Very high strength copper-titanium alloy with improved formability in the solution annealed condition

Abstract

The copper-titanium alloy according to the present invention contains at least 90% by mass of copper, 5-7% by mass of titanium, and 0.25-0.5% by mass of iron. The copper-titanium alloy has excellent ductility when solution-annealed and tempered, and high yield strength after aging treatment.

Description

[Technical field]

[0001] The present invention relates to copper alloys that can be used as substitutes for copper-beryllium (Cu-Be) alloys. [Background technology]

[0002] Cu-Be alloys are widely used in many applications, where they are especially valued for their combination of high electrical conductivity and very good mechanical properties. They combine extremely high ductility with a temper (Solution Annealed (SA) temper), allowing very high formability (elongation above 40%) and another temper (Age Hardened (AH) temper) with very high mechanical resistance (above 1 GaP). Nevertheless, Cu-Be alloys are destined to disappear, since Be is highly toxic and alloys with this element are gradually being banned. Copper-titanium (Cu-Ti) alloys are good substitutes for Cu-Be. Like Cu-Be, Cu-Ti alloys are age-hardenable alloys, i.e., under certain conditions, it is possible to dissolve the alloying element Ti in the copper solid phase, which has a face-centered cubic lattice. In this temper, often referred to as the solution-annealed (SA) temper, the material usually exhibits maximum formability. When Cu-Ti alloys are aged at moderate temperatures, usually between 300°C and 550°C, Ti forms fine, uniformly dispersed α-Cu alloys, which significantly increase the strength of the alloy. 4 The Ti tetragonal nanometastable phase (20-200 nm in size) precipitates. If the alloy is maintained at temperature for longer, the β-Cu phase is 4 Ti or Cu 3 The larger orthogonal stable phase, called Ti, forms as cells at the grain boundaries and is detrimental to the mechanical properties of the alloy, a phenomenon called "overaging."

[0003] Most of the current developments are focused on Cu for electronic applications. 3The objective is to prevent the formation of Ti and / or to increase the electrical conductivity of the Cu-Ti alloy. To overcome either of these challenges, the Ti content is often kept below 4 wt.%. U.S. Patent Application No. 2004 / 0136861 describes a copper alloy for use as a connector material having excellent bendability, 3 This publication discloses a copper alloy intended to be protected from Ti precipitation. This copper alloy contains 2-4 mass% Ti and 0.01-0.5 mass% of at least one element selected from a third element group consisting of Fe, Co, Ni, Cr, V, Zr, B, and P, with 50% or more of the total content of the third element group being present as second phase particles. The present invention focuses on any application of Cu-Be that requires only high mechanical resistance, but not good electrical conductivity. This allows the addition of large amounts of Ti, which would normally have a negative effect on electrical conductivity. It is known that with large amounts of Ti (>4 wt%) in the alloy, the Cu-Ti alloy exhibits a yield strength comparable to Cu-Be, but has low ductility in the solution annealed temper, due to the difficulty in maintaining Ti in solid solution during the water quench that terminates the solution annealing. For example, S. Nagarjuna et al., in their study of the effect of increasing the amount of Ti, obtained an elongation of only 23% for a Cu-Ti alloy containing 5.4 wt% Ti (see the paper “On the variation of mechanical properties with solute content in Cu-Ti alloys”, S. Nagarjuna et al., Materials Science and Engineering A259 (1999) 34-42).

[0004] US Patent No. 4,599,119 discloses age-hardened copper-titanium alloys containing 2-6% by weight, preferably 3-5% by weight, titanium, with an average grain size of 25 μm or less, preferably between 3-15 μm. The alloy may contain, in addition to copper and titanium, at least one element from the group consisting of iron, zirconium, chromium, boron and silicon, not exceeding 2% by weight in total. In this specification, it is believed that the small grain size improves the mechanical properties of Cu-Ti, such as isotropy, formability, fatigue strength, elongation and yield strength. The small grain size is obtained by suitable heat treatment, including a pre-annealing at moderate temperatures to form spherical precipitates described as secondary phases. No specific effect is specified regarding the possible use of iron, zirconium, chromium, boron or silicon. The patent does not address the problems on the ductility of the alloy caused by high amounts of titanium (more than 4%).

