Influence of Heat Treatment on Phases, Microstructures and Mechanical Properties of Laminated Fabric (SiC and Aluminosilicate)/Mullite Matrix Composites (Part 2)

摘要

Influence of heat treatment at 1000-1500 deg C for 24 h on phases, microstructures and mechanical properties was studied for laminated SiC satin or aluminosilicate plain fabric/mullite matrix composites. Composites were produced by a polymer impregnation and pyrolysis method (PIP) using a mullite precursor. A mullite precursor solution of the mixtures of Si(OC_2H_5)_4 and Al(NO_3)_3 was impregnated into the green layered fabric/mullite powder (filler) composite and was pyrolyzed at 500 deg C in air. This polymer impregnation and pyrolysis process was repeated 10 times. The SiC fabric (25-27 vol percent)/mullite matrix composite with a relative density 72-75 percent showed weight loss after heat treatment in an Ar atmosphere (oxygen partial pressure approx 0.75 Pa) at 1300-1500 deg C. This weight loss was due to the formation of volatile SiO gas resulting from the pyrolysis of mullite matrix (3Al_2O_3 centre dot 2SiO_2 (s) -> 3Al_2O_3 (s) + 2SiO (g) + O_2 (g)) and active oxidation of the SiC fiber (SiC (s) + O_2 (g) ->SiO (g) + CO (g)). The heat-treated SiC fabric/mullite matrix composites showed an elastic deformation in the initial stage of the stress-displacement curve, followed by pseudoductility. The strength (186 MPa) after the 1000 deg C heat treatment decreased to 17 MPa after the 1500 deg C heat treatment. The energy of fracture was 1-4 kJ/ m2 in the heat treatment temperature range from 1000 to 1500 deg C.On the other hand, the aluminosilicate fabric (25-30 vol percent )/mullite matrix composite with a relative density 71-73 percent showed no weight loss after heat treatment at 1000-1500 deg C in air. The porosity of the composite decreased with increasing heat treatment temperature because of the densification of the mullite matrix. This composite also showed pseudoductility after the heat treatment. The strength for the composite was slightly enhanced by increasing the heat treatment temperature.