A study on the microstructural evolution of Al-25 at. pct V-12.5 at. pct M (M = Cu, Ni, Mn) powders by planetary ball mi
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5/5/04
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A Study on the Microstructural Evolution of Al-25 At. pct V-12.5 At. pct M (M ⴝ Cu, Ni, Mn) Powders by Planetary Ball Milling KEUN YOUNG CHANG, KYOUNG IL MOON, and KYUNG SUB LEE The alloying behavior of Al-25 at. pct V-12.5 at. pct M (M ⫽ Cu, Ni, Mn) by planetary ball milling of elemental powders hours as been investigated in this study. In Al3V binary system, an amorphous phase was produced after 6 hours and the amorphous phase was mechanically crystallized after 20 hours. The large difference in the diffusivities between Al and V atoms in Al matrix results in the formation of the amorphous phase when the homogeneous distribution of all the elements in a powder was achieved at 6 hours. According to thermal analyses, the amorphous phase in the binary Al3V was crystallized at 350 °C. The addition of ternary elements (Cu, Ni, Mn) increased the activation energy for the crystallization to D022 phase by interfering with the diffusion process. Therefore, ternary element addition improved the thermal stability of the amorphous structures. The amorphous phase in the 12.5 at. pct Ni added Al3V was crystallized to D022 phase at 540 °C. The mechanical crystallization of the amorphous phase in the ternary element–added Al-V system either occurred later or was not observed during ball milling up to 100 hours. It is thought that the amorphous intermetallic compacts could be produced more easily in ternary element–added alloys by using an advanced consolidation method.
I.
INTRODUCTION
THE group IVA and VA transition metal trialuminides are very useful structural materials for applications in the aerospace industry owing to their low density, high specific strength and good oxidation, and corrosion resistance.[1,2,3] These materials, however, have an inherent problem of intermetallics—their lack of ductility at low temperatures. Three possible reasons have been proposed for the low ductility of the intermetallics:[4] 1. lack of a sufficient number of equivalent slip systems owing to their noncubic structure with low crystal symmetry; 2. intrinsic and extrinsic grain boundary weakness (such as low grain boundary cohesive strength); and 3. low cleavage strength. The group V A transition metal trialuminides have a stable D022 phase with tetragonal structure. Therefore, their poor ductility at low temperature is attributed to an insufficient number of equivalent slip systems. The L12 structure that is so closely related to D022 structure[5] has five independent slip systems with higher crystal symmetry. Many efforts have been made to synthesize Al3X trialuminide with a cubic L12 phase.[6,7,8] It has been reported that ternary element addition to Al3Ti and Al3Zr is known to increase the possibility to produce and stabilize the cubic L12 structure.[6,7,8] However, tests on cast ternary alloys having the L1 2 structure have shown that the
increase of symmetry alone is not enough to significantly increase the tensile ductility of these compounds.[9,10] In Al-V systems, there have been few reports about the p
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