| With the rapid development of automotive, medical, electronic, aerospace,equipment of national defense strategy and other fields, we required performance ofthe materials in the worst working condition to a new higher and more stringent level.In the field of materials structure, metal matrix composites prepared with variousexcellent properties has become an important development direction as new typeapplication and structure materials. Among them, aluminum matrix composites haveattracted much attention in the field of metal matrix composites, because of their highspecific stiffness and high specific strength and other excellent properties. The sizeand distribution of particles have an important influence on its reinforcement effects,with the same phase volume fraction of ceramic particles, if size of the particle issmaller, the amount of particles increases and spacing between the particles decreases,thus these will improve the material performance. In addition, there are a lot ofadvantages using in-situ method to fabricate metal matrix composite, such as cleansurface of particles phase, good interface wettability between particle and matrix,excellent interfacial bonding, smaller size and uniform distribution of particles. In thispaper, using the combustion synthesis and hot pressing sintering densificationtechnology, we fabricate Al matrix composites reinforced with nanometer size andmicrometer size hybrid TiC particles, and we research the effects of the ratio betweencarbon sources, different size of particles on evolution of microstructure andmechanism of strengthening and toughening on metal matrix composite, theseinnovative research works will provide the experimental basis to new preparationtechnologies of aluminum matrix composite reinforced by endogenous nanometer sizeand micrometer size hybrid ceramic particles.In this paper，using the high temperature combustion synthesis added hotpressing sintering densification technology, smelting method combined with remeltingintermediate alloy block, we fabricate the TiC-Al/7075Al matrix composites in Al-Ti-C system and the7075Al-Ti-C system and low ceramic particles volumeTiC-7075Al matrix composite successfully, and we analyze the effect of different ratiobetween carbon sources and the addition of Zn, Cu and Mg elements on organization,wear properties and compression performance of TiC/Al matrix composite, and revealtheir influence mechanism. In this paper, the main results are list as follows:(1) It reveals the influence laws of different carbon source C/CNTs ratio (C,3:1,1:1,1:3and CNTs) on TiC ceramic particles size, the maximum compressive strengthand yield strength of30vol.%TiC/Al composite: compared with carbon black,carbon nanotubes have small size and larger specific surface area, so its areas thatcontact with Al-Ti melt are bigger, carbon atom of carbon nanotubes more easilydiffuse into the Al-Ti melt to react with Al3Ti and fabricate TiC particles,nanotubes can reduce the initial temperature and the highest temperature ofreaction and refine TiC ceramic particles. with ratio of CNTs increasing, size andquantity of micron-sized TiC particles decrease, while size of the nano-sized TiCparticles decrease and the amount increase, which improve the strengtheningeffect of the TiC particles, the maximum compressive strength and yield strengthincrease. When CNTs as carbon source, the maximum compression strength andyield strength of composite material are highest, they are538.3MPa and417.5MPa, respectively, and when C/CNTs=1:1, with the optimal tissue, and mostuniform distribution of micron-size, nano-sized TiC particles, the compositematerial has the best compression fracture strain (28.3%).(2) It reveals that with the addtiaonal of Zn, Cu and Mg elements (5wt.%), the in-situTiC particles sizes decreaces, and maximum engineering compression strengthand yield strength increaces of30vol.%TiC/Al matrix composites with carbonsource C/CNTs=1:1, the reaction can occurs in the lower temperature, so that, thehighest temperature of reaction system decrease, interval time of exothermicreaction at a high temperature are short, and cooling rate increase, resulting indecreases of in-situ ceramic particle sizes and increases in the amout of particles.and the refinement effect: Zn>Mg>Cu. The Zn, Cu and Mg elements reinforcedcomposite through the refinement of TiC particle size, increase the amout of TiCparticles and solution strengthening effect, the strengthening effect: Mg>Cu>Zn,when additional of5wt.%Mg elements, maximum engineering compressionstrength and yield strength of composite reaches the maximum value, they are782.9MPa and612.3MPa respectively.(3) It reveals that with the increase of CNTs ratio among carbon source, which improve the distribution of TiC particles in the organization, the maximumengineering compression strength, yield strength and hardness increase of30vol.%TiC/7075Al matrix composite. Because of with the increase of CNTs,improved the distribution of TiC particles and the organization, when using CNTsas carbon source,30vol.%TiC/7075Al composite compression fracture strain ofthe best (21.7%). In addition, the refinement of TiC particle size, and the amout ofTiC particles increase, which improves the strengthening effect of in-situ TiCparticles, When CNTs as carbon source,30vol.%TiC/7075Al compositemaximum compression strength, yield strength, fracture strain rate andmicro-hardness reaches the maximum value, they are881.7MPa,597.3MPa,21.7%and265.3HV respectively.(4) It reveals that the low ceamic volume (1~3vol.%) TiC/7075Al composites areobviously refined by nano TiC ceramic particles. Nano TiC particles are added tothe metal solution, in the solidification, a small part as a heterogeneous core of-Al grains, most of the TiC ceramic particle are distribute at interface front thesolidification, hinder-Al crystal growth, and refine the-Al crystal morphologyfrom dendritic crystal into equiaxed crystal. size of-Al crystal in the cast-stateTiC/7075Al composites are refined from~92.8um (7075Al alloy) to~62.7m,~29.7um and~28.9um with additional of1vol.%,2vol.%and3vol.%. Whilethe addition of2vol.%and3vol.%TiC,-Al crystal morphology are refinedfrom dendritic crystal into equiaxed crystal in composite at cast-state, it is notconducive to refine these into smaller equiaxed crystal in the extrusion process,with the increase of the amount of TiC ceramic particles, TiC ceramic clusteraround grain boundaries will also increase, they still cluster around grainboundaries after extrusion process, which are not conducive to strengthening theproperties of composite materials. |
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