Anisotropy of functional properties of SiC composites with GNPs, GO and in-situ formed graphene

Anisotropy of functional properties of SiC composites with GNPs, GO and in-situ formed graphene

Ondrej HanzelRichard SedlákJaroslav SedláčekValéria BizovskáRoman BystrickýVladimír GirmanAlexandra KovalčíkováJán DuszaPavol Šajgalík

Abstract

This paper reports on anisotropy of functional properties of different silicon carbide-graphene composites due to preferential orientation of graphene layers during sintering. Dense silicon carbide/graphene nanoplatelets (SiC/GNPs) and silicon carbide/graphene oxide (SiC/GO) composites were sintered in the presence of yttria (Y2O3) and alumina (Al2O3) sintering additives at 1800 °C in vacuum by the rapid hot pressing (RHP) technique. It is found that electrical conductivity of SiC/GNPs and SiC/GO composites increases significantly in the perpendicular direction to the RHP pressing axis, reached up to 1775 S/m in the case of SiC/GO (for 3.15 wt.% of rGO). Also, thermal diffusivity was found to increase slightly by the addition of GNPs in the SiC/GNPs composites in the perpendicular direction to the RHP pressing axis. But, in the parallel direction, the addition of GNPs showed a negative effect. The formation of graphene domains was observed in reference sample SiC-Y2O3-Al2O3 sintered by RHP, without any addition of graphene. Their presence was confirmed indirectly by increasing electrical conductivity about three orders of magnitude in comparison to the reference sample sintered by conventional hot press (HP). Raman, SEM and TEM analysis were used for direct evidence of presence of graphene domains in RHP reference sample.

Keywords

Graphene nanoplateletsGraphene oxideSilicon carbideFunctional propertiesAnisotropy

 

Mechanical and tribological properties of alumina-MWCNTs composites sintered by rapid hot-pressing

Mechanical and tribological properties of alumina-MWCNTs composites sintered by rapid hot-pressing

Ondrej HanzelFrantišek Lofaj, Jaroslav Sedláček, Margita Kabátová, Monika Tatarková, Pavol Šajgalík

Abstract

Alumina – MWCNTs composites were prepared using a novel approach. This process comprises functionalization of MWCNTs and stabilization of alumina-MWCNTs dispersion with subsequent freezing, which resulted in formation of granulated powders with homogeneous distribution of MWCNTs. The granulated powders were sintered by rapid hot pressing (RHP) at 1550 °C. Relative densities, microstructural analysis, tribological properties, fracture toughness and bending strength of prepared composites were investigated to reveal the effect of MWCNTs. Compared to pure alumina, bending strength and fracture toughness of dense alumina-5 vol.% MWCNTs composites decreased about 37% and 18%, respectively. At higher MWCNT contents, strength remained almost constant and fracture toughness slightly increased. Thus, the positive effect of CNTs on fracture toughness was demonstrated despite their counteracting effect on the refinement of the microstructure.

Keywords

Al2O3 – MWCNT compositesRapid hot pressingTribological propertiesMechanical properties

 

Machinability analysis of multi walled carbon nanotubes filled alumina composites in wire electrical discharge machining process

Machinability analysis of multi walled carbon nanotubes filled alumina composites in wire electrical discharge machining process

Meinam Annebushan Singh, Deba Kumar SarmaOndrej Hanzel, Jaroslav Sedláček, Pavol Šajgalík

Abstract

The approach of machining ceramics with electrical discharge machining process is a great challenge till date due to its low electrical conductivity. Machining is made possible by reinforcing with a conductive phase which increases the overall electrical conductivity. Present work focuses on machining of multi walled carbon nanotubes filled alumina composites. Samples with concentrations ranging from 2.5 to 12.5 vol.% are considered for machining. At lower concentration of 2.5 vol.%, effective machining is not possible. Wire lag phenomena is observed during machining at 5 vol.% sample concentration. Proper machinability is observed with concentration of 7.5 vol.% or more. Also, long micro-cracks are obtained during machining that leads to the workpiece breakage. Spalling effect is observed as the most dominating material removal mechanism. A comparison between alumina composites and conducting metallic alloys were carried out for surface characteristics.

Keywords

AluminaMWCNTWire EDMMRRRa

 

 

 

Microstructure of plasma sprayed Al2O3-3wt% TiO2 coating using freeze granulated powder

Microstructure of plasma sprayed Al2O3-3wt% TiO2 coating using freeze granulated powder

Yiming Yao, Ola Lyckfeldt, Aurélien Tricoire, Dennis Lundström, Uta Klement

Abstract

This study is aiming at controlling the microstructure of plasma sprayed Al2O3-TiO2 composite coatings using freeze granulated powders. As sprayed and sintered Al2O3 + 3wt% TiO2 powders were air plasma sprayed with industry process parameters and compared with a commercial powder. The resulting coatings were investigated with respect to powder flowability, porosity and microstructure of the granules. The results showed that microstructure and melting fraction in the coatings could be tailored with the freeze granulation process and heat treatment conditions.

Keywords

Al2O3-TiO2, Freeze Granulation, Plasma Spray, Microstructure

ECerS2017

Welcome to our stand No 10 at the 15th Conference & Exhibition of the European Ceramic Society ECerS2017 July 9-13, 2017 in Budapest, Hungary. We look forward meeting with you and to discuss how we could support you with Freeze Granulation of your powder material for to make homogeneous granules for the manufacturing of high quality ceramics.