GB1601224A - Coated hard metal body - Google Patents

Description

(54) COATED HARD METAL BODY (71) We, SANDCO LIMITED, of 160 Elgin Street, Ottawa, Canada K1N 8S3, a Canadian Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to sintered hard metal bodies, such as cutting inserts, coated with thin and extremely wearresistant surface layers.

The use of titanium carbide and titanium nitride as surface layers on cutting tools has been known for a very long time, and double coatings of these materials have also been known for more than ten years; thus, for example, U.K. Patent Specification No.

762 931 described a cutting tool having a coating comprising a layer of titanium nitride on the substrate followed by a coating of titanium carbide. This specification was applied for in 1954, and there appears to have been little use made of this double coating. Hard metals coated with titanium carbide were introduced in the late 1960s, and these were quickly followed by titanium nitride coatings both of which proved to be very useful coatings for hard metals.

However the major wear that destroys a cutting insert arises in two areas, the first is on the clearance face of the insert where it contacts the work face and the second is on the rake face of the insert where it is subject to the continual high pressure flow of the chip. The extent of the wear in these two areas depends to a considerable extent on the material being cut and the conditions of cutting. Both titanium carbide and titanium nitride coatings offer significantly improved wear resistance in both areas but titanium carbide is superior to titanium nitride on the clearance face and titanium nitride may be equal to or in some cases even superior to titanium carbide on the rake face. In such cases a layer of titanium carbide on the clearance face and titanium nitride on the rake face would give protection against both kinds of wear.

It is impracticable to coat different faces of a carbide body with different materials, and the obvious solution is to coat one layer over the other. From the point of view of efficiency the correct order of the layers is almost certainly in the order of titanium nitride as the layer nearer the substrate, followed by a layer of titanium carbide because, the titanium carbide layer is the more wear-resistant and it is the occurrence of wear on the clearance face which causes deterioration of the carbide tool to the extent where it can no longer be used. The formation of two layers in this order was disclosed, as mentioned above, in U.K.

Patent Specification No. 762 931, and a further process for applying the layers, again in the same order, was disclosed in German Specification 1 954 366 by W.C.

Heraeus GmbH, a specification published in 1971.

The double-coated hard metal bodies which have come onto the market during recent years have been made by coating the substrate in the reverse order, i.e. first applying titanium carbide and then titanium nitride. The reason for this order of coating is probably the colour produced by the titanium nitride As explained in our patent specification 1 389 140 it is extremely useful for different hard metal grades to have a different appearance. The golden colour of the titanium nitride coating, which incidentally is extremely decorative and has been used for jewellery, is an indication to the user that the insert is a double coating.

We have decided to revert to the practice of putting the working coatings onto the substrate in the order suggested by U.K.

Patent Specification No. 762 931 and German Specification 1 954 366, that is to say applying first a coating consisting essentially of titanium nitride and then a coating consisting essentially of titanium carbide.

To leave the matter there would be confusing to the users of the inserts, who are accustomed to see the golden titanium nitride colour for the double layer inserts.

We propose therefore to place on top of the titanium carbide layer a thin colouring layer of titanium nitride or titanium carbonitride in the manner already disclosed in Specification 1 389 140. If titanium carbonitride is used for the outer colouring layer, the atomic ratio of N to C in this layer is preferably at least 3:1. As mentioned in that specification, even an extremely thin colour layer gives the body a stable colour, whilst not adversely affecting the properties of the layer beneath.

The present invention accordingly provides a sintered hard metal body containing at least one carbide besides binder metal, said body being provided with a thin layer consisting essentially of titanium nitride, followed by a thin layer consisting essentially of titanium carbide with an outer layer of titanium nitride or titanium carbonitride having a thickness of at the most 3 ecum.

The layers are preferably applied by chemical vapour deposition. The preferred thickness for the first layer which is essentially of titanium nitride, i.e. the one nearest the substrate, is between 1 and 6 llm preferably 2 to 4 \lem; the preferred thickness for the layer which is essentially of titanium carbide is 1 to 6 ,um, preferably 2 to 5 llm; and the thickness of the outer coating is at the most 3 llm and preferably between 0.2 and 2 llm.

