Brazing of Ti-Ni Shape Memory Alloy with Pure Titanium
Takeshi KUNIMASA, Masanori SEKI, Hiroki YAMAMOTO, Makoto NOJIRI, Keisuke UENISHI and Kojiro F. KOBAYASHI
Abstract:Ti-Ni shape memory alloy (NT-L) was brazed to commercial pure Ti (CPTi) with Ag-Cu filler (Bag-8) or Cu-Ti-Zr amorphous filler (MBF5004). The effect of brazing condition was nvestigated on the reaction layer formation as well as on the joint strength, and then their relation was discussed. When brazing was performed with Bag-8 under the brazing temperature lower than 1153K, four reaction layers were formed adjacent to brazing joints. The maximum joint strength was about 330MPa, and the fracture occurred around the Ti-Cu based intermetallic compound reaction layer isothermally solidified between CPTi base metals and Bag-8 filler during holding at brazing temperature. At an early stage of the isothermally solidified layer formation, the joint strength increased with its growth. When the thickness of the layer became larger, however, the joint strength decreased with the growth. For the joints brazed at the brazing temperature higher than 1193K with Bag-8, two reaction layers were formed. The maximum joint strength was about 350MPa, and the fracture occurred in the brazed layer consisted of ƒ¿Ti and Ti2(Ni,Cu). The thickness of the brazed layer was three times larger than that of Bag-8 filler, suggesting that NT-L base metal near the bondline melted during brazing by the diffusion of Ti to NT-L base metal. In the case of MBF5004, joint microstructure and fracture path were similar to the cases of Bag-8 being the brazing temperature higher than 1193K. The joint strength was larger for the joint using Bag-8 than that using MBF5004, and was almost the same as that of CPTi base metal. Key Words:shape memory alloy, titanium-nickel alloy, titanium, brazing, silver filler metal, titanium filler metal, tensile strength, intermetallic compound, microstructure, dissimilar joint