Hai Yun

Determining the Thermal Shock Elastic Behavior of Mullite Ceramic Regenerator Material by Ultrasonic Testing

Mullite material is a material commonly used in honeycomb regenerator, because in the process of using material under big temperature difference effect, so have a great demand for its thermal shock resistance. The used mullite ceramics were made by the direct solid phase sintering method, and the modulus of elasticity of the mullite ceramics measured by ultrasonic pulse-echo method in a thermal shock and thermal fatigue experiment, respectively. In the air-cooling condition, the study found the mullite ceramic without thermal shock that the longitudinal wave velocity and shear wave velocity respectively 3970(m/s) and 2492(m/s). After 45 times thermal shock of temperature difference of 800°C, longitudinal wave velocity and shear wave velocity decreased to 3910(m/s) and 2457(m/s), and the value of the modulus of elasticity changed 1020MPa. By observing the change of the elastic modulus value rule, can know the elastic deformation of thermal shock on the material performance of thermal shock damage. Moreover, the results can provide the data basis for the calculation of the residual strength and the numerical simulation of thermal stress.

Micro-Raman Analysis on Scratch of Si Surface Modified by Ion Implantation

Surface modification mechanism on scratch of ion implanted p-Si (100) is investigated by scanning electric microscopy and micro-Raman spectroscopy. Raman experimental results reveal that the amorphous Si appears near the scratch during the scratching process, while the ion implantation adjusts the structural parameters of the amorphous Si and changes the residual stress state of the surface scratch from tension to compression. Moreover, Raman experimental results reveal that the laser power synchronously decreases Raman shift and full width of half maximum intensity (FWHM). The laser heating effect can be neglected because a lower laser power is selected in our measurements.

Experimental investigation of p-Si (100) surface modified by ion implantation

Surface strengthening and residual stress in Ti+ implanted p-Si (100) wafers are investigated by scanning electron microscopy, X-ray diffraction, nano-indentation and micro-Raman spectroscopy. The experimental results revealed that the crystallinity decreases gradually in transition area, whose structure varies continuously from the crystalline Si to amorphous phase which appears in ion implanted area. Moreover, the hardness and elastic modulus increase gradually in the transition area. Compressive intrinsic-stress that comes from lattice mismatch between the implanted layer and Si substrate is one factor giving rise to residual stresses.

A method with exact phase-shifting values and its experimental techniques in shadow moire topography

According to the characteristic of the optical field arrangement, parallel illumination and parallel receiving in shadow moire method, that the reference grating and the shadow moire can be shifted equal distance at the same time, are proposed in this paper. First, the calculation formula for determining exact phase-shifting values and its experimental techniques were derived. Second, an exact simulation technique in shadow moire topography was constructed on the basis of the conceptions of geometrical interference mode for forming the virtual shadow moire fringes and the calculation formula of exact phase-shifting values. Third, to verify the validity of the calculation principle and simulation technique, the experimental results of the two typical models were offered, one was the cylinder and the other was sphere. These results indicate that the method proposed in this paper can improve the precision of three dimensional shape reconstructions and promote the development of shadow moire topography.