| ZrC ceramics,a member of ultra high temperature ceramics,have many advantages of high hardness,high melting point,good thermal conductivity and corrosion resistance and so on.However,the low fracture toughness and poor oxidation resistance are still obstacles for ZrC ceramics to be widely used.Based on bionics principle,two kinds of laminated ZrC-SiC matrix composites which used 80 vol.%ZrC-20 vol.%SiC as the substrate layer and 70vol% graphene(or carbon fiber)-10 vol.%ZrC-20 vol.%SiC as the interface layer have been successfully synthesized at 1900? and 30 MPa for 1h by tape casting,stacking and hot pressing in this study.The influence factors of two kinds of composites in preparation process were studied.Meanwhile,the physical properties,mechanical properties,thermal shock resistance and oxidation resistance of the composites were analyzed.In this paper,tape substrates were fabricated by tape casting.The results show that slurry which is fabricated when the bath temperature is between 36~40?,the milling time is between 10~12h,the stirring time is 12 h and the binder content is 20 wt.% is the most suitable for tape casting.The laminated composite material bodies were prepared by tape casting and then removed binders at 500? which had almost no effect on materials.It is due to the CO?CO2 and water will be separated from the body with the increase of temperature.The density of sintered ZrC-SiC based composites which prepared by bionics principle was fine,and the density of the composites which used graphene as interface layer was as high as 98.6%.The fracture toughness of two kinds of composites prepared by 70 vol.% graphene and 70 vol.% carbon fiber as the interface layer were up to 7.64MPa·m1/2 and 8.42 MPa·m1/2,much higher than the 5.07 MPa·m1/2 of the bulk ZrC-SiC composite ceramics.This is due to the fact that the section presents a stepped shape,and the multiple deflections occur in the process of crack propagation which results in an extension of the crack propagation path,weakening of the crack driving force and increase in the fracture work.After water quenching,the thermal shock resistance of the materials was characterized by residual strength.The results show that the thermal shock resistance of two kinds of composites prepared by 70 vol.% graphene and 70 vol.% carbon fiber as the interface layer are basically the same,whose critical thermal shock temperature ? T were 339?and 347?.The bending strength of the two kinds of composites decreased significantly after thermal shock test.It is because that thermal stress concentration which occurs on the surface and inside of the material after thermal shock test lead to many cracks.And the stress in the interior of the materials along the direction of defects and cracks causes fracture of the composites when the material is subjected to external pressure.After 2 hours oxidation at different temperatures,the oxidation experiments show that the weight of the composites increased first and then decreased with the increasing of oxidation temperature when the oxidation temperature is higher than 200?.And it is observed that the oxide thickness increased from 1?m to 10?m.This is because the ability of O to replace the C vacancy becomes stronger with the increasing temperature.Meanwhile,a ZrO2 oxide film formed on the surface of materials prevents further diffusion of oxygen when the oxygen concentration reaches a certain value.And the increase of oxide thickness is related to the oxidation channel generated by the oxidation products of CO and CO2.Owing to the layered structure of composites and the deflections and bridging of cracks by the interface layer,the fracture toughness of two kinds of composites prepared by 70 vol.% graphene and 70 vol.% carbon fiber as the interface layer can still reach to 3.31MPa·m1/2 and 4.01MPa·m1/2 after oxidation at 500? for 2h.And the flexural strength of two kinds of composites decreased to 100 MPa and 155 MPa.This is attributed to a large number of micro cracks were produced inside of the material,and then the crack expands rapidly when the material is subjected to external forces. |
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