JP7126656B2 - Copper alloy for cryogenic parts - Google Patents

Description

The present invention relates to a copper alloy for cryogenic members that can be used stably even in cryogenic environments such as liquid helium temperature, and in particular, in superconducting acceleration cavities and superconducting magnets in cryogenic and high magnetic field environments. It relates to a copper alloy for cryogenic members that can be stably used in

Superconducting acceleration cavities and superconducting magnets are used in various devices such as superconducting accelerators and measuring instruments for medical equipment. Liquid helium is used as a coolant for cooling these devices. Also, with the recent development of high-temperature superconducting materials, it is expected that liquid nitrogen and other low-cost refrigerants will be substituted for high-temperature superconducting magnets. There is a demand for metallic materials for cryogenic parts that can be stably used in such cryogenic environments in terms of material strength, hardness, low-temperature brittleness, thermal shrinkage, high/low thermal conductivity, and non-magnetism. there is

For example, in Patent Document 1, as a superconducting coil for an MRI (nuclear magnetic resonance) apparatus, a winding is applied to a cylindrical non-magnetic stainless steel winding frame having a cylindrical portion and a flange portion. A superconducting coil in which one end of a heat transfer member made of copper or aluminum is brought into close contact with the inner circumference of a cylindrical portion and the other end is connected to a refrigerator so that the heat generated by the winding is led to the refrigerator. is disclosed. By using copper or aluminum, which has a higher thermal conductivity than a winding frame made of stainless steel, as the heat transfer member, the outer peripheral portion of the winding can be efficiently cooled.

Patent Document 2 discloses a stainless steel whose mechanical strength can be increased by cold working and precipitation hardening as an austenitic non-magnetic stainless steel for a superconducting magnet component of a superconducting accelerator. It is known that non-magnetic austenitic stainless steel transforms into martensite by working to partially generate ferrite and acquires magnetism. Such alloys are said to have excellent austenite phase stability. In addition to excellent magnetic permeability at extremely low temperatures, it also has excellent mechanical properties at extremely low temperatures, such as low thermal shrinkage.

In Patent Document 3, in a superconducting accelerator that accelerates charged particles such as electrons and protons using a superconducting accelerating cavity, a coolant tank made of stainless steel is inserted into a superconducting accelerating cavity made of niobium, a superconducting material, by bolts. It is mentioned that if they are connected, the sealing performance is lowered due to the bolted connection during operation, and leakage is likely to occur. Therefore, the coolant tank is also made of the same niobium material as the superconducting accelerating cavity and joined by welding, or niobium is sputtered on the surface of the superconducting accelerating cavity made of copper and joined to the coolant tank made of stainless steel by brazing. etc. is disclosed.

JP-A-11-144940 JP 2007-262582 A JP-A-2000-150197

By the way, copper alloys are originally non-magnetic and are not magnetized by working or welding. In addition, it is expected to be used as a substitute material for non-magnetic stainless steel, etc., because it does not show a clear transition temperature of low-temperature embrittlement down to extremely low temperatures. Furthermore, as pointed out in Patent Document 3, it is also required to have excellent mechanical properties under heat cycles and cryogenic environments, and to improve stability while maintaining non-magnetism.

For example, when inserting a beam-focusing superconducting solenoid into a superconducting accelerating cavity cryomodule, the surrounding members may be magnetized by leakage magnetic fields during operation of the solenoid. When the superconducting cavity is heated above the critical temperature and then recooled (thermal cycling during operation), the magnetic field from the magnetized members is trapped in the superconducting cavity and the performance of the cavity is severely degraded. In order to prevent this, a complicated degaussing process is required after the solenoid is operated, and in some cases it cannot be degaussed sufficiently. Also, as a substitute for materials such as stainless steel 316L that are easily magnetized by machining or welding, members made of completely non-magnetic materials that are not magnetized even when a superconducting solenoid is operated are required.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a copper alloy for cryogenic parts such as superconducting accelerating cavities and superconducting magnets, which can be used stably at cryogenic temperatures and under strong magnetic fields.

