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

We report the mechanical characterization by multiscale indentation of particle reinforced dense 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). The morphology and particle size distribution of powder were evaluated as a function of milling time up to 10 h. Samples from the 10 h milled powders 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 a homogeneous dispersion of Al2O3 nanoparticles in the nickel matrix and effective reinforcing effects, which is the case of Ni/10 vol. % Al2O3 and Ni/15 vol. % Al2O3 samples. The highest hardness (4.68 ± 0.37 GPa) was obtained for Ni/15 vol. % 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/10 vol. % Al2O3 sample. The analysis of the load-depth curves confirmed the reinforcing of the MMNCs as a function of the alumina particle 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.