Study On The Gelcasting Of Boron Carbide-Aluminum Composites

Boron carbide is an important ceramic material, with excellent physical and chemical properties, such as a low density (2.52g/cm3) and high melting point (2450℃). However, its two major drawbacks are the low fracture toughness and the very high sintering temperature for pure boron carbide ceramics, which restrict its application. Aluminum has a low density, a low melting temperature and high ductility. Boron carbide- Aluminum composites with low density and high toughness have wide applications. Gelcasting is an in-situ forming process as the synthesis of concepts derived from colloid chemistry, traditional ceramics and polymer chemistry. The process is a promising method for complex shapes of ceramic materials with high ingredient uniformity and high reliability of performance.In this paper, B4C-Al composites were prepared by gelcasting. The effect of different dispersants, solvents, dispersant content, solid content, B4C-Al ratio on the viscosity of slurry were studied. High solid content and low viscosity slurry were prepared. The effects of solid content, B4C-Al ratio, initiator content, monomer ratio and vacuum disposal on the strength of green body were studied. Green body with high strength and homogeneous microstructure were prepared. The drying and sintering of green body were studied. Results came as follows:(1) B4C and Al powders were dispersed into n-octanol or n-butanol as dispersion medium and CH-10S or Tilo-20100 as dispersants, and the viscosity of the B4C-Al slurry is below 1000 mPa.s, and the B4C-Al slurry with good dispersion and solids loading up to 55vol% were obtained.(2) The strength and bulk density of green body increased with the increasing of the solid content. Polymerization time of the slurry decreased with the increasing of initiator. When the ratio of TMPTA/(TMPTA+HDODA) is 10 and the content of the initiator is 3vol%, the strength of green body is the highest. The strength of green body was improved by vacuum deairing. SEM Shows powders in green body compact closely and homogeneously. Particles in the green body are connected by slender polymer networks.(3) Green body was embedded in boron carbide powders and dried at 150℃for 5h. The method cannot only remove organic solvent from green body completely, but also avoid cracking and distorting. The sintered bodies were also obtained at 1300℃for 1h. SEM shows the microstructure is homogeneous. XRD shows the phases in the sintered products were B4C, Al4C3 and Al3BC .