[0005] No. 2,783,143 discloses an age hardenable copper-based alloy with improved strength and ductility in the age hardened temper. The alloy contains 1-10% titanium, 0.1-1.6% cobalt, 0.05-0.8% chromium, 0.04-0.62% nickel, 0.04-0.60% iron, 0.02-0.28% molybdenum, and 0.005-0.08% manganese. Preferably, the alloy contains 2-6% titanium, 0.2-0.8% cobalt, 0.1-0.4% chromium, 0.08-0.31% nickel, 0.075-0.3% iron, 0.035-0.14% molybdenum, and 0.01-0.04% manganese. Although not specified, the percentages given are believed to be atomic percentages. In the example shown, the titanium content is 4%, which corresponds to about 3% by weight. The patent focuses on ductility in the age-hardened temper and does not mention ductility before age-hardening, i.e., in the solution-annealed temper intended to achieve maximum formability. Furthermore, the patent does not address the problems caused to the ductility of the alloy by high amounts of titanium (greater than 4% by weight).

[0006] International Patent Application WO2021 / 143257 discloses a titanium-bronze alloy for explosion-proof equipment. The alloy contains 5-7% by weight titanium, 0.8-1.5% by weight aluminum, 0.1-0.3% by weight silver, 0.2-0.4% by weight iron, 0.03-0.08% by weight rare earth elements, and the remainder copper. The specification does not mention ductility in the solution annealed temper. Furthermore, the proposed alloy is expensive due to the presence of silver. Japanese Patent Application No. JP2021 / 050393 discloses a titanium copper alloy plate for vapor chambers. According to one example, the alloy contains 4.8% by weight titanium and 0.2% by weight iron. A comparative example is mentioned that contains 5.2% by weight titanium and 0.2% by weight iron. The alloy in this specification does not have optimal ductility in the solution annealed temper. Summary of the Invention

[0007] An object of the present invention is to provide a copper-titanium alloy that can have both excellent ductility in the solution annealed temper and high yield strength after aging treatment. For this purpose, a copper-titanium alloy is provided which comprises at least 90% by weight of copper, 5-7% by weight of titanium and 0.25-0.5% by weight of iron. The titanium content is preferably at least 5.2% by weight, preferably at least 5.5% by weight, preferably at least 6% by weight, preferably at most 6.5% by weight. The iron content is preferably at most 0.4% by weight and preferably at most 0.35% by weight. The copper-titanium alloy may further contain aluminum in an amount of 1.4 mass% or less, preferably in an amount of 0.1 to 1.4 mass%, preferably in an amount of 0.1 to 0.7 mass%, preferably in an amount of 0.1 to 0.6 mass%.

[0008] Preferably, the copper-titanium alloy contains no or almost no silver, i.e. the silver content in the alloy is at most 0.08% by weight, preferably at most 0.07% by weight, preferably at most 0.06% by weight. The present invention further provides a method for producing a copper-titanium alloy as defined above having improved formability, comprising a solution annealing step, including a heat treatment carried out at a temperature of at least 840°C, followed by a quenching (rapid cooling) step.

