| In anti-terror,anti-violence and modern warfare,armor can reduce casualties and damage to combat vehicles,and moreover improve success rate,therefore it is very necessary to study bulletproof armor.It is development trend of armor that is stronger,tougher,lighter,more functional and more efficient.TiB2 as a member of ceramic material can be used as a protective material for heavy armor due to its excellent properties,such as high melting point,high hardness,good chemical stability,good wear resistance and corrosion resistance,good thermal conductivity and electrical conductivity,high elastic modulus.In this paper,submicron TiB2 powders were prepared by boron/carbon thermal reduction method with adding a small amount of nanometre TiB2 as nucleating agent.TiB2-B4C composite ceramics and TiB2-SiC composite ceramics were prepared by pressureless sintering.The morphology and mechanical properties of composite ceramics were also investigated.TiB2-B4C composite ceramics and TiB2-SiC composite ceramics were maded into target plates.Anti-penetration mechanism of composite ceramics was analyzed.The results were as follows:1)Submicron TiB2 powders with TiO2,B4C and carbon black as raw materials were prepared by boron/carbon thermal reduction method.The amounts of B4C and carbon black,calcination temperature and holding time were studied and then phase composition and microstructure of the powders and the growth mechanism of TiB2 crystals were analyzed.It was result that amounts of B4C had a great influence on the phase and microstructure of TiB2 powders.Because B4C could be converted into B2O3 which has a low melting point and high vapor pressure,shortage of boron sources led to low purity of TiB2 powders.TiB2 powders had the highest purity,fine particle size and hexagonal microstructure by excess 20wt%B4C.Carbon black could promote the synthesis of TiB2 powders.TiB2 powder has high purity and fine particle size by the addition of excess 5wt%carbon black.TiB2 powders were effected by calcination temperature and holding time.TiB2 powders contained some oxide of Ti at calcination temperature for 1300?.TiB2 powders was prepared at calcination temperature for 1500?,and the peaks of TiB2 were only detected.The peaks of TiB2 and Ti3O5 were detected at calcination temperature for 1600?.The phases and microstructure of TiB2 powders were also affected by holding time.TiB2 powders contained the peaks of TiB2 and oxides of Ti while the holding time was 30min.The peaks of TiB2 were discovered when the holding time was respectively 60min,90min and 120min.The microstructure of the particles gradually evolved from irregular morphology to hexagonal prism with the holding time increasing.However,the holding time was longer and the particle size of TiB2 powders was larger.The optimum synthesis conditions were as follows:when 60.6wt%TiO2,25.1 wt%B4C and 14.3wt%carbon black synthesized TiB2 powders at 1500? for 60min.TiB2 formed a crystal nucleus and grew into a flake hexagonal prism by thermodynamic and kinetic analysis.2)TiB2-B4C composite ceramics were prepared by pressureless sintering.Green density,mass ratio of TiB2 to B4C,amounts of Ni,sintering temperature and holding time were studied,which affected the phase composition,microstructure and mechanical properties of the ceramics.The high green density was easily the sintering densification.The green density increased rapidly with the initial pressure and holding time increasing.The green density is the optimal for 2.18g/cm3 at initial pressure for 30MPa and holding pressure time for 5min under consideration strength and demoulding of green-pressing.When the mass ratio between TiB2 and B4C was 60:40,TiB2-B4C composite ceramics had the highest density for 95%and the best mechanical properties.The mechanical properties of TiB2 were improved by addition of B4C.Ni as sintering aid was added to further improve the density and mechanical properties of TiB2-B4C composite ceramics.The densification and mechanical properties of composite ceramics increased firstly and then decreased by the addition of 0.5wt%?3.5wt%Ni at sintering temperature for 2100? and holding time for 60min.Because liquid Ni promoted migration of the particles,the densitification and mechanical properties of composite ceramics was improved.The optimum densification and mechanical properties of TiB2-B4C composite ceramics were obtained adding 1.5wt%Ni.Sintering