Control and characterization of texture in CVD α-Al
CVD Alumina coating has been one of the most important materials for wear resistant application for many years. Recently, texture control in α-Al 2 O 3 has attracted increasing attention due to the possibility to further improve the anisotropic properties such as thermal conductivity and mechanical properties. The influence of process parameters on textures is complex. In the present application, the influence of nucleation surface condition and H 2 S on the texture in CVD α-Al 2 O 3 coatings has been investigated. It has been shown that without the addition of H 2 S, the crystal orientation in the Al 2 O 3 coatings is primarily dominated by the nucleation surface condition, whereas the effect of reactant composition on texture is minimal. On the other hand, in the presence of H 2 S during growth, reactant composition also plays an important role in affecting the crystal orientation. This effect is likely due to the strong interaction between the Al 2 O 3 surface and the H 2 S.
1. A coated article comprising:
a substrate; and
a coating adhered to the substrate, the coating comprising a layer of α-Al 2 O 3 deposited by chemical vapor deposition (CVD), the α-Al 2 O 3 layer comprising a gradient of two or more texture coefficients (TC) along thickness of the α-Al 2 O 3 layer, wherein the texture coefficients of the gradient are selected from the (012), (104), (110), (006), (113), (202), (024) and (116) growth directions and defined as:
TC
(
hkl
)
=
I
(
hkl
)
I
o
(
hkl
)
{
1
n
Σ
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),
wherein the gradient comprises a nucleation TC in the (110) growth direction and a bulk TC.
2. The coated article of claim 1 , wherein the nucleation TC has a value greater than 5 in the (110) growth direction.
3. The coated article of claim 2 , wherein the bulk TC has a value greater than 3 in the (012) growth direction.
4. The coated article of claim 2 , wherein the bulk TC has a value greater than 4 in the (006) growth direction.
5. The coated article of claim 1 , wherein the nucleation TC extends into the α-Al 2 O 3 layer a distance of up to 1 μm from a surface on which the α-Al 2 O 3 layer is deposited.
6. The coated article of claim 1 , wherein the nucleation TC extends into the α-Al 2 O 3 layer a distance of 50-500 nm from a surface on which the α-Al 2 O 3 layer is deposited.
7. The coated article of claim 1 , wherein growth directions of the nucleation TC and bulk TC are offset by at least 45 degrees.
8. The coated article of claim 1 , wherein growth directions of the nucleation TC and bulk TC are offset by 90 degrees.
9. A coated article comprising:
a substrate; and
a coating adhered to the substrate, the coating comprising a layer of α-Al 2 O 3 deposited by chemical vapor deposition (CVD), the α-Al 2 O 3 layer comprising a gradient of two or more texture coefficients (TC) along thickness of the α-Al 2 O 3 layer, wherein the texture coefficients of the gradient are selected from the (012), (104), (110), (006), (113), (202), (024) and (116) growth directions and defined as:
TC
(
hkl
)
=
I
(
hkl
)
I
o
(
hkl
)
{
1
n
Σ
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),
wherein the layer of α-Al 2 O 3 has a grain size gradient between a nucleation zone and a bulk zone, the bulk zone having larger grains with higher aspect ratio relative to grains of the nucleation zone.
10. The coated article of claim 9 , wherein the gradient comprises a nucleation TC and a bulk TC.
11. The coated article of claim 10 , wherein the nucleation TC is in the (110) growth direction.
12. The coated article of claim 11 , wherein the bulk TC is in the (006) growth direction.
13. The coated article of claim 11 , wherein the bulk TC is in the (012) growth direction.
14. The coated article of claim 10 , wherein growth directions of the nucleation TC and bulk TC are offset by at least 45 degrees.
15. The coated article of claim 10 , wherein growth directions of the nucleation TC and bulk TC are offset by 90 degrees.