Effect of consolidation pressure on phase evolution during sintering of mechanically alloyed Al86Ni8Y6 amorphous powders via spark plasma sintering

Mechanically alloyed amorphous Al86Ni8Y6 powders were consolidated by spark plasma sintering (SPS) and the effect of varying sintering pressure (100-400 MPa) on phase transformation and resulting mechanical property was studied. Fully amorphous Al86Ni8Y6 powder obtained via mechanical alloying exhibited good thermal stability with a wide glass transition range of 45 °C. Higher sintering pressure (400 MPa) during SPS resulted in (i) better densification (98%) with improved inter-particle bonding and moreover, (ii) retention of higher volume fraction (~92 vol%) of amorphous phase with lower amount of intermetallic nano-precipitates, indicating improvement in thermal stability of the amorphous phase. Vickers microhardness test showed improvement in hardness with increasing sintering pressure attributed to a larger fraction of the retained amorphous phase and better inter-particle bonding. Nanoindentation test exhibited similar trends in hardness and elastic modulus with wide variation in hardness and elastic modulus values attributed to the distribution of comparatively soft nanocrystalline Al and very hard intermetallic precipitates in the amorphous matrix.