In situ Formation of Carbide Particles in Liquid Aluminum

Abstract

The in situ formation and dispersion behavior of carbide particles in a liquid aluminum alloy has been investigated to develop a novel technique utilizing the spontaneous reaction among materials for fabricating aluminum matrix composites. Titanium, zirconium and hafnium carbide were in situ generated by the reaction between a liquid aluminum alloy containing the group IV_a element and Al₄C₃ particles. However, the reaction rate decreased in the order of titanium, zirconium and hafnium. On the other hand, the amount of in situ formed carbide in the aluminum alloy system containing group V_a element increased in the order of vanadium, niobium, tantalum depending on the thermodynamical stability of the carbide of each element.
The effects of processing variables, such as the kind and size of raw carbide, the alloying element and processing temperature on the in situ formation rate of TiC and ZrC have been estimated quantitatively. The experimental results were analyzed by the in situ reaction kinetic model based on the assumption that the overall reaction rate was controlled by both the interfacial reaction and the diffusion through the layer of the generated carbide particles. At the initial stage of the formation of TiC, the interfacial reaction rate is mainly controlling step. However, the process is gradually controlled by the diffusion at the later stage. Owing to the formation of fine circular carbide surrounding raw carbide particles, the in situ reaction rate decreased radically in the Al-Zr or Al-Hf system.