3946

3724

كارشناسي ارشد

استخراج فلزات

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1386

[شش]، 181، [II]ص.: مصور، جدول، نمودار

ص.ع. به: فارسي و انگليسي

محمد حسن عباسي، فتح الله كريم زاده

محمد حسين عنايتي

11/03/87

محمد علي گلعذار، كمال جانقربان

مهندسي مواد

ID3724

به فارسي و انگليسي: قابل رؤيت در نسخه ديجيتال

AbstractIn this research Synthesis of nanocrystalline NiTi powder and NiTi Al2O3 nanocomposite with 10and 20 weight percent Al2O3 by mechanical alloying MA in a planetary ball mill under argonatmosphere were investigated The structural evaluation of powders was studied by X raydiffraction XRD scanning electron microscopy SEM transmission electron microscopy TEM differential scanning calorimetry DSC and microhardness measurements Thermodynamic andkinetic analyses of the process were carried out using Miedema model and Coats Redfern methodrespectively The results showed that MA of Ni50Ti50 leads to the formation of nanocrystalline B2 NiTi At theearly stages of MA a lamellar structure of components is formed with the dissolution of Ti in Ni atthe same time With the progress of MA the resulting supersaturated solid solution becomes non stoichiometric and finally disordered stoichiometric NiTi with nanometeric grain size is formed Annealing of the milled powder leads to increase in long range order to 0 94 and formation of smallamounts of NiTi2 and Ni3Ti phases Thermodynamic analysis in this system revealed that the MAproduct of Ni50Ti50 is the phase with the most negative Gibbs free energy change amongstcompeting phases at the considered composition The results also showed that NiTi Al2O3 nanocomposite can not be synthesized by MA of powdermixture of Ni Ti Al2O3 in a steel cup but MA of a powder mixture containing NiO Al Ti Ni andmechanochemical reduction of NiO by Al showed that nanometric Al2O3 particles can be dispersedin nanocrysatalline NiTi matrix Nanocomposite formation mechanism depends on Al2O3 weightpercent It is diffusion controlled for NiTi 10wt Al2O3 and self propagating combustion for NiTi 20wt Al2O3 The presence of Al2O3 dispersoids in the NiTi matrix leads to increase of hardnessand decrease of grain growth and ordering degree and finally high thermal stability of NiTi duringannealing Kinetic analysis showed that NiO Al reaction has a chemical controlled mechanism in contractingcylinder model with 490 kJ activation energy MA caused kinetic model change to contractingsphere and activation energy decrease to 397 kJ

محمد حسن عباسي، فتح الله كريم زاده

محمد حسين عنايتي

محمد علي گلعذار، كمال جانقربان