Chaowen Li

Microstructure and interface structure studies of SiCp-reinforced Al (6061) metal-matrix composites

The microstructure and interface structure of the particle reinforced 6061-Al metal-matrix composites have been studied by optical microscopy, transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDX). The SiC particles are uniformly distributed in the matrix. The constituent phase observed in the matrix is Al-15(Mn,Fe,Cu)(3)Si-2. It has a BCC structure with lattice parameter a=1.28 nm. The SiC reinforcements are found to contain hexagonal alpha-SiC (including 6H alpha-SiC and 4H alpha-SiC) and cubic beta-SiC. Stacking faults are observed in the SiC particles. SIC reinforcements are well bonded with the matrix. In most cases, the interface between the SiC particles and the matrix is clean and no reaction product was observed. However, certain amount of oxygen and magnesium elements have been found at the interface. The reaction products at the interface are identified to be MgAl2O4, and MgO. The size of these particles are found to be of several nanometers

Microanalytical study of the hexagonal phase in an yttrium-containing low expansion superalloy

The resistance to stress-accelerated grain boundary oxygen embrittlement (SAGBO) in Fe-Ni-Co-Nb-Ti controlled low expansion superalloy has been improved by trace yttrium element addition. The platelet precipitates in the alloy have been studied by means of optical microscopy, transmission electron microscopy, convergent beam electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction technique. The crystal structure and the chemical composition of the platelet phase have been determined. The phase has a CaCu5-type crystal structure (space group P6/mmm) with lattice parameters a = 0.498 nm and c = 0.408 nm. The crystallographic orientation relationship between the phase and the matrix is found to be ( 1)(gamma)/(0001)(H), [(1) over bar 10](gamma)/[11 (2) over bar 0](H). High-resolution images show that the interface between the platelet phase and the matrix is semicoherent and some stacking faults have been found in the platelet phase