Secondary phase precipitate-induced localized corrosion of pure aluminum anode for aluminum–air battery

Understanding the influence of purities on the electrochemical performance of pure aluminum(Al)in alkaline media for Al–air batteries is significant.Herein,we comprehensively investigate secondary phase precipitate(SPP)-induced localized corrosion of pure Al in NaOH solution mainly based on quasi-in-situ and cross-section observations under scanning electron microscopy coupled with finite element simulation.The experimental results indicate that Al–Fe SPPs appear as clusters and are coherent with the Al substrate.In alkaline media,Al–Fe SPPs exhibit more positive potentials than the substrate,thus aggravating localized galvanic corrosion as cathodic phases.Moreover,finite element simulation indicates that the irregular geometry coupled with potential difference produces the non-uniform current density distribution inside the SPP cluster,and the current density on the Al substrate gradually decreases with distance.

MECHANISM OF SECONDARY M_(23)C_6 PRECIPITATION AROUND MC IN A COBALT-BASE SUPERALLOY

Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of the MC. Two mechanisms were suggested,i.e. the in situ reaction, MC+γ→M23C6+C, and the direct reaction, M+C→M23C6,in which MC acted as a carbon source.

Effect of cooling rate during quenching on the microstructure and creep property of nickel-based superalloy FGH96

The effect of cooling rate during quenching on the microstructure and creep property of nickel-based superalloy FGH96 was investigated. Three groups of samples were quenched continuously with three fixed cooling rates, respectively, then subjected to a creep test under a constant load of 690 MPa at 700℃. Clear differences in size of secondary γ′ precipitates, creep properties and substructure of creep-tested samples were observed. The quantitative relationship among cooling rate, the size of secondary γ′ precipitates, and steady creep rate was constructed. It was found that with increasing cooling rate, the size of secondary γ′ precipitates decreases gradually, showing that the relationship between the size of secondary γ′ precipitates and the cooling rate obeys a power law, with an exponent of about –0.6, and the creep rate of steady state follows a good parabola relationship with cooling γ′ precipitate size. For 235℃/min, FGH96 alloy exhibited very small steady creep rate. The density of dislocation was low, and the isolated stacking fault was the dominant deformation mechanism. With decreasing cooling rates, the density of dislocation increased remarkably, and deformation microtwinning was the dominant deformation process. Detailed mechanisms for different cooling rate were discussed.