Influence of Graphene and Graphene Oxide on Properties of Spark Plasma Sintered Si3N4 Ceramic Matrix

The sintering of ceramic matrix composites is usually carried out by raising the sintering temperature below the melting point of components. Spark plasma sintering (SPS) has the capability to densify ceramics at a relatively low temperature in a very short time. Two different additions, multilayered graphene (MLG) and graphene oxide (GrO), were added to Si3N4 ceramic matrix in various amount; 5 wt% and 30 wt%. The influence of reinforcing phase on final properties of spark plasma sintered Si3N4 composite was studied. The uniaxial-pressure-assisted SPS sintering resulted in a preferential alignment of both type of graphene in the Si3N4 ceramic matrix, leading to highly anisotropic properties with lower mechanical behavior but better tribological and electrical properties

The Effect of the Chemical Composition to the End-Properties of Ceramic Dispersed Strengthened 316L/Y2O3 Composites

In this paper the influence of chemical composition to the end-properties of ceramic dispersed strengthened 316L/Y2O3 composites ceramic has been studied. Two various compositions were studied and compared to reference 316L sintered sample. These two compositions are 316L/0.33 wt% Y2O3 and 316L/1 wt% Y2O3. The high-efficient attrition milling has been used for grain size reduction and oxide distribution in the austenitic matrices. Spark Plasma Sintering (SPS) was used as fast compaction method of the milled powders in order to avoid excessive grain growth. In this work it was found that changing the chemical composition by increase of the Y2O3 addition in the composite matrix improves the milling efficiency, increases the hardness of the 316L and reduces significantly the wear rate

HYBRID ALUMINUM MATRIX COMPOSITES PREPARED BY SPARK PLASMA SINTERING (SPS)

Aluminum Matrix composites have been intensively investigated over a long time due to their unique combination of beneficial properties including low density, high strength to weight ratio, increased hardness, advantageous tribology, corrosion resistance, etc. In the present work we studied the combined effect of various reinforcing phases including Al2O3, SiC, Si3N4 and graphene on the aluminum matrix. The composites were fabricated by powder metallurgical method, in which the powder blend was rapidly sintered by spark plasma sintering. The main conclusion was that hybrid composite can perform better only if the development of porosity is eliminated by improving the wettability of the reinforcing particles

SUBMICRON SIZED SINTERED ODS STEELS PREPARED BY HIGH EFFICIENT ATTRITION MILLING AND SPARK PLASMA SINTERING

ABSTRACTThis paper summarizes recent results for preparation, structural and mechanical investigation of oxide dispersed strengthened steel (ODS). Three commercial steel powders, two austenitic steel and one martensitic powders have been used as starting materials. One of the austenitic powders was used for morphological study during wet milling. The high efficient attrition mills are on the basis of this work assuring grains with nanostructure. The morphological changes during milling steps have been described. It was demonstrated that 4 hours milling in wet atmosphere are enough to realize steel powders with submicron dimensions. An efficient dispersion of nanosized oxides in ODS steels was achieved by employing high efficiency attrition milling. A combined wet and dry milling process of fine ceramic and steel particles has been proposed. Spark Plasma Sintering (SPS) was applied to realize submicron grained steel compacts. Grains with 100 nm mean size have been observed by scanning electron microscopy (SEM) in sintered austenitic ODS. In comparison, the sintered martensitic dry and combined milled ODS microstructure consisted of grain sizes with 100-300 nm in each case.KEYWORDS: ODS Steel, Spark Plasma Sintering (SPS), attrition milling, Nano-oxides, structural and mechanical investigationRESUMECet article résume des résultats récents relatifs à l’élaboration et la caractérisation structurale et mécanique d’un acier renforcé à l'oxyde (nuance appelée souvent ROD/ODS). Trois poudres commerciales d'acier, deux poudres austénitiques et une poudre martensitique ont été utilisées comme matières d’étude. Une des poudres austénitiques a été utilisée pour l'étude morphologique lors du broyage humide. Le broyage à haute efficacité est sur la base de ce travail assurant l’obtention de grains nanostructurés. Les modifications morphologiques au cours des étapes de broyage ont été bien décrites. Il a été démontré que 4 heures de broyage en atmosphère humide sont suffisantes pour réaliser des poudres d'acier de dimensions submicroniques. Une dispersion efficace des nano-oxydes dans les aciers ROD/ODS a été obtenue en utilisant un broyage spécifique. On a proposé un procédé de broyage humide et sec combiné à des particules de céramique et d'acier. La méthode de frittage par étincelle (spark plasma sintering (SPS)) a été appliquée pour élaborer des aciers compacts à grains submicroniques. Des grains ayant une taille moyenne de 100 nm ont été observés par microscopie électronique à balayage (MEB) dans les aciers ROD/ODS austénitiques frittées. En comparaison, la microstructure de l’acier ROD/ODS martensitique frittée a donné des grains de tailles de 100 à 300 nm dans les deux cas de broyage sec et de broyage combiné (humide et sec)

Grassland management in protected areas – implementaton of the EU biodiversity strategy in certain post-communist countries

The post-communist countries of Central-Eastern Europe (CEE) when implementing agricultural and conservation policies, face other challenges than Western European countries: (1) specifc institutional design for each, developed on the remnants of totalitarian system causing difculties for transposing directives; (2) different integration of Natura 2000 network into national protected area governance resulting in slow elaboration of the management plans; (3) farming landscapes were better preserved than in Western Europe, but lacking the continuity of extensive farming so large areas of conservation; and (4) formal protection of sites, lacking in many cases fnancial support. Tis paper summarizes: the historical background of the last century that changed the farming landscapes of the CEE countries and the challenges in the management of protected areas in an unsteady socio-economic and political context. Te results are focusing on the Czech Republic, Slovakia, Hungary and Romania. Two main conclusions are proposed. First, socialism and capitalism slowly abolished family farming, causing people to become disconnected from the landscape – a key element in conservation oriented grassland management. Second, the gaps of knowledge on different aspects of policy implementation sabotage the results of conservation initiatives