紅外線硬銲接合Ti25Ni50Hf25及Ti25Ni25Cu25Hf25形狀記憶合金之研究

Abstract

本研究旨在改善BAg-8填料對TiNi基合金之潤濕性，透過添加第三元素在TiNi基合金中或在銀基填料中添加小於5 wt%Ti元素之方式，以提高銲道機械性質，並提升銲道可靠度。在高真空環境下，使用三種銀基填料BAg-8、Cusil-ABA、Ticusil，紅外線硬銲同質接合Ti25Ni50Hf25形狀記憶合金；使用 BAg-8填料，同質接合Ti25Ni25Cu25Hf25形狀記憶合金。利用紅外線快速接合之特性，探討硬銲時間為3分鐘或5分鐘之銲道金相顯微組織、破壞模式以及剪應力強度。從實驗結果得知，Ti25Ni50Hf25/BAg-8/Ti25Ni50Hf25銲道中主要存在Ag-rich 相，Ag-Cu共晶組織和CuNiTi 相，微裂縫主要產生在CuNiTi相，硬銲之最佳條件為830°C持溫5分鐘，平均剪應力強度為100 MPa； Ti25Ni50Hf25/Cusil-ABA/Ti25Ni50Hf25銲道中主要存在 Ag-Cu 共晶組織、CuNiTi 相和少量 Cu5Hf 析出，微裂縫主要產生在CuNiTi、Cu5Hf相，硬銲之最佳條件為900°C持溫3分鐘，平均剪應力強度高達207MPa； Ti25Ni50Hf25/Ticusil/Ti25Ni50Hf25銲道中主要存在 Ag-rich 相、Cu-rich 相、Ag-Cu 共晶組織、TiCu2、散布在 TiCu2 相旁的 CuTi2 析出物、以及少量 Cu5Hf 相，微裂縫主要產生在TiCu2相與富Ti、Hf、Ni介金屬相，硬銲條件將900°C持溫5分鐘降為3分鐘時，平均剪應力強度差異不大，但其標準差下降11%，使銲道之可靠性提升。Ti25Ni25Cu25Hf25/BAg-8/Ti25Ni25Cu25Hf25銲道中主要存在 Ag-rich 相、Ag-Cu 共晶組織、Cu5Hf 和 CuNiTi 相所組成，微裂縫主要產生在CuNiTi、Cu5Hf介金屬相，硬銲條件為800°C持溫5分鐘，平均剪力強度77MPa，由於其銲道在基材與填料間界面產生較多脆性相，導致其標準差較高，達36%，使銲道偏脆性，可靠性較不佳。以上四種銲道均屬於脆性破壞。

This study aims to improve the wettability of BAg-8 filler on TiNi-based alloys. This is achieved by adding third elements to the TiNi-based alloy or incorporating less than 5 wt% of Ti element into the silver-based filler to enhance the joint mechanical properties and reliability. Under a high vacuum environment, three types of silver-based fillers, BAg-8, Cusil-ABA, and Ticusil, were used for infrared brazing of Ti25Ni50Hf25 shape memory alloy. BAg-8 filler was used for infrared brazing of Ti25Ni25Cu25Hf25 shape memory alloy. The characteristics of rapid infrared brazing were utilized to investigate the microstructure, failure mode, and shear strengths of brazed joints with a brazing time of either 3 minutes or 5 minutes. From the experimental results, it was found that in the Ti25Ni50Hf25/BAg-8/Ti25Ni50Hf25 joint, the main phases were the Ag-rich phase, Ag-Cu eutectic, and CuNiTi phase. Microcracks primarily occurred in the CuNiTi phase. The optimal brazing condition was 830°C holding for 5 minutes, resulting in an average shear strength of 100 MPa. In the Ti25Ni50Hf25/Cusil-ABA/Ti25Ni50Hf25 joint, the main phases were Ag-Cu eutectic, CuNiTi, and a small amount of Cu5Hf precipitates. Microcracks mainly formed in the CuNiTi and Cu5Hf compounds. The optimal brazing condition was 900°C holding for 3 minutes, with an impressive average shear strength of 207 MPa. In the Ti25Ni50Hf25/Ticusil/Ti25Ni50Hf25 joint, the main phases identified were the Ag-rich phase, Cu-rich phase, Ag-Cu eutectic, TiCu2, CuTi2 precipitates dispersed near the TiCu2, and a small amount of Cu5Hf. Microcracks primarily occurred at the interfaces between TiCu2 and (Ti,Hf,Ni)-rich intermetallic compounds. Reducing the brazing condition from 900°C holding for 5 minutes to 3 minutes showed minimal difference in average shear strength but reduced the standard deviation by 11%, thereby improving the reliability of the joint. In the Ti25Ni25Cu25Hf25/BAg-8/Ti25Ni25Cu25Hf25 joint, the main phases were the Ag-rich phase, Ag-Cu eutectic, Cu5Hf, and CuNiTi compounds. Microcracks primarily formed in the CuNiTi and Cu5Hf intermetallics. The brazing condition was 800°C holding for 5 minutes, resulting in an average shear strength of 77 MPa. Due to more brittle phases at the interface between the base metal and filler, the joint exhibited a higher standard deviation of 36% and lower reliability. All four types of brazed joints mentioned above showed brittle failure.