Processamento e caracterização estrutural de ligas NiTi com adição de cobre

Abstract

In this work, aspects of the microstructural behavior of the binary NiTi and ternary NiTiCu alloys in different compositions and thermal treatments were taken and compared, through microstructural characterization. By using arc melting process alloys were synthesized based on an almost equiatomic NiTi composition and with the addition of 5.0 and 10.0% at. Cu. Binary and ternary alloys, under different conditions, were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The alloys Ni51Ti49, (NiTi)90Cu10 and (NiTi)95Cu5 were subjected to 3 different heat treatments, and alloys in one of the conditions were subjected to optical microscopy (OM). The results show that the heat treatment strongly influences the microstructure and the phases formed depend mainly on the imposed cooling rate, where the martensitic phases are formed only when cooling is carried out in water and ice. Binary and ternary alloys, when subjected to cooling in water and aged at temperatures around 400 °C, present a predominantly austenitic microstructure, not evidencing the presence of martensitic phases. The alloy with 10% copper, even subjected to rapid cooling in water and ice, presented a predominantly austenitic matrix phase, showing that the addition of high copper content decreases the martensitic transformation temperature to very low temperatures or inhibits the formation of martensite entirely. However, the ternary alloy with 5% copper, rapidly cooled, showed an intermediate pre-martensitic B19 transformation.