Preparation And Characterization Of C_sf Reinforced Fe₃Al/Al₂O₃ Matrix Composites

As a typical material in structural ceramics,Al₂O₃ ceramics have many attractive advantages,including good mechanical strength,high chemical stability,electrical insulation performance and low dielectric loss.They are usually applied to withstand mechanical stress,corrosion,high temperature,insulation and other conditions.However,the application of alumina ceramics in engineering is limited to a great extent due to its low flexural strength,low toughness and high brittleness.In order to improve its brittleness and strength,alumina ceramics are genreally occur in the form of composite materials or multiphase ceramics.At present,the second phase toughening and fiber toughening are more common ways.In order to improve the properties of Fe₃Al/Al₂O₃,Fe₃Al and short carbon fiber(C_sf)were added into Al₂O₃ by sol-gel method.The effects of C_sf modified by Cu coating,SiC coating and PyC-SiC coating on microstructure and properties of Fe₃Al/Al₂O₃ composites was studied.The conclusiongs are as following:1.It was found that high purity Fe₃Al powders could be obtained by 20 hours ball milling and 800?annealing.Cu plate could be used as anode and Cu plate as cathode;Cu plating with uniform surface and diameter of 2?m could be obtained under 2 V and 30 min conditions;The surface of the SiC coating layer with a thickness of 1?m prepared by C_f:Si=1:1 was evenly flattened;Uniformly smooth PyC coating on C₃H₈:N₂=1:3,950?deposition time of 15 min,The surface of the PyC-SiC coating prepared by PyC:Si=1:1 was deposited at 1450?for 3 h without pores and cracks;2.The homogeneous distribution of Fe₃Al powder and C_sf in the matrix could be achieved by sol-gel method.At the same time,a relatively dense Fe₃Al/Al₂O₃composite material could be obtained under the conditions of temperature 1450?,pressure 20 MPa and heat-pressing for 45 min;The addition of Fe₃Al powder can improve the average hardness,flexural strength and fracture toughness of the composite to a certain extent,but the relative density and elastic modulus are reduced.The load-displacement curve of three-point bending changes from linear to non-linear,and the displacement increases.When C_sf is directly added into Fe₃Al/Al₂O₃ matrix,it will react with Fe and other metal elements,and its mechanical properties were lost,so it does not play the role of reinforcement;3.The Fe₃Al/Al₂O₃ composites were reinforced by carbon fiber surface copper plating,SiC deposition and PyC-SiC coating.It was found that the carbon fiber surface coating not only protects the carbon fiber from damage,but also introduces a strengthening mechanism,Cu and C_sf.The coefficient of thermal expansion is different.The interfacial bonding force of the composite is improved during the sintering process,which improves the mechanical properties of the composite.The SiC coating and the PyC-SiC coating are weakly combined with Al₂O₃.The debonding-extraction of the fiber and the fiber bridge The nonlinear stress relief caused by the toughening mechanism is an important factor for nonlinear variation,and provides the progressive failure mechanism required for toughening,so that the density and hardness of the composite are improved,and the flexural strength and fracture toughness are improved.The change of fiber content firstly increased and then decreased,while the load-displacement curve of three-point bending changed obviously from linear to nonlinear,and obvious nonlinear characteristics appeared.