|
|
SPARK PLASMA SINTERING OF BALL MILLED AND ATOMIZED POWDER BASED ON Fe-Al
Šíma, V. ; Minárik, P. ; Chráska, Tomáš
High-quality compacts were prepared using the spark plasma sintering (SPS) method from powders of similar composition Fe-Al-Zr-B. The properties of the sintered compacts are strongly dependent on the morphology and properties of the feedstock powder. The first powder was obtained by ball milling of the as cast alloy and the second was prepared by atomization under argon atmosphere. The morphology and structure of the two powders are compared and mechanical properties and microstructure of compacts prepared under the same conditions of the SPS procedure are discussed. The milled powder has an irregular morphology and shape of the polycrystalline particles, which have a completely disordered BCC structure with considerable internal stresses, high concentration of structural defects and the presence of aluminum oxide. The atomized powder particles are nearly spherical, polycrystalline with ordered B2 structure, with no significant signs of internal stresses and oxidation. Microhardness of particles of both powders was measured and compared with the microhardness of compact materials, the results of compression tests of compacts at room temperature were compared and discussed.
|
|
|
Microstructure and Properties of Spark Plasma Sintered Al-Zn-Mg-Cu Alloy.
Zyka, J. ; Málek, J. ; Pala, Zdeněk ; Andršová, I. ; Veselý, J.
High entropy alloys are a new material class with promising structural and mechanical properties in wide range of applications. In principle they consist of five or more elements in equimolar concentrations resulting basically in single phase microstructure. TaNbHfZrTi alloy was developed by Senkov for high temperature applications.\nSince all of these elements are biocompatible the TaNbHfZrTi alloy can be investigated as a prospective bio implant material. The alloy was prepared by vacuum arc melting, no annealing treatment was applied. Tensile test and hardness test at room temperature were performed with very good results: yield strength 1155 MPa, rupture strength 1212 MPa, Vickers hardness 359 HV30. Microstructure and fracture morphology was also investigated.
|
|
|
ATOMISTIC SIMULATIONS OF TWIN BOUNDARIES FACETING IN HCP MATERIALS
Ostapovets, Andriy
Deformation twinning is frequently observed in materials with hexagonal crystal lattice. It plays important role in plastic deformation of such materials. Twin regions have often lamellar shape and twin boundaries are usually oriented along invariant planes. However, non-invariant plane twin interfaces are also observed. Occurrence of such interfaces can be connected with interactions between twinning disconnections. Mechanisms of such interactions are discussed on the basis of atomistic simulations.
|
|
|
THE EFFECTS OF HIGH TEMPERATURE HELIUM GAS ON THE FRACTURE BEHAVIOUR OF ODS MA957
Rozumová, L. ; Hojná, A. ; Kalivodová, J. ; Bublíková, P. ; Hadraba, Hynek ; Di Gabriele, F.
Oxide-dispersion-strengthened steel (ODS) MA957 has been studied as a candidate material for Tritium Breeding Blanket for fusion reactors with helium coolant, where temperatures 250-650 degrees C are expected. Helium is one of type as primary coolant in High Temperature Reactor and Gas Cooled Fast Reactor with working temperature 500-1000 degrees C. \n\nThis work presents results of the study of behaviour of ODS (MA957) under influence of high temperature helium environment. Microstructure of the material and the interaction with He was investigated. The average exposure temperature was held at 720 degrees C. Subsequently, the surface changes were determined. Impact testing and material surfaces were studied in detail by means of SEM and TEM microscopy. It is essential to understand the He effect on microstructure and mechanical properties of structural materials since the He embrittlement in TBB may be significant.
|
|
|
The effect of σ-phase formation on long-term durability of SUPER 304H steel
Horváth, J. ; Král, Petr ; Janovec, J. ; Sklenička, Václav
This work presents results of the analysis of phases formed in a SUPER 304H steel during a medium-term static isothermal ageing (675 degrees C/15000 h). The investigations of the precipitates were especially focused on the occurrence of sigma-phase because its formation leads to the serious embrittlement. \nThe evaluation and distribution of brittle sigma-phase were determined on macroscopic level by using light microscopy/colour etching. The microstructure was also investigated on microscopic level by scanning electron microscopes Tescan Lyra 3 and JEOL JSM 5410 equipped by electron backscatter diffraction unit and by transmission electron microscope Jeol 2100F. This work also investigates the effect of sigma-phase formation on the impact strength of an aged state of SUPER 304H steel. For comparison reasons the microstructure and the mechanical properties of the initial as-received) state were also investigated. It was found that the formation of brittle sigma-phase in the aged and therefore degraded microstructure led to the significant decrease of the impact strength. The influence of brittle sigma-phase on long-term durability of the degraded steel regarding its insufficient impact strength is discussed.
|
|
| |
guest ::
