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Material development in the SI sub 3 N sub 4 system using glass encapsulated Hip'ing

Technical Report ·
DOI:https://doi.org/10.2172/7019849· OSTI ID:7019849
This report covers a two-year program to develop fully dense Si{sub 3}N{sub 4} matrix SiC whisker composites with enhanced properties over monolithic Si{sub 3}N{sub 4} materials. The primary goal was to develop a composite with a fracture toughness > 10 MPa{radical}m, capable of using high pressure glass encapsulated HIP'ing. Coating methods were developed to apply thin (<150nm) stoichiometric BN layers to SiC whiskers and also to apply a dual coating of SiC over carbon to the whiskers. Fracture toughness of the composites was determined to increase as the quantity of whiskers (or elongated grains) with their axis perpendicular to the crack plane increased. Of the interface compositions evaluated in this effort, carbon was determined to be the most effective for increasing toughness. The highest toughnesses (6.8--7.0 MPa{radical}m) were obtained with uniaxially aligned carbon coated whiskers. There was no evidence of the carbon coating compromising the oxidation resistance of the composites at 1370{degree}C.
Research Organization:
Oak Ridge National Lab., TN (United States); Norton Co., Northboro, MA (United States). Advanced Ceramics Div.
Sponsoring Organization:
DOE; USDOE, Washington, DC (United States)
DOE Contract Number:
AC05-84OR21400
OSTI ID:
7019849
Report Number(s):
ORNL/Sub-86-95906/2; ON: DE92041381
Country of Publication:
United States
Language:
English