| Carbon fiber reinforced alumina matrix composite(Csf/?-Al2O3)with high temperature resistance,corrosion resistance,high specific strength and high specific mode has been broadly applicated in the field of electronics and machinery.In order to improve alumina matrix reliability,Csf/?-Al2O3 and Cnt/?-Al2O3 composites were prepared by sol-gel with short carbon fiber and carbon nanotubes uniformly dispersed in the alumina ceramic matrix.The effects of Csf and Cnt content and preparation process on the mechanical properties of the composites were studied by means of XRD,SEM,three-point bending and one-sided notched beam method.The high temperature oxidation resistance of the composites was also studied.The main contents include the following aspects:?1?When the short carbon fiber content was 0vol%,5vol%,10vol% and 15vol%,the flexural strength and hardness of Csf/?-Al2O3 composites first increased and reached the peak values,then decrease with the increase of fiber content.However,the fracture toughness and density of the composites increased with the increasing of fiber content.The flexural strength and hardness reacheed maximum value of 336 MPa and 1770 HV at 5 vol% of Csf,respectively.?2?The effects of sintering aid and ball-milled method carbon fiber on the mechanical properties of composites were studied under Csf constant content of 10vol%.The flexural strength of Comp 1?65 MPa?without sintering aid was much lower than that of Csf10 mainly due to its loose microstructure,although the sintering temperature of Comp 1?1600 ??is higher than that of Csf10?1500 ??,indicating that the ball mill method and sintering aid greatly affected the mechanical properties of composites.?3?Effects of oxidation on fracture behavior,microstructure and mechanical properties of the short carbon fiber reinforced ?-Al2O3 composites(Csf5 and Csf10)were studied under 1000 °C in ambient atmosphere for up to 40 h.Weight loss percentages of the Csf/?-Al2O3 composites were increased with oxidation time increasing.Weight loss rate of Csf10 is larger than that of Csf5 during the oxidation.Csf5 exhibits a catastrophic fracture before and after oxidation whereas Csf10 changes from pseudo-plastic fracture to catastrophic fracture failure after 0.5h of oxidation.?4?The flexural strength of Csf/?-Al2O3 composites strongly depended on the retention carbon fiber content.With oxidation time increasing,the retention strength of the Csf/?-Al2O3 composites decreased,and Csf5 shows a higher retention strength than that of Csf10.With the oxidation time increasing,a large amount of small grain characterizes the Csf5 and Csf10 matrices.The substrate grain refinement is ascribed to a process of carbothermal reduction nitridation of Al2O3 evidenced by the formation of Al6O3N4.?5?The flexural strength and fracture toughness of Cnt/?-Al2O3 composites increased with the increase of carbon nanotube content.A constant content of short carbon fiber?5 vol%?was added into Cnt/?-Al2O3,and found that both flexural strength and fracture toughness of Cnt-Csf/?-Al2O3 composites were increased.The flexural strength and fracture toughness of Cnt/?-Al2O3 composites with 5vol% short carbon fiber content were 465 MPa and 7.1 MPa/m2,which were 36% and 13% of Cnt0.6.Meanwhile,the flexural strength of Cnt-Csf/?-Al2O3?465MPa?was 38% of Csf5?336MPa?,indicating that short carbon fiber and carbon nanotubes had significantly reinforcing and toughening effect in alumina. |
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