[0009] Other features and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] 1 is a graph showing the elongation before aging (in the solution annealed (SA) temper) as a function of yield stress (0.2% offset) after aging (age hardened temper). Data for Cu-XTi-0.3Fe alloys (nominal X equals 3, 5, or 6) is overlaid with commercial data for industrial CuBe-C17200 and C72900 alloys in various tempers. [Diagram 2] 1 is a graph showing the evolution of Vickers hardness of alloys Cu-6Ti and Cu-6Ti-0.3Fe over ageing at 450° C. due to the solution annealed temper. [Diagram 3] FIG. 1 is a graph showing the stress-strain engineering tensile curves of alloys Cu-6Ti and Cu-6Ti-0.3Fe in the solution annealed (SA) temper and in the prescribed peak aging condition (450° C. for 2 hours) aimed at achieving maximum strength while maintaining reasonable ductility in the age hardened (AH) temper. [Figure 4] 1 is a graph showing the evolution of yield stress with Ti content in the alloy in the solution annealed (SA) and age hardened (AH) tempers (450° C. for 2 hours). [Diagram 5] 1 is a graph showing the evolution of elongation at break with Ti content in the alloy in the solution annealed (SA) and age hardened (AH) tempers (450° C. for 2 hours). [Figure 6]FIG. 6(a) is a scanning electron microscope (SEM) photograph of Cu-6Ti as solution annealed (SA) temper after chemical electropolishing, where the precipitates are subsequently exposed and visible with a secondary electron detector. Hardness was measured at 320 Hv. FIG. 6(b) is a scanning electron microscope (SEM) photograph of Cu-6Ti-0.3Fe as solution annealed (SA) temper after chemical electropolishing, where the precipitates are subsequently exposed and visible with a secondary electron detector. Hardness was measured at 160 Hv. [Figure 7] FIG. 14 Transmission electron microscopy (TEM) taken along the zone axis B=(100) of alloys (a) Cu-6Ti and (b) Cu-6Ti-0.3Fe in the as-solution annealed (SA) temper; (c) and (d) are the corresponding diffraction patterns. [Figure 8] Figure 1 shows the X-ray diffraction (XRD) of Cu-6Ti (top curve, T6) and Cu-6Ti-0.3Fe (bottom curve, T7) in the solution annealed temper. Boxes I, II, and III in the upper right corner show three relevant enlargements of the spectrum. [Figure 9] Cu surface <100> FIG. 1 shows the X-ray diffraction (XRD) of three different alloys (Cu-6Ti-0.1Fe; Cu-6Ti-0.3Fe; Cu-6Ti-0.7Fe) in the solution annealed temper, magnified at angles 2θ corresponding to diffraction of [Figure 10] 1 is a scanning electron micrograph (SEM) of the alloys Cu-6Ti-0.3Fe and Cu-6Ti-0.7Fe as solution annealed and refined. [Figure 11] FIG. 1 is a diagram showing the hardness of three types of alloys (Cu-6Ti-0.3Fe; Cu-6Ti-0.3Fe-0.2Ag; Cu-6Ti-0.3Fe-1.2Al) after solution annealing and age hardening. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Copper-titanium alloys have been considered for the last century. They are conventionally produced by carrying out the following sequence: a) Casting: The elements of the alloy are mixed in the liquid phase at high temperature. An induction furnace is preferably used. The temperature is held for at least 1 minute over the liquidus temperature (which is about 1000°C), preferably between 1200°C and 1300°C. The alloy is preferably cast in a mold to ensure faster cooling of the melt and better homogeneity. Depending on the Cu-Ti alloy, a specific order and / or strategy for introducing the elements from the master alloy can be used. b) Homogenization: A homogenization heat treatment is necessary to homogenize the Ti that separates during the solidification process along the dendrites. Homogenization must be carried out between 880°C and 950°C (below the solidus temperature) and can last between 1 hour and 48 hours, depending on the size of the casting. The material is then cooled relatively slowly, preferably in a neutral atmosphere to avoid excessive oxidation. c) Forming (preferred but optional): Hot deformation between 750°C and 900°C and / or cold deformation can be performed to arrive at the final shape of the piece for a given application. Hot deformation increases the uniformity of the microstructure with smaller grains allowing larger deformations, while cold deformation provides better control of the geometry. d) Solution Annealed (SA): The alloy is heated and maintained at an elevated temperature for a specific time to dissolve the titanium in the solid phase and form a solid solution. The alloy is then rapidly cooled by water quenching to cool the microstructure. The alloy temper after water quenching is called the "solution annealed temper" or "SA temper". e) Aging or "Age Hardening": Aging is usually carried out at temperatures between 300°C and 550°C, depending on the prior cooling operation, to precipitate titanium and obtain maximum yield stress. The alloy temper after aging is called the "age hardened temper" or "AH temper".

[0012] At the end of the solution annealing, the alloy is soft and therefore can be easily deformed to assume its final shape. The alloy has a higher yield strength at the end of the aging process, but the yield strength depends on the Ti content. It has been shown that an increase in the Ti content up to 7% by weight increases the strength of the alloy in the age-hardened temper. However, it was then observed that if the alloy contains more than 4% by weight of Ti, it is not possible to maintain Ti in solid solution after water quenching. This results in a wave-like microstructure observed in the TEM (Transmission Electron Microscope). The mechanism behind this observation is a subject of debate, but it is always related to early precipitation, resulting in a large increase in strength and a decrease in ductility. This behavior is problematic because it makes it impossible to produce binary Cu-Ti alloys with high strength in the age-hardened temper (more than 850 MPa) and high formability in the solution annealed temper (more than 30% elongation).

