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8.12】W. G. Fahrenholtz
题目:Residual Stress...
 
2010-08-10 | 文章来源:高性能陶瓷材料研究部        【 】【打印】【关闭

题 目:Residual Stress Measurement in ZrB2-SiC Ultra-High Temperature Ceramics

报告人:W. G. Fahrenholtz 

     Department of Materials Science and Engineering
       Missouri University of Science and Technology, Rolla, USA

时 间:8月12日(周四)上午9:30-10:30

地 点:李薰楼468房间

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Abstract:

Residual stresses were measured in ZrB2-SiC ceramics using Raman spectroscopy and neutron diffraction. Silicon carbide additions improve the oxidation resistance of ZrB2-based ceramics by forming a passive SiO2-rich glassy scale at intermediate temperatures (~1200°C to 1700°C). In addition to providing better oxidation protection, the presence of SiC also leads to increased strength and fracture toughness of the resulting ceramics. Along with the increases in strength and toughness, the addition of SiC also leads to the development of residual thermal stresses, which are initially generated during cooling from the processing temperature due to the thermal expansion mismatch between ZrB2 and SiC. The thermal stresses impact the thermal shock resistance in addition to affecting other thermomechanical properties. Raman spectroscopy has been used to measure the compressive residual stress in SiC particles on the surface of the composite. Neutron diffraction was performed on a composite sample in order to measure residual stresses in both the ZrB2 matrix as well as the dispersed SiC phase. Samples of the composite materials, as well as pure ZrB2 and SiC powders, were heated to ~1800 °C. Neutron diffraction patterns were obtained at regular intervals upon cooling from 1800°C back to room temperature. Residual stresses in the composite were calculated by comparing the lattice spacings of ZrB2 and SiC in the composite to those of the individual powders. The point at which the composite lattice parameters started to deviate from those of the powders upon cooling was also determined, providing the temperature at which stresses start to accumulate. The stress values calculated from neutron diffraction and Raman spectroscopy were compared to finite element model predictions.

Short Bio: 

William G. (Bill) Fahrenholtz is a Professor of Ceramic Engineering in the Department of Materials Science and Engineering at the Missouri University of Science and Technology. Dr. Fahrenholtz holds B.S. and M.S. degrees in Ceramic Engineering from the University of Illinois at Urbana-Champaign and a Ph.D. in Chemical Engineering from the University of New Mexico. Dr. Fahrenholtz is known for his research on the processing and characterization of ceramics. His current research projects focus on the processing, microstructure, and properties of ZrB2 and other ultra-high temperature ceramics for aerospace applications as well as the deposition, characterization, and corrosion protection mechanisms of rare-earth based coatings for the corrosion protection of aluminum alloys.

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