Microstructure and phase evolution in spark-plasma-sintered Al86Ni6Y4.5Co2La1.5 glassy alloy |
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Authors: | Ram S. Maurya |
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Affiliation: | 1. Department of Metallurgical &2. Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India |
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Abstract: | Al86Ni6Y4.5Co2La1.5 amorphous powders synthesized after 200 h of mechanical alloying were spark plasma sintered at 25 and 400 MPa at 400 °C for 15 min. The sample sintered at 25 MPa showed precipitation of FCC-Al grains of sub-micron size attributed to a higher amount of localized high-temperature regions which favoured faster long-range atomic diffusion. On the contrary, the 400-MPa sintered sample showed the presence of nanocrystals (5–20 nm) distributed in an amorphous matrix. This is attributed to higher pressure sintering favouring local and short-range atomic redistributions. The higher amount of retained amorphous phase in the 400-MPa sintered sample could be accounted for by a smaller amount of localized high-temperature regions in comparison to those in 25-MPa sintered sample. High-pressure sintering induces shear fracturing and fragmentation of the brittle amorphous particles and provided better surface contact and packing density. The retention of a larger amount of amorphous phase and a higher relative density (96%) contributes to high microhardness (278 Hv) and nanoindentation hardness (3.7 GPa) of the 400-MPa sintered sample. |
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Keywords: | Amorphous alloy mechanical alloying spark plasma sintering crystallization HRTEM |
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