Shape-Memory Materials

Nickel-Titanium (NiTi) springs have been increasingly used in orthodontics; however, no optimum condition of heat treatment has been reported. Therefore, this research was conducted to determine the optimum heat-treatment temperature and duration for the fabrication of NiTi-closed coil springs by investigating their effects on thermo-mechanical properties. As-drawn straight NiTi wires of 0.2 mm diameter were used to fabricate closed coil springs of 0.9 mm lumen diameter. The springs were heat-treated at three different temperatures (400, 450, and 500 °C) with three different durations (20, 40, and 60 min). Electron Probe Micro-Analysis (EPMA) and Differential Scanning Calorimetry (DSC) were used to investigate element composition and thermo-mechanical properties, respectively. Custom-made NiTi closed coil springs composed of 49.41%-Ti and 50.57%-Ni by atomic weight, where their DSC curves of 500 °C presented the obvious endothermic and exothermic peaks, and the austenite finish temperature (Af) were approximately 25 °C. With increasing temperature, deactivation curves presented decreased plateau slopes generating higher superelastic ratios (SE ratios). At 500 °C, closed coil springs showed superelastic tendency with lower stress hysteresis. The thermo-mechanical properties were significantly influenced by heat-treatment temperature rather than duration. The optimum parameter appeared to be 500 °C for 40 min to produce appropriate force delivery levels, relatively low plateau slope, and lower hysteresis for orthodontic use.

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The Effects of Temperature and Time of Heat Treatment on Thermo-Mechanical Properties of Custom-Made NiTi Orthodontic Closed Coil Springs

Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. Therefore there has been a wide concern for studying the properties of those alloys. In this study polycrystalline alloys from shape memory alloy have been prepared successfully by thermal plasma spray in a wire form of 3 mm diameter in a graphite cast with three different ratios Ni50Ti50, Ni50.5Ti49.5 and Ni51Ti49. Its structure has been tested by means of X-ray diffraction technique. It has been noticed that annealing at 500° C helps to transform part of the material from an austenite phase into a martensite phase .It has also been noticed that increasing Ni proportion more than 50% to Ti in the alloy increases the martensite phase. The temperature of phase transformation as a function to the temperature of NiTi was calculated by using Differential Scanning Calorimeter (DSC) at a temperature between 100°C and -80.0°C in a scan rate of 10°C/min. The charts show that transformation from an austenite phase into martensite phase is done through an intermediate phase called (R-phase) which means there is no direct transformation, while transformation from martensite into austenite in heating cycle is direct. An exception to that is annealing Ni50Ti50 at a temperature of 400°Cwhere the transformation cycle is in two stages.

Jenan H. Taha

Papers

Effect of Annealing on the Transformation Behavior of NiTi Shape Memory Alloy

Effect of helium-neon laser on the lymphocyte cells and their dna

The Influence of Age on Pulmonary Function, A Cross Sectional Study on a Sample of Healthy Iraqi Males and Females Population