Infrared detector dewar cold finger and method of making

Abstract

The present application relates to a kind of infrared detector dewar cold finger preparation method, comprising the following steps: step 1: blank is processed, to form thin-walled tube, substrate base and welding ring;Step 2: thermal barrier coating is sprayed on the outer surface of thin-walled tube;Step 3: the inner hole of thin-walled tube with thermal barrier coating is finished;Step 4: protective shell is installed on the outer surface of thin-walled tube with thermal barrier coating and substrate base, bonding between protective shell and thermal barrier coating, welding between protective shell and substrate base;Step 5: dewar cold finger is subjected to high-low temperature impact test, and whether dewar cold is qualified is judged according to the detected leakage rate.The present application can effectively reduce the heat conduction performance by spraying thermal barrier coating on the outer surface of thin-walled tube, greatly reduces the static thermal load generated by the heat conduction effect of cold finger thin-walled part, and the safety and stability of material can be improved under the cooperation of thin-walled tube and thermal barrier coating.

Description

Technical Field

[0001] This invention relates to the field of Dewar cold finger technology, and particularly to an infrared detector Dewar cold finger and its preparation method. Background Technology

[0002] In the Dewar cooling assembly of an infrared detector, the Dewar assembly serves to encapsulate the infrared chip and provide it with a high-vacuum, heat-insulating cavity. The Dewar assembly is coupled to a refrigerator, which provides the cold source, cooling the infrared chip encapsulated inside the Dewar assembly to liquid nitrogen temperature for operation.

[0003] Because the Dewar assembly operates under a high vacuum, convective heat transfer is negligible. The overall static heat load of the Dewar assembly primarily results from the thermal radiation from external components such as the window mount, housing, chip, and surrounding cold shield, as well as the thermal conduction from the cold finger components. The thermal conduction capacity of the cold finger components accounts for approximately 50% of the total static heat load. Reducing the static heat load of the Dewar assembly not only lowers the steady-state current of the cryostat but also reduces the maximum current and the cooling time, playing a crucial role in detectors requiring fast startup and low power consumption.

[0004] In current processes, cold finger fabrication primarily relies on the machining of metal materials. To minimize heat conduction, the wall thickness of the cold finger needs to be reduced to a minimum. However, if the wall thickness is too thin, the mechanical strength is insufficient. Therefore, the wall thickness of the cold finger is generally chosen to balance ensuring mechanical strength with reducing heat transfer. Consequently, it is difficult to reduce the heat conduction portion of the Dewar's static heat load to a very low level. This paper proposes a cold finger for infrared detector Dewars and its fabrication method. Summary of the Invention

[0005] This invention provides a cold finger for an infrared detector dewar and a method for its fabrication, which reduces the static thermal load of the dewar assembly fabricated using the cold finger while ensuring that other properties such as the mechanical strength of the dewar assembly remain unchanged.

[0006] This invention provides a method for preparing a Dewar cold finger for an infrared detector, comprising the following steps: Step 1: Process the blank to form a thin-walled tube, a base plate, and a welding ring; Step 2: Spray a thermal barrier coating onto the outer surface of the thin-walled tube, so that the outer diameter of the thin-walled tube with the thermal barrier coating is greater than or equal to the outer diameter of the welding ring; Step 3: Finish the inner hole of the thin-walled tube with thermal barrier coating; Step 4: Install the protective shell on the outer surface of the thin-walled tube with thermal barrier coating and the base, and bond the protective shell and the thermal barrier coating together, and weld the protective shell and the base together to obtain the Dewar cold finger; Step 5: Conduct a high and low temperature impact test on the Dewar cold finger, and determine whether the Dewar cold finger is qualified based on the detected leakage rate.

[0007] In one embodiment, in step 2, a transition layer may be prepared on the surface of the thin-walled tube before the thermal barrier coating is applied.

[0008] In one embodiment, step 5, when conducting a high and low temperature impact test on the Dewar cold finger, is performed according to the following steps: Step 5.1: Immerse the Dewar cold finger in liquid nitrogen for at least 10 minutes; Step 5.2: Bake the soaked Dewar cold fingers at a temperature greater than 80°C for at least 10 minutes; Step 5.3: Repeat steps 5.1 and 5.2 at least 10 times.

