Preparation And Properties Of Hot-Pressed SiC/SiC_W-Y₂O₃ Composites Ceramics

Owing to their high strength,high hardness,and excellent abrasion resistance,etc.,silicon carbide（SiC）ceramics have been widely used in machinery,petrochemical industry,and other fields.However,the strong covalent bonding and low self-diffusion coefficient of SiC ceramics make it hard to sinter completely and get a compacted microstructure.Furthermore,high brittleness and low fracture toughness of SiC ceramic make it shows low reliability.In this study,to improve their sinterability and reliability,Y₂O₃and SiC_wincorparated SiC composite ceramics were prepared by hot-pressed（HP）sintering,the effect of Y₂O₃,SiC_w,and sintering temperature on the microstructure,phase composition,mechanical properties,and tribological behaviors of SiC/SiC_w-Y₂O₃composite ceramics were investigated.The materials composition and sintering process were optimized to possesses the optimal comprehensive performance of SiC/SiC_w-Y₂O₃composite ceramics.The main works and conclusions in this paper are as follows:（1）When the hot-pressed sintering temperature is 1800℃,SiC_wcontent is 10vol.%,the effects of Y₂O₃content（0,2.5,5,7.5,and 10 vol.%）on the microstructure,and various properties of SiC/SiC_w-Y₂O₃composite ceramics were studied.With Y₂O₃content increase,the microstructure becomes compacted,and the relative densities straightly increase,which proves that Y₂O₃can promote the densification of SiC composite ceramics.With Y₂O₃content increasing,the mechanical properties and tribological behaviors both increase first and then decrease,the morphology of the wear tracks shows a change from severe matrix cracking and stripping to the microcrack,debris shedding,and its embedded.When Y₂O₃content is 7.5%,the appropriate Y₂O₃additives can improve the microstructure,mechanical properties and wear resistance of SiC composite ceramics.When Y₂O₃content is 10%,It can be found that the microstructure exists excessive Y₂O₃which aggregated at the SiC grain boundaries,it can reduce the mechanical properties and tribological behaviors of SiC composite ceramics,aggravating the stripping phenomenon of SiC worn matrix.（2）When the hot-pressed sintering temperature is 1800℃,Y₂O₃content is 7.5vol.%,the effects of SiC_wcontent（0,5,10,and 15 vol.%）on the microstructure,and various properties of SiC/SiC_w-Y₂O₃composite ceramics were studied.With SiC_w content increase,the microstructure shows an increased amount of whisker pull-out,When SiC_wcontent increase from 0%to 10%,the density and wear resistance show no significant change,and the mechanical properties of SiC composite ceramics have been slightly improved,the wear track profiles gradually become smooth,and the wear morphologies show partly matrix stripping and scratches,belonging to slight abrasive wear.When SiC_wcontent is 15%,the whisker pull-out,bridging,and aggregation can be observed on the fracture morphology,which proves that excessive whisker addition makes whisker pullout,bridging,aggregation,and the obvious pores,the relative density,mechanical properties,and wear resistance of composite ceramics shows decrease than other 3 groups,and the worn surface shows severe cracking and stripping.（3）When Y₂O₃content is 7.5 vol.%,SiC_wcontent is 10 vol.%,the effects of different hot-pressed sintering temperatures（1750,1800,and 1850℃）on the microstructure,and various properties of SiC/SiC_w-Y₂O₃composite ceramics were studied.With the sintering temperature increase,the microstructure became compacted,and relative density gradually increased,proving that increased sintering temperature can promote the densification of SiC composite ceramics.With the sintering temperature increase,the mechanical and tribological properties increase first and then decrease,the morphologies of wear track change from severe fullow and stripping to debris shedding and the expansion of microcrack.When the sintering temperature is1850℃,the grains growth can be observed on the microstructure.The mechanical properties and wear resistance of SiC composite ceramic prepared in 1850℃are lower than in 1800℃,the further stripping of the wear surface can be attributed to the growth and coarsening of the grains.In summary,When Y₂O₃content is 7.5 vol.%,SiC_wcontent is 10 vol.%,the SiC/SiC_w-Y₂O₃composite ceramic fabricated by hot-pressed sintering at 1800℃possesses the optimal comprehensive performance.The relative density,Vickers hardness,fracture toughness,and flexural strength of the SiC/10SiC_w-7.5Y₂O₃composite ceramic are 97.0%,21.6 GPa,7.7 MPa·m^1/2,and 573.2 MPa,respectively,the specific wear rate is 1.6×10⁴μm³/（N·m）.