Microstructural And Phase Analysis Of Al Based Bulk Metallic Glass Synthesized By Mechanical alloying And Consecutive Spark Plasma Sintering With Varying Consolidation Pressure
Advanced Materials Letters,
2016, Volume 7, Issue 3, Pages 187-191
In the present work, Al86Ni8Y6 and Al86Ni8La6 powder blends were mechanically alloyed. Al86Ni8Y6 yielded full amorphous structure (150 h); whereas Al86Ni8La6 was partially amorphized after same duration of milling attributed to incomplete dissolution of solute ‘La’ in solvent ‘Al’. DSC experiment showed wider glass transition temperature range of ~ 44 o C (Tx - Tg = 268 o C-224 o C) in Al86Ni8Y6 amorphous powders; whereas no glass transition temperature was detected in Al86Ni8La6 powders. Further, Al86Ni8Y6 amorphous powders were consolidated via spark plasma sintering in the pressure range of 100-400 MPa. XRD and TEM analysis confirmed retention of larger fraction of amorphous phase in higher pressure sintered sample, attributed to suppression of mass transfer diffusion kinetics process. Higher pressure favored short range ordering leading to formation of various intermetallic phases; whereas comparatively faster diffusion in case of low pressure sintering promoted long range ordering forming nanocrystalline FCC-Al. Higher sintering pressure (say 400 MPa) consolidated sample resulted in better densification (~ 99 %) with improved inter-particle bonding and moreover, retention of larger volume fraction (~ 92 vol %) of amorphous phase with intermetallic nano-precipitates. Vickers microhardness test showed improvement in hardness with increasing sintering pressure attributed to higher fraction of retained amorphous phase and better inter-particle bonding.
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