[0009] In one implementation, step 5, determining whether the Dewar cold finger is qualified based on the detected leak rate, includes: Leak rate is detected using a leak detection device in conjunction with a helium mass spectrometer leak detector. Determine if the leakage rate is ≤5× Pa. / S, if so, then the Dewar cold finger is qualified.

[0010] This invention provides an infrared detector Dewar cold finger, manufactured using the aforementioned method, comprising: A metal substrate, the metal substrate comprising a thin-walled tube, a substrate base and a welding ring, the substrate base being disposed at one end of the thin-walled tube and the welding ring being disposed at the other end of the thin-walled tube; A thermal barrier coating is disposed on the outer surface of the thin-walled tube of the metal substrate; and A protective housing is fitted over the thermal barrier coating and connected to the top of the base.

[0011] In one embodiment, the lower end of the thermal barrier coating abuts against the top end of the substrate base, and the upper end of the thermal barrier coating abuts against the welding ring.

[0012] In one embodiment, the distance between the top of the protective housing and the welding ring is greater than or equal to 1 mm.

[0013] In one embodiment, the wall thickness of the thin-walled tube is 0.01 mm to 0.025 mm.

[0014] In one embodiment, the thickness of the thermal barrier coating is 0.2 mm to 0.5 mm.

[0015] In one embodiment, the thin-walled tube, the base plate, and the welding ring are integrally formed.

[0016] Compared with the prior art, the advantages of the present invention are that by spraying a thermal barrier coating on the outer surface of the thin-walled tube, the thermal conductivity can be effectively reduced, which greatly reduces the static heat load caused by the thermal conduction of the thin-walled part of the cold finger. With the cooperation of the thermal barrier coating, the thin-walled tube can ensure the airtightness, safety and stability of the cold finger. The protective shell ensures that there is sufficient mechanical strength between the thin-walled tube, the thermal barrier coating and the protective shell. Attached Figure Description

[0017] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0018] Figure 1 This is a schematic diagram of the structure of a metal matrix processed from the same metal material according to the present invention; Figure 2 This is a schematic diagram of the metal substrate blank structure of the present invention; Figure 3 This is a schematic diagram of the structure of the Dewar cold finger of the present invention; Figure 4 yes Figure 3 Schematic diagram of Part A; Figure 5 This is a schematic diagram of the Dewar cold finger leak rate test; Figure 6 This is a schematic diagram of the preparation method of the present invention; Figure label: 1. Thin-walled tube; 2. Welding ring; 3. Base; 4. Flange; 5. Leak detection base; 6. Sealing groove; 7. Inner cavity; 8. Protective shell; 9. Thermal barrier coating; 10. Weld; 11. Sealing ring; 12. Sealing rubber plug. Detailed Implementation

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Please refer to Figure 6 A method for preparing an infrared detector Dewar cold finger includes the following steps: Step 1: Process the blank to form a thin-walled tube, a base, and a welding ring. The outer diameter of the thin-walled tube 1 is machined to the required dimensions. The dimensions of other parts are machined with a finishing allowance, that is, the finishing allowance for the inner hole of the thin-walled tube 1 is 0.2mm to 0.5mm, and the finishing allowance for the dimensions of other parts is 0.1mm.

[0021] Step 2: The thermal barrier coating 9 is sprayed onto the outer surface of the thin-walled tube 1. One end of the thermal barrier coating 9 abuts against the top of the substrate base 3, and the other end abuts against the welding ring 2, so that the outer diameter of the thin-walled tube 1 with the thermal barrier coating 9 is greater than or equal to the outer diameter of the welding ring 2. The gap between the thermal barrier coating 9 and the protective shell 8 is not too large, ensuring that the protective shell 8 and the thermal barrier coating 9 can fit together. The amount of adhesive used for bonding is as small as possible, so that the protective shell 8 and the thermal barrier coating 9 can be tightly bonded, ensuring the supporting strength of the thin-walled tube 1. Atmospheric plasma spraying is often used to prepare the thermal barrier coating 9, and the thickness of the thermal barrier coating 9 sprayed on the outer surface of the thin-walled tube 1 is controlled between 0.2 mm and 0.5 mm.

