Scanning Kelvin force probe microscopy (SKPFM) and subsequent electron backscatter diffraction (EBSD) measurements were performed across the same area of a ferrite/pearlite microstructure for annealed S45C steel. Larger potential differences were observed at the heterogeneous phase boundaries between cementite and ferrite. The EBSD measurements confirmed the dependence of potential on the crystallographic orientation of the ferrite phases. Specific orientation relationships between ferrite and cementite phases were observed when both phases nucleated in the same pearlite colony, however, such relationships were not valid when nucleation occurred in separate colonies. The heterogeneous phase boundaries exhibiting larger potential differences, in addition to having no specific orientation relationship, could be considered as a highly plausible candidate location for corrosion initiation. Thus, combined SKPFM and EBSD analyses are a powerful technique to improve the evaluation of the corrosion initiation process in ferrite/pearlite microstructures with respect to potential difference and crystallographic orientation relationships.
In this study, porous ADC12 (Al-Si-Cu alloy) and an A1050 (commercially pure aluminum) dense plate were joined by press working during foaming. The A1050 dense plate was first heated using an optical heating device, and then the ADC12 precursor was placed on the A1050 dense plate. Next, we attempted to join porous ADC12, and the A1050 dense plate by press working during the foaming of porous ADC12. It was shown that porous ADC12 and the A1050 dense plate can be joined by press working during foaming while maintaining the pore shape of porous ADC12. The joined samples exhibited joining strengths higher than the tensile strength of the porous ADC12 itself.
Fig. 3 Photographs of light heating and press working processes.
The effect of the DC electric field/current on the crack healing behavior was examined in 8 mol％ yttria-stabilized cubic zirconia (8Y-CSZ) polycrystals. Microcracks formed in 8Y-CSZ using the micro Vickers technique was healed under the flash conditions at sample temperatures of 1040℃ and 1230℃ by controlling the DC electric field/current. At high temperatures, releasing the external energies, which were stored by the indentation as the elastic/plastic strains and new crack surfaces, would be driving forces for the crack healing. Thus, the crack healing takes place some extent even for the static annealing without the DC electric field/current and the healing length becomes larger in the cracks formed at the larger loads. As compared to the static annealing, the healing behavior was accelerated by several times under the flash event condition even at the same temperatures. This suggests that the accelerated healing behavior cannot be explained only by the thermal activated processes, but ascribed to non-thermal processes accelerated by the flash event. Since the grain growth behavior was accelerated under the flash condition, the flash event enhanced the healing behavior of the microcrack damages by accelerating the diffusional processes.
Fig. 5 Typical SEM images of the microcrack (a) before and (b)(c) after the flash healing treatment for 10 min at Ts,p = 1230℃; the microcrack was formed in the center area ③ (Fig. 1) of the sample by the Vickers indentation test at P = 9.8 N.