Cutting insert having ceramic coating
A cutting tool insert has a multilayer ceramic coating. The multilayer ceramic coating is a stratified structure of alternating sub layers of an oxide material and interfacial layers of a second material having good adhesion with the oxide material. The ceramic coating is deposited by chemical vapor deposition; each subsequently deposited interfacial layer serving to terminate a previously deposited oxide material sub layer and to serve as a surface for deposition of a subsequent oxide material sub layer. The second material is a solid solution of at least one element of the oxide material in a hard material.
1. A coated cutting insert comprising a substrate and a CVD-deposited multilayer ceramic coating formed over the substrate, the multilayer ceramic coating comprising:
alternating layers of α-Al 2 O 3 and an interfacial layer; wherein:
the α-Al 2 O 3 layers and the interfacial layers adhere to one another, with opposite sides of at least one interfacial layer adhering to different α-Al 2 O 3 layers; and
the interfacial layer is a solid solution of oxygen and aluminum in a matrix of TiCN, TiC or TiN.
2. The coated cutting insert according to claim 1 , wherein
the multilayer ceramic coating comprises at least five layers including three layers of α-Al 2 O 3 alternating with two layers of said interfacial layer.
3. The coated cutting insert according to claim 1 , wherein:
the interfacial layer is selected from the group consisting of TiAlON, TiAlOC and TiAlCON.
4. The coated cutting insert according to claim 3 , wherein:
the interfacial layer is TiAlCON.
5. The coated cutting insert according to claim 1 , wherein:
a ratio of a thickness of an α-Al 2 O 3 layer to a thickness of an interfacial layer is between 7 and 15.
6. The coated cutting insert according to claim 1 , further comprising:
an undercoat layer between the substrate and the ceramic coating, said undercoat layer comprising a hard material.
7. The coated cutting insert according to claim 6 , wherein:
the hard material of the undercoat layer is selected from the group consisting of TiC, TiCN and TiN.
8. The coated cutting insert according to claim 7 , wherein:
said undercoat layer has a thickness in the range of 2 μm to 15 μm.
9. The coated cutting insert according to claim 6 , further comprising:
a bonding layer between the undercoat layer and the ceramic coating.
10. The coated cutting insert according to claim 9 , wherein:
the bonding layer is one from the group consisting of:
(a) a layer of TiOCN;
(b) a layer of TiAlOCN;
(c) a layer of TiOCN followed by a layer of TiAlOCN; and
(d) a sandwich structure comprising a first layer of TiOCN followed by a layer of TiAlOCN followed by a second layer of TiOCN.
11. The coated cutting insert according to claim 9 , further comprising:
a base layer between the substrate and the undercoat layer.
12. The coated cutting insert according to claim 11 , wherein:
the base layer comprises TiN.
13. The coated cutting insert according to claim 12 , wherein:
the base layer has a thickness of between 0.1 μm and 1.5 μm.
14. The coated cutting insert according to claim 11 , further comprising:
an outer layer of TiN above the multilayer ceramic coating.
15. The coated cutting insert according to claim 14 , wherein:
said outer layer of TiN is absent from rake faces of the cutting insert.
16. The coated cutting insert according to claim 1 , further comprising:
a base layer formed over the substrate;
an undercoat layer formed over the base layer, the undercoat layer comprising a hard material; and
a bonding layer formed over the undercoat layer and below the multilayer ceramic coating.
17. The coated cutting insert according to claim 16 , further comprising:
an outer layer of TiN formed above the multilayer ceramic coating.
18. The coated cutting insert according to claim 16 , wherein:
the base layer comprises TiN;
the undercoat layer is selected from the group consisting of TiC, TiCN and TiN;
the bonding layer comprises a sandwich structure of TiOCN, TiAlOCN and TiOCN; and
the interfacial layer comprises TiAlCON.
19. A method of forming a CVD-deposited multilayer ceramic coating over a cutting insert having a substrate, the method comprising:
depositing, over said substrate, alternating layers of α-Al 2 O 3 and an interfacial layer such that the α-Al 2 O 3 layers and the interfacial layers adhere to one another, with opposite sides of at least one interfacial layer adhering to different α-Al 2 O 3 layers; wherein the interfacial layer is a solid solution of oxygen and aluminum in a matrix of TiCN, TiC or TiN.
20. The method according to claim 19 , comprising:
depositing the interfacial layer over an immediately preceding α-Al 2 O 3 layer prior to development of a columnar structure in said immediately preceding α-Al 2 O 3 layer.
21. The method according to claim 19 , wherein:
deposition of the interfacial layer over an immediately preceding α-Al 2 O 3 layer serves as a surface for deposition of a subsequent oxide α-Al 2 O 3 layer.
22. The method according to claim 19 , further comprising:
depositing a base layer over the substrate;
depositing an undercoat layer over the base layer, the undercoat layer comprising a hard material;
depositing a bonding layer over the undercoat layer and below said alternating layers of α-Al 2 O 3 and an interfacial layer.
23. The method according to claim 22 , wherein:
the base layer comprises TiN;
the undercoat layer is selected from the group consisting of TiC, TiCN and TiN;
the bonding layer comprises a sandwich structure of TiOCN, TiAlOCN and TiOCN; and
the interfacial layer comprises TiAlCON.
24. The method according to claim 22 , further comprising:
depositing an outer layer of TiN over the multilayer ceramic coating.
25. The method according to claim 24 , further comprising:
selectively removing said outer layer of TiN from rake faces of the cutting insert.