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High fatigue-strength options for brazed structures. Samuli Heikkinen, CLIC meeting 22.2.2008. -. To be confirmed. -. +. Higher strength is generally achieved by blocking the dislocation motion Dislocations can block the movement of each others if the dislocation density is high
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Samuli Heikkinen, CLIC meeting 22.2.2008 - To be confirmed - +
Higher strength is generally achieved by blocking the dislocation motion • Dislocations can block the movement of each others if the dislocation density is high • Cold working increases the dislocation density • Impurities can block the dislocation motion alloying GlidCop Cold worked and material has high dislocation density. GlidCop has “naturally” high density 1*10²² 1/m³ of small 7 nm Al2O3 particles (average spacing 46 nm). Elevated temperatures does not modify the Al2O3 particles. Dislocation density decreases and the material becomes slightly softer. Cu-Zr Cold worked material has high dislocation density and aged material has high density 2.6*10²³ 1/m³ of small 1-4 nm Cu5Zr precipitates (average spacing 16 nm). Elevated temperatures (700°C) “overage” the material decrease Cu5Zr precipitate density to 0.7*10²¹ 1/m³ and increase their size to 40 nm (average spacing 113 nm) softer material. Cu-OFE Cold worked material has high dislocation density. Elevated temperatures (>150°C) decrease the dislocation density and result in a softer material. Grain size has only a secondary effect. For annealed copper smaller grain size can increase the strength by blocking the dislocations moving freely in the grain. For cold worked copper the difference is not significant. σ σ σ Small grain size High grain size Cw + aging cw Cw + aging 0 0 0 Small grain size is typically 50-100 µm. Dislocation density can be for copper 10¹² 1/cm² (spacing 10 nm) Heated layer of CLIC structures is about 20 µm.
Fatigue strengths [MPa] (CLIC lifetime values) RF fatigue Criteria: visually observed damage (RF still happy) Mechanical fatigue Criteria: crack planned CLIC limit 56ºC
Candidates: Cu-OFE (C10100),CuZr (C15000),GlidCop Al-15 Laser Ultrasound RF RF
Fatigue by RF experiments Cu-OFE_1 (ΔT ~ 70ºC) after N=2*10^6 CuZr_2 (ΔT ~ 70ºC) after N=10^7 Cu-OFE_2 (ΔT ~ 110ºC) after N=2*10^6 Cu-OFE_2 (ΔT ~ 70ºC) after N=10^7 CuZr_1 (ΔT ~ 100ºC) after N=10^7 Fatigued zone “soft” CuZr! No change in RF performance was observed during the runs! RF breakdown zones 110ºC 70ºC 70ºC