The copper alloy for cryogenic members according to the present invention contains Ni: 1.5 to 9.0%, Si: 0.4 to 2.5%, and Cr: 0.2 to 1.5% by mass%. , the balance is Cu and unavoidable impurities, and the Ni/Si ratio is set to 3.8 to 4.1 to dissolve Cr in the Cu matrix and precipitate a Ni—Si intermetallic compound. It is characterized by having a thermal conductivity of 100 W/m·K or more at room temperature and an impact value of 15 J/cm ² or more in a Charpy test (JIS Z 2242 compliant) at liquid nitrogen temperature.

According to this invention, by strengthening the Cu matrix, the stability of mechanical properties in thermal cycles and in cryogenic environments is high, and in cryogenic and high magnetic fields such as superconducting acceleration cavities and superconducting magnets. It does not show any mechanical deterioration even if it is in contact, and can be used stably.

In the above-described invention, the component composition may further contain Sn: 0.1 to 0.3%, and may have an impact value of 50 J/cm ² or more. Moreover, it may be characterized in that at least Mn and Zr are set to 0.05% or less as the unavoidable impurities. According to such an invention, the strength of the matrix can be further increased, and it can be used more stably even at extremely low temperatures and in a high magnetic field.

1 is a table showing chemical compositions of copper alloys used in examples according to the present invention. It is a list of the results of various tests of Examples.

An example of a copper alloy for cryogenic components according to the present invention is described below.

The copper alloy for cryogenic members in this embodiment contains, by mass %, Ni: 1.5 to 9.0%, Si: 0.4 to 2.5%, and Cr: 0.2 to 1.5%. It is a copper alloy that can be used (see Fig. 1). Furthermore, by setting the Ni/Si mass ratio to 3.8 to 4.1, the Ni—Si intermetallic compound is precipitated to consume Si, and the precipitation of the Cr—Si intermetallic compound is suppressed. to maintain the solid solution of Cr in the Cu matrix. At this time, solid solution strengthening is achieved by sufficiently dissolving Cr, and precipitation hardening by Ni—Si intermetallic compounds is also attempted, and the synergistic effect of both strengthening mechanisms is obtained to achieve higher mechanical strength. ing. Then, it is homogenized by heat treatment so that the thermal conductivity at room temperature is 100 W/m K or more and the impact value in the Charpy test (JIS Z 2242 compliant) at liquid nitrogen temperature (77 K) is 15 J/cm ² or more. It regulates gender.

Such a copper alloy is highly stable in mechanical properties under thermal cycles and in cryogenic environments by strengthening the Cu parent phase as described above, and is highly stable in cryogenic and high magnetic fields around superconducting magnets. Even if there is, it does not magnetize and does not exhibit mechanical deterioration, and can be used stably.

In addition, by adjusting the composition of such a copper alloy, the thermal conductivity at cryogenic temperatures can be adjusted from high to very low, suppressing the amount of heat penetration and the generation of thermal stress due to temperature changes in the environment in which it is used. , with high resistance to thermal fluctuations. Furthermore, such a copper alloy is excellent in machinability. In the superconducting accelerating cavity, the copper alloy of this embodiment is compatible with niobium and niobium alloys, and when used as screws/nuts for tightening the flange of the cavity, galling with the flange screws does not occur. In addition, when assembling a superconducting cavity, it is necessary to avoid contamination of the inside of the cavity with dust as much as possible, but the screw tightening work during assembly of the cavity generates very little dust.

In other words, the copper alloy for cryogenic members according to this example is suitable for highly clean members such as superconducting accelerator cavities, threaded members, and the like.

In addition, the composition of such a copper alloy for cryogenic members may further contain Sn: 0.1 to 0.3%. At this time, it is preferable that the impact value in the Charpy test at the liquid nitrogen temperature (77K) can be 50 J/cm ² or more.

Moreover, at least Mn and Zr may be 0.05% or less as unavoidable impurities. At this time, the matrix strength can be further increased, which is preferable.

In addition, in such a copper alloy, for example, after sufficiently performing solution treatment at a holding temperature of 850 to 950 ° C., aging treatment is performed at 450 to 550 ° C. so as to obtain a predetermined thermal conductivity. Thus, a copper alloy having excellent mechanical properties in an extremely low temperature environment can be obtained.

