Preparation And Toughening Mechanism Of Beta-Sialon Whisker And Carbon Fiber Reinforced Bas Composites

Barium aluminosilicate(Ba Al₂Si₂O₈,BAS)is an advanced glass-ceramic material known for the excellent mechanical property and wear resistance,high hardness and high-temperature stability,which possesses high application value.However,the intrinsic brittleness of the BAS has become the neck problem for its broad application,so related researches have focused on strengthening and toughening of the material.In this work,based on the two toughening methods of whisker reinforcement and fiber reinforcement,two composite materials are prepared with BAS glass-ceramics as the matrix,and the response relationship between internal structure and macro-mechanical properties is established,and the toughening mechanism is studied.Firstly,Barium aluminosilicate(BAS)glass-ceramic consisting of internal?-Sialon whiskers are prepared by the carbothermal reduction nitridation method.The growth of Sialon whiskers follows the VLS growth mechanism,and the carbon source provides growth points for Sialon.Therefore,the carbon source content is the main factor affecting the growth content of the internal Sialon whiskers,in the range of2.5-3.5wt.%carbon content,the fiber content increases with the carbon content,and the whisker diameters are in the range of 50-200 nm and the length reaches the micron level.As the carbon content reaches 3.5wt.%,the internally generated whisker content reaches 26 wt.%,and the Sialon whiskers are closely arranged to form a network structure.Through a significant strengthening and toughening effect,the maximum bending strength can reach 74.5±3.5 MPa through the pressureless sintering process,and the maximum fracture toughness can reach 3.2±0.20 MPa?m^1/2.When the carbon content continue to raise,whiskers tend to aggregate,resulting in an increase in the diameter of the whiskers to 1?m,and a decrease in the Sialon content and toughening effect.It is worth noting that the composite was prepared by pressureless sintering of the powder precursor.The shape of the sintered sample well inherits the shape of the crucible,that is to say,the shape of the sintered container could be copied,and this feature can solve the problem of the size and shape complexity of the hot pressing sintering restrictions,which exhibits strong industrial application potential.In the second part,the modified carbon fiber reinforced BAS glass-ceramic composites dope with Fe³⁺were studied.Through proper content of Fe³⁺doping,the graphitization of the amorphous carbon on the surface of the carbon fiber in the Cf/BAS composite can generate to a pyrolytic graphitic carbon intermediate layer structure.When the Fe³⁺content reaches 1wt.%,an intermediate layer structure with a thickness of about 500 nm is formed on the fiber surface,which can effectively improve the mechanical properties of the material.The bending strength and tensile strength of the sample are improved,which reach 347.33±5.86 MPa and 98.341±5.23MPa,and are increased by 53.5%and 157.89%,compared with no Fe³⁺doped sample.And excessive Fe³⁺addition will corrode the carbon fiber,resulting in small holes on the fiber surface and cause damage to the structure.Based on the research object of C_f/BAS composite material with intermediate layer structure,combined with in-situ loading technology and digital image correlation technology(DIC),the response link of microstructure-local strain-macromechanical properties has been established,and it is more in-depth study the role of the intermediate layer structure in the fracture process.Its function can be summarized as adjusting the bonding strength of the matrix and the fiber,facilitating the transfer of load and the debonding of the fiber;the internal layered pyrolytic graphite hinders the crack and deflects the crack.The internal damage process of the material can be described as:the crack initiates from the thermal defect at the junction of the matrix and the fiber,expands along the direction perpendicular to the fiber orientation,deflection and the initiation of secondary cracks occur at the intermediate layer,and the load is transferred to the interface.After the interface is debonded,the fiber is pulled out from the matrix and bears the main load until it fails...