JP6688654B2 - Titanium copper alloy wire and method for manufacturing titanium copper alloy wire - Google Patents

Description

  The present invention relates to a titanium-copper alloy wire having high conductivity and a method for manufacturing a titanium-copper alloy wire.

  Copper alloys are used in many fields as connectors and wiring materials for electronic devices. If this is classified by use, it can be considered to be power use and signal use.

  The electric power application is a case where it is used for a part such as a motor or a connector for a large current. For electric power applications, copper alloys are required to have high electrical conductivity. On the other hand, the signal application is a case where it is used for a connector of a memory, a wire harness, or the like. In signal applications, copper alloys are weak in the amount of current they flow, and therefore are not required to have high conductivity, but are required to have strength against deformation for wiring and external stress.

  In order to give strength to a copper alloy, the type and amount of additional elements are adjusted. As a tendency, when the conductivity of the copper alloy is increased, the strength is decreased, and when the strength is increased, the conductivity is decreased. Therefore, there is a strong demand for a copper alloy that can simultaneously achieve high conductivity and high strength that are in a trade-off relationship.

  Among copper alloys, it is a copper-beryllium alloy that is said to have high electrical conductivity in addition to strength. The copper-beryllium alloy exhibits a conductivity of 20 to 70% IACS and a tensile strength of 700 to 1500 MPa depending on the composition conditions. However, since beryllium is rare and has toxicity at the same time, a copper alloy having a composition not using beryllium is being studied.

  Titanium is known as an element that can effectively improve the strength of a copper alloy. Further, in the case of an alloy containing titanium in an amount of 1.0 to 5.0% by weight, after passing through the steps of solution treatment and aging treatment, the alloy is fine with a size of several tens of nm or less and the crystal structure is cubic or tetragonal. It is also known that a Cu-Ti-based precipitate phase (which is referred to as a second phase with respect to a copper-rich copper mother phase (first phase)) is uniformly formed in crystal grains. When the aging treatment time is further increased, the Cu-Ti-based alloy has a lamellar shape (layered) with a size of several μm or more and a coarse shape and an orthorhombic crystal structure in competition with the formation of the second phase. It is also known that a precipitate phase (this is called the third phase) is generated and grows from the grain boundaries.

  The fine second phase is recognized as the preferred precipitate phase because it significantly improves the strength of the material. On the other hand, it is known that the formation of the coarse third phase not only causes the deterioration of the material strength because it corrodes the second phase, but also reduces the fatigue characteristics and the impact resistance.

  Patent Document 1 introduces a titanium-copper alloy containing 2.5 to 4.5% by weight of titanium and the balance of copper and unavoidable impurities. This titanium-copper alloy is characterized by having a 0.2% proof stress of 850 MPa or more and an electrical conductivity of 18% IACS. This has a structure in which the second phase (cubic or tetragonal) is homogeneously finely dispersed in the copper matrix (first phase).

  Further, in Patent Document 1, among the steps of hot rolling, cold rolling, solution treatment, aging treatment, and cold rolling after aging, by increasing the temperature of the solution treatment, the crystal grain size is increased. The point is to increase the ratio and reduce the proportion of the third phase (orthorhombic) that precipitates at the grain boundaries.

Japanese Patent Application No. 2011-195881 Japanese Patent Laid-Open No. 06-192801

  It can be said that the titanium-copper alloy of Patent Document 1 has a relatively high level of balance between strength and conductivity as a titanium-copper alloy. However, it cannot be said that the conductivity and the strength are also sufficient.

  The present invention, as a result of intensive studies in view of the above problems, the third phase, which was supposed to only cause a decrease in material strength, is subjected to a high processing rate, so that the strength (hardness) of the second phase is exhibited. ) It has been completed by finding out that higher characteristics are expressed. The titanium-copper alloy wire according to the present invention has a tensile strength of 1300 MPa and a conductivity of 30% IACS, and a tensile strength of 1600 MPa and a conductivity of 18% IACS at a high balance level.

More specifically, the titanium-copper alloy wire rod according to the present invention,
A titanium-copper alloy wire rod comprising 1 to 15% by weight of titanium and the balance of copper and unavoidable impurities,
With the first phase of the copper mother phase in which the content of titanium is lower than the charged amount,
A Cu-Ti-based precipitate phase in which the content of titanium is higher than the charged amount,
Consists of a cubic or tetragonal second phase and an orthorhombic third phase,
The proportion of the third phase in the Cu—Ti based precipitate phase is 50% or more and 100% or less,
The shape of the third phase is characterized in that the lamellar structure disappears.

  In the titanium-copper alloy wire according to the present invention, 50% by weight or more, preferably 70% by weight or more of the Cu-Ti-based precipitate phase dispersed in the copper matrix (first phase) has an orthorhombic structure. Since it is composed of phases and has been subjected to wire drawing work above a certain level, high conductivity can be maintained even in a high strength state.

  In conventional titanium-copper alloy wire rods, the second phase having a cubic or tetragonal crystal structure is contained in the copper matrix (first phase) in a weight percentage of about several percent (at the same time, a third phase (orthorhombic) is also formed). However, the weight ratio of the second phase is larger than that of the third phase), and it was finely dispersed to achieve high strength. However, the titanium-copper alloy wire according to the present invention has a relatively large amount of the orthorhombic third phase (more than the proportion of the second phase), and its shape is fine in the form of fibers or needles. Since it is dispersed, it can exhibit high conductivity and high strength at the same time.

