Relation between composition, microstructure and oxidation in iron aluminides

The relation between chemical composition, microstructure and oxidation properties has been investigated on various FeAl based alloys, the aim being to induce changes in the microstructure of the compound by selective oxidation of aluminium. Oxidation kinetics that was evaluated on bulk specimens showed that, due to fast diffusion in the alloys, no composition gradient is formed during the aluminium selective oxidation. Accordingly, significant aluminium depletion in the compound could be observed in the thinnest part of oxidised wedge-shape specimens. Another way to obtain samples of variable aluminium content was to prepare diffusion couples with one aluminide and pure iron as end members. These latter specimens have been characterised using electron microscopy and first results of oxidation experiments are presented

The fine structure of the comparative

The paper provides evidence for a more articulated structure of the comparative as compared with the one in Bobaljik (2012). We propose to split up Bobaljik's cmpr head into two distinct heads, C1 and C2. Looking at Czech, Old Church Slavonic and English, we show that this proposal explains a range of facts about suppletion and allomorphy. A crucial ingredient of our analysis is the claim that adjectival roots are not a-categorial, but spell out adjectival functional structure. Specifically, we argue that adjectival roots come in various types, differing in the amount of functional structure they spell out. In order to correctly model the competition between roots, we further introduce a Faithfulness Restriction on Cyclic Override, which allows us to dispense with the Elsewhere Principle

Mechanical Behavior of a Metastable Austenitic Stainless Steel

The mechanical properties of metastable austenitic steel corresponding to the AISI301 were characterized by means of tensile testing and cupping tests. High sensitivity to the strain rate was observed. The fracture mechanism in tensile specimens changed from the combination of cleavage and ductile dimpled rupture at lower strain rates to entire ductile dimpled rupture at higher strain rates. Fracture mechanisms were very different in deep drawn cups. After deep drawing tests, delayed cracking occurred. Main fractographic feature observed in cracked deep drawn cups was the intergranular decohesion. The mechanical behavior was described by a two-phase model incorporating the martensitic transformation. Identification of parameters was carried out on complex loading paths (tensile test, shear test, cyclic loadingunloading)

Mechanical Properties and Fracture of an Intermetallic Alloy Fe-28Al-4Cr-0.1Ce (at %)

Structure, mechanical properties and fracture of a vacuum cast and hot deformed Fe-28Al-4Cr-0.1Ce (at %) alloy were studied. The material was extruded at 1 140 °C and the samples then annealed in the temperature range from 500 to 800 °C, in the D03 and B2 ordered regions. Mechanical properties were evaluated from Vickers hardness and tensile tests. Structure was examined by optical and electron metallography. Besides coarse Ce bearing particles in the matrix, a Cr-Fe precipitate has also been found, mainly on the grain boundaries. Annealing at 700 and 800 °C leads to recovery of the dislocation structure and to the corresponding decrease of the yield stress. The fracture mechanism depends on the thermal treatment of the alloy and on the test temperature. Micromorphology of fracture surfaces was characterized by different fractographic features, including transgranular cleavage, intergranular decohesion and ductile dimple fracture. Maximum room temperature ductility of 4.3 % was achieved after hot extrusion and annealing for 2 h at 700 °C

High Temperature Oxidation of Spark Plasma Sintered and Thermally Sprayed FeAl-Based Iron Aluminides

The presented work deals with the oxidation resistance of spark plasma sintered and thermally sprayed FeAl-based intermetallics. Gas-atomized binary single phase Fe-43(at.%)Al and dual phase Fe-55(at.%)Al powders were used for spark plasma sintering and/or thermal spraying. Coatings were deposited by two different plasma spray technologies - gas and water stabilized plasma guns. The prepared samples were exposed to oxidation in artificial air at 700°C. The mass gain was measured during oxidation at 700C up to 1000 h. Microstructures, phase and chemical compositions of the formed scales were characterized after the exposition by means of scanning electron microscopy, X-ray diffraction and electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy)

High temperature oxidation of spark plasma sintered and thermally sprayed FeAl-based iron aluminides

The presented work deals with the oxidation resistance of spark plasma sintered and thermally sprayed FeAl-based intermetallics. Gas-atomized binary single phase Fe-43(at.%)Al and dual phase Fe-55(at.%)Al powders were used for spark plasma sintering and/or thermal spraying. Coatings were deposited by two different plasma spray technologies - gas and water stabilized plasma guns. The prepared samples were exposed to oxidation in artificial air at 700°C. The mass gain was measured during oxidation at 700C up to 1000 h. Microstructures, phase and chemical compositions of the formed scales were characterized after the exposition by means of scanning electron microscopy, X-ray diffraction and electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy)

Mechanically Alloyed High-entropy Alloys Compacted by Spark Plasma Sintering

Since 2004, materials research got a new impulse that completely changed the formerly chosen approach towards alloy design. Up to these days, the alloys were designed as systems with a main constituent that was further intentionally alloyed with small amounts of elements enhancing the alloy properties. The clearly distinguishable main element was, accordingly to the newly announced concept, completely removed due to the formation of equiatomic CoCrFeNiMn alloy with a single-phase FCC solid solution [1]. This opened a branch of the new field of research, that since then, focused on alloys characterized by a high configurational entropy that stabilizes the formation of disordered solid solutions. As the research of the new material concept proceeded, the formerly mentioned rigid borders became more loosely defined, stating that the content of elements may vary between 5 – 35 at. %, the mixing enthalpy stabilizes the formation of the solid solution while the atomic diameters, as well as valence electron concentration, shall be also considered

Effect of Heating Rate on the Formation of Intermetallics during SHS Process

Self-propagating high-temperature synthesis is a simple and efficient method for the synthesis of various compounds including ceramics and intermetallics. In this process, the compressed mixture of elemental or master alloy powders is ignited or heated to initiate the exothermic reactions leading to the formation of desired compounds. In order to control the process efficiently, the effect of several important parameters has to be determined in each applied alloy system. Previous results showed that those parameters are: initiation temperature, process duration, pressure used for compression and heating rate. This paper is devoted to the description and explanation of the effect of the heating rate on the formation of intermetallics during self-propagating high-temperature synthesis in Fe-Al and Ni-Ti systems. Differential thermal analysis of compressed powder mixtures under various heating conditions and microstructure observation of samples prepared by various heating rates using electric resistance heating and spark plasma sintering were carried out. The effect of heating rates on the formations of intermetallics in studied systems is discussed in this paper