Friction stir welding tool made of cemented tungsten carbide with nickel and with a AL2O3 surface coating

1. A friction stir welding tool made of cemented carbide comprising WC grains in a binder phase, wherein said welding tool is completely coated with a surface coating consisting of a first surface coating and a second surface coating, the first surface coating being an inner layer selected from the group consisting of a Ti carbide layer, Ti nitride layer, Ti carbonitride layer, Ti oxicarbide layer, Ti oxicarbonitride layer, Zr carbide layer, Zr nitride layer, Zr carbonitride layer, Zr oxicarbide layer and Zr oxicarbonitride layer, and the second surface coating being an outer layer of Al 2 O 3 that has an average thickness of more than 5 μm, said cemented carbide including from 3 wt-% to 10 wt-% Ni, wherein said surface coating is a CVD coating.

2. The friction stir welding tool according to claim 1 , wherein said second surface coating is an outermost surface coating of Al 2 O 3 and said first surface coating is of TiN.

3. The friction stir welding tool according claim 1 , wherein the thickness of the first surface coating is more than 0.3 μm and less than 6 μm.

4. The friction stir welding tool according to claim 1 , wherein said cemented carbide comprises from 4 to 5 wt-% Ni.

5. The friction stir welding tool according claim 1 , wherein said cemented carbide comprises from 3 to 10 wt-% Co.

6. The friction stir welding tool according to claim 1 , wherein said cemented carbide comprises from 4 to 5 wt-% Co.

7. The friction stir welding tool according to claim 1 , wherein said cemented carbide comprises 0.8-1.2 wt-% of Cr and/or Mo.

8. The friction stir welding tool according to claim 1 , wherein said cemented carbide comprises 0.01 to 0.4 wt-% Fe.

9. The friction stir welding tool according to claim 1 , wherein said cemented carbide comprises 85-95 wt-% WC with an average WC grain size of 2-25 μm.

10. The friction stir welding tool according to claim 1 , wherein said tool includes two probes, each probe contacting a material to be welded during a friction stir welding process, wherein said probes are arranged opposite to each other, such that when the first probe is active in a friction stir welding process, the second probe is inactive.

11. A method of producing a friction stir welding tool made of cemented carbide comprising WC grains in a binder phase by completely CVD coating the welding tool with a surface coating consisting of a first surface coating and a second surface coating, the first surface coating being an inner layer selected from the group consisting of a Ti carbide layer, Ti nitride layer, Ti carbonitride layer, Ti oxicarbide layer, Ti oxicarbonitride layer, Zr carbide layer, Zr nitride layer, Zr carbonitride layer, Zr oxicarbide layer and Zr oxicarbonitride layer, and the second surface coating being an outer layer of Al 2 O 3 that has an average thickness of more than 5 μm, the cemented carbide including from 3 wt-% to 10 wt-% Ni, wherein said surface coating is a CVD coating.

12. A method of using a friction stir welding tool in a friction stir welding process, comprising the steps of:

providing a friction stir welding tool made of cemented carbide comprising WC grains in a binder phase, the tool being completely coated with a surface coating consisting of a first surface coating and a second surface coating, the first surface coating being an inner layer selected from the group consisting of a Ti carbide layer, Ti nitride layer, Ti carbonitride layer, Ti oxicarbide layer, Ti oxicarbonitride layer, Zr carbide layer, Zr nitride layer, Zr carbonitride layer, Zr oxicarbide layer and Zr oxicarbonitride layer, and the second surface coating being an outer layer of Al 2 O 3 that has an average thickness of more than 5 μm, the cemented carbide including from 3 wt-% to 10 wt-% Ni, wherein said surface coating is a CVD coating; and

using the friction stir welding tool in the friction stir welding process, wherein said process is performed in a welding atmosphere of N 2 or Ar.