3 is a graph showing a hardening curve when aging a Cu-3.2 wt% Ti alloy at 450 ° C., and a volume fraction of precipitates generated during aging. It is a graph which shows comparison of hardness and electric conductivity of an overaged wire and a peak aged wire. It is an XRD measurement chart of the Cu-Ti type | system | group precipitation phase in the overaged wire which concerns on this invention. It is the SEM photograph which looked at the cross section of the cylindrical rod material of the peak aging processing base material and the overaging processing base material. It is a cross-sectional SEM photograph of the overaged wire rod drawn to a diameter of 1.28 mm. It is a cross-sectional SEM photograph of the overaged wire rod drawn into diameters of 0.58 mm and 0.40 mm. It is a cross-sectional SEM photograph of the overaged wire rod processed to a diameter of 0.3 mm. It is a 40,000 times SEM photograph of the longitudinal section (section in the length direction) of the overaged wire rod drawn to 0.3 mm. It is a SEM photograph which extracted and separated the Cu-Ti type | system | group precipitation phase (3rd phase: crystal structure is an orthorhombic crystal) of the overaging process base material and the diameter of 3.0 mm and 1.28 mm overaging wire. It is the SEM photograph which extracted and separated the Cu-Ti type | system | group precipitation phase (third phase: crystal structure is orthorhombic) of the overaged wire with diameters of 0.58 mm and 0.30 mm. It is the SEM photograph which extracted and separated the Cu-Ti type | system | group precipitation phase (third phase: crystal structure is an orthorhombic crystal) of the over-aged wire with diameters of 0.30 mm and 0.10 mm. It is a figure which shows the calculation method of a volume fraction.

  The titanium copper alloy wire rod according to the present invention will be described below with reference to the drawings and examples. In addition, the following description illustrates one embodiment and one example of the present invention, and the present invention is not limited to the following description. The following description can be modified without departing from the spirit of the present invention.

  The titanium-copper alloy wire according to the present invention is manufactured as follows. First, a predetermined amount of copper and titanium are mixed and melted. A casting is obtained from the melt. The amount of titanium is 1 to 15% by weight, preferably 1 to 6% by weight, more preferably 2 to 5% by weight. If the amount of titanium is too much, the workability will decrease. If the amount is too small, the strength of the titanium-copper alloy wire will not be exhibited. The rest is copper and inevitable impurities.

  The casting is molded. This is to obtain the shape required for the final processing. For example, when the wire drawing is finally performed, the casting is processed into a rod having a diameter of about several mm. This is done while the casting is hot. This process can be called a hot rolling process.

  Next, the processed bar material is subjected to solution treatment. In this solution treatment step, a copper solid solution containing titanium is obtained. The solution treatment is performed by holding at a temperature of 800 ° C. to 1200 ° C. for 1 to 3 hours and then rapidly cooling. By the solution treatment, the cast product formed becomes a single phase (state) of a copper solid solution containing titanium in supersaturation. This is called a supersaturated solid solution. The solution treatment may be performed multiple times. For example, the obtained bar may be cold-rolled to change its shape, and the solution treatment may be repeated each time.

  The supersaturated solid solution is subjected to an aging treatment. Usually, the aging condition that gives the highest hardness is called the peak aging condition. This depends on the temperature. Usually temperatures between 300 ° C. and 700 ° C. are used. The lower the temperature, the longer the processing time is required. However, the lower the temperature, the higher the obtained strength tends to be.

  Under the peak aging condition, a Cu-Ti based precipitate phase is generated in the copper mother phase (first phase). Under the peak aging condition, the fine second phase (several tens of nm) having a cubic or tetragonal crystal structure occupies most of the Cu-Ti based precipitate phase, and this is homogeneously dispersed, so that the hardness is improved. The third phase, which has an orthorhombic crystal structure, is also formed together with the second phase, but the volume fraction is still low under peak aging conditions (equal to or less than the second phase), and the size is several μm or more. The shape is lamellar (layered).

It is known that the third phase having this shape hardly contributes to the strengthening of the material, and when the third phase develops, the strength decreases because the volume fraction of the second phase relatively decreases. The composition of both the second phase and the third phase is Cu ₄ Ti. The tetragonal one is also called αCu ₄ Ti, and the orthorhombic one is also called βCu ₄ Ti.

  In the titanium-copper alloy wire according to the present invention, this aging treatment is not a normal peak aging condition, but is aged for a time longer than the peak aging condition, and the aging treatment is performed until the hardness decreases. This is called an overaging condition. More specifically, one example of the overaging condition is a condition of a temperature of 450 ° C. and 400 hours.

  However, as described below, other aging conditions may be used as long as it can be confirmed that more than half of the Cu—Ti based precipitate phase generated by the aging treatment is the third phase (orthorhombic). That is, if it is confirmed that the proportion of the third phase in the Cu-Ti-based precipitate phase (second phase + third phase) is 50% by weight or more, preferably 70% by weight or more, under other aging conditions. It may be.

  The ratio of the second phase and the third phase (the unit is “%”) is calculated from the result of XRD as described later. However, since the second phase and the third phase have different crystal structures but have the same composition, the ratio calculated from the result of XRD may be directly used as the “wt%”. Further, if the weight ratio of the Cu-Ti-based precipitate phase is known, this can be converted into a volume fraction (%) from a known specific gravity value.

