Papers by Keyword: Columnar Crystal

Abstract: This paper described the microstructure feature of the first short circuit and the second short circuit of copper wires in the electrical equipment line fire. The cause of fire is evaluated and analyzed by the difference in microstructure between the first short circuit and the second short circuit of copper wire. It would provide scientific and favorable evidence for the department of fireman to clear up a case of fire.

Abstract: A variety of electrical apparatus used in daily life can cause fires because of internal or external factors. During cause identification of an electrical fire, the first short circuit melted marks of copper wire have been considered highly important because they are direct proofs. Additionally, overloaded short circuit caused by the overload of current due to excessive electrical usage can give rise to an electrical fire. Despite extensive research on the first short circuit in fire scenes, the overloaded short circuit remains difficult to be distinguished because of the limitation of commonly used testing methods. Conventional metallographic method is intuitionistic and simple, but may not provide detailed data of crystals such as misorientation of grains. Here a new method (electron backscattered diffraction, EBSD) is applied for identification of the first and overloaded short-circuited melted marks of copper wires in electrical fire scenes. Results show obvious morphological distinctions in melted marks of copper wires between the first and overloaded short circuits. Qualitative and Quantitative differences obtained from the contrast of the above two short circuit situations may assist for cause identification of electrical fires in the future.

Abstract: The influence of pulse electric field on the columnar crystals growth has been studied by employing pulse electric field vertically to the solid/liquid interface during unidirectional solidification. The results showed that the pulse electric field was favorable to columnar crystals growth with the increase of pulse electric field intensity when the liquid phase was the positive electrode of pulse electric field. The formation of equiaxed crystal was accelerated when the degree of composition supercooling in front edge of solid/liquid interface reached the degree of nucleation supercooling by pulse electric field. When the liquid phase was the negative electrode of pulse electric field, the growth of columnar crystals was hindered, and the formation of equiaxed crystal was accelerated by pulse electric field.

Abstract: This paper has systematically studied the evolving process of column crystals of Ti46Al0.5W0.5Si alloys that is directionally solidified by rectangular cold crucible. The results showed that: the solid/liquid interface presented convex to the liquid metal due to the complicated influences by cold crucible. Overheating temperature and new crystal nucleus had great effects on the growth continuity and the stability of column crystals. Furthermore, the precipitation phases have been studied. As a result, the methods for controlling growing process of columnar crystals have been submitted, which are playing a critical role in optimizing experimental parameters and devising the construction-elements of cold crucible.