Reference is made above to the two lower coatings being essentially of titanium nitride and essentially of titanium carbide respectively. If the coatings are applied by chemical vapour deposition, there will certainly be a stratum of titanium carbonitride forming an inter-layer between the substrate and the titanium nitride and a further small quantity of titanium carbonitride in the titanium carbide coating. The first-mentioned titanium carbonitride layer will be formed by carbon migration from the substrate; the titanium carbonitride in the titanium carbide coating will result mainly from interdiffusion or from the fact that during the interchange from the nitride-forming gas mixture to the carbide-forming gas mixture there will be some remanent nitrogencontaining gas in the gas mixture.

WHAT WE CLAIM IS: 1. A sintered hard metal body containing at least one carbide besides binder metal, said body being provided with a thin layer consisting essentially of titanium nitride, followed by a thin layer consisting essentially of titanium carbide with an outer layer of titanium nitride or titanium carbonitride having a thickness of at the most 3 clam.

2. A coated hard metal body according to claim 1, wherein the thickness of the outer layer is between 0.2 and 2 ,um.

3. A coated hard metal body according to claim 1 or claim 2, wherein the thickness of the essentially titanium nitride layer closest to the body is between 1 and 6 ,um.

4. A coated hard metal body according to claim 3, wherein the thickness of the essentially titanium nitride layer closest to the body is between 2 and 4 ,um.

5. A coated hard metal body according to any one of the preceding claims, wherein the thickness of the essentially titanium carbide layer is between 1 and 6 iim.

6. A coated hard metal body according to claim 5, wherein the thickness of the essentially titanium carbide layer is between 2 and 5 llm.

7. A coated hard metal body according to claim 1 substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. applying first a coating consisting essentially of titanium nitride and then a coating consisting essentially of titanium carbide. To leave the matter there would be confusing to the users of the inserts, who are accustomed to see the golden titanium nitride colour for the double layer inserts. We propose therefore to place on top of the titanium carbide layer a thin colouring layer of titanium nitride or titanium carbonitride in the manner already disclosed in Specification 1 389 140. If titanium carbonitride is used for the outer colouring layer, the atomic ratio of N to C in this layer is preferably at least 3:1. As mentioned in that specification, even an extremely thin colour layer gives the body a stable colour, whilst not adversely affecting the properties of the layer beneath. The present invention accordingly provides a sintered hard metal body containing at least one carbide besides binder metal, said body being provided with a thin layer consisting essentially of titanium nitride, followed by a thin layer consisting essentially of titanium carbide with an outer layer of titanium nitride or titanium carbonitride having a thickness of at the most 3 ecum. The layers are preferably applied by chemical vapour deposition. The preferred thickness for the first layer which is essentially of titanium nitride, i.e. the one nearest the substrate, is between 1 and 6 llm preferably 2 to 4 \lem; the preferred thickness for the layer which is essentially of titanium carbide is 1 to 6 ,um, preferably 2 to 5 llm; and the thickness of the outer coating is at the most 3 llm and preferably between 0.2 and 2 llm. Reference is made above to the two lower coatings being essentially of titanium nitride and essentially of titanium carbide respectively. If the coatings are applied by chemical vapour deposition, there will certainly be a stratum of titanium carbonitride forming an inter-layer between the substrate and the titanium nitride and a further small quantity of titanium carbonitride in the titanium carbide coating. The first-mentioned titanium carbonitride layer will be formed by carbon migration from the substrate; the titanium carbonitride in the titanium carbide coating will result mainly from interdiffusion or from the fact that during the interchange from the nitride-forming gas mixture to the carbide-forming gas mixture there will be some remanent nitrogencontaining gas in the gas mixture. WHAT WE CLAIM IS:

1. A sintered hard metal body containing at least one carbide besides binder metal, said body being provided with a thin layer consisting essentially of titanium nitride, followed by a thin layer consisting essentially of titanium carbide with an outer layer of titanium nitride or titanium carbonitride having a thickness of at the most 3 clam.

2. A coated hard metal body according to claim 1, wherein the thickness of the outer layer is between 0.2 and 2 ,um.

3. A coated hard metal body according to claim 1 or claim 2, wherein the thickness of the essentially titanium nitride layer closest to the body is between 1 and 6 ,um.

4. A coated hard metal body according to claim 3, wherein the thickness of the essentially titanium nitride layer closest to the body is between 2 and 4 ,um.

5. A coated hard metal body according to any one of the preceding claims, wherein the thickness of the essentially titanium carbide layer is between 1 and 6 iim.

6. A coated hard metal body according to claim 5, wherein the thickness of the essentially titanium carbide layer is between 2 and 5 llm.

7. A coated hard metal body according to claim 1 substantially as herein described.