Isothermal oxidation study on NiMnGa ferromagnetic shape memory alloy at 600-1000 degrees C


KÖK M., Pirge G., AYDOĞDU Y.

APPLIED SURFACE SCIENCE, vol.268, pp.136-140, 2013 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 268
  • Publication Date: 2013
  • Doi Number: 10.1016/j.apsusc.2012.12.033
  • Title of Journal : APPLIED SURFACE SCIENCE
  • Page Numbers: pp.136-140

Abstract

Oxidation behavior of NiMnGa alloy has been investigated under isothermal temperature by thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy equipped with an energy dispersive X-ray (SEM-EDX) spectroscope systems. The Ni-28.5Mn-20.5Ga alloy (composition in atomic percent) was exposed to oxygen atmosphere isothermally, i.e., between 600 degrees C and 1000 degrees C, for 1 h. A gravimetric method was used to determine the oxidation kinetics; weight gain per unit area as a function of time. It was determined that the oxidation constant increases significantly with isothermal temperature. Activation energy of the oxidation was found to be 152 kJ/mol. X-ray diffraction patterns of the heat-treated samples contain oxide peaks, mainly belonging to Mn3O4. X-ray analyses demonstrate that the amount of the oxide increases with isothermal temperature while that of martensite phase decreases. The scanning electron microscopy equipped with an energy dispersive X-ray (SEM-EDX) spectroscope analysis also gives the same result. According to magnetic measurements, the saturation of NiMnGa alloys decreases with rising isothermal oxidation temperature. (C) 2012 Elsevier B. V. All rights reserved.