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|Title:||Processing and Characterization of Silicon-Carbide Whisker/alumina Matrix Composites|
|Author(s):||Vaughn, Wallace Lee|
|Doctoral Committee Chair(s):||Homeny, Joseph,; Ferber, Mattison K.,|
|Department / Program:||Ceramics Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Engineering, Materials Science|
|Abstract:||The purpose of this investigation was to evaluate the role of interfaces in the fracture toughness behavior of SiC whisker/$\rm Al\sb2O\sb3$ matrix composites. Composites of greater than 99.5% density were produced by hot pressing mixtures of submicron $\rm Al\sb2O\sb3$ powder and SiC whiskers. Two sources of whiskers were utilized, Silar SC-9 whiskers from Arco Metals Co. and SCW # 1-S whiskers from Tateho Chemical Industries Co. Ltd.
The mechanical properties were measured as a function of whisker content. The composites showed a strength increase from 350 MPa for an unreinforced $\rm Al\sb2O\sb3$ to 660 MPa for a 30 volume percent Arco SiC whisker/$\rm Al\sb2O\sb3$ matrix composite. The fracture toughness increased from 4.0 MPa$\sp.\surd$m for the unreinforced alumina to 8.7 MPa$\sp.\surd$m for the Arco SiC whisker/$\rm Al\sb2O\sb3$ matrix composite.
The fracture toughness of the composites varied widely with the surface chemistry of the whiskers. Composites were prepared using the as received Arco and Tateho whiskers and whiskers modified in hydrogen/argon and hydrogen/nitrogen atmospheres. The surface chemistry of the whiskers were measured by XPS techniques. The fracture toughness varied from 4.1 MPa$\sp.\surd$m for the Tateho as received SiC whisker/$\rm Al\sb2O\sb3$ matrix composite to 8.7 MPa$\sp.\surd$m for the Arco as received SiC whisker/$\rm Al\sb2O\sb3$ matrix composite. The modified whisker composites showed intermediate levels of fracture toughness. The level of toughness could be correlated with the elemental surface chemistry of the whiskers.
Several models describing the fracture toughness mechanism were evaluated for the composites studied. The SEM evaluations and fracture toughness data indicate that the most probable toughening mechanism is crack bridging by whiskers that pullout of the matrix.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2014-12-16|