Journal of the Japan Institute of Metals and Materials

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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 T_s_,_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. Fullsize Image

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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. Fullsize Image

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