  By the aging treatment under the overaging condition, the proportion of the titanium-rich Cu-Ti-based precipitate phase in the copper matrix (first phase) increases. In addition, the proportion of the fine second phase (cubic or tetragonal) in the Cu-Ti-based precipitate phase is reduced, and instead the third phase (orthorhombic) having a lamellar (layered) structure is formed. Dominated. Normally, in a titanium-copper alloy wire rod, the Cu-Ti-based precipitate phase generated under the peak aging condition is strengthened by preferentially generating the second phase (cubic crystal or tetragonal crystal). A copper alloy wire uses a third phase (orthorhombic) that forms under overaging conditions. Conventionally, the formation of the third phase has not been considered preferable as a factor that reduces the strength. The material obtained by subjecting the supersaturated solid solution to the aging treatment under this overaging condition becomes the base material for wire drawing. Hereinafter, this base material is referred to as "overage-treated base material".

  The third phase (orthorhombic) in the copper matrix (first phase) changes from a lamellar shape to a fiber shape or a needle shape due to wire drawing. In other words, the lamellar (layered) tissue disappears. In the case of a base metal that has been subjected to an aging treatment under peak aging conditions (hereinafter referred to as a "peak aging-treated base metal"), the increase in strength becomes saturated when the area reduction rate is increased.

  On the other hand, in the titanium-copper alloy wire rod according to the present invention, the increase in strength due to the improvement in the area reduction rate is increased even when the surface area reduction rate at which the increase in the strength of the peak aging-treated base metal is saturated is increased. Keep doing Therefore, at a certain area reduction ratio or more, the strength of a wire rod made of a peak aging treated base metal (hereinafter referred to as “peak aging wire rod”) is higher than the strength of a wire rod made of an overage treated base metal (hereinafter, “the overaged wire rod (the titanium according to the present invention) The strength of the copper alloy wire))) is increased. The mechanism of action of this property is not clear, but the third phase, which has an orthorhombic crystal structure, is dispersed in the material with a relatively high volume fraction, and the shape is coarse and lamellar. It is considered that the main reason is that it is fiber-like or needle-like with a large aspect ratio.

  Regarding the electrical conductivity, the overaged wire has a sufficiently high copper concentration (low titanium concentration) in the copper matrix (first phase), and therefore has a higher electrical conductivity than the peak aged wire. Then, even if the area reduction ratio becomes high and the conductivity decreases, it is possible to maintain the state higher than that of the peak aging wire.

  The wire drawing process is a process in which the diameter of the base material is reduced and the length thereof is extended by using a die or a roll. The titanium-copper alloy wire according to the present invention has a processing rate (area reduction rate) from the base material of 80% or more, preferably 90% or more, more preferably 99% or more. Note that the area reduction rate cannot be 100% due to the definition of the area reduction rate. However, even if there is a feasible upper limit value for the minimum diameter that can be processed, if the thickness of the base material is made thicker, theoretically the area reduction rate approaches 100%. Therefore, it can be said that the upper limit of the area reduction rate is less than 100%. Further, a wire material having a round wire cross-section after wire drawing can be further processed into a flat wire or a deformed wire having a cross-sectional shape other than a circle by further rolling or wire drawing using a deformed die.

  In the overaged wire produced in this manner, the crystal structure of the third phase remains orthorhombic, but the shape is fiber-like or needle-like. Although the ratio of the Cu-Ti-based precipitate phase (second phase + third phase) to the total amount of titanium-copper alloy wire varies depending on the composition of the base metal alloy, the weight fraction is 1% by weight or more and 30% by weight or less, more preferably Is 5% by weight or more and 30% by weight or less, and most preferably 10% by weight or more and 30% by weight or less. However, in the case of the overaged wire according to the present invention, most of the Cu-Ti-based precipitate phase is the third phase, so the above range can be said to be substantially the range of the third phase.

  In the peak aging wire, the weight fraction of the Cu-Ti based precipitate phase (second phase + third phase) is 2% by weight or less. That is, the weight fraction of the third phase (orthorhombic) of the peak-aged wire does not exceed 1% by weight. Further, the volume fraction of the third phase having the orthorhombic structure in the overaged wire was calculated to be 1% or more and 35% or less (the calculation method of the deposition fraction of the third phase will be described later). The titanium content of the third phase is 10% by mass or more and 100% by mass or less, and the titanium content of the first phase is 0% by mass or more and 1% by mass or less.

  As described above, the titanium-copper alloy wire according to the present invention produces a solid solution of a titanium-copper alloy from a copper material and a titanium material, performs overaging treatment on the solid solution, and positively develops a third phase having an orthorhombic structure. A multi-phase structure that has been mechanically precipitated is obtained. A material having this multi-phase structure serves as a base material (overage-aged base material). Then, the base material is further processed to obtain the titanium-copper alloy wire according to the present invention.

Examples will be shown below.
<Casting>
Oxygen-free copper having a purity of 99.99% and pure titanium having a purity of 99.99% were subjected to high frequency melting and hot forged to obtain a casting having a diameter of 25 mm and a length of 255 mm. The composition at this time was a titanium-copper alloy containing 4.2 mol% (3.2% by weight) of titanium.

  This casting was held in the atmosphere at 900 ° C. for 1 hour. Then, it was put in water and cooled. This process is a homogenization process. Note that this processing can be omitted.

  The homogenized casting skin was excised. This is because impurities on the surface are removed so that the impurities are not mixed in the solution treatment and the aging treatment described below. By this treatment, the casting was formed into a rod having a diameter of 23 mm and a length of 255 mm.

  Next, tap forging was applied to this bar material. The tap forging is to process a bar material into a shape along the processed groove while striking the casting with a pair of tap metal molds having a groove having a semispherical cross section. By this treatment, the bar material was processed into a shape having a diameter of 15 mm and a length of 700 mm.

  Next, this rod was subjected to solution treatment. The solution treatment was performed using a muffle furnace at 900 ° C. for 1 hour. After the heat treatment, it was rapidly cooled to room temperature. The solution treatment is completed by heat treatment and quenching. Note that this treatment may be referred to as a first solution heat treatment treatment in order to distinguish it from a heat treatment described later.

