2.2. Characterization

The sectional morphology and chemical binding state of C and C/B₄C coatings on SiC fibers were analyzed respectively by scanning electron microscope (SEM, FEI nano 450, Hillsboro, OR, USA), as well as ESCALAB-250 X-ray photoelectron spectrum (XPS, Waltham, MA, USA) using Al Ka radiation as the X-ray source with an energy of 1 keV. The consolidated composite specimens designated for microstructural observation by SEM were cut along the cross-section, polished, and etched in a 10% HF + 30% HNO₃ solution. Specimens for transmission electron microscope (TEM) observation were cut from the composites in two directions, perpendicular to the cross-section and in the radial direction of the fiber, by FEI Quanta 200 FEG focused ion beam milling (FIB, Hillsboro, OR, USA) [28]. The interfacial reaction products were investigated by field emission JEOL 2010F TEM (Tokyo, Japan,) and the chemical compositions of the sub-layer in interfacial zones were further examined by energy-dispersive X-ray spectrometer (EDS) equipped in TEM. In order to study the kinetics of interfacial reaction, the composite samples were heat treated in vacuum at 800, 850, 900, and 950 °C for 36, 64, 100, 144, and 196 h, respectively. The total thickness of RL for these heat treatment samples was measured by SEM. Nanoindenter (Nano Test Xtreme, Micro Materials, Wrexham, UK) was employed to evaluate the interfacial debonding strength via fiber push-out test with the sample slices with 0.35 ± 0.01 mm thickness [29]. Two tensile samples were prepared for each HIP consolidated specimen with the gauge dimensions of Φ3 × M6, as shown in Figure 2, and the composite material inside the tensile specimen was ~2.8 mm in diameter. The room temperature tensile tests were performed at an extension rate of 1 mm/min, using the Inspekt Table 100 kN model universal testing machine. The fractographies were observed by SEM and laser scanning confocal microscope (LSCM, KEYENCE VK-100, Osaka, Japan).

Tensile specimens of SiC_f/Ti₂AlNb.