees and at least 5% of all grain boundaries in the polycrystalline α-Al 2 O 3 layer have a misorientation of greater than 5 degrees up to 15 degrees as determined using a field-emission scanning electron microscope (FESEM) and an electron backscatter diffraction (EBSD) detector; and wherein the polycrystalline α-Al 2 O 3 layer has a texture coefficient (TC) greater than 6 for the (006) growth direction, the texture coefficient being defined as:
T
C
(
hkl
)
=
I
(
hkl
)
I
o
(
hkl
)
{
1
n
∑
I
(
hkl
)
I
o
(
hkl
)
}
-
1
where
I(hkl)=measured intensity of the (hkl) reflection
I o (hkl)=standard intensity of the (hkl) reflection according to International Center for
Diffraction Data (ICDD) card 43-1484
n=number of reflections used in the TC calculation
(hkl) reflections used in the TC calculation are (012), (104), (110), (006), (113), (202), (024) and (116).
2 . The coated cutting tool of claim 1 , wherein at least 6% of all grain boundaries in the polycrystalline α-Al 2 O 3 layer have a misorientation of greater than 5 degrees up to 15 degrees.
3 . The coated cutting tool of claim 1 , wherein 7-10% of all grain boundaries of polycrystalline α-Al 2 O 3 layer have a misorientation of 2-5 degrees and 6.5-10% of all grain boundaries of polycrystalline α-Al 2 O 3 layer have a misorientation of greater than 5 degrees up to 15 degrees.
4 . The coated cutting tool of claim 1 , wherein a ratio of grain boundaries in the polycrystalline α-Al 2 O 3 layer having misorientation of 2-5 degrees to grain boundaries having misorientation of greater than 5 degrees up to 15 degrees has a value of 0.7 to 1.8.
5 . The coated cutting tool of claim 4 , wherein the ratio is 0.9-1.7.
6 . The coated cutting tool of claim 4 , wherein the ratio is 1.3-1.6.
7 . The coated cutting tool of claim 4 , wherein the ratio is 1.4-1.7.
8 . The coated cutting tool of claim 1 , wherein the polycrystalline α-Al 2 O 3 layer has a thickness of 1-20 μm.
9 . The coated cutting tool of claim 1 , wherein the polycrystalline α-Al 2 O 3 layer has a columnar grain structure.
10 . The coated cutting tool of claim 1 , wherein the TC (006) is greater than 7.
11 . The coated cutting tool of claim 1 , wherein the polycrystalline α-Al 2 O 3 layer has a texture coefficient (TC) greater than 5 for the (0 0 12) growth direction, the texture coefficient being defined as:
T
C
(
hkl
)
=
I
(
hkl
)
I
o
(
hkl
)
{
1
n
∑
I
(
hkl
)
I
o
(
hkl
)
}
-
1
where
I(hkl)=measured intensity of the (hkl) reflection
I o (hkl)=standard intensity of the (hkl) reflection according to International Center for
Diffraction Data (ICDD) card 42-1468
n=number of reflections used in the TC calculation
(hkl) reflections used in the TC calculation are (012), (104), (110), (113), (116), (300) and (0 0 12).
12 . The coated cutting tool of claim 11 , wherein the TC (0 0 12) is greater than 6.
13 . The coated cutting tool of claim 12 , where in a ratio of TC (006) to TC (0 0 12) is greater than 1 up to 1.2.
14 . The coated cutting tool of claim 1 , wherein the coating further comprises one or more inner layers between the layer of polycrystalline α-Al 2 O 3 and the substrate.
15 . The coated cutting tool of claim 14 , wherein the one or more inner layers comprise one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements selected from the group consisting of non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table.
16 . The coated cutting tool of claim 15 , wherein one or more inner layers comprise a TiCN layer.
17 . The coated cutting tool of claim 1 , wherein the coating further comprises one or more outer layers over the multiphase refractory layer.
18 . The coated cutting tool of claim 1 , wherein the substrate comprises cemented carbide comprising metallic binder in an amount of 1-15 weight percent.
19 . The coated cutting tool of claim 1 , wherein the substrate comprises cemented carbide comprising metallic binder in an amount of 5-12 weight percent.