The Study of Infrared Brazing Ti50Ni50 Shape Memory Alloy
Date Issued
2006
Date
2006
Author(s)
Shiue, Ren-Haur
DOI
zh-TW
Abstract
The study comprises the dissimilar or similar joining of Ti50Ni50 SMA by infrared brazed. Microstructure evolution, reaction path and shear strength of infrared brazed Ti50Ni50 and Ti-6Al-4V joints using BAg-8 braze alloy have been investigated. The braze alloy can readily wet on Ti-6Al-4V, but not on Ti50Ni50. Titanium dissolves from Ti-6Al-4V to enhance the wettability of braze alloy on Ti50Ni50 during brazing. The joint is mainly comprised of hypoeutectic silver and copper for specimen infrared brazed below 850oC. The silver does not react with both substrates. The copper is readily reacted with titanium vigorously to form TiCu4, Ti3Cu4, TiCu and Ti2Cu phases in Ti-6Al-4V side and form CuNiTi phase in Ti50Ni50 side. The average shear strength of the specimens infrared brazed below 850oC is about 200 MPa. Although the presence of interfacial CuNiTi phase is beneficial to the wettability of molten braze alloy on Ti50Ni50 substrate, it is detrimental to the bonding strength of the infrared brazed Ti50Ni50/BAg-8/Ti-6Al-4V joint. The infrared brazed Ti50Ni50 alloy using Cusil-ABA® and Ticusil® active braze alloys are also investigated. The Ag-Cu eutectic braze alloy can readily wet Ti50Ni50 substrate by minor titanium addition. The brazed Ti50Ni50/Cusil-ABA®/Ti50Ni50 joint is mainly comprised of Cu-rich, Ag-rich and CuNiTi phases. However, the brazed Ti50Ni50/Ticusil®/Ti50Ni50 joint causes more vigorous reaction between filler metal and substrate, resulting in the exhaustion of copper from the molten braze, and forming TiCu2 interfacial layer confirmed by EPMA and XRD tests. The TiCu2 phase is less detrimental to the shape memory effect than CuNiTi phase during the shape recovery bending test. Shear strength of brazed joints exceeds 200MPa for both braze alloys if the brazing time exceeds 180 seconds. However, thick interfacial CuNiTi and TiCu2 layers can deteriorate the shear strength. Infrared brazing Ti50Ni50 shape memory alloy using pure Au and Au-20Cu has been evaluated. Based on the bending test results, the shape memory effect of brazed joint using Au filler metal is superior to that using Au-20Cu braze alloy. The shape recovery ratio of the joint using Au filler is identical to that of Ti50Ni50 substrate, and there is no crack on the brazed joint after bending test. Consequently, the pure Au filler metal demonstrates the potential application in brazing Ti50Ni50 shape memory alloy.
Subjects
Ti50Ni50
Ti-6Al-4V
紅外線硬銲接合
BAg-8
形狀記憶性質
界面顯微組織演化
剪力強度
Ti50Ni50 alloy
infrared brazing
shape memory effect
microstructural evolution
shear strength
Type
thesis
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