Zhiyuan Xiao

Bio: Zhiyuan Xiao is an academic researcher from Northwestern Polytechnical University. The author has contributed to research in topics: Raman spectroscopy & Microstructure. The author has an hindex of 7, co-authored 10 publications receiving 119 citations.

Microstructure evolution of C/Mo double-coated SiC fiber reinforced Ti6Al4V composites

Abstract: C/Mo double-coated SiC fiber reinforced Ti6Al4V (SiCf/C/Mo/Ti6Al4V) composites fabricated by foil-fiber-foil (FFF) were thermally exposed for the purpose of investigating thermal stability of the C/Mo duplex coating at high temperatures of 700–900 °C. It is revealed in the study that the SiCf/C/Mo/Ti6Al4V composites have an excellent thermal stability at temperature below 700 °C compared to the poor thermal stability at 800 °C. When the composites were thermally exposed at 900 °C for 100 or 200 h, a large number of TiC, Ti2AlC or Ti3AlC particles were identified as reaction products in the matrix by means of energy-dispersive spectrometer analysis, X-ray diffraction analysis and transmission electron microscopy. The formation mechanism of these particular phases was analyzed in terms of thermodynamics, composition condition and element diffusion path. In addition, the longitudinal tensile performance of the composites thermally exposed under 900 °C/200 h was tested at room temperature, and the corresponding failure behavior was analyzed.

Microstructure and thermal residual stress analysis of SiC fiber through Raman spectroscopy

Abstract: SiC fiber-reinforced metal matrix composite is an interesting material for aerospace industry because of its excellent properties. However, these properties are greatly influenced by fiber microstructure and thermal residual stresses introduced by the preparation of the composites. Due to complicated preparation technology, microstructure and thermal stress along SiC fiber radius varies, which makes characterization difficult. Raman spectroscopy is a non-destructive technique which provides information, at micrometer scale, on the phase composition and the crystalline state (structure and texture) of materials. Line scanning was used to assess microstructure along SiC fiber radius embedded in Ti64. The SiC coating is subdivided into three concentric parts across the fiber diameter, according to the differences in intensity and width of SiC transverse optical phonon (TO) band. Part 2 is considered to be a buffer zone connecting Part 1 and Part 3 with different deposition conditions, respectively. Amorphous Si is detected throughout fiber radius, while crystalline Si is only detected in the outer part. Thermal residual stress along fiber radius in the composite was calculated by using SiC TO band shifts with a bare fiber as reference. A cylindrical model was also used to compare with the stress data obtained from Raman shift. Copyright © 2013 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article.

Effect of C/Mo duplex coating on the interface and mechanical properties of SiCf/Ti6Al4V composites

Abstract: SiC fiber (with C/Mo duplex coating) reinforced Ti6Al4V-matrix composites were fabricated by vacuum hot pressing. Tensile property of the as-prepared composites was tested at room temperature. In order to study the interfacial thermal stability of the composites, vacuum thermal exposure of the as-prepared composites was carried out at 700 °C and 800 °C for different duration. The interfacial microstructure of the as-prepared and thermally-exposed composites was investigated by means of scanning electron microscope and energy dispersive spectrometer. The results indicate that the interfacial phase sequence of the as-prepared composite is SiC|C/Mo|TiC|Moresidual+β-Ti|β-Ti+α-Tiprimary|Ti6Al4V from SiC side to the matrix. The interfacial microstructure has no obvious evolution when the composites were thermally exposed at 700 °C, which indicates an excellent thermal stability of C/Mo duplex coating. Furthermore, there still exists C/Mo duplex coating at the interface when the composites were thermally exposed at 800 °C for up to 100 h. Therefore, the C/Mo duplex coating exhibits a more outstanding thermal stability than a single Mo coating at elevated temperatures below 800 °C. The tensile strength of the as-prepared composites was a little higher than that of the composites with only C coating, which should attribute to the good effect of the C/Mo duplex coating.

The one phonon raman spectrum in microcrystalline silicon

Abstract: The red shift and the broadening of the Raman signal from microcrystalline silicon films is described in terms of a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons. The relationship between width and shift calculated from the known dispersion relation in c-Si is in good agreement with available data. An increase in the decay rate of the optical phonons predicted on the basis of the same model is confirmed experimentally.