Watch Hairspring Alloy Composition for Faster Zero-CTE Stabilization
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Solution Overview
Problem
Current binary Nb-Ti alloys used for watch spiral springs face challenges such as long production times due to slow titanium precipitation and the formation of fragile martensitic phases, which hinder deformation and increase production difficulties.
Innovation Solution
A ternary alloy composition comprising niobium, titanium, and zirconium or hafnium, with specific weight percentages, is developed, allowing for accelerated precipitation and reduced production times, along with a heat treatment process that finalizes the precipitation of titanium and zirconium or hafnium within 4 to 8 hours at 400°C to 600°C, and the addition of trace elements like tungsten and molybdenum to enhance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If binary Nb-Ti alloys are used for spiral springs, then the alloy can achieve a CTE close to zero through precipitation of titanium, but the production time becomes very long (8-30 hours) due to slow precipitation rate
Solution Approach 1:
Zirconium or hafnium are introduced as intermediary elements that accelerate the precipitation process. These elements act as mediators between the niobium matrix and titanium precipitation, facilitating faster formation of the desired two-phase microstructure while maintaining the CTE close to zero. The presence of Zr/Hf reduces the precipitation time from 8-30 hours to a much shorter duration.
Solution Approach 2:
The chemical composition parameters are changed by adding Zr or Hf to the Nb-Ti alloy system. This creates a ternary alloy system (Nb-Ti-Zr or Nb-Ti-Hf) where the additional elements modify the precipitation kinetics. The specific weight percentages of Nb (40-84%), Ti (16-55% total with Zr/Hf), and Zr/Hf (10-25%) are optimized to achieve both fast precipitation and desired CTE.
2Reliability
If high percentage of titanium is used in Nb-Ti alloy, then the CTE can be reduced close to zero, but brittle martensitic phases form that make deformation difficult or impossible
Solution Approach 1:
The alloy composition parameters are modified by introducing Zr or Hf elements and optimizing the Ti content. This parameter change prevents the formation of brittle martensitic phases while maintaining the ability to achieve CTE close to zero through controlled precipitation. The specific composition ranges ensure the alloy remains ductile and deformable.
Solution Approach 2:
The invention creates a composite alloy system combining Nb, Ti, and Zr/Hf elements that work synergistically. The Zr/Hf elements modify the microstructure formation behavior, preventing brittle phase formation while enabling the desired precipitation characteristics. This composite approach maintains both manufacturability and CTE control.
3Productivity
If the alloy composition is optimized for fast precipitation, then production time is reduced, but the CTE control and chronometric performance may be compromised
Solution Approach 1:
The composition parameters are precisely optimized to achieve both fast precipitation and CTE control. The specific weight percentages of Nb (40-84%), Ti (16-55%), and Zr/Hf (10-25%) create a balanced system where the precipitation kinetics are accelerated while the final microstructure maintains the desired CTE close to zero. The interaction between these elements is key to resolving this contradiction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ternary alloy reduces production time, minimizes secondary errors, and achieves a multiphase microstructure with a thermoelastic coefficient close to zero, suitable for maintaining chronometric performance across varying temperatures, while ensuring high elastic limit and ease of deformation.
Implementation Method 1
the final heat treatment step to finalize the precipitation of titanium and zirconium and/or hafnium is carried out in a time of between 4 and 8 hours at a holding temperature of between 400°C and 600°C
Implementation Method 2
a heat treatment process that finalizes the precipitation of titanium and zirconium or hafnium within 4 to 8 hours at 400°C to 600°C
Data Source
AI summary
The present invention relates to a spiral spring for use in a balance wheel of a watch movement, characterized in that the spiral spring is made of an alloy consisting of: - Nb, Ti, and at least one element selected from Zr and Hf, - optionally at least one element selected from W and Mo, - possible traces of other elements selected from O, H, Ta, C, Fe, N, Ni, Si, Cu, Al, with the following weight percentages: ∘ an Nb content between 40 and 84%, ∘ a total Ti, Zr, and Hf content between 16 and 55%, ∘ a W and Mo content between 0 and 2.5% respectively, ∘ a content for each of said elements selected from O, H, Ta, C, Fe, N, Ni, Si, Cu, Al between 0 and 1600 ppm, with the sum of said traces less than or equal to 0.3% in weight. The present invention also relates to the method of manufacturing the spiral spring.