Tijun Chen

The microstructure of Ni layer on single-walled carbon nanotubes prepared by an electroless coating process

The single-walled carbon nanotubes (SWNTs, diameter: 2∼3 nm), which were obtained in the suspension of purification solution, with Ni-P coating layers were obtained by an electroless deposition process. The SWNTs before and after coating were characterized by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). An Ni-P layer on individual nanotube with thickness of 20 nmcan be obtained after the deposition process. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis of Ni-P SWNTs before and after heat treatment show that the heat treatment caused the transformation of the amorphous Ni-P layer to the nanocrystalline Ni-P (crystalline Ni and Ni3P intermetallic compound) layer. The XRD pattern of SWNTs with Ni-P layers after heat treatment revealed that the crystal structures of Ni in plating layer contained: hexagonal closepacked (hcp) structure and face-centered cubic (fcc) structure. The lattice parameters of Ni (fcc) and Ni3P are larger than the bulks, indicting that the lattice expansion has taken place. However, the lattice parameter of Ni (hcp) has no difference from the bulks.

Die-filling process during the thixoforming of a ZA27 alloy cylindrical rod

The die-filling process during thixoforming of a ZA27 alloy cylindrical rod was deduced by analyzing microstructural characteristics in the semi-solid ingot prior to and after forming, and by analyzing the phenomena occurring during this thixoforming. These characteristics referred to some constituent segregation, such as a liquid-phase segregation and an inhomogeneous distribution of primary solid particles. The results indicated that the die-filling process could be properly deduced by using the method developed in this paper. The inhomogeneous distribution of primary solid particles in the formed rods mainly resulted from the inhomogeneous distribution in the semi-solid ingot. The detailed distribution was determined by the sequence of the die-filling. However, the aforementioned liquid segregation was mainly attributed to the die-filling process. The sequence of the die-filling process was from the bottom of the cylindrical cavity to the top and from the edge to the inner part of the cavity.

A New Method for Production of Nondendritic Semisolid ZA27 Alloy

In this article, a new method for the production of nondendritic semisolid ZA27 alloy available for thixoforming was developed. The results indicated that a semisolid microstructure with small and spherical primary particles could be obtained when the alloy had been treated for 3 h at 370°C and then partially remelted at semisolid temperature of 460°C. This method could not only overcome some inevitable shortcomings resulting from using some present popular approaches but also simplify the procedure of thixoforming. The coarsening of dendritic arms through merging during solid solution treatment and then separating from the dendrites during partial remelting were the main methods by which such a microstructure was formed.