The influence of the stress-induced martensite on the corrosion behavior of a β CuAlBe shape memory alloy after 60 days of immersion in a 3.5 % NaCl solution has been analyzed. The stress-induced martensite was retained in the sample after a load-unload compression cycle up to a pseudoelastic deformation of 4.5 %. Compression tests were carried out with a Shimadzu Autograph-DSS-10T universal testing machine at room temperature, and a constant cross-head speed of 1 mm/min.
The presence of martensite needles on a β matrix induced the localized corrosion of the β phase. The corrosion products and the morphology of the attack has been studied by means of an Olympus BX60 microscope (OM), and a JEOL JSM-6460LV scanning electron microscope (SEM). To estimate the surface composition of different zones of the samples, energy dispersive X-ray spectroscopy (EDX) analysis under SEM was employed. To identify the phase structure of the corrosion products film formed during the immersion, X-ray diffraction (XRD) measurements were carried out using a PANanalytical X’Pert Pro PW3373 and a PANanalytical X’Pert MPD X-ray diffractometers with normal and low incident angle. For investigation of crystallographic nature, TOF-SIMS analysis with C-TOF integrated on FIB-SEM Tescan LYRA3 and an EBSD camera NordlysMax3 were used.
The results obtained in the present work suggest that the presence of the stacking faults in the martensite phase would protect the martensite needles from corrosion. The corrosion of the alloy occurs by dealuminization, where β phase located in the areas between the needles of martensite is dissolved due to the preferential loss of aluminum. From the EBSD results, it is proposed that the mechanism of dealloying is dissolution of the alloy and redeposition of copper.
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