[0013] The invention is based on the observation that a small addition of Fe (0.25-0.5%, preferably 0.25-0.4%, preferably 0.25-0.35%, by weight) in combination with a high content of Ti (5-7%, preferably 5.2-7%, preferably 5.5-7%, preferably 5.5-6.5%, by weight) results in the suppression of such early precipitation and the maintenance of titanium in solid solution. This allows the alloy's elongation in the solution annealed temper to be doubled and then to reach plastic deformations (elongations) of more than 40% and even more than 50%, while maintaining or even improving the yield strength of the alloy in the age hardened temper (more than 900-1000 MPa). To achieve higher and more isotropic mechanical properties, the grain size is preferably less than 30 μm.

[0014] The content of Cu in the alloy of the present invention is at least 90% by weight. Excellent results are obtained only when only Cu, Ti and Fe (and unavoidable impurities) are present in the alloy. The addition of one or more other elements such as Co, Zr, Si, P, Ni, Sn, Zn, Pb, Mn, Mg, As, Sb and Cr is not excluded in the present invention, but no improvement in terms of ductility in the solution annealed temper and yield strength in the age hardened temper is observed with the addition of such elements. A worsening of the results in terms of Cu-Ti-Fe may even occur when the added element, e.g. Co, reacts with Fe. The technical effect in the present invention really depends on the action of Fe in combination with a high content (5-7% by weight) of Ti. Specifically, in such a high range of Ti, a small addition of Fe significantly improves the ductility of the alloy. Unlike the other elements mentioned above, Fe has a special effect on the precipitation and ductility of Ti. Its role is expected to be in solid solution or through the formation of new nanoprecipitates, but not through the formation of secondary phases as described in US 2004 / 0136861. Given the high titanium content in the present invention, the solution heat treatment of the solution annealing (step d) above) is carried out at a temperature of at least 840°C, preferably at least 850°C, preferably at least 880°C. EXAMPLES

[0015] Detailed test results are now described with reference to the accompanying drawings. The Cu-Ti-Fe alloys on which these results are based were produced as follows: Various model alloys T1, T2, T3, T4, T6 and T7 were cast from high purity copper metal, iron and titanium sponge. Approximately 500 g of metal was weighed and melted in a sealed induction furnace under argon gas. After holding at 1250°C for 5 minutes, the alloys were poured into graphite crucibles to form ingots of 150x50x11 mm. The resulting chemical composition was analyzed at the center of each ingot by inductively coupled plasma atomic emission spectrometry (ICP-AES) and is given in mass percentage in the table below.

[0016] [Table 1]

[0017] The designation "<0.01" means that the presence of the corresponding element in the alloy is not measurable. Si in alloys T1-T7 is an impurity. Similarly, P in alloy T2 is an impurity. Thermomechanical treatment was adapted to the amount of Ti for each alloy. To ensure good dynamic recrystallization and small equiaxed grains, the ingots were homogenized to eliminate solidification chemical segregation, and then hot rolled (HR) in three successive passes at 850°C under air to reduce the thickness to plates of 11 mm to 3.6 mm. The alloys were successively cold rolled (CR), solution annealed with argon flux, and water quenched (SA). These steps were repeated multiple times to reach a thickness of 0.5 mm. The SA temperature and CR were adjusted to reach a grain size of less than 60 μm. To reach better, more isotropic mechanical properties, a grain size of less than 30 μm is preferred. These samples are referred to as SA tempers in the following. Some of the specimens were aged at 450° C. under Ar gas for 2 hours to produce a temper designated the AH (age hardened) temper.

[0018] Figure 1 shows a graph aimed at demonstrating the main advantages of the Cu-6Ti-0.3Fe alloy (alloy T7) compared to the standard substitutes Cu-Be (C17200), binary Cu-Ti (iron-free alloys T1, T3 and T6), and Cu-Be (C72900). Due to the small addition of Fe, the Cu-Ti(-Fe) alloy combines good formability before aging with very high yield strength after aging.

