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The effects of the SnO2 passive film and micro-galvanic corrosion on the corrosion behavior of as-extruded Mg-9Li-5Al-xSn (x = 0, 0.5 and 1.0 wt.%, LA95) alloys were investigated. As the Sn content increased from 0.5 to 1.0 wt.%, Sn was first dissolved and then precipitated Mg2Sn. The SKPFM results indicated that the Volta potential difference of AlLi/a-Mg, Mg2Sn/a-Mg and β-Li/α-Mg was 370, 200 and 120 mV, respectively. The electrochemical experiment results indicated that the corrosion resistance of LA95-0.5 wt.% Sn alloy was significantly improved (98.7%), which can be attributed to the local protective film containing SnO2 that prevented the contact of the electrolyte solution and the cathode. In the LA95-1.0 wt.% Sn alloy, excessive Sn precipitated Mg2Sn weakening the protective effect of SnO2 film. The corrosion mechanism after Sn addition in as-extruded LA95-xSn alloy was discussed. [ABSTRACT FROM AUTHOR]

The effect of Al addition on the microstructure and corrosion behavior of CoNiVAl x medium entropy alloys (MEAs) was investigated. Results indicated that the enhanced corrosion resistance caused by Al addition might be attributed to the dominant role of Al in stabilizing the passive film. The difference in the Volta potentials of FCC and B2 phases indicated the existence of microgalvanic coupling, which suggested that the B2 phase served as a localized cathode while the FCC matrix and FCC lath acted as anodes. This accounted for the pitting mechanism of CoNiVAl x MEAs via Al addition. [Display omitted] • Al addition shows positive effects on the corrosion resistance of CoNiVAl x medium-entropy alloys (MEAs). • The relationship between the microstructure and corrosion behavior is established. • The presence of the B2 phase constitutes the microgalvanic coupling with the FCC matrix and the FCC laths. • The pitting mechanism and enhanced corrosion resistance of CoNiVAl x MEAs via Al addition are clarified. [ABSTRACT FROM AUTHOR]

[Display omitted] • The F− and pH dependent corrosion behaviour of Ti80 alloy in seawater is studied. • The F− has few effects on cathodic reaction but vital effects on anodic process. • The pH plays a significant role in determining the cathodic and anodic processes. • The special cathodic and anodic parameters of Ti80 alloy are determined. • The intergranular β phase shows higher Volta potential than the equiaxed α phase. Herein, we systematically investigate the corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in artificial seawater with various fluoride ion (F−) concentrations and pH values using electrochemical, static immersion measurements and surface characterizations. Results of electrochemical tests manifest that increasing the F− concentration and/or reducing pH value can deteriorate the corrosion performance of Ti80 alloy due to the dissolution of the compact passive film into the porous passive film. Besides, the electrochemical parameters obtained from polarization curves indicate that the F− concentration has few effects on the cathodic reaction but noticeable promoting effects on the anodic process, whereas the increase of pH plays a significant role in inhibiting both cathodic and anodic processes. In addition, surface characterizations reveal the preferential dissolution of the equiaxed α phase compared to the intergranular β phase, resulting from its relatively low Volta potential. We also interpret the F− concentrations and pH values dependent corrosion behaviour based on the mixed potential theory and illustrate the corrosion mechanisms associated with F− in artificial seawater. We believe that the insights into the F− concentration and pH value dependent corrosion behaviour can provide practical guidelines for the design and development of Ti alloys with high-corrosion resistance. [ABSTRACT FROM AUTHOR]

This study elucidated the corrosion behavior of Ti-0.3Mo-0.8Ni-2Al- x Zr (x = 0, 1, 2, 3, 4 and 5 wt.%) alloys utilizing electrochemical techniques and first-principles calculation. Results revealed that the Zr addition refined the lamellar α phase, and the corrosion resistance was monotonically enhanced by increasing the Zr content. The corrosion morphologies indicated that the β phase was more susceptible to corrosion than the α phase possessing a higher Volta potential and work function. The oxide film of the surface acted as a major corrosion influence factor instead of the microstructure of the matrix in determining the corrosion performance of Ti-0.3Mo-0.8Ni-2Al- x Zr alloys. • Trace Zr additions improve corrosion resistance. • The evolution process of interphase corrosion is expounded systematically. • Investigated corrosion resistance of α and β phases by experiments and first-principles calculation. • There is micro-galvanic corrosion between α and β phases where β phase acts as anode. Zr addition decreases the work function of β phase and increases galvanic corrosion tendency. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Ti 2 Cu of corrosion activity is composed of a "micro-galvanic cell" with α-Ti. • The lamellar Ti 2 Cu increased the Cu ion release caused by more galvanic interface. • The antibacterial rate of L-Ti 2 Cu is 99.5 %, due to the rapid release of Cu ions. The influence of morphology of the Ti 2 Cu phase on biological corrosion and antibacterial properties of Ti-Cu alloy was investigated by micro-galvanic corrosion. Elongated "micro-galvanic cells" were formed between lamellar Ti 2 Cu phase (L-Ti 2 Cu) and α-Ti matrix due to the different Volta potentials. The corrosion rate (V corr) of L-Ti 2 Cu was twice that of granular Ti 2 Cu phase (G-Ti 2 Cu) because lamellar Ti 2 Cu phase had more galvanic interface. The release of Cu2+ ions in L-Ti 2 Cu was 55 % higher than G-Ti 2 Cu, reaching 99.5 % of the antibacterial rate in L-Ti 2 Cu and providing a great potential in clinical application for dental implants. [ABSTRACT FROM AUTHOR]

• The surface potential of the phases in AZ91–xGd alloys was characterized by AFM. • Nd–rich phases with lower surface potentials obviously improved corrosion resistance. • The polarization resistance of the AZ91–1.0Nd alloy is 3.9 times than that of matrix. • The effect of micro–galvanic corrosion was weakened after the addition of Nd. • Corrosive film containing Nd 2 O 3 inhibited the occurrence of micro–galvanic corrosion. The effects of surface micro–galvanic corrosion and corrosive film on the corrosion resistance of AZ91–xNd alloys was evaluated by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM), and electrochemical measurements. The microstructural morphologies showed that the formations of Al 2 Nd and Al–Mn–Nd phases were observed in AZ91–Nd alloy. According to the results of SKPFM, the Nd–rich phases were slightly noble than the β–Mg 17 Al 12 phase but less than the Al–Mn phase. Consequently, AZ91–1.0Nd alloy with dispersed Nd–rich phases showed the largest polarization resistance values of 5129 Ω·cm2, about 3.9 times than that of AZ91 (1313 Ω·cm2). The main factors affecting the corrosion resistance of AZ91–xNd alloys were as follows: (i) the suppression of surface micro–galvanic couple corrosion, since the Volta potential difference (secondary phases/α–Mg) was reduced after Nd addition, the effect of surface micro–galvanic corrosion was weakened, thereby enhancing the corrosion resistance of the tested alloy (AZ91); (ii) corrosive film, the uniform corrosive film containing Nd 2 O 3 isolated the specimens and the electrolyte, which suppressed the penetration of harmful anions (OH–, C O 3 2 -) and inhibited the occurrence of surface micro–galvanic corrosion of AZ91–Nd alloys. [ABSTRACT FROM AUTHOR]