  Groove roll processing was further applied to the bar material that had been subjected to the solution heat treatment. By this groove roll processing, a wire having a diameter of 3 mm was processed. This wire was heat-treated at 900 ° C. for 10 minutes in an argon gas atmosphere, and then returned to room temperature by indirect quenching by replacing with a nitrogen gas flow atmosphere. This process may be called the second solution heat treatment.

  Next, these wires were aged. FIG. 1 shows a hardening curve when Cu-3.2 wt% Ti alloy (Ti is 3.2 wt% and the rest is copper and inevitable impurities) is aged at 450 ° C. (FIG. 1 (a)), and 1 shows the volume fraction of precipitates formed during aging (FIG. 1 (b)).

  In FIG. 1A, the horizontal axis is the aging time (h) and the vertical axis is the Vickers hardness (HV). In FIG. 1B, the horizontal axis represents the aging time (h), and the vertical axis represents the volume fraction (%) of the precipitate. FIG. 1 (b) is a bar graph showing cubic (white long bar), tetragonal (black long bar), orthorhombic (shaded bar) and total amount of deposits (crossed square) for each aging time. It was It should be noted that cubic crystals (white long bars) are hardly visible in the graph when the aging time exceeds 10 hours due to the small existence ratio.

  From the age hardening curve of FIG. 1 (a), the peak aging condition was 450 ° C. for 12 hours, and the overaging condition was 450 ° C. for 408 hours. These samples are base materials for wire drawing. As described above, the base material subjected to the peak aging condition is referred to as "peak aging treated base material", and the base material subjected to the overaging condition is referred to as "overage treated base material". Further, the titanium-copper alloy wire rod obtained from these base materials by wire drawing is referred to as "peak-aged wire rod" or "over-aged wire rod".

  Looking at the transition of the volume fraction of the second phase (cubic or tetragonal) and the third phase (orthorhombic) in the alloy shown in FIG. 1 (b), it can be seen that the peak aging wire (12 hour aging material) The volume fraction of the Cu—Ti based precipitate phase (second phase + third phase) was 1.8%, of which the volume fraction of the third phase was about 0.7%. On the other hand, in the overaged wire (408 hour aged material), the volume fraction of the Cu—Ti-based precipitate phase (second phase + third phase) is 18%, of which the volume fraction of the third phase is 17%. It was 0.5% or more.

  The wire drawing process was performed by a die process so that the diameters of the respective base materials became smaller in order. Further, for both the peak-aged wire and the overaged wire, samples were prepared while changing the area reduction rate, and the evaluation items were measured by the following evaluation device.

  The Vickers hardness was measured using a Vickers hardness meter. The measurement was performed on the cross section of the wire rod that had been drawn. As the measuring device, MITUTOYO HM-101 was used. The measurement conditions were a load of 200 gf and a load time of 10 seconds. The Vickers hardness was measured at 12 points or more per sample, and the maximum and minimum values were excluded, and the average was taken as the Vickers hardness. Therefore, the unit is (HV0.2).

  The tensile strength was measured by using a tensile tester with a gauge length of 100 mm and a tensile speed of 5 mm / min. And the maximum load point was made into the tensile strength (MPa).

  The electrical conductivity was measured by measuring the resistance of a wire cut to 20 to 30 cm using a Nano Volt / Micro Ohm Meter 34420A manufactured by Agilent Technologies. The measured value was converted into the percentage (% IACS) with respect to the electric conductivity of the standard annealed copper wire by IACS (International Annealed Copper Standard).

  For the evaluation of the composition, SEM (Scanning Electron Microscope: Scanning Electron Microscope), FESEM (Cold Field Emission Scanning Electron Microscope: Cold Cathode Field Emission Scanning Electron Microscope), and TEM (Transmission Electron Microscopy) are used. The shape was observed.

  The volume ratio of the third phase was obtained by image processing of cross-sectional observation by SEM. Since the overaged wire has a long fiber shape or a needle shape in the length direction, the ratio of the third phase in the cross-sectional area can be read as a volume ratio. In the case of the overaged wire, the second phase is minute and the second phase is minute, so the second phase was ignored in the calculation of the volume ratio obtained from the cross-sectional area.

  Composition analysis was performed using XRD (X-ray diffraction: X-ray diffraction) and ICP (Inductively Coupled Plasma). In XRD, a Cu tube (X-ray wavelength: 0.1542 nm) was used.

  In particular, when calculating the ratio (%) of the second phase and the third phase in the Cu-Ti based precipitate phase, XRD was used. The ratio of the Cu-Ti-based precipitate phase to the total amount was obtained by weight% using the extraction separation method described later. Since the densities of the second phase and the third phase are known values, the volume fraction can be obtained from this. The volume fraction for the third phase can be obtained from the above-mentioned method or from XRD.

  The results are shown in FIG. 2A shows the relationship between hardness and true strain, and FIG. 2B is a graph showing the relationship between conductivity and true strain. In each graph, the horizontal axis is true strain (no unit), and the vertical axis is Vickers hardness (HV0.2: abbreviated as “HV” in the present specification and claims) in FIG. 2) is the electric conductivity (% IACS). The true strain (e) is obtained by e = ln (A0 / A), where A0 is the cross-sectional area of the wire before drawing and A is the cross-sectional area of the wire after drawing (“ln”). Is the natural logarithm).

