Fabrication and properties of a dense SiC NWs‐toughened α‐Si ₃ N ₄ composite coating on porous Si ₃ N ₄ ceramics

Abstract A dense SiC nanowires‐toughened α‐Si ₃ N ₄ coating was prepared using a two‐step technique for protecting porous Si ₃ N ₄ ceramic against mechanical damage, and effect of SiC nanowires content on microstructures and properties of the coating were investigated. XRD, SEM and TEM analysis results revealed that as‐prepared coatings consisted of α‐Si ₃ N ₄ , O'‐Sialon, SiC nanowires and Y–Al–Si–O–N glass phase. Furthermore, Vickers hardness of the coated porous Si ₃ N ₄ ceramics increased gradually with the increasing SiC nanowires content from 0 to 10 wt%, which is attributed to the gradual improvement in intrinsic elastic modulus (E), hardness (H) and H ³ /E ² of the coatings. But, when the SiC nanowires content was 15 wt%, the thickness of the coating became relatively thinner, so that its protective ability was weakened and Vickers hardness started to decrease accordingly. Meanwhile, the assistance of SiC nanowires enhanced fracture toughness of the coatings obviously because SiC nanowires in the coatings can produce various toughening mechanisms during mechanical damage. When the SiC nanowires content was 10 wt%, its fracture toughness reached the maximum value, which was 6.27 ± 0.05 MPa·m ^1/2 .