Development of SiC Whisker/Chopped SiC Fiber-Reinforced (Ca(0.6), Mg(0.4))Zr4(PO4)6 Ceramic Matrix Composites. Ph.D. Thesis
SiC whisker reinforced (Ca(0.6), Mg(0.4))Zr4(PO4)6 (CMZP) matrix composites containing 10, 20, and 30 vol% whiskers were produced using a glass encapsulated hot isostatic pressing (HIPing) technique. The best HIPing temperature, pressure, and time conditions to optimize composite density and strength were determined to be 1050 deg C, 103 MPa, and 0.25 h. SiC whisker strengthens and toughens CMZP. For 20 and 30 vol% whisker contents, flexural strength is improved from about 90 to 124 and 129 MPa, and fracture toughness is increased by 39% and 74%, respectively. Crack deflection and crack bridging by SiC whisker are found to be two major toughening mechanisms, while the rough surface and irregular shape of SiC whiskers in addition to localized whisker-matrix bonding are factors contributing to strengthening. SiC whisker/CMZP composites containing 20 and 30 vol% whiskers exhibit rising fracture resistance, K{sub R}, from 1.31 and 1.79 MPa-m(exp 1/2) to 2.12 and 2.58 MPa-m(exp 1/2), respectively, with increasing crack length from 0 to 400 microns. The composites also exhibit a higher flexural strength at 858 +/- 1 deg C than at room temperature due to improved whisker-matrix bonding at elevated temperatures. The thermal expansion of HIPed SiC whisker/CMZP composites is comparable to that of HIPed monolithic CMZP. Chopped NICALON(TM) SiC fiber/CMZP composites were prepared by HIPing as well as by hot pressing. The best HIPing conditions for the densification of composites containing 10 and 20 vol% fibers were found to be 1150 deg C/103.4 MPa/0.5 h. An increase of 18% in fracture toughness over monolithic CMZP is attained for the HIPed SiC fiber/CMZP composite containing 20 vol% chopped fibers due to fiber pullout. HIPed SiC fiber/CMZP composites exhibit higher density and strength than hot pressed ones. The strengthening and toughening effects of chopped SiC fiber on CMZP are significantly less than those of SiC whisker.
- Research Organization:
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)
- OSTI ID:
- 218155
- Report Number(s):
- N-96-21313; NIPS-96-34954; TRN: 9621313
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
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