Preparation And Properties Of Carbon Fiber Reinforce Low Expansion Las Glass Ceramics

Carbon fiber reinforced Li₂O-Al₂O₃-SiO₂ glass-ceramic composite was prepared by sol-gel method combined with vacuum hot-pressing sintering.The composition ratio of the raw material was determined by the design ratio of beta-spodumene and betaeucryptite.The influence of raw material ratio,hot-pressing temperature and B4 C doping amount on phase composition,microstructure,room temperature mechanical properties,thermal expansion coefficient and high temperature mechanical properties are mainly studied.Through a series of experimental comparisons,the carbon fiber reinforced LAS glass-ceramic composite with nearly zero thermal expansion coefficient and high temperature mechanical properties was obtained.The main research results are as follows:In LAS glass-ceramic composite materials with different design ratios,the main crystalline phase is equal to that of beta-spodumene.According to Scherrer formula,the grain size is between 29.4 nm and 87.7nm.In the XRD diffraction pattern,beta-eucryptite crystalline phase was found.The ratio of raw materials has little effect on the mechanical properties of composites at room temperature.With 1300? sintering temperature,the flexure strength of the 9H-1X composite is 407.83 ±14.99 MPa.At the same time,the fracture toughness of the 7H-1X composite is 5.36 ±0.59 MPa·m1/2.Under argon atmosphere,the thermal expansion coefficient of different ratio LAS glass-ceramic composite with sintering temperature 1300? increase slowly when text temperature raise up.Among these composite materials,the 7H-1X has the lowest thermal expansion coefficient.Below 600?,the thermal expansion coefficient of the 7H-1X composite is between 10.3².1×10-8 K-1,which is much lower than beta spodumene.In the air atmosphere,the thermal expansion coefficient of the composite material increase at first then decrease.But the thermal expansion coefficient is still less than 10× 10-7·K-1.Under 1000? high temperature and argon atmosphere,flexure strength of the composite material increase first and then decrease when the ratio of beta-spodumene raw material added.The flexure strength of 7H-1X composites under 1000? high temperature and argon atmosphere is 689 MPa,which is 1.9 times higher than flexure strength at room temperature.The high temperature flexure strength of 7H-1X composite was further explored,and it was found that the high temperature flexure strength of the 7H-1X composite first increased and then decreased sharply with the increase of test temperature.When the test temperature is 1100?,the flexure strength of 7H-1X composite is 724.1 MPa,which is the most highest between other temperature.The sintering temperature also has a significant influence on the properties of composite materials.With the increase of sintering temperature,the flexure strength of 7H-1X composite increase slowly,and reach 425.44±35.42 MPa when sintering temperature is 1350?.As for fracture toughness and flexure strength under 1000?,they increase first then decrease when sintering temperature build up.After adding B4 C,the phase composition of 7H-1X composite material did not change significantly.However,it was found from the SEM diagram that,with the increase of B4 C content,the matrix was more evenly coated on the carbon fiber surface.When the amount of B4 C was 3⁴wt%,the flexural strength and fracture toughness both increased.The maximum flexural strength of 4wt% B4C-7H-1X composite was 539.7±112MPa,and the maximum fracture toughness of 3wt% B4C-7H-1X composite was 9.6 ± 0.6 MPa·m1/2.Different content of B4 C reduces the 7H-1X composite's thermal expansion coefficient and the flexural strength under 1000?high temperature.By means of XRD analysis,the beta spodumene?201?crystal plane diffraction peak of 7H-1X composites with different B4 C content after 1000? high temperature testing,except for 3 wt % B4C-7H-1X composites,intensity increased.