Tailoring the properties of spark plasma sintered SiAlON containing graphene nanoplatelets by using different exfoliation and size reduction techniques: Anisotropic mechanical and thermal properties

SiAlON ceramics are intensively used in different areas but still there is a need to improve the mechanical and thermal properties as well as ease of machinability and reduce the weight. In this study, the effect of graphene nanoplatelets (GNPs) exfoliation and dispersion techniques on the microstructure and properties of SiAlON ceramics were investigated. For this purpose, 2, 4 and 8 wt% GNPs were dispersed by using traditional sonication and newly proposed microfluidization techniques. Then, composites were densified in spark plasma sintering (SPS) furnace. Scanning electron microscope (SEM), x-ray diffraction analyses (XRD) and property measurements were performed in through-plane and in-plane directions. The microfluidization technique found to be more effective than sonication for the exfoliation, size reduction and homogenization of GNPs. Addition of GNPs prepared by both techniques increased the fracture toughness and in-plane direction thermal conductivity whereas decreased the hardness and through-plane direction thermal conductivity of the SiAlON.     

Microstructure and properties of a graphene platelets toughened boron carbide composite ceramic by spark plasma sintering

A kind of B₄C/SiC composite ceramic toughened by graphene platelets and Al was fabricated by spark plasma sintering. The effects of graphene platelets and Al on densification, microstructure and mechanical properties were studied. The sintering temperature was decreased about 125–300?°C with the addition of 3–10?wt% Al. Al can also improve fracture toughness but decrease hardness. The B₄C/SiC composite ceramic with 3?wt%Al and 1.5?wt% graphene platelets sintered at 1825?°C for 5?min had the optimal performances. It was fully densified, and the Vickers hardness and fracture toughness were 30.09?±?0.39?GPa and 5.88?±?0.49?MPa?m^1/2, respectively. The fracture toughness was 25.6% higher than that of the composite without graphene platelets. The toughening mechanism of graphene platelets was also studied. Pulling-out of graphene platelets, crack deflection, bridging and branching contributed to the toughness enhancement of the B₄C-based ceramic.     

Mechanical properties and microstructures of reduced graphene oxide reinforced titanium matrix composites produced by spark plasma sintering and simple shear extrusion

The present research was conducted to improve the mechanical properties of pure titanium, in which a composite reinforced with reduced graphene oxide (RGO) nanosheets was fabricated using spark plasma sintering (SPS) method and was subjected to severe plastic deformation (SPD) process at room temperature with simple shear extrusion (SSE). Its mechanical properties were investigated in terms of tensile and yield strengths applying tension and hardness tests. Moreover, characterizations were accomplished through field emission scanning electron microscopy (FE-SEM) equipped with EDS, light microscopy (LM), and X-ray diffraction (XRD). The obtained results revealed that the grain growth was observed for all the samples in the annealing step, yet the elongation in the highest percentage of RGO was severely limited. Following SSE, the grain size decreased in the severe plastic deformation and consequently, mechanical properties of composite improved. In this regard, the hardness improved from 373 HV after SPS to 536.5 HV after two passes of SSE for composite reinforced by 0.1% RGO; moreover, tensile strength enhanced up to 969 MPa. This nanocomposite might be utilized in diverse fields, particularly in bio applications.     

Preparation of tungsten diboride by a combination of boro/carbothermal reduction process and spark plasma sintering

Submicron tungsten diboride (WB₂) powder was successfully synthesized with the ratio of WO₃:B₄C:C = 2:1.1:5. The effects of carbon sources (carbon black or graphite) and heat treatment temperatures (1100, 1200, 1300 ℃) on the phase composition and microstructure of the as-synthesized WB₂ powder samples were studied. The results showed that ultrafine WB₂ powders with oxygen content of 1.65 wt% and 2.04 wt% were obtained by carbon black and graphite at 1300 ℃, respectively. The relatively density of the as-sintered WB₂ samples achieve ~ 91 % and ~ 87 % without any kind of sintering additive after spark plasma sintering at 1500 °C under 30 MPa for 10 min. The formation mechanism of the WB₂ powders synthesized by boro/carbothermal reduction was proposed and verified by thermodynamic calculation according to the phases present in the powder synthesized at different temperatures.     

In situ thermal reduction of graphene oxide in a styrene–ethylene/butylene–styrene triblock copolymer via melt blending

We report an in situ thermal reduction of graphene oxide (GO) in a styrene–ethylene/butylene–styrene (SEBS) triblock copolymer matrix during a melt‐blending process. A relatively high degree of reduction was achieved by melt‐blending premixed GO/SEBS nanocomposites in a Haake mixer for 25 min at 225 °C. Infrared spectral results revealed the successful thermal reduction of, and the strong adsorption of SEBS on, the graphene sheets. The glass transition temperature of polystyrene (PS) segments in SEBS was enhanced by the incorporation of thermally reduced graphene oxide (TRGO). The resultant TRGO/SEBS nanocomposites were used as a masterbatch to improve the mechanical properties of PS. Both the elongation at break and the flexural strength of PS/SEBS blends were enhanced with the addition of the TRGO. Our demonstration of the in situ thermal reduction of GO via melt blending is a simple, efficient strategy for preparing nanocomposites with well‐dispersed TRGO in the polymer matrix, which could be an important route for large‐scale fabrication of high‐performance graphene/polymer nanocomposites. © 2013 Society of Chemical Industry