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Corrosion fatigue growth of zirconium in boiling nitric acid

沸騰硝酸中でのジルコニウムの腐食疲労成長

本岡 隆文; 木内 清

Motooka, Takafumi; Kiuchi, Kiyoshi

ジルコニウムの疲労亀裂成長挙動を、沸騰硝酸中と室温大気中で荷重制御下で研究した。大気中での疲労亀裂成長は金属組織に強く影響を受けた。これはジルコニウム特有のHCP構造に起因する機械的強度の異方性が原因であった。硝酸中では大気中に比べて約4倍亀裂成長が速かった。硝酸中では、亀裂成長は特徴的な機構で行われていることが破面観察からわかった。つまり、破面形態は、応力腐食割れ時に見られる擬劈開面と大気中で見られる疲労ストライエーションが混在したものであった。亀裂成長速度が低いところでは 擬劈開面が支配的であり、亀裂成長が速いところでは延性破面が支配的であった。

The fatigue crack growth of a commercial grade zirconium has been studied in boiling nitric acid and in air at room temperature under tensile load control. The fatigue crack growth rate in air is strongly dependent on the crystallographic texture. It is interpreted based on the crystal anisotropy on mechanical strength in the hexagonal closed pack structure of zirconium. The fatigue crack growth rate in nitric acid is about four times higher than that in air. Texture is found to have an effect on the fracture path in nitric acid. Microfractography of the fracture surfaces shows that the corrosion fatigue growth has a characteristic mechanism. The fracture surface consists of a mixture of grains: some broken by pseudo-cleavage as seen in stress corrosion cracking, and the others broken by fatigue with striation as seen in air. In the low crack growth rate regime pseudo-cleavage is dominant, whereas in the high crack growth rate regime the main fracture mode is ductile fracture.

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パーセンタイル:36.89

分野:Materials Science, Multidisciplinary

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