Mechanical Characterization by Multiscale Indentation of Particle Reinforced Nickel-Alumina Metal Matrix Nanocomposites Obtained by High-Kinetic Processing of Ball Milling and Spark Plasma Sintering

Abstract

Mechanical characterization by multiscale indentation of dense particle reinforced Ni/Al2O3 metal matrix nanocomposites (MMNC) obtained by high-kinetic processing (HKP) of ball milling of the powders with a systematic variation of alumina nanoparticles fractions (from 1 to 20 vol.%) and spark plasma sintering (SPS) is here reported. The morphology and particle size distribution of powder were evaluated as a function of milling time at 2 h intervals up to 10 h. Samples from the processed powders after 10 h were densified by SPS. The mechanical properties of the sintered samples were obtained by micro and nanoindentation using diamond tips of Vickers and Berkovich geometry, respectively. The combination of HKP and SPS allowed obtaining a homogeneous dispersion of Al2O3 nanoparticles in the nickel matrix and effective reinforcing effects, which is the particular case of Ni/10 vol.% Al2O3 and Ni/15 vol.% Al2O3 samples. The highest hardness (4.68 ± 0.37 GPa) was obtained for Ni/15vol% Al2O3 MMNC, which is almost twice that of pure nickel (2.45 ± 0.22  GPa) processed at the same conditions. The highest elastic modulus (346 ± 30 GPa) was obtained for the Ni/10vol% Al2O3 sample. The analysis of the load-depth curves confirmed the reinforcing of the MMNCs as a function of the alumina particles content. Discussion of the possible reinforcing mechanisms is also included. The Ni/Al2O3 MMNC sintered specimens exhibit outstanding mechanical property results, which make them candidates for various high-temperature applications.

Keywords: Ni-metal matrix nanocomposite, particle reinforced, multiscale indentation, Spark plasma sintering