  The diameter corresponding to the true strain is shown on the upper side of each graph. That is, the true strain is described as a value corresponding to the diameter reached by wire drawing. The diameter of the base material that has not been drawn is 3 mm. Therefore, the area reduction rate (ratio of the cross-sectional area before processing and the cross-sectional area reduced by the processing) can be uniquely calculated with respect to the diameter after the wire drawing processing described below.

  In each graph, square marks are overaged wire rods and diamond marks are peak aged wire rods. In addition, in FIG. 2A, the hardness of the wire rod obtained by wire-drawing the oversolubilized solid solution that has been subjected to the solution heat treatment before the aging treatment is also indicated by a circle.

  With reference to FIG. 2A, the Vickers hardness of the overage-treated base material (diameter 3.0 mm) was 200 HV or less. However, when the diameter was set to 2.0 mm (area reduction rate: 66%), the Vickers hardness sharply improved to 200 HV or higher (240 HV).

  In addition, the hardness of the peak-aged wire is higher than that of the overaged wire while the area reduction rate is low (the diameter after processing is large). On the other hand, the overaged wire rod has a higher hardness as the area reduction rate increases (the diameter after processing decreases), and the peak ageed wire rod has a diameter exceeding 0.175 mm (area reduction rate 99.66%). It became higher (more than 330 HV).

  Further, in the peak-aged wire, even if the diameter after processing was made thinner than about 0.3 mm, the hardness was hardly improved. On the other hand, in the overaged wire, even if the diameter after processing was 0.3 mm (area reduction rate 99.00%, 295 HV) or more, the hardness increased as the area reduction rate improved.

  The relationship between the hardness (true circle) and the true strain (diameter after processing) of the material after solution treatment (circle mark) has a tendency similar to that of the peak-aged wire. However, the overaged wire has a very different tendency. In other words, it can be said that the properties of the base material changed significantly due to the overaging treatment from the properties before the aging treatment.

  With reference to FIG. 2 (b), the electrical conductivity of the overaged wire is about twice as high as that before processing, as compared with the peak-aged wire. Then, although the area reduction rate became higher (the diameter after wire drawing became smaller) and the conductivity gradually decreased, it was possible to maintain a higher conductivity than in the case where the peak aging treated base material was used. .

  Specifically, what was 29% IACS in the state of the overage-treated base material did not change when the diameter was set to 2.0 mm. After that, when the diameter is 1.28 mm (area reduction rate 81.8%) (arrow A in FIG. 2B), there is already an increasing tendency, and the diameter is around 0.66 mm (area reduction rate 95.2%). The maximum value was 34% IACS. At this time, the Vickers hardness was 263 HV.

  In the region where the surface reduction rate is higher than that (the region where the diameter is small), the conductivity and the Vickers hardness showed opposite tendencies. That is, the Vickers hardness continued to increase and the conductivity decreased. When the diameter was set to 0.3 mm (area reduction rate 99%), the electrical conductivity was 30% IACS and returned to the level of the overage-treated base material. The Vickers hardness at this time was 295 HV. When the diameter is 0.175 mm (area reduction 99.66%), the conductivity is 21% IACS, and when the diameter is 0.1 mm (area reduction 99.89%), the conductivity is 17% IACS. Met. The Vickers hardness was 330 HV and 343 HV, respectively. The conductivity when the diameter was 0.1 mm was higher than 16% IACS which is the maximum value of the conductivity of the peak aging wire.

  Regarding the overaged wire, the tensile strength was also measured for some samples. In wire drawing, the tensile strength was 1390 MPa and the conductivity was 30% IACS when the diameter was 0.3 mm (area reduction rate 99%: true strain 4.6: 295 HV). Further, when the diameter was 0.1 mm (area reduction 99.89%: true strain 6.8: 343 HV), the tensile strength was 1640 MPa and the electrical conductivity was 17% IACS. All are high values that have never been reported in conventional titanium-copper alloys. The tensile strength and hardness are considered to be almost proportional. Therefore, in FIG. 2A, even if the vertical axis is read as tensile strength, the tendency of the peak-aged wire and the overaged wire does not change.

FIG. 3 shows a sample in which the overage-treated base metal in FIG. 2 has a diameter of 0.3 mm after wire drawing, and the copper-rich copper base phase (first phase) is dissolved in nitric acid and filtered. Therefore, only the Cu-Ti-based precipitate phase (second phase + third phase) is separated (hereinafter, this method is referred to as "extraction separation method". Using the extraction separation method is also referred to as "extraction separation". .) The XRD measurement results are shown below. The vertical axis represents intensity (arbitrary unit), and the horizontal axis represents 2θ (°). According to XRD, the maximum diffraction peak (peak of [020] plane) of Cu ₄ Ti having an orthorhombic structure at 2θ of 41.52 ° was detected. This is because most of the Cu-Ti based precipitate phase (second phase + third phase) is composed of the third phase (orthorhombic), and the fraction of the second phase (cubic or tetragonal) is small. Is shown.

In the usual peak aging wire, most of the Cu—Ti-based precipitate phases are tetragonal in the second phase, so the maximum peak of the [121] plane is observed at 2θ of 42.3 °. Therefore, it can be distinguished from the orthorhombic third phase. Table 1 shows the relationship between the mirror index 2θ of tetragonal Cu ₄ Ti and the strength (relative value), and Table 2 shows the relationship between the mirror index 2θ of the orthorhombic Cu ₄ Ti and the strength (relative value). Show.

  In addition, the fine tetragonal second phase and the orthorhombic layered third phase are usually competitively precipitated. Therefore, as shown in FIG. 3, whether the peak of the [020] plane of the third phase can be clearly confirmed, or 50% by weight or more when the fraction of the third phase (orthorhombic) was calculated by the Rietveld method, If it is preferably 70% by weight or more, it may be judged that it is the titanium-copper alloy wire according to the present invention.

