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PRESENTATION
- 1. Shape Memory Alloys(SMA) By Devin Rowe
- 2. Shape Memory Effect(SME) SME is the ability in some materials to recover from a large amount plastic deformation thus returning to some preset shape after exposure to a environmental stimuli. • First displayed by a Au-Cd alloy in 1932. • Many types of SM materials exist. Ex) Ceramics, polymers, gels and metals • SMA are arguably the most important.
- 3. What is aSMA SMAs are defined by having two properties 1. SME • Environmental stimuli in most cases are a thermal-cycle. 2. Superplasticity AKA Pseudoelasticity • The ability of a material to exhibit large recoverable strains while deformed within a temperature range that is characteristic of a specific alloy • Normally not as important in most applications as SME
- 4. SME in SMAs Austenite(NiTi) Martensite (NiTi) Micrographs are from http://www2.lbl.gov/ritchie/Library/PDF/Robertson-MatSci2006.pdf
- 5. SME in SMAs Deformation •Starting in the fully twinned martensitic phase the material deforms as a result of shear stress. • Deformation results in the partial or full detwinning or the martensitic phase. Animation is from http://www.doitpoms.ac.uk/tlplib/superelasticity/shape_memory1.php
- 6. SME in SMAs Heating •Heating up the material begins the recovery of shape. • Heating above the As cause the material to transform into austenite. • Austenite remembers is original shape and thus shifts back as it transforms. Animation is from http://www.doitpoms.ac.uk/tlplib/superelasticity/shape_memory1.php
- 7. SME in SMAs Cooling •Once the original shape is recovered the piece is cooled. • Once below the Ms temperature the material begins transforming into martensite again • To retain the grains original shape martensite begins to twin, bringing the process full circle Animation is from http://www.doitpoms.ac.uk/tlplib/superelasticity/shape_memory1.php
- 8. Types of SMA Firsttype discovered in 1932, a Au-Cd alloy Made popular in 1958 after the discovery of Ni-Ti alloy Since then many types discovered • Examples include Cu, Ti, Fe, Zn, Hf based alloys Most commonly used SMAs are Cu-Al and Ni-Ti based alloys
- 9. Manufacturing and processing •Made by the same processes used for there base metal • NiTi follows similar process for Ti- very reactive • Tighter alloying composition- baseline for transformation Temperature • Same general metal working processes • Mostly done by customer • Transformation Temperature adjustment • Cold Working- raises it • Annealing- fixes it • Thermal cycling- lowers it • Training
- 10. Training The process thatteaches SMAs to remember a desired shape Training steps • Firmly fix the SMA into a desired shape • SMA is then annealed at temperatures and times that are unique to the alloy • Cool the piece back to the martensite phase and undo restraints
- 11. Applications • Vibration dampeners •Vascular stents • The metal in dental braces are often SMA with low As temperature • Some metal Glasses frames are made with SMAs- Pseudoelesticity • Actuators*- SMAs make a light weight alternative to other actuators *If spring had the same volume as a standard rolling die the rock could have weighed about 30lbs
- 12. High-Temperature Shape MemoryAlloys (HTSMA) SMA Actuators have long been sought for use in Aerospace and Automotive industries Problem is that most SMA have low transformation temperatures • Ni-Ti based is in a range of ±100oC, ±200oC for Cu-Al based • Temperatures needed, up to 1000oC Aero and 300oC Auto Promising results for Ni-Ti-Pt/Pd and Cu-Al-Ta alloys. • Temperatures at around 1100oC and 500oC respectively
- 13. HTSMA (continued) Other thingsto consider • Work output • if it can’t do the work its useless • Cost • Ni-Ti-Pt/Pd • Money saved may out weigh the weight saved • Thermal stability • Yield strengths of Austenite and Martensite phases