7. The Ni-Ti system contains the Ni-Ti phase that forms the basis of Nitinol, the most well known shape memory alloy. Sh

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7 The Ni Ti System Contains The Ni Ti Phase That Forms The Basis Of Nitinol The Most Well Known Shape Memory Alloy Sh 1 (371.88 KiB) Viewed 14 times

7. The Ni-Ti system contains the Ni-Ti phase that forms the basis of Nitinol, the most well known shape memory alloy. Shape memory alloys are materials that have the interesting and useful property of being able to be deformed at lower temperatures, but regaining their original form when heated up above a specific temperature. Stents for use in vascular surgery application are the best known use case. Before implantation in a blood vessel, the stent resembles a thin rod. This is the deformed, squished down state of the stent. After it is placed inside the blood vessel, it heats up tot he body temperature, and regains it's original shape, opening up into a hollow mesh cylinder, stabilizing the walls of the blood vessel. This transition temperature can be tuned by changing the composition of the alloy. The Ni-Ti system is quite complex. a. What is the maximum solubility of Ti in Ni and at what temperature does this occur? b. For pure Ti at 900°C, how much Ni do we need to add in order to achieve a microstructure consisting of 20 wt% TizNi grains surrounded with finely distributed layers of Ti and Ni (.e. eutectic layers)? Assume there are no more transformations below 600°C. C. What is the composition and phase distribution of an alloy with 15 wt% Ni at 1050°C? How much does the temperature need to drop to achieve a Ti-phase of 8 wt% Ni? Atomic Percent Nickel 30 40 50 60 80 90 1800 10 20 70 100 1670°C 1600 L 1455°C 1400 1380°C 1310°C 1304" Temperature °C 1200 TiNi 1118°C (Ni) 1000 084" (TI) 942°C 882°C TiNig 800 765°C Hati) TiaNi 930°C 10 20 30 40 50 60 70 80 600 0 Ti Weight Percent Nickel 100 Ni = a. - 12 wt% Ti @ 1304 °C b. Ini = 0,123 BT gri = 0,11; gſi = 0,25; 9pti = 0,714; 9l = 0,286; AT = 215 °C C. = =