GB2378187A

GB2378187A - Wear Resistant Metal Boride Coatings

Info

Publication number: GB2378187A
Application number: GB0217718A
Authority: GB
Inventors: Peter Albany Dearnley
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-08-01
Filing date: 2002-07-31
Publication date: 2003-02-05
Anticipated expiration: 2022-07-31
Also published as: GB0217718D0; GB2378187B; GB0118755D0

Abstract

A coated article where the coating is a waer resistant metal boride. Preferably, the boride is based on group IIIa and Iva transition metals, in particular WB, W<SB>2</SB>B<SB>5</SB>, W<SB>2</SB>B, CrB, CrB<SB>2</SB>, MoB or Mo<SB>2</SB>B<SB>5</SB> may be used. The coating may comprise multiple layers of metal borides. Preferably the coated article may be formed of titanium or a cemented carbide, and may be used as a cutting tool for metals and alloys. A method of coating an article is also claimed, where the coating is applied by PVD or CVD. The preferred method of application is magnetron sputter deposition.

Description

Wear Resistant Boride Based Coatings The present invention relates to novel coating materials and to methods related thereto.

In particular, the invention relates to novel coatings which provide an original solution to the problem of high rates of wear that are produced on cutting tool materials that are used to machine titanium and its alloys. The said coatings may also be used for the wear protection of cutting tool materials that are used for the machining of other metals and their alloys, particularly aluminium and its alloys.

Titanium and its alloys are widely used for components in aero-engines, automotive parts and medical devices, e. g. dental or orthopaedic prosthetic implants. The manufacture of such components largely utilises metal cutting or machining processes, e. g. turning, drilling and milling. In these processes, titanium and alloys thereof, causes very high rates of wear of existing cutting tool materials. This is due to a combination of physical and chemical wear mechanisms.

Extensive metal cutting tests have shown that"straight grade"cemented carbides (tungsten carbide-cobalt alloys) are the best available tool materials compared to alternatives such as"steel cutting grade"cemented carbides, ceramics based on aluminium oxide, zirconium oxide, silicon nitride or sialon.

Previous attempts have been made to develop coatings for the protection of cemented carbides or high speed steel alloys, such coatings being designed to improve wear resistance and tool life when machining ferrous materials. However, such coatings are unsuited for machining titanium, and alloys thereof, the latter typically comprising a single or multiple layers of titanium carbide, titanium nitride, titanium carbo-nitride and/or aluminium oxide.

The main problem with titanium materials is that, inter alia, the titanium will itself have a degree of reaction with, e. g. a cutting tool carbide.

We have now surprisingly found that certain coating materials, based on a variety of boride compounds, can be successfully applied to existing cutting tool materials enabling them to achieve a significant improvement in wear resistance when the surface engineered tools are used to cut titanium, and alloys thereof. One of the preferred embodiments applies such coatings to straight grade cemented carbides.

The coatings are secured to the said substrates by the use of appropriate inter-layers based on metals or alloys of the transition metal series.

Thus, according to the invention we provide an article comprising a titanium resistant coating which comprises a boride compound.

Although one object of the present invention is to provide a novel coated cutting tool, the coating may be applied to the titanium itself to provide it with a prolonged life span.

Although a variety of boride compounds may be used, preferred borides are transition metal borides. More especially, the transition metal boride may comprise a metal selected from a Group IIIa or a Group VIa transition metal. Alternatively, combinations of any of the aforementioned metal borides may be used.

When the metal is a Group Tilla metal, then it is preferably selected from Scandium or Yttrium.

Group VIa metals are most preferred, in which case the metal may be selected from Chromium, Molybdenum and Tungsten. Tungsten or Chromium are the most preferred metals.

Examples of such borides include, but are not limited to WB, W2Bs, W2B, CrB, CrB2, MoB and M02Bs. WB and CrB are the most preferred borides.

The protective wear resistant coating may comprise a single or multiple layers of metal borides bonded to a substrate, e. g. a cemented carbide, or other suitable substrate, with a transition metal or an alloy layer based on the transition metal elements.

Although any substrate may be used, in the case of a cutting tool a cemented carbide substrate is especially preferred, such a cemented carbide substrate will typically have a composition of 85 to 96 weight per cent tungsten carbide and 4 to 15 weight per cent cobalt.

The transition metal boride coatings may be in a crystalline or non-crystalline (amorphous) state, or between the said states or any combination of the two states.

The substrate used may vary depending upon the nature of the article to which the substrate is to be applied. Thus, the substrate may comprise a cemented carbide, high speed steel alloy, or a ceramic based material, e. g. based on aluminium oxide, zirconium oxide, silicon nitride, sialon or some other suitable hard material.

