Fig. 37 Martensite in nitinol (Ni-50at.%Ti) shape memory alloy revealed by etching using equal parts HNO 3 , acetic acid, and hydrofluoric acid, and viewed using bright field (a) and Nomarski DIC (b). Nomarski DIC reveals more detail compared with bright field. More

Fig. 24 Scanning electron microscopy micrographs showing (a) nitinol stent strut cracking and (b) fatigue fracture surface after prolonged ultrasonic cleaning More

Fig. 26 Scanning electron microscopy images of fractured low-strength nitinol wire device. (a) Overview of fractured wire showing secondary cracks at the compressive side of the sharp shape-set bends, as marked by white arrows. (b) High-magnification view of fracture surface exhibiting More

Fig. 26 (a) Nitinol wires. (b) General view of the fracture surface showing surface defects and massive corrosion, magnification 150×. (c) Detail of the fracture surface showing a ductile fracture, magnification 3500×. (d) Acicular microstructure and the progression of lateral cracking. (e More

Fig. 27 SEM image of fractured nitinol stent More

Fig. 28 SEM image of striations on fractured nitinol stent More

Fig. 29 SEM image of cracks from other locations on the nitinol stent More

Fig. 30 SEM image showing a nitinol wire in compression with cracks at the intrados and no cracking at the extrados More

Fig. 32 SEM image of compression-induced cracks in a nitinol wire sample subjected to 50% strain More

Fig. 33 SEM image of slip lines and cracks in a compression-damaged nitinol wire sample subjected to 31% strain More

Fig. 34 Metallographic image of intrados cracks in compressed and released nitinol wire sample. Cracks initiate in shear during compression and grow in tension upon release More

Fig. 1 Representative stress-strain curve of a superelastic Nitinol tube specimen. The test was conducted at 37 °C (100 °F) according to ASTM F2516 using a video extensometer to track the true strain on the specimen. The inset shows a closeup of the 6% load-unload portion of the stress-strain More

Fig. 3 Backscattered electron micrographs of a Nitinol wire fractured by ductile tensile overload, showing necking and cup-and-cone fracture morphology. (a) Overview of the fractured wire showing drawing and necking of the sample. Original magnification: 100×. (b) Higher-magnification More

Fig. 4 Backscattered electron micrograph of a Nitinol wire fractured in pure torsion. Twisting of the wire draw lines can be seen on the outer surface of the wire. Original magnification: 125× More

Fig. 7 Backscattered electron (BSE) micrographs of a Nitinol wire that failed in overload due to compressive damage-induced cracking. (a) BSE micrograph of the entire fracture surface. The 45° shear crack or lip that led to overload failure is at the top portion of the fracture surface More

Fig. 8 Backscattered electron micrograph of an embrittled Nitinol wire. The wire was soaked in 85% phosphoric acid at 90 °C (195 °F) for 30 minutes to hydrogen charge the specimen. The specimen was then aged at room temperature for approximately 20 hours post-charging to allow for hydrogen More

Fig. 12 Backscattered eletron micrographs of a hydrogen embrittled Nitinol stent strut that was fractured in bending. (a) Overview of the entire fracture surface where the origin can be observed towards the bottom left corner of the strut. A general thumbnail origin with tiny microvoids More

Fig. 13 Backscattered micrographs of a hydrogen-embrittled Nitinol wire that was fractured in bending. (a) Overview of the wire fracture surface where a general thumbnail origin can be observed toward the bottom right corner of the wire fracture surface. Original magnification: 1000×. (b) High More

Fig. 14 Secondary electron micrographs of a fractured Nitinol strut. (a) Overview of the strut fracture surface. Original magnification: 450× (b) Higher-magnification micrograph near the top right corner of the fracture where fatigue striations are present. Original magnification: 1000× More