  As described above, in the titanium-copper alloy wire rod according to the present invention, most of the Cu—Ti-based precipitate phase becomes orthorhombic by the overaging treatment, and the hardness that improves with respect to the true strain (area reduction rate) is: It is considered that the characteristics that continued to rise without being saturated were obtained. Moreover, as shown in FIG. 3, it is easy to remove the copper mother phase (first phase) with nitric acid, sample only the Cu—Ti based precipitate phase, and then measure the XRD (extraction separation method). It is possible to determine whether or not the third phase (orthorhombic) is formed in an amount of 50 wt% or more, preferably 70 wt% or more.

  The content of titanium in the third phase was about 20% by weight before wire drawing. In the case where the wire was drawn to a diameter of 0.3 mm, it was about 27% by weight. This is clearly higher than the titanium content (3.2% by weight) when the titanium-copper alloy was charged. That is, the third phase contains more titanium than the amount of titanium charged as the titanium-copper alloy, and at least 10% by weight or more, preferably 15% by weight or more, and most preferably 20% by weight or more. It should be noted that an increase in the content of titanium in the third phase is not considered to hinder compatibility between strength and conductivity, so the upper limit of the content of titanium in the third phase is 100% by weight. May be.

  In addition, the content of titanium in the copper matrix (first phase) in the state of the matrix before wire drawing was 0.58% by weight. When this was wire-drawn to a diameter of 0.1 mm, the titanium content was 0.92% by weight. Although the titanium content was slightly increased by the wire drawing, the titanium content in the first phase was obviously lower than the charged amount and was 1.0% by weight or less at most. Further, even if the content of titanium in the first phase becomes small, it is not considered that the strength and the conductivity are made compatible with each other. Therefore, the lower limit of the content of titanium in the first phase is 0% by weight. May be. The content of titanium in the first phase was determined by measuring titanium in a solution in which the first phase was dissolved by an extraction separation method by ICP analysis.

  FIG. 4 shows SEM photographs of the cross-sections of the cylindrical rods of the peak-aged base metal and the overaged base metal. FIG. 4 (a) is a 50,000 times photograph of the peak aging treated base metal, and FIG. 4 (b) is a 600 times photograph of the overage treated base metal. The thick white lines in the photograph (thick black lines with the same length are shown below the photograph) are 100 nm and 10 μm, respectively. A cross section perpendicular to the length direction of the drawn wire rod is called a cross section, and a cross section in the length direction of the wire rod is called a vertical cross section.

  The peak aging-treated base material (Fig. 4 (a)) shows only a smooth cross section (not shown) at a magnification of 600 times, but when the magnification is increased to 50,000 times, it has a size of several tens nm. It was observed that the slag precipitate was uniformly dispersed. On the other hand, the overage-treated base material (Fig. 4 (b)) has a cell-like structure composed of a stacked lamellar (layered) structure and a copper matrix, which is about 600 times as large as the cross section of bundled paper. It was also observed at magnification.

  This cellular structure occupied 90% of the entire visual field when viewed in a visual field of 600 times. The point calculation method was used for this measurement. For the point calculation method, the ratio of the number of points corresponding to the cell-like tissue was used out of 400 points (lattice points on a 20 × 20 grid) arbitrarily selected in a field of view of 600 times.

  The weight fraction of the Cu-Ti based precipitate phase (second phase + third phase) in the present alloy can be measured by the extraction separation method. That is, the ratio of the weight of the sample before dissolution in nitric acid and the weight of the Cu-Ti-based precipitate phase (second phase + third phase) recovered by the extraction separation method is the Cu-Ti-based precipitate phase (second phase). + Third phase) weight fraction. The weight fractions of the second phase and the third phase can be calculated by XRD measurement of the precipitate phase recovered by the extraction separation method and Rietveld analysis.

  In the case of the overaged wire rod in this example, the Cu-Ti-based precipitate phase (second phase + third phase) was 17% by weight with respect to the whole sample before wire drawing, and the third phase was 16.5%. It accounts for weight% or more (97% of the Cu-Ti based precipitate phase is the third phase). When wire drawing is performed from 3.0 mm to 0.1 mm in the in-line system, the Cu-Ti-based precipitate phase (second phase + third phase) is 1.6 wt% with respect to the entire sample, and the second phase is not detected. It was (That is, the third phase occupies 1.6% by weight. As described above, in the titanium-copper alloy wire rod according to the present invention, the weight fraction of the third phase depends on the composition and surface reduction rate of the overage-treated base metal. Although it changes, it has been confirmed that the weight fraction is 1% by weight to 30% by weight.

  FIG. 5 is a SEM photograph of a cross section of the overage-treated base material drawn by wire drawing to a diameter of 1.28 mm (area reduction rate 81.79%: 34% IACS). The magnification is 10,000 times. The lamellar structure is flattened and divided. Also, although not shown, the third phase was oriented in the longitudinal direction and stretched to 5 μm or more when viewed in a longitudinal section. That is, the third phase is deformed like a strip, and the strip-shaped third phases are bundled and the cut cross section is seen in FIG. Then, this state is a state in which the conductivity indicated by an arrow A in FIG.

  Although the overaged wire in this state has a hardness lower than that of the peak-aged wire, the conductivity is more than doubled, and it can be a useful material that has never existed before. That is, it can be said that the overaged wire according to the present invention starts to increase in conductivity when the strip-shaped third phase is observed. As shown in FIG. 5, this specific observation method is a lamellar shape if a white line with a length of several μm is observed over the entire field of view in a SEM photograph of a cross section viewed at a magnification of 10,000 times. It may be judged that is divided.

