Scanning Transmission Electron Microscopy of SiAlON/Graphene Nano Platelets Composites Obtained with a Novel Homogenization Approach

Abstract

SiAlON ceramics have gained attraction as an engineering material due to their superior mechanical properties, thermal stability, creep resistance and corrosion resistance [1]. Thanks to its properties these ceramics are used for engineering applications like cutting tools, ball bearings and etc, where not only the mechanical properties but also thermal conductivity has significant importance in order to remove produced heat from work zone [2]. Graphene is the most promising candidate to improve thermal conductivity due to its extraordinary thermal properties to overcome heat transfer problem from work zone [3]. Graphene addition can also improve the electrical conductivity of naturally electrical insulator SiAlON ceramics and this can allow electro-discharge machining for shaping and manufacturing. The aim of this study is to characterize the graphene platelets containing SiAlON ceramic matrix composites by using transmission electron microscopy techniques. For this purpose composite samples were prepared by using spark plasma sintering of SiAlON forming powders (Si 3 N 4 , AlN, Al 2 O 3 , CaCO 3 , Y 2 O 3 , and Sm 2 O 3) and 4 wt% graphene flakes exfoliated by microfluidization process with commercial microfluidizer (Microfluidics M-110P) with 30,000 psi constant pump pressure for 16 cycles. Powder mixture was homogenized with ball mill prior to spark plasma sintering at 1950°C under 50MPa for 10 minutes. Transmission electron microscopy sample was prepared by conventional mechanical polishing method followed by Ar-ion beam thinning (Leica Microsystems EM-RES101). Electron transparent samples were examined by using 200kV field emission TEM (JEOL-JEM2100F) in STEM mode with HAADF detector (Model 3000, Fischione) and energy dispersive spectroscopy (EDX JEOL-JED2300T). XRD results, which are not given in here, showed that only β-SiAlON and graphene phases exist after sintering.