From the View of Crystal Chemistry Change of the Chemical Composition From Austenite to martensite (i Nickel concentration effect Preparation of NiTi: heating Ni and Ti elements together above m.p. (1200-1300 C). NiTi can tolerate Expand-12% small deviations in chemical composition around 1:1 stoichiometry before the shape memory effect is lost. Change of the Chemical Composition Ti Ni based alloys SMAs (i) Adding impurity meta Although there are many SMAs, such as Ti-Ni, Cu-Al Ni, Cu-Zn- Al Au-Cd, Mn-Cu, Ni-Mn- Ga, and Fe-based A small quantity of impurity atoms the may be present alloys, most of the practical SMAs are Ti-Ni-based nay influence the transition temperature allovs, since other SMAs are usually not ductile(or Example: By substitution of Ni with Pd or Pt will fracture. Ti- Ni-based alloy tune the transition temperature to as high as superior to other SMAs in many respects. They exhibit 50-60% elongation and tensile strength as high as several hundred degrees mechanical properties among intermetallics and can actural ma have a very high resistance to corrosion and abrasion.9 From the View of Crystal Chemistry: From Austenite to Martensite a0 / 2 ® a a c 0 ® Expand~12% Expand~12% Change of the Chemical Composition (i) Nickel concentration effect: Preparation of NiTi: heating Ni and Ti elements together above m.p. (1200-1300oC). NiTi can tolerate small deviations in chemical composition around 1:1 stoichiometry before the shape memory effect is lost. Change of the Chemical Composition (ii) Adding impurity metal A small quantity of impurity atoms the may be present may influence the transition temperature. Example: By substitution of Ni with Pd or Pt will tune the transition temperature to as high as several hundred degrees. Ti-Ni-based alloys SMAs Although there are many SMAs, such as Ti-Ni, Cu-Al￾Ni, Cu-Zn-Al, Au-Cd, Mn-Cu, Ni-Mn-Ga, and Fe-based alloys， most of the practical SMAs are Ti-Ni-based alloys, since other SMAs are usually not ductile (or not ductile enough) or are of low strength and exhibit grain-boundary fracture. Ti-Ni-based alloys are superior to other SMAs in many respects. They exhibit 50~60% elongation and tensile strength as high as 1000 MPa. To our knowledge, they possess the best mechanical properties among intermetallics and can be used as structural materials as well. They also have a very high resistance to corrosion and abrasion