Study On The Preparation And Properties Of BNNTs-B₄C/TiB₂-B₄C Laminated Ceramic Composite

BNNTs-B₄C tape film and TiB₂ tape film were prepared by aqueous tape casting using Si powder as the sintering aids of matrix layer of boron carbide?B₄C?,boron nitride nanotubes?BNNTs?as the tough agents of matrix layer,PEI as dispersant,CMC as binder and glycerinum as plasticizer.BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite was prepared by hot-pressing sintering through laminating with the hard layer of titanium diboride?TiB₂?at different thickness ratio.The influences of dispersant content and pH value on the viscosity of suspensions were studied.The influences of binder content,R value and milling time on the rheological properties of BNNTs-B₄C slurry and the tensile strength of green tapes were studied.The influences of dispersant content,binder content,R value,solid content and milling time on the rheological properties of TiB₂ slurry were studied.The results indicated that BNNTs-B₄C tape film of high quality could be prepared with the 3wt% PEI as dispersant,7.2wt% CMC as binder,0.9 as R value,3h as milling time.The TiB₂ slurry with high solid content of 55wt%could be prepared with the 2wt% PEI as dispersant,5wt% CMC as binder,0.9 as R value,11 h as milling time.The influences of thickness ratio and component of hard layer on the microstructure and mechanical properties of BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite were studied.The toughening mechanisms of BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite were studied.The phase composition and microstructure of BNNTs-B₄C /TiB₂-B₄C composite were analyzed by XRD and SEM.The bending strength and fracture toughness of laminates were tested.The results showed the best mechanical properties of BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite were achieved at 2040? and 30 MPa for 30 min when the ratio of thickness of base layer and hard layer was 1.8 and the composition of hard layer was 80wt%TiB₂+20wt%B₄C.The flexural strength and fracture toughness reached 598.63 MP and 7.84MPa·m1?2,which increased by 28.82% and 11.68% compared with BNNTs-B₄C/TiB₂ samples.The mechanisms of BNNTs and laminated strtucture toughening BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite were studied.The study showed that the mechanisms of BNNTs toughening matrix layer were the pulling out,bridging of BNNTs,crack deflection and residual stress toughening;the toughening mechanisms of laminated strcture was crack deflection and residual stress toughening.The improvement of the mechanical properties of BNNTs-B₄C/TiB₂-B₄C laminated ceramic composite resulted from the interaction of above all toughening mechanisms.