Next, the results of tests conducted to investigate physical properties and mechanical properties of the above copper alloy for cryogenic members will be described.

Tests were conducted on the copper alloys having the composition shown in FIG. 1, ie, Examples 1 and 2. In both Examples 1 and 2, after holding at 950 ° C., Cr is sufficiently dissolved by solution treatment of cooling with water, and Ni-Si intermetallic compound is precipitated by aging treatment at 550 ° C. is.

FIG. 2 shows the results of various tests. Thermal conductivity, thermal expansion coefficient, tensile test, and hardness test were all performed under room temperature environment, impact test was performed at 77 K (liquid nitrogen temperature), and Example 2 was impacted at 4 K (liquid helium temperature) A test was conducted. The impact test was a Charpy impact test conforming to JIS Z 2242.

As shown in the figure, the thermal conductivity was 100 W/m·K or more in both Example 1 and Example 2, and the thermal expansion coefficient was 17×10 ⁻⁶ /K in both cases. That is, it has a relatively high thermal conductivity and a relatively small coefficient of thermal expansion. As a result, even when the temperature changes, the member can be used without being subjected to a large thermal stress. For example, phosphor bronze has a similar coefficient of thermal expansion, but the thermal conductivity is smaller than those of Examples 1 and 2, and a relatively large thermal stress is applied to the member due to temperature changes. put away.

Moreover, as a result of measuring the thermal conductivity at an extremely low temperature of 2K, a value of 4 W/mK, which is smaller than the thermal conductivity (10 W/mK) of a niobium material in a superconducting state, was obtained. If the copper alloy of this embodiment is used for pipe piping in a cryostat for superconducting cavities, it is possible to greatly reduce heat intrusion from the outside.

Moreover, both Example 1 and Example 2 exhibited sufficiently high values of tensile strength of 650 MPa or more and yield strength of 550 MPa or more, and elongation of 13% or more was sufficient. For example, phosphor bronze has similar elongation, but tends to have lower tensile strength and yield strength. Also, the hardness was 210 Hv or more in both Examples 1 and 2, but the phosphor bronze tends to be lower than this.

As for the Charpy impact test, both Example 1 and Example 2 obtained a high impact value of 15 J/cm ² or more. In particular, in Example 2 containing Sn in the range of 0.1 to 0.3%, a higher impact value of 50 J/cm ² or more could be obtained.

As described above, in this example, it has a high thermal conductivity, a small thermal expansion coefficient, and a very low thermal conductivity at cryogenic temperatures, and the stability of mechanical properties in heat cycles and cryogenic environments and can block heat penetration at extremely low temperatures. In addition, the impact value in the Charpy test at extremely low temperatures was also high. Moreover, the copper alloys shown in Examples 1 and 2 exhibit non-magnetism even at extremely low temperatures. In other words, it does not exhibit mechanical deterioration even in extremely low temperatures and high magnetic fields like superconducting magnets, and can be used stably.

Although the embodiments according to the present invention and modifications based thereon have been described above, the present invention is not necessarily limited to these, and a person skilled in the art can deviate from the gist of the present invention or the scope of the appended claims. Various alternatives and modifications may be found without further ado.

Claims (3)

% by mass, Ni: 1.5 to 9.0%, Si: 0.4 to 2.5%, Cr: 0.2 to 1.5%, the balance being Cu and inevitable impurities having the composition
By setting the Ni/Si ratio to 3.8 to 4.1, dissolving Cr in the Cu matrix and precipitating the Ni—Si intermetallic compound,
A copper for cryogenic parts, characterized by having a thermal conductivity of 100 W/m K or more at room temperature and an impact value of 15 J/cm ² or more in a Charpy test (JIS Z 2242 compliant) at liquid nitrogen temperature. alloy. 2. The copper alloy for cryogenic members according to claim 1, wherein said composition further contains Sn: 0.1 to 0.3% and has an impact value of 50 J/cm ² or more. 3. The copper alloy for cryogenic members according to claim 1, wherein at least Mn and Zr are 0.05% or less as the unavoidable impurities.

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