Infrared Brazing of Ti 50 Ni 50 Shape Memory Alloy and Inconel 600 Alloy with Two Ag-Cu-Ti Active Braze Alloys
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TRODUCTION
TI50NI50 shape memory alloy (SMA) undergoes a thermoelastic martensitic transformation and exhibits an excellent shape memory effect, superelasticity, and damping capacity.[1,2] It has been applied in microelectro-mechanical systems such as micropumps and microactuators.[3] In one application, shape memory actuators are used to replace exploding bolts utilized in petrochemical equipment and nuclear power plants.[4] The shape memory actuator is joined with an infrastructure made of stainless steel or nickel-based alloy. Therefore, dissimilar brazing of Ti50Ni50 SMA and stainless steel/nickel-based alloy is an important issue in such an application. In our previous study, dissimilar infrared brazing of Ti50Ni50 SMA and AISI 316L stainless steel (SS) using two silver-based active fillers, Cusil-ABA and Ticusil, was evaluated.[5] The materials were successfully joined with maximal shear strengths of 237 MPa for Ticusil filler metal brazed at 1223 K (950 C) for 60 seconds and only 66 MPa for Cusil-ABA filler metal brazed at 1143 K (870 C) for 300 seconds. Experimental results indicated that the presence of the interfacial Ti-Fe-(Cu) REN-KAE SHIUE is with the Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, ROC. SHYI-KAAN WU is with the Department of Materials Science and Engineering, National Taiwan University, and also with the Department of Mechanical Engineering, National Taiwan University. Contact e-mail: [email protected] SHENG-HAO YANG is with the Department of Mechanical Engineering, National Taiwan University. Manuscript submitted February 26, 2016. Article published online December 19, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
layer was detrimental to the shear strength of all joints. The 316L SS has a composition of Fe-17Cr-12Ni-2.5Mo (in wt pct),[6] in which iron is the main element, and a Ti-Fe-(Cu) layer forms at the interface of the 316L SS side after infrared brazing. In order to prevent the formation of the brittle Ti-Fe-(Cu) layer, another Ni-based alloy, Inconel 600 alloy (Special Metals Corp., New Hartford, NY, USA) (Ni-14.0~17.0 Cr-6.0~10.0 Fe in wt pct), which has much less iron, was selected to study infrared brazing with Ti50Ni50 SMA. Dissimilar brazing of Inconel 600 and ceramics has been reported previously.[7–10] Chen et al. used traditional brazing to join Inconel 600 alloy to Si3N4 using Ag-27Cu-2Ti (in wt pct) filler metal and found that the bonding could be attributed to the diffusion of Ag and Cu along the grain boundaries of the Inconel 600 alloy.[7] Lee brazed Inconel 600 alloy to Al2O3 using Ag-27Cu-3Ti (in wt pct) filler metal with a 150 lm thickness and found that, after brazing at 1113 K (840 C) for 1200 seconds, the joints contained perimeter and zone cracks resulting in fracture.[8] Inconel alloys are similar to 316L SS in that a stable and passivating oxide layer forms to protect the surface.[11] Despite their excellent corrosive resistance, these oxide films also act as a barrier to the wettability between Inconel 600 and g
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