Study and suppression of the microstructural anisotropy generated during the consolidation of a carbonyl iron powder by field-assisted hot pressing

Published OnlineA spherical carbonyl iron powder was consolidated by the field-assisted hot pressing technique using graphite tools at two different temperatures, both above the austenitizing temperature. The microstructures obtained exhibited a compositional gradient in carbon along the consolidated material. Thus, the outer rim of the cylindrical samples was composed of cementite and pearlite that gradually turned to pearlite, leading to a fully ferritic microstructure at the core of the sample. The increase in the temperature has led to a higher introduction of carbon within the sample. The interposition of a thin tungsten foil between the graphite die/punches and the powders has significantly reduced the diffusion of the carbon through the iron matrix and has suppressed the microstructural anisotropy.Publicad

Korrosionsmechanismen von Chrom/Nickelschmelzen an Verdampferwerkstoffen: Poster zur DKG Tagung, Hermsdorf, 22.-24.03.2010

Die Korrosionsmechanismen an konventionellen hBN/TiB2 Aluminiumverdampfermaterialien durch Chrom/Nickelschmelzen werden im Vergleich zu neu entwickelten Werstoffen auf Basis des gleichen Materialsystems verglichen und der chemische und zeitliche Ablauf der Korrosion durch Chrom/Nickel beschrieben

Preparation and properties of B6O/TiB2-composites

B 6O/TiB 2 composites with varying compositions were produced by FAST/SPS at temperatures between 1850 and 1900°C following a non-reactive or a reactive sintering route. The densification, phase and microstructure formation and the mechanical and thermal properties were investigated. The comparison to an also investigated pure B 6O material showed that the addition of TiB 2 in a non-reactive sintering route promotes the B 6O densification. Further improvement was obtained by sintering reactive B-TiO 2 mixtures which also results in materials with a finer grain size and thus in enhanced mechanical properties. The fracture toughness was significantly improved in all composites and is up to 4.0MPam 1/2 (SEVNB) and 2.6-5.0MPam 1/2 (IF method) while simultaneously a high hardness of up to 36GPa (HV 0.4) and 28GPa (HV 5) could be preserved. The high temperature properties at 1000°C of hardness, thermal conductivity and CTE were up to 20GPa, 18W/mK and 6.63×10 -6/K, respectively

Field-assisted densification of superhard B6O materials with Y2O3/Al2O3 addition

B6O is a possible candidate of superhard materials with a hardness of 45 GPa measured on single crystals. Up to now, densification of these materials was only possible at high pressure. However, recently it was found that different oxides can be utilized as effective sintering additives. In this work the effect of addition of Y2O3/Al2O3 on the densification behaviour as a function of applied pressure, its microstructure evolution, and resulting mechanical properties were investigated. A strong dependence of the densification with increasing pressure was found. The material revealed characteristic triple junctions filled with amorphous residue composed of B2O3, Al2O3 and Y2O3, while no amorphous grain-boundary films were observed along internal interfaces. Mechanical testing revealed on average hardness of 33 GPa, a fracture toughness of 4 MPam1/2, and a strength value of 500 MPa

Field-Assisted Sintering Technology / Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments

Field-assisted sintering technology/Spark plasma sintering is a low voltage, direct current (DC) pulsed current activated, pressure-assisted sintering, and synthesis technique, which has been widely applied for materials processing in the recent years. After a description of its working principles and historical background, mechanical, thermal, electrical effects in FAST/SPS are presented along with the role of atmosphere. A selection of successful materials development including refractory materials, nanocrystalline functional ceramics, graded, and non-equilibrium materials is then discussed. Finally, technological aspects (advanced tool concepts, temperature measurement, finite element simulations) are covered