Microstructure and nanoindentation analysis of Mg-SiC nanocomposite powders synthesized by mechanical milling

Mixtures of magnesium powder and SiC nanoparticles at various volume fractions were mechanically milled to produce nanocrystalline Mg-SiC nanocomposites. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the milled powders. The microstructural evidences revealed that mechanical milling is a proper method to achieve a uniform distribution of the SiC nanoparticles, even up to 10% in the Mg matrix. Based on the results, higher volume fraction of the SiC nanoparticles raise the value of measured microstrain and reduce the crystallite size of the Mg matrix. The TEM results pointed to the fact that no deformation twinning takes place in the nano-structured Mg matrix even after severe plastic deformation through mechanical milling and the presence of hard SiC nanoparticles up to 10 vol%. The effects of nanoparticle volume fraction on mechanical properties of the milled Mg-SiC nanocomposites were evaluated using nanoindentation tests. The results clearly showed a significant enhancement of nanohardness and reduced elastic modulus in the milled powders compared to that of the reference material namely as-received pure magnesium. It was found that the SiC nanoparticles (even up to 10 vol%), well distributed in the magnesium matrix, remarkably improve the reduced elastic modulus and nanohardness of the nanocomposite powders.