  FIG. 6A is a SEM photograph of a cross section of the overage-treated base material having a diameter of 0.58 mm (area reduction ratio 96%: true strain 3.36: 263 HV). The magnification is 10,000 times. It was possible to observe that the lamellar structure was further divided, and that a white fine structure (third phase) with a length of about 1 μm was divided into a unit of several to a dozen units. Further, in the SEM photograph at this magnification, there was no tissue having a white portion exceeding 3 μm. That is, the length was 3 μm or less. It was speculated that the lamellar structure was elongated in the lengthwise direction and further thinned.

  FIG. 6B is an SEM photograph when the overaged base metal has a diameter of 0.40 mm (area reduction rate 98%: true strain 4.03: 275 HV). The magnification is 35,000 times. The white tissue (third phase) was divided into several hundreds of nm (1 μm or less) in length.

  FIG. 7 is a SEM photograph of a cross-section of an overaged wire rod obtained by processing the overageed base material to a diameter of 0.3 mm (area reduction rate 99%, true strain 4.6: 295 HV). 7A is 5,000 times, and FIG. 7B is 35,000 times. It was considered that the large lamellar structure before processing shown in FIG. 4B was deformed and curved, and was divided into fibers. In FIG. 7B, a fine structure having a cross-sectional width of about 100 nm is observed as white. This part is the third phase.

  FIG. 8 is a 40,000-time SEM photograph (HAADF (High-Angle Annular Dark Field) image) of a longitudinal section in the longitudinal direction of the overaged wire of FIG. 7. The black line in the length direction is the second phase. An arrow (corresponding to a length of 1 μm) indicating the direction of the tissue is marked on the left side of the photograph. The direction of the structure runs in the length direction of the overaged wire.

  It can be confirmed that the black stripes (third phase) in the photograph have a length of at least about 1 μm in the length direction. Considering the photograph of FIG. 6 (b), the third phase of the overaged wire has a rectangular cross section with a width of about 100 nm and is formed into a needle shape with a length of about 1 μm (or more). It is believed that In addition, the needle-like shape means a shape whose length in a vertical cross section is 5 times or more of the longest length in a horizontal cross section. In addition, even if the ratio can be called needle-like, or if the ratio is greater than 2 μm, it may be called fiber-like tissue.

  Next, the state of the third phase obtained by the extraction separation method from FIG. 9 is shown. FIG. 9 (a) is a 6,000 times photograph of an overaging treated member (diameter 3 mm), and FIG. 9 (b) is a 5,000 times photograph of a diameter 1.28 mm (area reduction rate 81.8%). Is. The cross section corresponds to FIGS. 4B and 5.

  In FIG. 9A, it is observed that the lamellar structure, the third phase, remains as a layered structure. That is, the lamellar structure can be observed as a stacked layered structure when the third phase is extracted and observed by the extraction separation method. On the other hand, as shown in FIG. 9 (b), when wire drawing was performed at a surface reduction rate of 80% or more, a large layered structure was not observed.

  In this way, comparing the second phase of the overage-treated base metal and the third phase of the overaged wire material subjected to wire drawing, when wire drawing at an area reduction rate of 80% or more, a large layered third phase Tissue disappears. When the surface reduction rate was 80% or more, the lamellar structure having a size of at least 3 μm × 3 μm disappeared.

  FIG. 10 (a) is a photograph showing a diameter of 0.58 mm (area reduction rate 96.3%) 8,000 times, and FIG. 10 (b) is a diameter of 0.30 mm (area reduction rate 99%). It is a photograph of 1,000 times. The cross section corresponds to FIG. 6 (a) and FIG. 7. Even if the area reduction rate exceeded 90%, a small layered structure was observed. Specifically, a layered structure having a size of 2 μm × 2 μm or more was not observed. However, when the area reduction rate exceeded 99%, the layered tissue itself was not observed, and the entire visual field became a needle-shaped tissue.

  FIG. 11 (a) is a 20,000 times photograph of a diameter of 0.30 mm (area reduction rate 99%), and FIG. 11 (b) is a photograph of a diameter of 0.10 mm (area reduction rate 99.9%) 20, It is a 000x photo. When the area reduction rate exceeds 99%, needle-like tissues with a length of 2 μm or less are also scattered, and when the area reduction rate is 99.9%, almost all tissues become needle-like tissues with a diameter of 2 μm or less. It was As described above, the third phase of the overage-treated base material, which was a layered structure, is stretched by wire drawing to become a needle-shaped structure, and further stretched into pieces having a length of 2 μm or less.

  Even if the ratio is a needle-like structure, if the structure having a length of 2 μm or less is called a grain, it can be said that the layered structure becomes a needle-shaped structure and is transformed into a fine grain structure.

  As described above, in the titanium-copper alloy wire rod according to the present invention, when the third phase is extracted by the extraction separation method and observed by SEM, the layered structure larger than 3 μm × 3 μm square disappears at the observation of 5,000 times magnification. Yes (area reduction of 80% or more). Further, when observed at a magnification of 8,000 times, if the entire visual field has a needle-like structure (area reduction rate of 99% or more), the hardness becomes higher and the layered structure larger than 2 μm × 2 μm square disappears. There is. Further, when observed at a magnification of 20,000, if the entire surface of the visual field has a substantially granular structure (area reduction ratio of 99.9% or more), the hardness becomes extremely high.