[0022] Step 3: Finish machining the inner hole of the thin-walled tube 1 with thermal barrier coating 9. After the thermal barrier coating 9 is prepared, the dimensions of other parts of the metal substrate are first finished to the theoretically designed dimensions, and then the inner hole of the thin-walled tube 1 is finished to obtain an inner diameter of φ7.6 (0 / +0.01) mm, so that the wall thickness of the thin-walled tube 1 is 0.01 mm to 0.025 mm.

[0023] Step 4: Install the protective housing 8 onto the outer surface of the thin-walled tube 1 with the thermal barrier coating 9 and the base 3, and bond the protective housing 8 to the thermal barrier coating 9. Simultaneously, weld the protective housing 8 to the base 3 to achieve a Dewar cold finger. The inner diameter of the protective housing 8 is 0.03mm to 0.05mm larger than the outer diameter of the thermal barrier coating 9. The protective housing 8 is fitted over the thermal barrier coating 9, and the gap between the protective housing 8 and the thermal barrier coating 9 is filled and bonded using a low-temperature adhesive to form an adhesive layer. The low-temperature adhesive maintains good adhesion performance under both room temperature and low temperature (-196℃) conditions, ensuring the stability of the adhesive layer under temperature shock conditions and consistently forming a good bonded and cured layer between the thermal barrier coating 9 and the protective housing 8. The lower end of the protective housing 8 abuts against the top end of the base 3, and laser welding is used to complete the welding at weld 10, ensuring sufficient mechanical strength between the protective housing 8, the thermal barrier coating 9, and the thin-walled tube 1 of the metal substrate. In this embodiment, 920FL low-temperature adhesive or other adhesives that can maintain stable performance in the range of -200℃ to +100℃ are used.

[0024] Step 5: Conduct a high and low temperature shock test on the Dewar cold finger and determine its qualification based on the detected leakage rate. The high and low temperature shock test should be conducted according to the following steps: Step 5.1: Immerse the Dewar cold finger in liquid nitrogen for at least 10 minutes; Step 5.2: Bake the immersed Dewar cold finger at a temperature greater than 80°C for at least 10 minutes; Step 5.3: Repeat steps 5.1 and 5.2 at least 10 times.

[0025] Determining the Dewar cold finger's compliance based on the detected leak rate involves using a leak detection device in conjunction with a helium mass spectrometer and a sealing rubber plug to determine if the leak rate is ≤5× Pa. / S, if so, then the Dewar cold index is qualified. The leak rate detection method is as follows: Figure 5 As shown, since this embodiment uses a thermal barrier coating to prepare a thermal barrier coating on the outer surface of a thin-walled metal tube, the thermal barrier coating and the thin-walled metal tube are different material systems with different coefficients of thermal expansion. If the preparation process is unstable, cracks may occur under high and low temperature impacts. Therefore, in order to ensure the quality of the cold finger after preparation, the qualification of the cold finger is tested.

[0026] To better implement this invention, in one embodiment, in step 2, a transition layer may also be prepared on the surface of the thin-walled tube 1 before spraying the thermal barrier coating 9. The transition layer is used to improve the thermal compatibility and oxidation resistance between the thin-walled tube 1 and the thermal barrier coating 9.

