Phase Evolution-Dependent Nanomechanical Properties of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 Spark Plasma-Sint
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ODUCTION
ALUMINUM-BASED bulk metallic glasses (BMGs) possess more than two times compressive strength and elastic modulus compared to their crystalline counterparts.[1,2] However, Al-based glass forming compositions are off-eutectic in nature leading to low reduced glass transition temperatures (Trg < 0.5).[3,4] Thus, the synthesis of Al-based BMGs requires very high cooling rates (105 to 106 k/s), which restricts the dimension of Al-based BMGs in the micrometer range (~ 250 lm max.).[3,4] Yang et al. derived Al86Ni8Y6 (at. pct) composition based on efficient cluster packing (ECP) model with enhanced glass forming ability (GFA) and improved the thickness to 600 lm via wedge casting technique.[1,5] The GFA and, thus, thickness were further improved to 1 mm diameter via copper mold ASHUTOSH SAHU, SOUMITRA DINDA, and TAPAS LAHA are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. Contact e-mail: [email protected] RAM SAJEEVAN MAURYA is with the Department of Metallurgy Engineering and Materials Science, Indian Institute of Technology Indore, Indore 453552, India. Manuscript submitted March 16, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
casting technique after partially replacing Ni and Y with Co and La, in case of Al86Ni6Y4.5Co2La1.5 (at. pct) composition.[1,5] However, this dimension is still not large enough for structural applications and required further improvement. Consolidation of amorphous powders via advanced sintering techniques such as spark plasma sintering (SPS) gives an alternate to synthesize larger dimension (diameter > 10 mm, thickness > 4 mm) Al-based BMGs.[6–14] Both uniaxial pressure and DC pulse current are applied simultaneously in SPS.[15] Intense joule heating along with arguable generation of plasma waves promote faster sintering with a heating rate up to ~ 1000 C/min.[15] The plasma waves, spark impact pressure, and applied high uniaxial pressure also assist in removing oxide layers from particle surfaces, and thus, good particle bonding is obtained in a short duration.[12–15] However, literature shows that the maximum densification achieved by consolidating Al-based mechanically alloyed amorphous powders via SPS can reach up to ~ 94 pct.[6–10] Wei et al. and Wang et al. have consolidated mechanically alloyed Al75Ni10Ti10Zr5 and Al76Ni8Ti8Zr4Y4 amorphous powders by applying uniaxial pressures of 3 and 4 GPa, respectively, in the temperature range of 450 C to 550 C to achieve complete densification.[16,17] The reason behind difficulty
in densification of Al-based mechanically alloyed amorphous powders can be ascribed to the contaminations present in the powder material, which restrict the viscous flow and diffusion of atoms during sintering.[18] On the other hand, gas atomization is a very costly and complicated process, and thus, synthesizing Al-based bulk amorphous alloys by consolidating gas-atomized amorphous powders would not be that cost effective. Synthesizing amorphous powders by milling amorphous
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