BME ppt for unit 2 - Shape memory alloys.pptx

Shape Memory Alloys (SMAs) are unique materials that can return to a predetermined shape when subjected to a specific temperature or other external stimuli. Here’s a detailed overview of their properties, mechanisms, applications, and types:

1. 9 Shape Memory Alloys Dr. D. Sudar vizhi , Assistant Professor ( Sl.G ), Department of Biomedical Engineering

2. SHAPE MEMORY ALLOYS Nitinol - which is an alloy of Ni and Ti - 'shape memory' alloy. By exploiting this shape memory property, a designer can programme a nitinol implant to change its shape or dimensions in response to an increase in temperature small enough to be well tolerated by the adjacent tissues in which it is embedded.

3. SHAPE MEMORY ALLOYS The shape memory phenomenon is a consequence of a particular solid state reaction that occurs in nitinol as it is cooled from an elevated temperature through a range of temperatures called the critical transition temperature range (TTR). At temperatures in excess of approximately 650°C,nitinol is composed largely of the equiatomic intermetallic compound NiTi , in which the atoms are arranged in a highly symmetric cubic crystalline arrangement and the properties are unique to this thermodynamically stable phase.

4. SHAPE MEMORY ALLOYS As the alloy is cooled through the TTR, the high temperature phase is transformed through small scale coordinated atom displacements into an entirely different metastable phase of much lower crystal symmetry called martensite . The properties of this phase are very different from those of the high temperature phase. For example, both the modulus of elasticity and the yield strength are much lower. It has got good strain recoverability, notch sensitivity and has got excellent fatigue and corrosion resistance.

5. Nitinol has been extensively used in dentistry because of its resilience and shape memory property. Devices made from the alloy include flexible wire clasps, prestretched wire and band or double wedge materials for rapid wedging or separation of teeth. APPLICATIONS