A BALANCE-SPRING INTENDED TO EQUIP A BALANCE OF A WATCH MOVEMENT

Abstract

The present invention relates to a balance-spring intended to equip a balance of a watch movement, which balance spring comprises an Nb-Ti core made of an alloy consisting of: - niobium: balance to 100% by weight, - titanium: between 5 and 95% by weight, - traces of elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the total amount constituted by all of said elements being between 0% and 0.3% by weight, wherein the Nb-Ti core is coated with a layer of a first material selected from the group comprising niobium, tantalum, vanadium and an austenitic stainless steel, in particular 316L grade steel, said layer of the first material having a thickness of between 20 nm and 10 µm.

Specification

Description:SOFT COPY ATTACHED , Claims:WE CLAIM:

1. A balance-spring intended to equip a balance of a watch movement, which balance spring comprises an Nb-Ti core made of an alloy consisting of:
- niobium: balance to 100% by weight,
- titanium: between 5 and 95% by weight,
- traces of elements selected from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said elements being present in an amount between 0 and 1600 ppm by weight, the total amount constituted by all of said elements being between 0% and 0.3% by weight,
characterised in that the Nb-Ti core is coated with a layer of a first material selected from the group comprising niobium, tantalum, vanadium and an austenitic stainless steel, in particular 316L grade steel, said layer of the first material having a thickness of between 20 nm and 10 µm.

2. The balance-spring as claimed in claim 1, wherein the layer of the first material has a thickness of between 300 nm and 1.5 µm.

3. The balance-spring as claimed in claim 1 or 2, wherein the layer of the first material has a thickness of between 400 nm and 800 nm.

4. The balance-spring as claimed in any one of claims 1 to 3, wherein the first material is niobium.

5. The balance-spring as claimed in any one of claims 1 to 4, wherein the Ti content is between 40 and 65% by weight, preferably between 40 and 49% by weight and more preferably between 46 and 48% by weight.

6. The balance-spring as claimed in any one of claims 1 to 5, wherein the Nb-Ti core has a two-phase microstructure including niobium in beta phase and titanium in alpha phase.

7. The balance-spring as claimed in any one of claims 1 to 6, wherein it has an elastic limit greater than or equal to 500 MPa, preferably 600 MPa, and a modulus of elasticity less than or equal to 120 GPa, preferably less than or equal to 100 GPa.

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