Influence of the temperature on the structure of an amorphous Ni46Ti54 alloy produced by mechanical alloying
Inst. de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-970,
Campinas, SP, Brazil
2 Depto de Física, Centro Politécnico, Universidade Federal do Paraná, 81531-990, Curitiba, Paraná, Brazil
3 Departamento de Física, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
Corresponding author: a firstname.lastname@example.org
Revised: 4 July 2008
Published online: 30 July 2008
The evolution of the local atomic order of an amorphous Ni46Ti54 alloy produced by mechanical alloying as a function of temperature was studied by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. XRD measurements at several temperatures (25 °C, 350 °C, 412 °C, 430 °C, 450 °C and 515 °C) were performed and analyzed using the reverse Monte Carlo (RMC) simulations method or the Rietveld refinement procedure. The experimental total structure factor for samples at 25 °C and 350 °C, which are amorphous in nature, were simulated by using the RMC method, and the local structures of the alloy at both temperatures were determined, indicating a decrease in its density as the temperature increases. At 412 °C, the XRD pattern shows a partially crystalline sample, indicating that the crystallization process is in progress. At 430 °C, 450 °C and 515 °C, the XRD measurements indicate the presence of two crystalline phases, NiTi and NiTi2, whose structural parameters (lattice parameters, coherently diffracting domains (CDD) sizes, microstrains and relative amount of phases) were determined using the Rietveld refinement procedure. DSC measurements at different heating rates furnished the crystallization temperature, enthalpy and activation energy of the crystallization process, and these values are similar to those found in other amorphous alloys of the Ni-Ti system. They also showed the existence of a second exothermic process, which was related to diffusive processes in the crystalline phases, which could be associated with the changes in the CDD sizes happening from 450 °C to 515 °C.
PACS: 61.43.Dq – Amorphous semiconductors, metals, and alloys / 81.20.Ev – Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation / 61.43.Bn – Structural modeling: serial-addition models, computer simulation / 65.60.+a – Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2008