Welding Microstructure and Joint Structure Design of the TC4/Ni Dewar Cold Finger
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摘要: 针对微型节流制冷型红外焦平面探测器杜瓦冷指，选取TC4/Ni的钎焊形式，从钎焊方法和钎料类型的焊缝微观组织以及接头结构设计的可靠性等方面对TC4/Ni的钎焊工艺进行了研究。结果表明，结合应力、形变和降温时间仿真以及防锈蚀分析结果，研究TC4/Ni冷指端面结构钎焊工艺具有一定工程实用意义；并通过正交试验确定了高温真空钎焊+AgCu28钎料组合的较佳工艺方案，满足对控制元素偏析和减少焊接脆性相生成的目的；同时综合考虑钎透率、充耐压试验及剪切强度测试的结果，确定锥形焊缝为较佳焊接结构。Abstract: The brazing process of TC4/Ni for a Dewar cold finger with a miniature Joule–Thomson-cooled infrared focal plane detector was selected, and the brazing process of TC4/Ni was investigated based on the microstructure of the brazing method and solder type and the reliability of the joint structure. The results show that research on the brazing process of the TC4 /Ni cold finger end-face structure has practical significance in engineering by combining the simulation results of stress, deformation, and cooling time with the analysis results of rust prevention and corrosion. Through an orthogonal test, an improved process scheme of the high-temperature vacuum brazing + AgCu28 brazing filler metal combination was determined, which could control element segregation and reduce the formation of the welding brittle phase. Based on the penetration rate, stamping, high-voltage holding, and shear strength tests, the conical weld was the best welding structure.
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Keywords:
- dewar cold finger /
- vacuum brazing /
- TC4 titanium alloy
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图 3 杜瓦冷头封装结构模型网格划分
Figure 3. Mesh generation of dewar cold head packaging structure model
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图 5 两种冷指端面结构芯片降温时间曲线对比情况
Figure 5. Comparison of cooling time curves of two cold finger end structure chips
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图 7 AgCu28钎料高温真空钎焊扫描电镜照片
Figure 7. SEM photo of high temperature vacuum brazing with AgCu28 Solder
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图 8 AgCuNi钎料高温真空钎焊扫描电镜照片
Figure 8. SEM photo of high temperature vacuum brazing with AgCuNi solder
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图 9 AgCu28钎料高频真空钎焊扫描电镜照片
Figure 9. SEM photo for high frequency vacuum brazing of AgCu28 solder
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图 14 冷指端面芯和环脱落(螺纹结构)
Figure 14. The cold finger core falls off from the end face of the cold finger(Thread structure)
表 1 4J36合金与纯Ni材料参数的对比
Table 1 Material parameters comparison of between 4J36 alloy and pure Ni
Cold finger materials Coefficient of thermal expansion
/(10-6/K)Thermal conductivity
/(W/m·K)4J36 1.8 17.3 Ni 9.8 90.7 
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表 2 两种冷指端面结构的芯片应力、应变及降温时间结果对比汇总
Table 2 Comparison and summary of chip stress, strain and cooling time results of two cold finger end structures
Brazing structure TC4+4J36 TC4+Ni Chip stress max/MPa 29.33 34.72 Chip strain max/μm 2.75 2.93 Cooling time/s 20 9
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表 3 TC4的化学成分
Table 3 TC4 alloy chemical composition
(wt/%) Elements Content Al 5.5−6.8 V 3.5−4.5 Fe ≤0.3 O ≤0.2 C ≤0.1 N ≤0.05 H ≤0.015
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表 4 纯Ni的化学成分
Table 4 Ni Chemical composition
(wt/%) Elements Ni Cu Fe Mg Si Mn Content ≥99.5 ≤0.1 ≤0.1 ≤0.1 ≤0.1 ≤0.05
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表 5 钎料的化学成分、熔点及规格
Table 5 Chemical composition, melting point and specification of filler metal
Brazing materials Main components/% Melting temperature
/℃Ag Cu Ni AgCu28 72±1.0 28±1.0 - 779 AgCuNi 70±1.5 28±1.0 2±0.5 779-815
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表 6 钎焊温度及保温时间
Table 6 Brazing temperature and holding time
Brazing method Brazing materials AgCu28
Binary alloyAgCuNi
Ternary alloyHigh-temperature vacuum brazing 830℃, 5 min 850℃, 5 min High-frequency vacuum brazing 20 A, 60 s 23 A, 60 s
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表 7 主要成分分析结果
Table 7 Main composition analysis results
Region Main components Content
/%Notes A Ag 70−73 Light white
phaseCu 25−28 B, C Ni 5−10 Dark gray phase Cu 85−90 D Ti 75−85 Light gray phase Cu 12−23
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表 8 试验结果统计
Table 8 Test result statistics
Test projects Straight Step Thread Conical Welding results Normal Normal Falling off Normal Brazing permeability 100% 80% - 95% Pressurize 2 MPa, (10 minutes 3 times) × Normal - Normal Pressurize 3 MPa, (10 minutes 3 times) - Normal - Normal Pressurize 4 MPa, (10 minutes 3 times) - Normal - Normal Withstand voltage 2 MPa, (once 5 minutes) - Normal - Normal Judgement × √ × Better
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表 9 剪切强度测试对比结果
Table 9 Comparison results of shear strength test
Welding structures Shear strength test/MPa Average value
/MPaStraight 15.96 15.12 14.36 15.05 Step > 23.42 > 23.42 > 23.42 > 23.42 Thread 1.67 1.44 1.26 1.39 Conical > 23.42 > 23.42 > 23.42 > 23.42
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