水銀標的における耐ピッティング損傷向け2重被覆ステンレス板の開発

Development of double-layered coated stainless steel plate against pitting damage in mercury target

川合 將義*; 二川 正敏  ; 直江 崇   ; 山村 力*; 五十嵐 廉*

Kawai, Masayoshi*; Futakawa, Masatoshi; Naoe, Takashi; Yamamura, Tsutomu*; Igarashi, Tadashi*

大強度陽子加速器施設J-PARCの核破砕中性子源の水銀標的は、パルス幅1マイクロ秒,25Hzの陽子ビームを受けてパルス中性子を発生する。入射陽子ビームパワーが極めて大きく、水銀中にバブルの発生消滅に伴う圧力波によって水銀容器や入射窓がピッティング損傷を受ける。材料表面を硬化処理により若干の寿命延伸効果を得られるが、母材表面の疲労が大きく、目標は達成されない。その疲労を抑止するため圧力波減衰用の材料を挟みこんだ2重膜被覆ステンレス板の効果について有限要素法で解析し、また実験研究を実施した。

A serious problem encountered when a liquid-Hg target is used for MW-class pulsed spallation neutron source is pitting damage caused to vessel walls. This pitting damage is due to the impact of cavitation-bubble collapse immediately after intense proton beams are made incident on the target. Pitting damage is thought to be as important as or more important than radiation damage in determining the life time of the target. An effectiveness of an SS/Au-double-layer-coated SS plate in reducing pitting damage is investigated. An FEM analysis reveals that the Au layer absorbs the impact from the surface plate and significantly reduced the stress on the SS substrate. SS/Au/SS specimens are fabricated by using the diffusion bonding method, and the development of pitting damage is investigated by using the MIMTM. The specimens are then analyzed by EDX for determining the thickness of the diffusion layer and by laser microscopy for detecting micro-cracks and the extent of pitting damage.