[0019] More specifically, FIG. 1 shows on the y-axis the elongation before aging (after quenching; solution annealed temper), a value related to the formability of the alloy in this temper, and on the x-axis the yield stress of the alloy after aging, a value related to its resistance in working conditions. This graph is relevant for all applications, such as Bourdon tubes for manometers, which require very high formability to produce products with complex shapes and high mechanical properties under working conditions. The Cu-Be alloy (represented in the graph by squares) is by far the best in this dual behavior. However, the addition of 0.3% Fe by weight to Cu-Ti alloys (open circles) with a Ti content of 5% or 6% by weight makes it possible to approach the behavior of Cu-Be, which is much closer than the commercial C72900 alloy, represented in the graph by black triangles. Figure 2 shows the evolution of hardness of Cu-6Ti (alloy T6) and Cu-6Ti-0.3Fe (alloy T7) as a function of ageing time at 450°C. It can be observed that the addition of 0.3% by weight of Fe to the Cu-6Ti alloy first increases the maximum hardness from 330 Hv to 350 Hv, but also stabilizes this hardness, especially at 450°C. This is because the addition of small amounts of Fe is reported in the literature to promote the formation of the stable phase β-Cu at the grain boundaries. 4 Ti (or Cu 3 We show that limiting overaging, one of the main challenges in Cu–Ti alloys, is always associated with the formation of Ti.

[0020] Figure 3 shows that Cu-6Ti-0.3Fe (Alloy T7) is softer than Cu-6Ti (Alloy T6) in the solution annealed (SA) temper and harder than Cu-6Ti in the age hardened (AH) temper. This property can be highly valued, for example, in the watch industry. In the solution annealed temper, the addition of only 0.3% Fe by weight in Cu-6Ti improves the elongation by a factor of two and the yield stress is almost halved. Such an exceptional effect was not expected. It can be explained by the absence of spinodal decomposition in the solution annealed temper, which can be made possible by the addition of small amounts of Fe. Cu-6Ti-0.3Fe also exhibits a very favorable balance between yield strength and elongation in the age-hardened temper. This balance between strength and formability is better than that in commercial Cu-Be alloys and standard commercial Cu-15Ni-8Sn substitutes. Unlike comparable commercial alloys on the market, Cu-6Ti-0.3Fe in the age-hardened condition can reach yield stresses in excess of 1 GPa with elongations in excess of 15%.

[0021] Figures 4 and 5 show the evolution of yield stress and elongation at break as a function of the Ti content in the alloy, in the solution annealed and age hardened tempers, respectively, for the alloys Cu-Ti and Cu-Ti-Fe (0.3% Fe by weight) processed as described above, and for a binary Cu-Ti alloy with a grain size of 60 μm, disclosed in the publication "On the variation of mechanical properties with solute content in Cu-Ti alloys", S. Nagarjuna et al., Materials Science and Engineering A259 (1999) 34-42, and processed as described in said publication. These figures illustrate that a high Ti content (5-7% by weight) must be included in order to noticeably observe the described benefits of Fe microaddition. The physical mechanism by which the addition of trace amounts of Fe is effective is illustrated in Figures 6 and 7. Nanoprecipitates in alloy Cu-6Ti (alloy T6) are aligned in the direction <200> From Figures 6(b) and 7(b), it can be observed that the small addition of Fe in the alloy completely suppresses such premature precipitation.

[0022] FIG. 8 shows the X-ray diffraction (XRD) of Cu-6Ti (top curve, alloy T6) and Cu-6Ti-0.3Fe (bottom curve, alloy T7) in the solution annealed temper. FIG. 8 confirms the premise of the mechanism explained above. It is known that early precipitation, sometimes associated with spinodal decomposition, produces a side band effect in the XRD. This effect is clearly visible in FIG. 8 for the curve obtained from alloy T6. For the curve obtained from alloy T7, the peak corresponding to Cu is much thinner due to the absence of spinodal decomposition. This observation is in good agreement with FIG. 6 and FIG. 7. Enlarged view I shows the typical broadening of the Cu peak due to spinodal decomposition in the binary Cu-6Ti system. Such broadening is absent in Cu-6Ti-0.3Fe, revealing the effect of Fe in preventing precipitation during water quenching.

[0023] In order to avoid spinodal decomposition, it is necessary to have a sufficiently high Fe content. Figure 9 shows the X-ray diffraction (XRD) results for three different alloys (Cu-6Ti-0.1Fe; Cu-6Ti-0.3Fe (Alloy T7); Cu-6Ti-0.7Fe) in the solution annealed temper. The shoulders visible on either side of the diffraction peaks, known in the literature as shoulder effect, are evidence of the presence of spinodal decomposition. One finding of the present invention is to add Fe in the solution annealed temper to suppress this spinodal decomposition and maintain the ductility of the alloy. The results show that spinodal decomposition appears when the Fe content is too low (0.1 wt% Fe), but disappears when the Fe content is higher (0.3 wt% Fe). 0.3 wt% Fe appears to be the optimum concentration to effectively eliminate this spinodal decomposition and the associated shoulder effect in the diffraction peaks. However, the Fe content should not be too high because otherwise a large amount of undesirable TiFe intermetallic compounds will form, which negatively affect the ductility and mechanical properties of the alloy. Such a large amount of intermetallic compounds is visible in Figure 10 for Cu-6Ti-0.7Fe.