[0027] Example 1 First, the metal substrate is processed. Specifically, the outer diameter of the thin-walled tube 1 is machined to the required accurate size φ7.6 (+0.03 / +0.05) mm, with finishing allowances left for other component dimensions. The finishing allowance for the inner hole of the thin-walled tube 1 is 0.2 mm to 0.5 mm; the finishing allowance for other component dimensions is 0.1 mm. A transition layer and a thermal barrier coating 9 are prepared using atmospheric plasma spraying. In this embodiment, the material of the thin-walled tube 1 is TC4 titanium alloy, because its coefficient of thermal expansion is 9.5 × 10⁻⁶. / ℃, which is significantly different from common ceramic layer materials, such as zirconia ceramic layer material (YSZ), whose coefficient of thermal expansion is 11.5× If a photothermal conversion coating (LTHC material) is used as a thermal barrier coating 9 on the outer surface of the thin-walled tube 1, it is easy to cause interfacial thermal stress cracking. Therefore, a transition layer is pre-prepared on the surface of the thin-walled tube 1 of TC4 titanium alloy by laser cladding or thermal spraying. The transition layer can be a high-entropy alloy or MCrAlY bonding layer to improve thermal matching and oxidation resistance. During the preparation process, the temperature of the metal substrate must be controlled below 600℃ to avoid phase transformation of TC4 titanium alloy, which would lead to a decrease in mechanical properties. After the thermal barrier coating 9 is completed, the other parts of the metal substrate are first precision machined, and then the inner hole of the thin-walled tube 1 is precision machined to make the inner diameter of the thin-walled tube 1 φ7.6 (0 / +0.01) mm. The wall thickness of the thin-walled tube 1 reaches 0.01 mm-0.025 mm. In this embodiment, the thickness is preferably 0.02 mm. This wall thickness will cause the cross-sectional area of ​​the thin-walled tube 1 of the metal substrate to be reduced to one-fifth of the cross-sectional area of ​​the metal cold finger thin-walled tube 1. Therefore, the heat conduction load generated by the thin-walled tube 1 is reduced to 20% of the original level. After the thermal barrier coating 9 is prepared, the inner diameter of the protective shell 8 is processed so that the inner diameter of the protective shell 8 is 0.03mm to 0.05mm larger than the outer diameter of the thermal barrier coating 9. Low-temperature adhesive is used to fill and bond the protective shell 8 and the thermal barrier coating 9. The distance between the top of the protective shell 8 and the welding ring 2 is equal to 1mm to ensure that the protective shell 8 will not generate significant heat conduction with the welding ring 2. The heat load generated by the heat conduction of the cold finger generally accounts for 50% of the overall static heat load of the Dewar. Since the thermal barrier coating 9 made of LTHC material has good heat insulation properties, it can isolate the heat effect radiated from the Dewar shell and reduce the radiative heat transfer between the Dewar shell and the cold finger. As a result, the static heat load of the entire Dewar assembly can be reduced to 60% or even lower than that of the original structure.

[0028] Among them, the thermal conductivity of LTHC material is less than 0.1 W / (m·K), which is 1 / 80 of that of TC4 titanium alloy. Since the introduced heat loss is almost negligible, while ensuring a certain wall thickness of the thin-walled tube 1, the airtightness technical requirement of the cold index can be guaranteed to meet ≤5× Pa. / S technical specifications. LTHC material has low thermal conductivity and high insulation. When sprayed on the surface of thin-walled tubes, it can maintain the integrity of the thermal barrier coating during use and is not easy to peel off, so that the thermal barrier coating is firmly bonded to the thin-walled tube.

[0029] The transition layer is not a necessary layer. As long as the sprayed thermal barrier coating 9 can guarantee the high and low temperature impact and leakage rate of the cold finger, it is acceptable. In this embodiment, setting a transition layer is the preferred option.

[0030] Example 2 The thin-walled tube 1 is made of high-temperature alloy. The transition layer needs to be designed with gradient, such as MCrAlY, TaC and YSZ. The material close to the thin-walled tube 1 is MCrAlY. MCrAlY, TaC and YSZ are set from the inside to the outside in sequence, and the difference in thermal expansion coefficient is less than or equal to 10%. The rest of the preparation steps are the same as in Example 1.

[0031] Regarding the thermal barrier coating 9, composite aerogel coatings, industrial-grade zirconia / alumina composite ceramic coatings, and graphene-reinforced ceramic coatings can also be used. Composite aerogel coatings have a thermal conductivity as low as 0.028–0.03 W / (m·K), and through nanostructure design, they suppress heat conduction, achieving a dry film thickness of up to 3.5 mm without cracking after spraying. Industrial-grade zirconia / alumina composite ceramic coatings have a thermal conductivity of 1.2–2.0 W / (m·K). Graphene-reinforced ceramic coatings have a thermal conductivity of 0.5–1.0 W / (m·K) and offer a 3-fold improvement in wear resistance. The selection of the thermal barrier coating 9 must ensure compliance with high and low temperature shock resistance and leakage rate requirements for cold fingers.