  As described above, when the titanium-copper alloy wire according to the present invention is subjected to wire drawing to a surface reduction rate of about 99% (295 HV), the third phase has an acicular structure. In such a case, the volume fraction of the third phase can be obtained from the cross-sectional photograph. This is because the structure is almost needle-shaped in the length direction, and therefore the area ratio of the third phase (the portion that appears white in the SEM photograph) in the photograph of the cross section can be directly regarded as the volume ratio.

  The method of obtaining the volume fraction will be described more specifically. FIG. 12 shows a method for obtaining the volume ratio (area ratio in the photograph) of the third phase from the photograph of FIG. 7 (b). The sample was an overaged wire, and it was confirmed by the extraction separation method that 95% or more of the precipitate phase formed in the copper matrix (first phase) was occupied by the third phase (orthorhombic). Already done. Further, the third phase (orthorhombic) does not change into a different crystal structure by wire drawing.

  Referring to FIG. 12, first, a photograph was taken in a state in which the contrast was most visible with an SEM (FIG. 12 (a)). Next, I loaded this into the existing image processing software. The image processing software is not particularly limited, but it is desirable that the image processing software be capable of binarizing the read image and having a function of obtaining a histogram of a white portion. Here, "Adobe Photo Shop CS (manufactured by Adobe Systems Inc.)" was used.

  Next, "Grayscale" was selected as the image / mode. Next, “level correction” was selected in image / color tone adjustment, and the input level was adjusted to the maximum and minimum values of the histogram waveform (FIG. 12 (b)).

  "Monochrome 2 gradations" was selected for the image / mode, and "Divided into 2 gradations based on 50%" was selected for "Type" (FIG. 12 (c)).

  Select "Grayscale" in the image / mode and set the size ratio to 1. Then, if the number of white pixels and the total number of pixels are read in the histogram, the ratio is obtained as the volume fraction. Here, since the values of all pixels are “223256” and the number of pixels is “44037”, in the SEM photograph of FIG. 7B, the area ratio of the white portion is 19.7% with respect to the entire visual field. Was calculated.

  As explained above, this area ratio may be re-read as the volume fraction. Therefore, it can be said that the volume fraction of the third phase is 19.7% in the sample of the example subjected to the wire drawing to the area reduction rate of 99% (diameter 3.0 mm to diameter 0.3 mm).

  The volume fraction was 35% or more in the sample drawn from the overage-treated base material to a surface reduction ratio of 66% (240 HV). In addition, in other samples having different titanium contents, the volume fraction of the samples drawn to a diameter of 0.1 mm was 1.2%. Of course, the third phase of these samples was orthorhombic.

  Therefore, in the titanium-copper alloy wire rod according to the present invention, it can be said that the volume fraction of the third phase obtained from the cross section is 1% or more and 35% or less. The weight fraction of the third phase uses the extraction separation method, and the volume fraction is the value obtained from the image obtained by the SEM photograph of the cross section. You don't have to.

  As described above, the titanium-copper alloy wire according to the present invention, after the solution treatment, is subjected to the overaging treatment, the third phase forms an orthorhombic crystal, and the high conductivity is imparted although the strength is reduced. To do. By providing the base material with a high area reduction rate, high hardness (strength) can be imparted and high conductivity can be maintained.

  The titanium copper alloy wire according to the present invention can be suitably used mainly as a connector material for signals.

Claims (9)

A titanium-copper alloy wire rod comprising 1 to 15% by weight of titanium and the balance of copper and unavoidable impurities,
With the first phase of the copper mother phase in which the content of titanium is lower than the charged amount,
A Cu-Ti-based precipitate phase in which the content of titanium is higher than the charged amount,
Consists of a cubic or tetragonal second phase and an orthorhombic third phase,
The proportion of the third phase in the Cu—Ti based precipitate phase is 50% or more and 100% or less,
The shape of the third phase is a titanium-copper alloy wire rod in which a lamellar structure has disappeared.   The titanium-copper alloy wire rod according to claim 1, wherein the lamellar structure is a structure larger than 3 µm x 3 µm.   The weight fraction of the Cu-Ti-based precipitate phase is 1% by weight or more and 30% by weight or less with respect to the total amount of the titanium-copper alloy wire rod. Titanium-copper alloy wire described in.   Content of titanium of the said Cu-Ti type | system | group precipitation phase is 10 weight% or more, The titanium copper alloy wire rod of any one of Claim 1 thru | or 3 characterized by the above-mentioned.   The titanium-copper alloy wire rod according to any one of claims 1 to 4, wherein the content of titanium in the first phase is 1.0% by weight or less.   The titanium-copper alloy wire rod according to any one of claims 1 to 5, wherein the Vickers hardness of the third phase is 200 HV or more. Mixing 1 to 15% by weight of titanium and copper to obtain a casting,
A hot rolling step of forming the casting at a high temperature to obtain a bar material,
A solution treatment step of rapidly cooling the bar from a high temperature to obtain a supersaturated solid solution;
A step of performing an overaging treatment in which a third phase having an orthorhombic crystal structure precipitates in the precipitation phase of the supersaturated solid solution in an amount of 50% or more of the precipitation phase to obtain an overage-treated base material;
A method for producing a titanium-copper alloy wire rod, comprising a step of drawing the overage-treated base material to obtain a titanium-copper alloy wire rod.   The method for producing a titanium-copper alloy wire according to claim 7, wherein, in the drawing step, the reduction area of the titanium-copper alloy wire is 80% or more and less than 100%.   The method for producing a titanium-copper alloy wire according to any one of claims 7 and 8, wherein the diameter of the titanium-copper alloy wire is 0.3 mm or less in the drawing step.