The dynamic solidification of ternary Ag38.5Cu33.4Ge28.1 eutectic alloy within a 35 kHz ultrasonic field is investigated and compared with both its equilibrium solidification by DSC method and its rapid solidification...The dynamic solidification of ternary Ag38.5Cu33.4Ge28.1 eutectic alloy within a 35 kHz ultrasonic field is investigated and compared with both its equilibrium solidification by DSC method and its rapid solidification in drop tube. The volume fractions of the primary （Ge） phase and pseudobinary （Ag＋ε2） eutectic solidified within ultrasonic field are larger than those formed under equilibrium state, whereas that of ternary （Ag＋ε2＋Ge） eutectic exhibits the reverse trend. During rapid solidification, the liquid alloy droplet directly solidifies into ternary （Ag＋ε2＋Ge） eutectic if its diameter is smaller than 350 um. The ultrasound stimulates the nucleation of alloy melt and prevents the bulk undercooling. With the increase of sound intensity, the primary （Ge） phase transfers from faceted dendrites to nonfaceted blocks with blunt edges, and its grain size is remarkably reduced. Both pseudobinary （Ag＋ε2） and ternary （Ag＋ε2＋Ge） eutectics experience a morphological transition from regular to anomalous structures. This indicates that their cooperative growth mode is replaced by independent growth of eutectic phases under the combined effects of cavitation and acoustic streaming. The ultrasound also shows a prominent coarsening effect to the pseudobinary （Ag＋ε2） and ternary （Ag＋ε2＋Ge） eutectics.展开更多
文摘利用1064 nm的红外激光辐照铅靶,采集了激光能量20 mJ下铅激光等离子体在350~380 nm范围内发射光谱的时空演化谱。根据PbⅠ373.995 nm特征谱线的半高全宽计算了等离子体的电子密度,得到了电子密度随空间位置的演化趋势。分析了铅原子四条特征谱线(Pb I 357.274 nm、Pb I 363.958 nm、Pb I 368.348 nm、Pb I 373.995 nm)的中心波长随着延迟时间和空间位置的变化。结果发现,随着空间距离的增加,谱线的中心波长都向着短波的方向不断地移动。利用等离子体膨胀理论模型,从多普勒效应方面对实验结果进行了解释。
基金supported by the National Natural Science Foundation of China(Grant Nos.50971105 and 51201136)Doctoral Fund of Ministry of Education of China(Grant No.20126102120059)+1 种基金Aviation Foundation of China(Grant No.2012ZF53069)Technology Foundation for Selected Overseas Chinese Scholar,ShaanXi Province,NPU Excellent Personnel Supporting Project of Ao Xiang Star,and Fundamental Research Fund of Northwestern Polytechnical University(Grant No.JC20110280)
文摘The dynamic solidification of ternary Ag38.5Cu33.4Ge28.1 eutectic alloy within a 35 kHz ultrasonic field is investigated and compared with both its equilibrium solidification by DSC method and its rapid solidification in drop tube. The volume fractions of the primary （Ge） phase and pseudobinary （Ag＋ε2） eutectic solidified within ultrasonic field are larger than those formed under equilibrium state, whereas that of ternary （Ag＋ε2＋Ge） eutectic exhibits the reverse trend. During rapid solidification, the liquid alloy droplet directly solidifies into ternary （Ag＋ε2＋Ge） eutectic if its diameter is smaller than 350 um. The ultrasound stimulates the nucleation of alloy melt and prevents the bulk undercooling. With the increase of sound intensity, the primary （Ge） phase transfers from faceted dendrites to nonfaceted blocks with blunt edges, and its grain size is remarkably reduced. Both pseudobinary （Ag＋ε2） and ternary （Ag＋ε2＋Ge） eutectics experience a morphological transition from regular to anomalous structures. This indicates that their cooperative growth mode is replaced by independent growth of eutectic phases under the combined effects of cavitation and acoustic streaming. The ultrasound also shows a prominent coarsening effect to the pseudobinary （Ag＋ε2） and ternary （Ag＋ε2＋Ge） eutectics.
