Análise da influência do tratamento térmico de recozimento nas propriedades da liga ni54mn21ga25

Abstract

The scientific development on Heusler alloys has demonstrated the great innovations that this class of compounds offers. Alloys of this category attract attention due to their important characteristics, such as magnetic shape memory effect, magnetocaloric effect, and large magnetoresistance effect. Magnetic shape memory alloys can be activated not only in the presence of a thermal stimulus, but also by the presence of an external magnetic field. An adequate physical and microstructural characterization is an essential precondition for designing and modeling magnetic field actuation systems. This context motivated the development of this research, which aimed to determine the influence of heat treatment on the properties of the Ni54Mn21Ga25 alloy. The adopted methodology consisted of determining the annealing parameters of temperature (1000 °C and 1050 °C) and time (6 hours and 26 hours). Through the variation of the heat treatment, the influence of temperature and time on the phase transformation temperatures, microstructure, chemical composition, permeability and Curie temperature was evaluated. From the results it is concluded that the raw melt sample presented austenitic and martensitic phases at room temperature, while the samples annealed for 6 hours presented martensitic phases at room temperature and finally, the samples annealed for 26 hours presented martensitic phases and γ phases at room temperature. Annealing performed at 1000 °C and 1050 °C for 6 hours was satisfactory for obtaining the martensitic phase at room temperature. From the permeability analysis it was possible to obtain the curves with characteristic behavior of this property in Ni-Mn-Ga alloys. From the Tc of the raw melt sample it was observed that annealing performed at 1000 °C for 6 hours reduced the Tc while annealing at 1050 °C for 6 hours increased the Tc. Increasing the annealing temperature from 1000 °C to 1050 °C performed for 26 hours showed an increase in Tc, however little variation was observed.