Characterization and control of the fiber-matrix interface in ceramic ...

94
fracture of individual Nicalon filaments with modifying interlayers and a
thin coating of silicon carbide could be observed in situ.
Lengths of Nicalon yarn were washed in acetone, and while still
immersed in the solvent, individual filaments were collected. The fibers
were placed into the fixtures and affixed with graphite cement.
Thin
films of the precoat materials were deposited at conditions similar to
those used to coat preforms before infiltration (Table 9.1).
A final
coating of Sic was deposited at 1475 K, an MTS flow of 0.165 g/min, a
hydrogen flow of 250 cm3/min, and a pressure of 3 KPa. The reduced
pressure was necessary to produce the smooth uniform deposits needed to
observe the segmented fracturing upon testing.
9.9 Fiber Tensile Strength
Nicalon tows were glued into graphite fixtures and washed in acetone
to remove the sizing.
The yarns were coated with the chosen intermediate
layers using the conditions given in Table 9.1.
The mounted fibers were
heat treated at 1475 K in flowing argon for 25 hours to simulate
infiltration thermal conditions.
Epoxy was added to the empty cavities
of the fixtures, and the fibers were tested while held in tension.
The
strengths of the fibers were calculated from the maximum recorded loads.