Wear protection layer

Details Wear protection layer Wear protection layer

1997-07-31

2001-06-12

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C428S472000, C428S698000, C428S699000

Reexamination Certificate

active

06245446

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention resides in a wear protection coating comprising of a plurality of layers including a first layer of a metallic hard material dispose directly on a substrate and additional layers disposed on the first metallic hard material layer including in a periodic repetitive arrangement metallic hard and non-metallic materials.
Such a wear protection layer is known for example from DE AS 29 17 348. This patent publication discloses a compound body comprising a base with one or several hard metal layers of different composition without bonding metals, each having a thickness of 1 to 50 &mgr;m. One of the hard material layers with thickness of 0.02 to 0.1 &mgr;m (20 to 100 nm) each, wherein the hard material composition of each individual layer is different from the hard material composition of the two adjacent single layers. A preferred embodiment of the wear protection layer resides in a first layer of titanium-carbide disposed on the base on which alternately a multitude of layers of the metallic hard materials titanium carbide, titanium nitrate or titanium carbon nitride on one hand, and, on the other hand, the heteropolar hard materials aluminum oxide or zirconium oxide are disposed. The final outer layer may comprise aluminum oxide with a small nitrogen content.
Another wear protection layer is known from DE 3512986 Al. The various layers of metallic hard material may be combinations of the following metallic hard materials: TiC/TiN; TiC/TiB
2
; TiN/TiB
2
; TiB
2
/WC; TiB
2
/Ti(C
1
N); TiB
2
/Ti
1
V)C; TiB
2
/(Ti,W)C; (Ti,V)B
2
//(Ti,V)C; (Ti,Nb)B
2
/(Ti,Nb); VB
2
/TiN; VB
2
/WC; HfB
2
/TaC; ZrB
2
/TaC or ZrB
2
/NbC.
It is important that there is a large number of interfaces in the complete layer structure. This provides for a tension-free tenacious protection layer which has good adherence to the base and is very wear resistant. Such wear protection layers are particularly suitable for the coating of metal cutting tools. The wear protection layer can be formed by cathode sputtering wherein several cathodes of various hard metallic material are used and the substrate (base) is disposed on a rotating plate, moved periodically through the deposit areas of the various cathodes.
EP 0 006 534 A2 disclose a wear protection layer which comprises at least five, but preferably more than ten, individual layers of which at least two have different compositions. The first layer disposed on the substrate consists of a carbide and the final outermost layer consists of a boride or a carbide and the intermediate layers comprise carbides, nitrides, oxides, borides or mixtures thereof. As carbides and nitrides, especially compounds with the elements Hf, Zr, Ta and titanium are proposed which are metallic hard materials. The borides preferably comprise compounds including Hf, Ta, Ti, Zr, and N. As oxides the heteropolar hard metals Al—, Hf—, Zr—, Be— and titanium-oxide are proposed.
DE 31 52 742 C2 discloses a cutting tool with a multilayer coating. The layers of the coating consist of a nitride or carbide of a metal of the IV. side group of the periodic system (Ti, Zr, Hf) and of a nitride, carbide, boride or silicide of a metal of the VI. (side) group (Cr, MO, W). These compounds include elements of the group of the hard metals. The layers are disposed alternately in relatively large numbers, the thicknesses of the metal compounds of the IV. group being 0.05 to 0.5 &mgr;m and the thicknesses of the metal layer of the VI. group being 15 to 40% of the layer thicknesses of the metal compounds of the IV. group. The coating comprises up to
500
individual layers.
It is the object of the present invention to provide a wear protection layer which comprises a plurality of individual layers wherein the mechanical, physical and chemical properties of hard metal materials are combined with those of other hard materials. Furthermore, the wear protection layer should have a very low friction coefficient with regard to ceramic and metallic friction partners and a hardness of over 4000 HVO,05.
SUMMARY OF THE INVENTION
In a wear protection layer comprising, disposed on a substrate, a plurality of individual layers including a first individual layer of a metallic hard material disposed directly on the substrate, periodically repeated composite arrangements of three individual layers comprising two individual layers of different metallic hard materials and one individual layer consisting of a covalent hard material are disposed on the first individual layer of a metallic hard material whereby the mechanical, physical and chemical properties of the metallic hard materials are combined with the properties of the covalent hard materials.
The group of metallic hard materials comprises the borides, carbides and nitrides of the transition metals, particularly titanium nitride and titanium carbide as well as the mixed crystals thereof. The covalent hard materials include the borides and nitrides of aluminum, silicon and boron as well as diamond.
The combination of metallic and covalent hard materials in a single layer facilitates the utilization of the different mechanical, physical and chemical properties of the hard materials. By the periodically alternating arrangement of single layers of these hard materials the mechanical properties (hardness toughness, adhesion) and the chemical behavior (high-temperature corrosion, diffusion, oxidation) of multi-layer coatings are optimized.
Covalent hard materials are basically unsuitable as single layers on metallic substrates for metal cutting operations or, because of the high covalent bonding part, they cannot be used as jointure material since they do not adhere well to metallic substrates, they are brittle and they have high internal tensions. However with the arrangement of the covalent hard material layers according to the invention these negative properties are eliminated. The internal tension can be greatly reduced by a small thickness of the individual layers of covalent hard materials whereby their mechanical stability and adhesion is substantially improved. The thickness of the individual layers of the covalent hard material should be almost one half, but preferably less than one fifth of the thickness of the individual layers of the metallic hard material, preferably between 1 and 30 nm or, even better, between 1 and 5 nm. The individual layers of the metallic hard material can have a thickness of up to 500 nm. Inspite of their comparatively small thickness, the periodically arranged individual layers of covalent hard material provide for a substantial increase in hardness of the whole wear protection layer.
The first individual layer of the wear protection layer disposed on the substrate comprises a metallic hard material preferably TiN, or TiC. These hard materials adhere particularly well to the steels and hard metals generally used for making tools. On the first individual layer, there is disposed a series of additional individual layers of metallic and covalent hard materials. All individual layers together form a multiply repeated combination of three individual layers, in such a way that a second combination of three individual layers is attached to the first combination and at least a third combination is attached to the second combination of three individual layers. The combination of the three individual layers comprises two individual layers of two different metallic hard materials such as TiN and TiC and a single layer of the covalent hard material. The number of covalent hard material layers should be at least three; the wear protection layer consequently comprises at least 9 individual layers. For the individual layers of the covalent hard material, the compounds B
4
C, Si
3
N
4
, BN, Sialon (mixed crystal (SiAl)
3
, (N,O)
4
, carbon, CB
x
N
y
, CN
x
and mixtures thereof with or without the addition of metals are used.
With the introduction of individual layers of the covalent hard material the crystallite growth and consequently, the epitosis of the metallic hard material layers is interrupted whereby the numbe

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