Fabrication And Performance Of C_f/SiC-Al Composites

Aluminum matrix composites reinforced with single-phase silicon carbide（SiC）or carbon fiber（C_f）have the advantages of high specific strength,good wear resistance,high thermal conductivity,high temperature resistance,and low thermal expansion coefficient,and have been widely used in aerospace,Rail transit and new energy vehicles and other fields.C_fhas long/short fibers,and silicon carbide has the form of particles（SiC_p）,fibers（SiC_f）,and three-dimensional through-shape(SiC_int).Using different forms of C_fand SiC hybrid reinforced aluminum matrix composites（C_f/SiC-Al）can not only make up for the shortcomings of the existing C_f/Al and SiC/Al composites,but also fully taking advantage of the complementary relationship of different reinforcing phases opens up a new path for the research of high-performance aluminum matrix composites.However,reports on C_f/SiC-Al composites so far have basically focused on the study of mechanical properties,and detailed data on thermophysical properties,mechanical properties,friction and wear properties,and ablation resistance are scarce.Therefore,multi-dimensional design and systematic study of C_fand SiC hybrid reinforced aluminum matrix composites have important theoretical and practical significance for the development of aluminum matrix composites.In this dissertation,the related basic scientific researches were carried out on the functional design,process improvement,microstructure observation and performance analysis of C_f/SiC-Al hybrid composites.According to the performance requirements of electronic packaging materials,automotive brake disc materials and sweat-resistant ablation materials for aluminum matrix composites,three different C_f/SiC-Al hybrid composites were designed in this paper.The porous preforms of chopped carbon fiber/silicon carbide particles（C_f/SiC_P）and silicon carbide-coated carbon fiber(C_f/SiC_int)were prepared by pyrolysis method,and then three types of C_f/SiC-Al hybrid composites with different functional properties were prepared by vacuum pressure infiltration method.C_f/SiC_p-Al electronic packaging material with reinforcement content of about 60 vol.%,C_f/SiC_p-Al（C_f/SiC_p-Al）brake disc material with different C_fcontent and 30 vol.%SiC content,respectively and ablation resistant C_f/SiC_int-Al composites.The effect of carbon fiber content on the interfacial microstructure and sum of two types of hybrid C_f/SiC_p-Al composites was investigated,and the effect of silicon carbide content on C_f/SiCint preforms and C_f/SiC_int-Al composites was investigated.The results show that the prepared two types of C_f/SiC_p-Al composites have uniform structure and dense material.A small amount of Al₄C₃is formed at the interface between C_fand Al matrix,while the interface between SiC and Al matrix is straight.In the C_f/SiC_int-Al composites,the aluminum matrix is isolated or continuously distributed in the C_f/SiC_intpreforms.The microstructure of the composite material is greatly affected by the content of silicon carbide,and the density decreases with the increase of the content of silicon carbide.The room temperature three-point flexural strength of C_f/SiC_p-Al hybrid composites was studied.The results show that the flexural strength of the two types of C_f/SiC_p-Al hybrid composites increases with the increase of C_fcontent,and the flexural strength is between 336 and 445 MPa.Comparing the mechanical properties of porous C_f/SiC_intpreforms and hybrid composites with C_f/SiC_int-Al,it is found that the aluminum matrix filling the pores of C_f/SiC_intpreforms can improve its mechanical properties.The flexural strength value of the 2D C_f/SiC_int-Al composite material perpendicular to the direction of the carbon cloth layer is 349.8 MPa,which is 1.58times that of the direction parallel to the carbon cloth layer（220.7 MPa）.The 3D C_f/SiC_intpreforms with SiC volume fractions of 12.6%,17%,31%and 42%after pressureless infiltration of ZL102 aluminum alloy,the flexural strength perpendicular to the direction of the carbon cloth layer is greatly increased by 530%and 680%,300%and 10%respectively.The thermophysical properties of C_f/SiC-Al composites were studied.The results show that the thermal expansion coefficient（25～450℃）is lower than 4.5×10^-6K^-1due to the existence of pores and the negative expansion of C_f.Compared with gray iron HT300,cast steel ZG230-450,vermicular iron Ru T380 and forged steel 38Cr Mo V brake disc materials,the thermal expansion coefficient of the C_f/SiC_p30-Al composite material is equivalent to or smaller,and the thermal conductivity is about 3 times that of them.The thermal expansion coefficient and thermal conductivity of C_f/SiC_p-Al composites with a reinforcement content of about 60 vol.%can meet the requirements of electronic packaging materials for thermophysical properties.The dry friction and wear properties of C_f/SiC_p-Al composites with different carbon fiber contents were systematically studied by an on-screen end-face wear tester.The results show that the friction coefficient of the friction pair composed of C_f/SiC_p-Al composite and Wanfu brake pads has a low dependence on braking pressure and a high dependence on braking speed.The friction coefficient of C_f/SiC_p-Al composites is between 0.3 and 0.39.With the increase of carbon fiber content,the wear rate of the friction pair is greatly reduced,and the friction coefficient data band is gradually narrowed.The instantaneous friction of C_f/SiC_p-Al composites Coefficient stability is improved.The friction coefficient of C_f/SiC_p-Al composite material/Wanfu friction pair is slightly lower than that of HT250/Wanfu friction pair,and the comfort and wear resistance are better than HT250/Wanfu friction pair.Oxygen-acetylene flame was used to evaluate the ablation resistance of C_f/SiC-Al composites,and the ablation resistance mechanism was studied.The results show that the 240 s linear ablation rate of C_f/SiC_int-Al composites is between 10^-3mm·s^-1～10^-4mm·s^-1.The anti-ablation mechanism is mainly reflected in the following three aspects:first,the melting endothermic and splash dissipation of the aluminum matrix during the ablation process;second,the thermal barrier and oxygen barrier effects of the self-healing protective film;third,the protective effect of the healing protective film against thermal erosion.