When the article is a cutting tool, the tool materials may be of any shape, usually in the form of an insert, as for example, according to the ISO designation system, with or without the incorporation of a suitable chip control groove.

The coated cutting tool of the invention have the specific aim of increasing wear resistance of existing cutting tool insert materials, for the machining of titanium and its alloys, where the said machining processes include, inter alia, turning, facing, milling and drilling.

The coated cutting tool may also be used for improving the wear resistance of existing cutting tool insert materials used for the machining of other metals and alloys, especially aluminium and its alloys, where the said machining processes are turning, facing, milling and drilling.

The thickness of the boride coating may vary and may preferentially be from 1 to 75 um, more preferably 10 to 25 J. m, although the thickness of the coatings maybe varied according to the specifics of the selected machining process.

The coatings of the invention can be applied using conventionally known processes. However, a preferred process is vapour deposition, e. g. physical vapour deposition (PVD) or chemical vapour deposition (CVD) methods. A preferred embodiment deploys one of the PVD methods, magnetron sputter deposition.

Thus, according to a further feature of the invention we provide a method of coating an article with a boride compound as hereinbefore described.

The article of the invention may vary. The article may be a cutting tool, metal forming die, oil/gas industry components e. g. valve components; automotive components, e. g. valve spring retainers, steering racks, hub shafts; medical devices, e. g. orthopaedic implants, dental implants, surgical cutting tools. With the aforementioned articles the article itself comprises titanium and thus the coating is applied to the article. However, when the article is a cutting tool or forming die the titanium protection is achieved by coating the tool e. g. a carbide tool rather than a finished article.

The invention will now be described with reference to the following example.

In the following Example 1, there are given results which demonstrate the improved wear resistance conveyed by the said coatings during metal cutting tests.

EXAMPLE 1 Continuous dry turning tests on commercial purity titanium is performed using the following conditions :

Workpiece C. P. Ti Cutting speed 200 m/min Feed rate 0.25 mm/rev Depth of cut 1. 5 mm Insert style CNMA 120412 The following results regarding the wear resistance of the cutting tool inserts are obtained.

Cutting tool insert Inter-layer Rake face war rate relative to variant type uncoated WC-6%Co .......

.......

Uncoated WC-6%Co 1 WB (12 m) - coated Group VIa WC-6%Co element(s) 0.8 CrB (12 m) - coated Group VIa 0.5 WC-6%Co element(s) 0.5

Claims

Claims 1. An article comprising a titanium resistant coating wherein the coating comprises a metal boride compound.
2. An article according to claim 1 characterised in that the metal boride is a transition metal boride.
3. An article according to claim 2 characterised in that the transition metal boride is selected from a Group III and a Group VI transition metal.
4. An article according to claim 3 characterised in that the metal boride is

1 A r--OUp TTT-% TT-f mi-tnl selected from a Group Ilia and a Group VI a transition metal.
5. An article according to claim 4 characterised in that the transition metal is a Group IIIa metal selected from Scandium or Yttrium.
6. An article according to claim 4 characterised in that the transition metal is a Group VIa metal selected from Chromium, Molybdenum and Tungsten.
7. An article according to claim 6 characterised in that the metal boride is selected from the group WB, W2Bs, W2B, CrB, CrB2, MoB, and M02Bs.
8. An article according to claim 6 characterised in that the transition metal is Tungsten or Chromium.
9. An article according to claim 7 characterised in that the metal boride is WB and/or CrB.
10. An article according to claim 1 characterised in that the boride coating has a thickness of from 1 to 75 m.

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11. An article according to claim 10 characterised in that the coating has a thickness of from 10 to 25 um.
12. An article according to claim 1 characterised in that the coating comprises multiple layers of metal borides bonded to a substrate.
13. An article according to claim 1 characterised in that the substrate is a cemented carbide.
14. An article according to claim 13 characterised in that the cemented carbide has a composition of 85 to 96 weight per cent tungsten carbide
15. An article according to claim 14 characterised in that cemented carbide comprises 4 to 15 weight per cent cobalt.
16. An article according to claim 1 characterised in that the substrate is titanium.
17. An article according to claim 1 characterised in that the article is a cutting tool.
18. An article according to claim 17 characterised in that the cutting tool is suitable for machining of other metals and alloys, including titanium and/or aluminium and its alloys.
19. A process for manufacturing an article according to claim 1 characterised in that the process comprises vapour deposition, e. g. physical vapour deposition (PVD) or chemical vapour deposition (CVD) of the metal boride.
20. A process according to claim 1 characterised in that the method comprises PVD.

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21. A process according to claim 20 characterised in that the PVD comprises magnetron sputter coating deposition.
22. An article substantially as described with reference to the accompanying examples.