Microstructure and corrosion resistance of Ni-Ti-Al multi-layer laminates manufactured by explosive welding with subsequent rolling

In the present work, an explosive welding technique was used to manufacture novel multi-layer laminates consisting of nickel (Ni), titanium (Ti), and aluminium (Al). Produced laminates were subsequently plastically deformed using symmetrical and asymmetrical rolling. The aim of the study was to correlate the changes in the microstructure that occur during the applied processes with the corrosion resistance of the samples. Two planes were characterized - an outer Ni surface and a cross-section of the laminates. In the first case, the changes caused by the welding and rolling, i.e., reduction in grain size and increase in the fraction of low angle grain boundaries and geometrically necessary dislocations, were insufficient for influencing the corrosion resistance in two examined environments - 0.1 M sodium sulphate (Na2SO4) and 0.5 M sodium chloride (NaCl). When cross-sections of the samples were analyzed, electrochemical experiments in sodium chloride revealed distinct changes between the samples with higher susceptibility to localized corrosion of the laminate, as the presence of Ti and Ni accelerated the corrosion processes and active dissolution of the Al layer. After rolling, the corrosion current density was lowered. The examination of the surface after the tests revealed that corrosion attack occurred only in Al layers, where numerous pits were observed. After rolling, a smaller number of pits are present compared to the sample directly after explosive welding.