[0032] Cold fingers are formed by integral metal processing, or composite cold fingers are obtained by brazing different types of materials and then precision machining, such as... Figure 2 As shown, the base and the thin-walled metal tube are metal base blanks made of two different materials, which can be processed to obtain the following structure: Figure 1 The shape of the metal substrate is shown. A cold finger typically consists of a base and a thin-walled tube. One-piece cold fingers are generally made of TC4 titanium alloy; composite cold fingers typically have a stainless steel base and a high-temperature alloy tube with a wall thickness of 0.08mm to 0.15mm. At room temperature, TC4 titanium alloy has a thermal conductivity of 7.95 W / (m·K), while high-temperature alloys have a thermal conductivity of 10.4 W / (m·K). The cold finger, being an all-metal material, has a relatively high thermal conductivity, resulting in a larger static heat load on the Dewar assembly. During cold finger manufacturing, the thin-walled tube is made thinner. To compensate for the strength issues caused by the thinner wall, four ceramic support rods are added at the cold stage to ensure mechanical strength and performance. In this embodiment, by setting a thermal barrier coating 9 and a protective shell 8 on the outer surface of the thin-walled tube 1, the thermal conductivity of the cold finger to the outside is effectively reduced, while ensuring the mechanical strength of the Dewar assembly. The static thermal load of the Dewar assembly can be reduced to 60% of that of the Dewar structure, which has a significant improvement on the performance indicators of the detector assembly such as low power consumption, fast start-up, and long life.

[0033] This invention also provides a Dewar cold finger for an infrared detector, such as... Figure 1As shown, the material prepared using this method includes: a metal substrate, a thermal barrier coating 9, and a protective shell 8. The metal substrate is the main structure of the Dewar cold finger and includes a thin-walled tube 1, a substrate base 3, and a welding ring 2. The wall thickness of the thin-walled tube 1 is 0.01 mm to 0.025 mm. The substrate base 3 is located at one end of the thin-walled tube 1, and its inner cavity 7 communicates with the thin-walled tube 1. The other end of the thin-walled tube 1 is provided with the welding ring 2. The thermal barrier coating 9 is applied to the outer surface of the thin-walled tube 1 of the metal substrate. The protective shell 8 is fitted onto the thermal barrier coating 9 and connected to the top of the substrate base 3. The distance between the top of the protective shell 8 and the welding ring 2 is greater than or equal to 1 mm to ensure that the protective shell 8 does not generate significant heat conduction with the top welding ring 2 of the metal substrate.

[0034] Specifically, the metal substrate also includes a flange 4, a sealing groove 6, and an inner cavity 7. The inner cavity 7 communicates with the interior of the thin-walled tube 1. The flange 4 is circumferentially located on the outside of the substrate base 3. The sealing groove 6 is annular and located at the bottom of the substrate base 3. During leak detection, a sealing ring 11 is installed in the sealing groove 6 to seal the connection between the substrate base 3 and the leak detection base 5. The welding ring 2 is used for assembly and welding with other metal parts. The inner cavity 7 is used for coupling assembly with the push cylinder liner of the refrigeration unit. The metal substrate can be made of a single material or a combination of multiple materials.

[0035] The protective shell 8 is welded to the top of the base 3. The material selection of the protective shell 8 should ensure good laser welding with the base 3. For example, both the base 3 and the protective shell 8 are made of stainless steel or titanium alloy.

[0036] To better implement this invention, refer to Figure 3 and Figure 4 As shown, in one embodiment, the lower end of the thermal barrier coating 9 abuts against the top end of the substrate base 3, and the upper end of the thermal barrier coating 9 abuts against the welding ring 2. The thickness of the thermal barrier coating 9 is 0.2mm to 0.5mm. Both the lower ends of the thermal barrier coating 9 and the protective shell 8 are connected to the top end of the substrate base 3. The top end of the substrate base 3 has a stepped structure, gradually decreasing in height from the thin-walled tube 1 outwards. That is, the lower end of the protective shell 8 is lower than the lower end of the thermal barrier coating 9, and the lower part of the protective shell 8 can enclose the thermal barrier coating 9.

