Densification of Yb-Al-Si-O microcrystalline glass-modified Yb₂Si₂O₇ bond coats below 1450 °C for SiC_f/SiC composites via segmented liquid-phase sintering

Rare-earth disilicate Yb₂Si₂O₇(YbDS) is a promising candidate for environmental barrier coatings (EBCs), but its densification typically requires temperatures above 1500 °C, exceeding the thermal processing limit (∼1450 °C) of SiC_f/SiC composites. In this work, Yb-Al-Si-O (YbAS) microcrystalline glass was introduced and a segmented liquid-phase sintering strategy was proposed to achieve densification under constrained temperatures. YbAS microcrystalline glass forms a liquid phase at 1400-1450 °C, promoting particle rearrangement. However, liquid-phase instability during conventional one-step sintering leads to morphological instability and limited densification. Segmented sintering stabilizes the YbDS skeleton and enables controlled liquid-phase-assisted densification. A dense YbAS-YbDS composite with a relative density exceeding 95% was achieved at 1445 °C with 35 wt% YbAS. A dense bond coat (∼200 μm) was successfully fabricated on SiC_f/SiC composites, exhibiting good interfacial bonding and a distinct pinning effect, with a bonding strength of 19.8 ± 1.5 MPa.