Estudo da viabilidade de alguns reagentes na revelação da microestrutura de uma liga nitinol de concentração equiatômica por meio de ataque químico e eletrolítico

Abstract

NiTi alloys demonstrate high corrosion resistance due to the formation of a passive layer on the surface of the alloy composed mainly of TiO2. This property imposes a barrier to reveal the microstructure of Niti alloys. Currently, the most efficient etchant is Kroll’s etchant, which is composed of a very toxic substance, hydrogen fluoride. This text presents a study of the capability of a couple etchants to reveal the microstructure of a Nitinol alloy of equiatomic composition by means of chemical and electrolytic etching. Samples were prepared by means of hot mounting (specimens that have undergone chemical etching) and cold mounting (specimens that have undergone electrolytic etching). The reactants that are appled in this paper are recommended by the ASTM E 407 – 07 for the etching of nickel, titanium, and Nitinol alloys. None of the applied reactants was capable of evidencing the grain boundaries of the material. It was also noticed that the best results were accomplished by the Kroll’s reactants (Kroll 1 and Kroll). It is observed that both chemical etchants were inefficient in revealing the microstructure of the alloy. However, the electrolytic etchants, especially the reactant 3 ( 5ml - H2SO4 and 50ml - water), were capable of evidencing features associated with the drawing processing to which the NiTi wire has been submitted.