[0037] To better implement this invention, refer to Figure 1 As shown, in one embodiment, the thin-walled tube 1, the base 3, and the welding ring 2 are integrally formed.

[0038] Compared with cold fingers made of pure metal materials, the cold finger prepared in this embodiment maintains the same mechanical strength and other indicators, but its thermal conductivity is reduced by 90%. The static thermal load of the Dewar assembly prepared by this cold finger can reach 60% of that of the Dewar assembly prepared by the cold finger. The static thermal load index is significantly reduced. At the same time, no additional support rod structure is needed at the top of the cold finger. This cold finger can promote the reduction of steady-state power consumption, the shortening of cooling time, the reduction of maximum power consumption, and the extension of service life of the cooled detector Dewar assembly.

[0039] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a Dewar cold finger for an infrared detector, characterized in that, Includes the following steps: Step 1: Process the blank to form a thin-walled tube, a base plate, and a welding ring; Step 2: Spray a thermal barrier coating onto the outer surface of the thin-walled tube, so that the outer diameter of the thin-walled tube with the thermal barrier coating is greater than or equal to the outer diameter of the welding ring; Step 3: Finish the inner hole of the thin-walled tube with thermal barrier coating; Step 4: Install the protective shell on the outer surface of the thin-walled tube with thermal barrier coating and the base, and bond the protective shell and the thermal barrier coating together, and weld the protective shell and the base together to obtain the Dewar cold finger; Step 5: Conduct a high and low temperature impact test on the Dewar cold finger, and determine whether the Dewar cold finger is qualified based on the detected leakage rate.

2. The method for preparing the infrared detector Dewar cold finger according to claim 1, characterized in that, In step 2, a transition layer may be prepared on the surface of the thin-walled tube before spraying the thermal barrier coating.

3. The method for preparing the Dewar cold finger of the infrared detector according to claim 1, characterized in that, In step 5, the high and low temperature impact test on the Dewar cold finger is carried out according to the following steps: Step 5.1: Immerse the Dewar cold finger in liquid nitrogen for at least 10 minutes; Step 5.2: Bake the soaked Dewar cold fingers at a temperature greater than 80°C for at least 10 minutes; Step 5.3: Repeat steps 5.1 and 5.2 at least 10 times.

4. The method for preparing the infrared detector Dewar cold finger according to any one of claims 1-3, characterized in that, In step 5, determining whether the Dewar cold finger is qualified based on the detected leak rate includes: Leak rate is detected using a leak detection device in conjunction with a helium mass spectrometer leak detector. Determine if the leakage rate is ≤5× Pa. / S, if so, then the Dewar cold finger is qualified.

5. An infrared detector Dewar cold finger, manufactured using the method described in any one of claims 1-4, characterized in that, include: A metal substrate, the metal substrate comprising a thin-walled tube, a substrate base and a welding ring, the substrate base being disposed at one end of the thin-walled tube and the welding ring being disposed at the other end of the thin-walled tube; A thermal barrier coating is disposed on the outer surface of the thin-walled tube of the metal substrate; as well as A protective housing is fitted over the thermal barrier coating and connected to the top of the base.

6. The infrared detector Dewar cold finger according to claim 5, characterized in that, The lower end of the thermal barrier coating abuts against the top end of the substrate base, and the upper end of the thermal barrier coating abuts against the welding ring.

7. The infrared detector Dewar cold finger according to claim 6, characterized in that, The distance between the top of the protective shell and the welding ring is greater than or equal to 1 mm.

8. The infrared detector Dewar cold finger according to claim 5, characterized in that, The wall thickness of the thin-walled tube is 0.01 mm to 0.025 mm.

9. The infrared detector Dewar cold finger according to claim 6, characterized in that, The thickness of the thermal barrier coating is 0.2 mm to 0.5 mm.

10. The infrared detector Dewar cold finger according to claim 6, characterized in that, The thin-walled tube, the base plate, and the welding ring are integrally formed.

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