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shape memory alloys
Ni-Ti shape memory alloys exhibit the shape memory effect and super elasticity. They consist of roughly equal parts nickel and titanium. Ni-Ti alloys can deform at low temperatures but return to their original shape when heated. This allows applications like self-expanding stents. Ni-Ti alloys are expensive but have advantages like high corrosion resistance and can be electrically controlled. Common applications include aircraft flaps, bone plates, and arterial reinforcement.
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shape memory alloys
- 1. Ni- Ti ShapeMemory Alloys By Sara Hamid Shahatha Applied Sciences Department Ph.D Materials Technology
- 2. Out lines What isSMA Advantages, disadvantages and properties Manufacturing Application
- 3. Shape Memory Alloys Metalsthat can be deformed at one temperature but when heated or cooled, return to their “Original” shape Shape memory materials have two phases, stable at low and high temperatures Shape memory alloys exhibit two unique properties, known as the shape memory effect and super elasticity.
- 4. Phenomenon of PhaseTransformation in Shape Memory Alloys Austenite • High temperature phase •Cubic Crystal Structure Martensite •Low temperature phase •Monoclinic Crystal Structure Twinned Martensite Twinning enables plastic deformation, hence superelasticity.
- 5. Shape Memory Effect First Linearly Elastic Plastic Deformation Start SMA Deformation reaches saturation Deformation Recovered byHeating Upon unloading remaining deformation is present If the Material Cooled Down ,it will recovered
- 6. Types of MemoryEffect The basic phenomenon is characterized by a deformed sample changing shape occurs only during (Heating-Cooling) which has no effect on its shape, this process is called one-way shape memory effect A sample can have one shape when cold, change to a second shape when heated and returns, to its original shape when cooled again, all without mechanical load. Shape change occurs in two directions, during both heating and cooling, this process is called two-way shape memory
- 7. Super Elasticity orPseudo Elasticity Occurs without temperature change. Based on stress induced. This property allow SMA’s to bear large amount of stress without undergoing permanent deformation.
- 8. Ni-Ti Shape MemoryAlloys They worked with NiTi alloy in 1950’s & 1960’s ,this metal alloy is composed of nickel and titanium 1:1 atomic ratio (Nickel 55% & Titanium 45%) in order to bring the transition temperature range down to 37 °C the amount of Cobalt added to the alloy is (1.6%). It contains these two elements at approximately equal atomic percentages. E.g. nitinol 55 NiTi particularity exhibits superealstic behavior 10°C -125°C
- 9. Advantages & Disadvantagesof Shape Memory Alloys Advantages 1. High power / weight ratio 2. High corrosion resistance 3. Can be electrically controlled
- 10. Advantages & Disadvantagesof Shape Memory Alloys Disadvantages 1.Has poor fatigue properties 2. Highly expensive
- 11. Properties of ShapeMemory Alloys 1. The yield strength of shape-memory alloys is lower than that of conventional steel, but some compositions have a higher yield strength than plastic or aluminum. 2. high level of recoverable plastic strain that can be induced. 3. The maximum recoverable strain these materials can hold without permanent damage is up to 8% for some alloys. This compares with a maximum strain 0.5% for conventional steels
- 12. Manufacture of ShapeMemory Alloys By Casting Using Arc Vacuum Melting Using electromagnetic induction to melt material in vacuum. Electro induction generates eddy current in the alloy. Eddy current generated heats and melts the alloy.
- 13. Application of ShapeMemory Alloys 1. Bone plates 2. Aircraft flaps that change direction of airflow depending upon temperature 3. Reinforcing of Arteries & Veins
- 14. Application of ShapeMemory Alloys Shape Memory Effect Ni-Ti Stent 4th generation
- 15. Types of ShapeMemory Alloys Alloys of metals having the memory effect at different temperatures and at different percentages of its solid solution contents: 1. Cu-Zn-Al 2. Cu-Al-Ni 3. Ni-Ti (50 at.% Ti, nitinol, which stands for Nickel Titanium Naval Ordinance Laboratory)
- 16. Conclusion SMA’s have thepotential to be used effectively in advanced application like medicine, aircraft and aerospace. The high cost of SMAs is a major limiting factor for its wider use in the construction industry,. Their ability to allow the development of smart structures with active control of strength and stiffness and ability of self- healing and self-repairing opens the door for exciting opportunities, making them the construction material of the future.