The effect of Hf on the grain refinement of as-cast aluminum was investigated using optical microscopy, electron microscopy and X-ray diffraction. The result shows that the grain size of studied alloy decreases effect...The effect of Hf on the grain refinement of as-cast aluminum was investigated using optical microscopy, electron microscopy and X-ray diffraction. The result shows that the grain size of studied alloy decreases effectively with the addition of Hf,Hf can react with Al to form Al3Hf particles during the solidification, the primary Al3Hf particles are highly potent nucleants for Al and the nanoscale coherent Al3Hf particles can inhibit the grain growth by pinning effect. The grain refinement mechanism of studied alloys was verified by the solute theory and the crystallography study, and it can be divided into two distinct types: At low Hf contents, there are no primary Al3Hf phases to form, the acquired grain refinement is primarily attributed to the constitutional undercooling induced by the Hf solute. At medium and high Hf contents, both Hf solute and Al3Hf particles contribute to the refinement.展开更多
(K,Na)NbO_(3)(KNN)-based lead-free piezoceramics have been the spotlight in search for practically viable candidates to replace the hazardous but dominating lead-containing counterparts.In this work,BaTiO_(3)(BT)modif...(K,Na)NbO_(3)(KNN)-based lead-free piezoceramics have been the spotlight in search for practically viable candidates to replace the hazardous but dominating lead-containing counterparts.In this work,BaTiO_(3)(BT)modified KNN ceramics were fabricated by spark plasma sintering(SPS)and the influence of BT content as well as sintering temperature on the phase structure,microstructure,and electrical properties were investigated.It was found that the 0.96(Na_(0.5)K_(0.5))NbO_(3)-0.04BaTiO_(3)(BT4)ceramics sintered at 1000℃have the optimal performance.Additionally,in-depth analysis of the electrical hysteresis revealed that the internal bias field originating from accumulation of space charges at grain boundaries is responsible for the asymmetry in the hysteresis loops.展开更多
基金Project(SGRI-WD-71-13-001) supported by the Scientific and Technological Project of State Grid Corporation of China
文摘The effect of Hf on the grain refinement of as-cast aluminum was investigated using optical microscopy, electron microscopy and X-ray diffraction. The result shows that the grain size of studied alloy decreases effectively with the addition of Hf,Hf can react with Al to form Al3Hf particles during the solidification, the primary Al3Hf particles are highly potent nucleants for Al and the nanoscale coherent Al3Hf particles can inhibit the grain growth by pinning effect. The grain refinement mechanism of studied alloys was verified by the solute theory and the crystallography study, and it can be divided into two distinct types: At low Hf contents, there are no primary Al3Hf phases to form, the acquired grain refinement is primarily attributed to the constitutional undercooling induced by the Hf solute. At medium and high Hf contents, both Hf solute and Al3Hf particles contribute to the refinement.
基金National Nature Science Foundation of China(Grants No.51572143,51302144,51332002)the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20130002120031)the Tsinghua University Initiative Scientific Research Program(Grant No.20131089230).
文摘(K,Na)NbO_(3)(KNN)-based lead-free piezoceramics have been the spotlight in search for practically viable candidates to replace the hazardous but dominating lead-containing counterparts.In this work,BaTiO_(3)(BT)modified KNN ceramics were fabricated by spark plasma sintering(SPS)and the influence of BT content as well as sintering temperature on the phase structure,microstructure,and electrical properties were investigated.It was found that the 0.96(Na_(0.5)K_(0.5))NbO_(3)-0.04BaTiO_(3)(BT4)ceramics sintered at 1000℃have the optimal performance.Additionally,in-depth analysis of the electrical hysteresis revealed that the internal bias field originating from accumulation of space charges at grain boundaries is responsible for the asymmetry in the hysteresis loops.
