Differential scanning calorimetry (DSC) analyses of superelastic and nonsuperelastic nickel-titanium orthodontic wires

Abstract

The purpose of this study was to determine the transformation temperatures for the austenitic, martensitic, and rhombohedral (R) structure phases in representative as-received commercial nitinol (NiTi) orthodontic wire alloys, to reconcile discrepancies among recent publications. Specimens were examined by differential scanning calorimetry (DSC) over a temperature range from approximately -170 degrees C to 100 degrees C, with a scanning rate of 10 degrees C per minute. Two different pathways, with the intermediate R structure either absent or present, were observed for the transformation from martensitic to austenitic NiTi, whereas the reverse transformation from austenitic to martensitic NiTi always included the R structure. The enthalpy (delta H) for the transformation from martensite to austenite ranged from 0.3 to 3.5 calories per gram. The lowest delta H value for the nonsuperelastic Nitinol wire is consistent with a largely work-hardened, stable, martensitic microstructure in this product. The DSC results indicate that the transformation processes are broadly similar in superelastic, body-temperature shape-memory, and nonsuperelastic NiTi wires. Differences in bending properties for the NiTi orthodontic wires at room temperature and 37 degrees C are due to the relative proportions of the metallurgical phases in the microstructures.

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…As known, transformations temperatures can be determined by differential scanning calorimetry [221,222], dilatometry [223] or electrical resistivity [224,225]. However, transformation temperatures of the thermal affected regions in NiTi welds have been mostly determined by differential scanning calorimetry, despite their small dimensions.…”

Application of Plasma Immersion Ion Implantation for Surface Modification of Nickel-titanium Rotary Instruments

“…Subsequently, the specimen was cooled from 100 back to 70 to obtain the cooling DSC curve. Linear heating or cooling rate was a standard 10 per minute 19) for each analysis. The DSC cell was purged with dry nitrogen at a rate of 50 cm Temperature calibration of the DSC apparatus was performed with deionized water and indium.…”

“…In addition, recent studies 17,18) published in endodontic literature have indicated that the structure of NiTi rotary instruments can be conveniently investigated by differential scanning calorimetry (DSC). With this analytical technique, the difference in thermal power supplied to a test specimen and an inert control specimen heated at the same rate is measured very accurately 19,20) .…”

Effect of laser welding parameters on the austenite and martensite phase fractions of NiTi

“…Conventional analytical techniques for determining the phase transformation characteristics of NiTi shape memory alloys are differential scanning calorimetry (DSC) [7,8] and X-ray diffraction [9,10] using conventional lab sources. However, these techniques are not suited to provide the spatial resolution required for an in-depth understanding of the microstructural changes occurring along both the heat affected and fusion zones due to the laser welding procedure.…”