Abstract <p>This paper is concerned with the corrosion behaviour of the high nickel TiNi alloy in coarse-grained and ultrafine-grained states in solutions of acids of different molarity. In addition, an analysis of the corrosion products on the surface of the samples after the test was carried out using X-ray photoelectron spectrometry. The results of the X-ray photoelectron spectrometer showed that no corrosion products were found during the tests in HCl solutions of different concentrations. The spectra of oxygen in the C=O compound, titanium in the TiO₂ compound and nickel are observed on the surface.</p>