Luminescent Eu3+-doped transparent alumina ceramics with high hardness

The Eu3+-doped transparent aluminas were prepared by wet shaping technique followed by pressureless sintering and hot isostatic pressing. The effect of dopant amount on microstructure, real in-line transmission (RIT), photoluminescence (PL) properties, hardness and fracture behaviour was studied. The RIT decreased with increasing amount of the dopant. The PL emission spectra of Al2O3:Eu3+ ceramics exhibited predominant red light emission with the highest intensity (under 394 nm excitation) for material containing 0.125 at.% of Eu3+ and colour coordinates (0.645, 0.355) comparable with commercial red phosphors. The doping resulted in hardness increase from 26.1 GPa for undoped alumina to 27.6 GPa for Eu-doped sample. The study of fracture surfaces showed predominantly intergranular crack propagation micro-mechanism

Fracture Resistance of 14Cr ODS Steel Exposed to a High Temperature Gas

This paper studies the impact fracture behavior of the 14%Cr Oxide Dispersion Strengthened (ODS) steel (ODM401) after high temperature exposures in helium and air in comparison to the as-received state. A steel bar was produced by mechanical alloying and hot-extrusion at 1150 °C. Further, it was cut into small specimens, which were consequently exposed to air or 99.9% helium in a furnace at 720 °C for 500 h. Impact energy transition curves are shifted towards higher temperatures after the gas exposures. The transition temperatures of the exposed states significantly increase in comparison to the as-received steel by about 40 °C in He and 60 °C in the air. Differences are discussed in terms of microstructure, surface and subsurface Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) observations. The embrittlement was explained as temperature and environmental effects resulting in a decrease of dislocation level, slight change of the particle composition and interface/grain boundary segregations, which consequently affected the nucleation of voids leading to the ductile fracture

A Novel Composite Material Designed from FeSi Powder and Mn 0.8

A design of the novel microcomposite material composed of spherical FeSi particles and Mn0.8Zn0.2Fe2O4 ferrite is reported together with a characterization of basic mechanical and electrical properties. The sol-gel autocombustion method was used for a preparation of Mn0.8Zn0.2Fe2O4 ferrite, which has a spinel-type crystal structure as verified by XRD and TEM analysis. The final microcomposite samples were prepared by a combination of the traditional PM compaction technique supplemented with unconventional microwave sintering process of the prepared green compacts. The composition and distribution of the secondary phase formed by the spinel ferrite were examined by SEM. It is demonstrated that the prepared composite material has a tight arrangement without any significant porosity, which manifests itself through superior mechanical properties (high mechanical hardness, Young modulus, and transverse rupture strength) and specific electric resistivity compared to the related composite materials including resin as the organic binder

Behavior of W-based materials in hot helium gas

Materials for the plasma facing components of future fusion reactors will be subjected to complex loading and various forms of interaction with low Z species (hydrogen isotopes and helium). The divertor components will be among the most intensely loaded, as they will have to transfer heat loads up to 10–20 MW/m2. Besides the plasma facing surface being irradiated by highly energetic deuterium, tritium and helium particles from the burning plasma, the opposite surface will be exposed to a cooling medium at elevated temperature. Helium- and water-based cooling systems are currently being considered. While tungsten is the prime candidate material for the plasma facing components, in the helium-cooled divertor designs, it is also foreseen as a structural material, together with ferritic–martensitic steels. The behavior of these materials in He atmosphere at elevated temperatures has been little studied thus far, and therefore is the subject of the current work. A number of W-based materials (pure tungsten and some of its alloys) prepared by powder metallurgy techniques was exposed to He atmosphere at 720 C and 500 kPa for 500 h. Morphological surface changes were observed by SEM, chemical and phase composition was analyzed by EDS and XRD, respectively. The internal microstructure was observed by a combination of SEM, FIB and TEM techniques. Mechanical properties were determined by instrumented indentation. Some alloys developed a thin oxide layer, in some cases new morphological features were observed, while some samples remained mostly intact. The observed changes are correlated with specific compositions and microstructures

Thermal ageing of Eurofer´97 steel

Ferritic-martensitic reduced activation steel Eurofer´97 of 9Cr-1W(V-Ta) type is leading candidate for structural material for in-vessel and first wall components (outboard blanket) of proposed fusion reactors. The utilization of the Eurofer´97 steels is limited up to a temperature about 550°C. On the other hand the efficiency enhancement of the proposed fusion reactors to the level suitable for energy production is predetermined by increase of temperature in fusion tokamak reactor. The long term exploitation of the steel at high temperatures leads to extensive microstructural changes. The aim of the work is to investigate the influence of long term thermal ageing on fracture properties of Eurofer´97 steel. High thermal ageing of the steel was simulated by step cooling treatment. Charpy impact tests were performed before and after thermal ageing. No evident changes in impact properties have been registered when comparing the properties of the steel in as-received and in step-cooled state

Embrittlement of EUROFER´97 steel due to thermal exposition

Ferritic-martensitic reduced activation steel Eurofer´97 is leading candidate for structural material for in-vessel and first wall components of proposed fusion reactor DEMO. The utilization of the Eurofer´97 steels is limited up to a temperature of about 550°C. The aim of the work is to investigate the influence of long term thermal ageing on fracture properties of Eurofer´97 steel. Short term thermal ageing of the steel was simulated by step cooling treatment. Long term thermal ageing was simulated by isothermal ageing at 550 °C/5000 h. No evident changes in Charpy impact energy have been registered when comparing the properties of the steel in as-received and in step-cooled state. Outstanding embrittlement of the steel was observed after long term isothermal ageing: transition temperatures shift by about 5 °C. Risk of grain boundary weakening by phosphorus segregation is very low while the carbide coarsening could led to outstanding embrittlement of the Eurofer´97 steel

Fracture behaviour of high-chromium 9% and 14% Cr-Mo and Cr-W steels

The paper describes the influence of the microstructure (coming from the chemical composition and extrusion shape) of 9 and 14%Cr- W(Mo)-Ti-Y2O3 ODS steels prepared by mechanical alloying and subsequent hot-extrusion on their impact properties. The chemical composition and corresponding microstructure plays a major role on the impact properties. 9Cr-2W ferritic-martensitic steel present lower upper shelf energy (USE) about 7 J and a lower ductile to brittle transition temperature (DBTT) about -30°C compared to 14Cr-1W ferritic steel one. The transition energy curves of low-activation ferritic 14Cr-1W ODS steel was shifted by about 50°C toward lower temperatures and USE by about 4 J towards higher energies. The extrusion shape also plays a role on the impact properties. The texture caused by the forming process strongly influenced the impact behaviour of the steels. The extensive splitting of the fracture surfaces of plate shaped steel comparing with steels extruded as bar was found