[0024] As already stated, the addition of one or more elements in the alloy according to the invention is not excluded. Figure 11 shows the hardness of Cu-6Ti-0.3Fe in solution annealed and age hardened tempers without Ag or Al in the alloy (left graph), with 0.2% Ag in the alloy (middle graph) and with 1.2% Al in the alloy (right graph). Unexpectedly, Al softens the alloy in the solution annealed temper, i.e. improves the ductility in that temper without reducing the hardness in the age hardened temper. However, the content of Al must be low enough to avoid the formation of intermetallic compounds with Fe. Preferably, aluminum is present in the alloy in a content of 0.1-1.4%, preferably 0.1-0.7%, preferably 0.1-0.6% by weight. Concerning Ag, the graph in Figure 11 shows that it has no positive effect on the mechanical properties of the alloy (hardness in the solution annealed temper is not reduced and hardness in the age hardened temper is not improved). Considering the very high cost of Ag, the alloy according to the invention preferably contains no or almost no Ag, i.e. the content of silver in the alloy is at most 0.08% by weight, preferably at most 0.07% by weight, preferably at most 0.06% by weight. Thus, an alloy containing only Cu, Ti, Fe and Al (and unavoidable impurities) may be particularly advantageous.

[0025] The alloy according to the invention can replace Cu-Be alloys in all very high strength alloy applications requiring good mechanical properties and not good electrical conductivity, such as Bourdon tubes of high pressure manometers, parts of watches (e.g. watch cases, gears, escapements, balances, springs, shafts, oscillating weights, plates, bridges, hands, dials, discs, etc.), ball roller bearings and bushings, especially for the aircraft and aerospace industries, and dies for plastic extrusion.

Claims

1. A copper-titanium alloy comprising at least 90% by weight copper, 5-7% by weight titanium, and 0.25-0.5% by weight iron.

2. 2. The copper-titanium alloy of claim 1, wherein the titanium content is at least 5.2% by weight.

3. 2. The copper-titanium alloy of claim 1, wherein the titanium content is at least 5.5% by weight.

4. 2. The copper-titanium alloy of claim 1, wherein the titanium content is at least 6% by mass.

5. The copper-titanium alloy according to any one of claims 1 to 4, wherein the titanium content is at most 6.5% by mass.

6. The copper-titanium alloy according to any one of claims 1 to 4, wherein the iron content is at most 0.4% by mass.

7. The copper-titanium alloy according to any one of claims 1 to 4, wherein the iron content is at most 0.35% by mass.

8. The copper-titanium alloy according to any one of claims 1 to 4, containing only copper, titanium, iron and unavoidable impurities.

9. The copper-titanium alloy according to any one of claims 1 to 4, further comprising aluminum in a content of 1.4 mass% or less.

10. The copper-titanium alloy according to any one of claims 1 to 4, further comprising 0.1 to 1.4 mass% aluminum.

11. 5. The copper-titanium alloy according to claim 1, further comprising aluminum in a content of 0.1 to 0.7% by mass, preferably 0.1 to 0.6% by mass.

12. 11. The copper-titanium alloy of claim 10, containing only copper, titanium, iron, aluminum and unavoidable impurities.

13. A copper-titanium alloy according to any one of claims 1 to 4, which does not contain silver or contains silver in an amount of 0.08% by mass or less, preferably 0.07% by mass or less, preferably 0.06% by mass or less.

14. Use of the copper-titanium alloy according to any one of claims 1 to 4 for manufacturing a Bourdon tube.

15. Use of the copper-titanium alloy according to any one of claims 1 to 4 for manufacturing watch parts.

16. 5. A method for producing a copper-titanium alloy according to any one of claims 1 to 4, comprising a solution annealing step, which comprises a heat treatment carried out at a temperature of at least 840°C, followed by a quenching step.

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