temperature and holding time has an important effect on the densification and mechanical properties of TiB2-B4C composite ceramics.The driving force of sintering was insufficient and the density of sintering was not high at low sintering temperature.The good densification and mechanical properties of composite ceramics due to the strong sintering driving force at 2100?.The mechanical properties decreased due to particles growth at 2150?.The sintered particles grew up with holding time increasing.When the holding time was 60 min,the densification and mechanical properties of the sintered body were the optimal.The hardness,flexural strength and fracture toughness of TiB2-B4C composite ceramics were optimal for 20.4GPa,330MPa and 5.7MPa·m1/2,respectively.Finally,the mechanism of densification and toughness of TiB2-B4C composite ceramics was analyzed.Defects among particles and capillary force could promoted the sintering of composite ceramics.The crack deflection occured in the sintered body to improve its toughness.3)TiB2-SiC composite ceramics were prepared by pressureless sintering.Mass ratio of TiB2 to SiC,amounts of B4C and graphene,sintering temperature and holding time were studied,which affected the phase composition,microstructure and mechanical properties of the ceramics.The relative density,hardness,flexural strength and fracture toughness was the optimal for 95.5%?17.8GPa,211.4MPa and 2.78MPa·m1/2 by the additions of 25wt%SiC.TiB2-SiC composite ceramics with B4C as additives further improve the densification of TiB2 because B4C could remove oxide on the surface of TiB2 and SiC.For the sintering of non-oxide ceramics,oxides prevent their densification.Adding 1wt%B4C,the relative density,hardness,flexural strength and fracture toughness of TiB2-SiC composite ceramics were the optimal for 97.3%,21.6GPa,265.2MPa and 4.8MPa·m1/2.Graphene is a new type of carbon material,which is a kind of two-dimensional honeycomb crystal with a layer of atomic thickness and thinnest crystal and the toughest material in the world now.In order to further improve the properties of TiB2-SiC composite ceramics,graphene powder was added into composite ceramics.The mechanical property of composite ceramics was the optimal with adding 2wt%graphene.The migration between the particles would be blocked and the densification would be decreased due to lamellar graphene.However,due to its lamellar connection between particles,the crack of the sintered body could be deflected.The mechanical properties of the sintered body were improved owing to hindering the further propagation of the crack.The densification of TiB2-SiC composite ceramics firstly increased and then decreased with the sintering temperature increasing,which was the optimal at 2100? for 90min.The hardness,flexural strength and fracture toughness of TiB2-SiC composite ceramics were optimal for 27.8GPa,337.19MPa and 5.7MPa m1/2,respectively.Finally,the mechanism of densification and toughness of TiB2-SiC composite ceramics was analyzed.When B4C removed oxides on the surface of TiB2 and SiC.The densification of TiB2-SiC composite ceramics could be promoted.For mechanical properties,crack deflection and fracture mode changed from intergranular fracture to transgranular fracture mode,which promoted the improvement of mechanical properties.4)The optimal TiB2-B4C composite ceramics and TiB2-SiC composite ceramics were sintered to prepare ceramic bulletproof plates.The thickness of two composite ceramics plates was the same for 10mm and the area of two composite ceramics plates was 205 mm×185 mm.Two composite ceramics plates weren't penetrated after shooting with 12.7mmAPI projectile.Based on the results of the target test,the failure form of ceramic core,back plate and projectile were observed.The deformation of back plate was symmetrical when point of bullet contact was in the center area.However,the deformation of back plate was asymmetric when point of bullet contact deviated from the central area.The mechanical properties of TiB2-SiC composite ceramics was better than that of TiB2-B4C composite ceramics.The process of projectile penetration into ceramic plate was analyzed by projectile velocity and depth of indentation of back plate.It was found that the penetration resistance of TiB2-SiC composite ceramics was better than that of TiB2-B4C composite ceramics. |
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