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Vol.37, No.10, 1238 ~ 1246, 1999
Title
A Study on the Microstructure of Nanocrystalline Al-Ti Alloys Synthesized by Ball Milling in a Hydrogen Atmosphere and Hot Extrusion
문경일Kyoung Il Moon,이경섭Kyung Sub Lee
Abstract
Nanocrystalline Al-Ti alloy powder was produced by reactive ball milling (RBM) in a hydrogen atmosphere. The microstructure of as-RBMed powder was nanocomposite type consisted of nano-sized Al and nano-sized TiH₂. Thermal analysis of as-milled powder showed that the decomposition of TiH₂ and the subsequent formation of Al₃Ti occurred at 370∼480℃. The powder was consolidated by hot extrusion at 500℃. The grain size of as-extruded specimens decreased with decreasing consolidation temperature and shortening consolidation time before hot extrusion. The grain size was about 50∼100㎚ for Al-5at.%Ti and about 100∼200㎚ for Al-10at.%Ti. The hardness of Al-5at.%Ti specimens synthesized by RBM and subsequent hot extrusion wag 25∼75% higher than that of Al-8wt.%Ti alloys produced by mechanical alloying (MA) in Ar atmosphere and hot extrusion. Room temperature and high temperature (300, 400, 500℃) tensile strengths of RBM Al-5at.%Ti alloys were superior to those of MA Al-8wt.%Ti alleys. But the ductility of RBM alloys decreases. It is considered that the deterioration in ductility of nanocomposite Al-Ti alloys was attributed to the increase of the interface area between Al and Al_3Ti and its high energy. SEM fractograph showed that fracture progressed intergranularly.
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