Fabrication And Properties Of High Volume Fraction TiC_x/TiB₂/TiC_x-TiB₂Reinforced Aluminum Matrix Composites

With the rapid and sustainable development of the aerospace, defense, industry andother fields in our country, the requirements for the comprehensive properties of thematerials are higher and higher. The metal matrix composites, especially the aluminummatrix composites have got extensive attention due to their special and excellentcomprehensive properties. Metal matrix composites possess attractive thermal stability, highspecific modulus, high specific strength and other thermophysical and mechanical propertiesdue to the combination of the metal properties of high toughness and ductility and theceramic properties of high strength and elastic modulus. Thus, they have been extensivelyapplied in the aerospace, automobile industry and other fields as structure materials.Compared with the whisker and fiber reinforced aluminum matrix composites, the ceramicparticles reinforced aluminum matrix composites have been extensively investigated due theeasy fabrication and low cost. Because the high volume fraction reinforcements usually leadto the defects such as cavities and cracks, which would be detrimental to the properties of thematerials, working on the fabrication of the high volume fraction ceramic particlesreinforced aluminum matrix composites is scarce. Most study is focus on the investigation ofthe low content （0-30%） ceramic reinforced metal matrix composites. It is widelyrecognized that the properties of the metal matrix composites are controlled by the size,volume fraction and distribution of the reinforcements as well as by the microstructure andnature of the matrix–reinforcement interfaces, i.e., high volume fraction of fine, thermallystable reinforcement yields higher mechanical properties of composite. Moreover, the highvolume fraction ceramics reinforced aluminum matrix composites possess lower thermal expansion coefficient, which could be well satisfy the requirements of the ceramic particlereinforced aluminum matrix composites in the field of electronic packaging. Thus, theinvestigation on the mechanical and thermophysical properties of the high volume fractionceramic particles reinforced aluminum matrix composites has important significance.The main approaches of improving the properties of the materials are the selectionoptimization of the fabrication process, element alloying of the matrix and heat treatment,etc. The composites fabricated by the in situ method take the advantages of uniformdistribution of the finer stable ceramic particles and cleaner interfaces between the particlesand matrix, etc. In this paper, we fabricated the TiC_x/Al, TiB₂/Al and TiC_x-TiB₂/Alcomposites by the in situ method of combustion synthesis and hot press consolidation usedthe Al-Ti-C, Al-Ti-B and Al-Ti-B₄C systems, and investigated the effect of type,morphology and content of the ceramics as well as the addition of the elements of Mg andZn on the microstructures and properties of these three in situ composites. The effect of theaddition of Mo, V and Cu on the microstructures and properties of TiB₂/Al composite hasalso been investigated in detail. The influence mechanism of the effect of different alloyingelements addition on compression properties of the three composites has been revealed.Meanwhile, comparative analysis of the strain rate sensitivity of the composites has alsobeen conducted. In addition, the influence mechanism of the effect of ceramic type on theabrasive wear properties, thermal conductivities and thermal expansion properties of the highvolume fraction ceramic particles reinforced aluminum matrix composites has also beenrevealed. The study results are list as follows:（1） It reveals that the addition of Mg could effectively refine the size of the ceramicparticles in the three composites. The heat in the reaction systems is consumed by theevaporation of Mg due to its higher vapor pressure, resulting in decreases in thecombustion temperature and the subsequent ceramic particle sizes. The Zn additioncould also refine the ceramic size in the TiC_x/Al composite, while has little effect on theceramic size in the TiB₂/Al and TiC_x-TiB₂/Al composites. The reason for the refinementof the TiC_xparticles is the consumption of the heat by the evaporation of Zn due to itshigher vapor pressure, resulting in decreases in the combustion temperature in the Al-Ti-C system and the subsequent ceramic particle sizes. The addition of Mo and Vcould both refine the size of TiB₂particles. However, the addition of Cu has little effecton the size of TiB₂particles.（2） It reveals that the compression strength of the TiB₂/Al composites increases first thendecreases with the increase in the content of TiB₂particles, while the fracture straindecreases. The compression strength of the TiC_x-TiB₂/Al composites increases with theincrease in the content of ceramic content, while the fracture strain increases first thendecreases. The addition of Mg could effectively enhance the compression strength of theTiC_x/Al and TiC_x-TiB₂/Al composites and improve the fracture strain of the TiB₂/Alcomposites. The combined addition of Mg and Zn could improve the compressionstrength and fracture strain of the TiC_x/Al composite simultaneously. The addition of Cu,Zn, V and Mo could enhance the compression strength of the TiB₂/Al composite.（3） It reveals that the addition of Mg could effectively enhance the compression strength ofthe three composites due to the solid solution strengthening effect of Mg and therefinement of the size of the ceramics. The addition of V, Mo and Zn could enhance thecompression strength of the TiB₂/Al composite due to the solid solution strengtheningeffect of V, Mo and Zn in the α-Al matrix, respectively. The influence mechanism of theeffect of Cu on the compression properties of the TiB₂/Al composite is the precipitationstrengthening of finer second phase θ′during the heat treatment.（4） It is found that the yield strength of the TiC_x/Al and TiB₂/Al composites increases withthe increase in the strain rate, while the work-hardening capacity decreases. The fracturestrain of the two composites is not significantly influenced by the strain rate. Thecompression strength of the TiC_x/Al composite increases obviously with the increase inthe strain rate; while that of the TiB₂/Al composite is almost not changed. The TiC_x/Alcomposite possesses the stronger strain rate sensitivity than that of the TiB₂/Alcomposite.（5） It reveals that the wear volume loss of the TiC_x/Al, TiB₂/Al and TiC_x-TiB₂/Alcomposites increases with the increase in the applied load. The TiB₂/Al compositepossesses the best wear resistance and the TiC_x/Al composite possesses the worst wear resistance due to the higher hardness of TiB₂particles than that of the TiC_xparticles.With the increase in the temperature, the thermal conductivity of the TiC_x/Al, TiB₂/Aland TiC_x-TiB₂/Al composites all decreases slightly, while the thermal expansioncoefficient increases. The TiC_x-TiB₂/Al composite possesses the highest thermalconductivity which is about140W·m^-1·K^-1. The thermal expansion coefficient ofTiC_x-TiB₂/Al composite is9.5×10^-6/oC at100oC, which is higher than TiB₂/Al, lowerthan the TiC_x/Al composites.The achievements got in this paper offer a new fabricate technology and scientific studyapproach for the aluminum matrix composites, as well as offer a certain theoretical basis forthe performance optimization of the composites. Consequently, it would further satisfy theextensive application of the composites in the structure and engineering field.