April 2001 Influence of Interfaces on Mechanical Behavior and Lifetime of Hi-Nicalon/(PyC/SiC) Sic Fiber Matrix um (b) 2 μm lu HN/(C/SiC)o and HNT/(C/SiC)o minicomposite lifetimes re- ing conditions. This rovided an upper bound for the flects the significant contribution of treated fibers perating on the The lifetimes obtained for the This contribution involves the previously mentioned effect of /(C/SiC)10 minicomposites compared satisfactorily with the fiber/coating interface. However, better resistance to oxidation obtained for the HN/BN/SiC minicomposites of the Hi-Nicalon fibers(slow crack growth) may also influence the lifetime. This influence will be assessed by an investigation of the oxidation resistance of fibers V. Conclusions For comparison purposes, lifetime data for HN/BN/SIC mini composites with BN interphases are also plotted in Fig. 8. These SiC/SiC minicomposites reinforced with treated Hi-Nica lata were reported elsewhere. 9The test conditions were similar fibers possess strong fiber/coating interfaces. When associated to those described in the present paper. However, the applied load with pyrocarbon/silicon carbide(PyC/SiC) nanoscale multilay was not given. This load was estimated from the stress on the fiber ered interphases deposited via pressure-pulsed chemical vapor if fully loaded, which was used by mosher to describe the infiltration(P-CVD), these strong interfaces lead to interestingHN/(C/SiC)10 and HNT/(C/SiC)10 minicomposite lifetimes re￾flects the significant contribution of treated fibers. This contribution involves the previously mentioned effect of the fiber/coating interface. However, better resistance to oxidation of the Hi-Nicalon fibers (slow crack growth) may also influence the lifetime. This influence will be assessed by an investigation of the oxidation resistance of fibers. For comparison purposes, lifetime data for HN/BN/SiC mini￾composites with BN interphases are also plotted in Fig. 8. These data were reported elsewhere.18,19 The test conditions were similar to those described in the present paper. However, the applied load was not given. This load was estimated from the stress on the fiber if fully loaded, which was used by Morsher18 to describe the loading conditions. This stress provided an upper bound for the stress operating on the fiber. The lifetimes obtained for the HNT/(C/SiC)10 minicomposites compared satisfactorily with those obtained for the HN/BN/SiC minicomposites. V. Conclusions SiC/SiC minicomposites reinforced with treated Hi-Nicalon fibers possess strong fiber/coating interfaces. When associated with pyrocarbon/silicon carbide (PyC/SiC)n nanoscale multilay￾ered interphases deposited via pressure-pulsed chemical vapor infiltration (P-CVI), these strong interfaces lead to interesting Fig. 9. SEM images showing interfacial regions in minicomposites after static fatigue tests at 700°C in air: (a) HN/(C/SiC)10, (b) HNT/(C/SiC)10, (c) HN/C, and (d) HNT/C. April 2001 Influence of Interfaces on Mechanical Behavior and Lifetime of Hi-Nicalon/(PyC/SiC)n/SiC 793