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

PHASE EVOLUTION IN Ni-48 at.% TI SHAPE MEMORY ALLOY PREPARED BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

In Ni rich Ni–Ti alloys, various phases such as hexagonal Ni3Ti, cubic NiTi2 and rhombohedral Ni4Ti3 appear during heat treatment. The presence of these precipitates affects the shape memory effect and superelasticity in an important manner. In this paper we present a study of the phase evolution during annealing of the Ni–48at.%Ti shape memory alloy elaborated by self-propagating high-temperature synthesis (SHS). Morphology and crystallography of the phases were examined by means of light metallography, scanning electron microscopy (SEM), neutron and X-ray diffraction, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Besides the phases mentioned in the\nliterature, a Ni-rich phase with the composition near Ni3Ti2 stoichiometry and having a cubic symmetry was found. This phase develops from Ni4Ti3 particles during slow (furnace) cooling from the temperature of 1000 °C. Its particles have the form of thin platelets coherent with the (B2) NiTi matrix. The orientation relation is either cube-to-cube, [111]P || [115]B2 and (1-10)P || (1-10)B2 or [011]P || [011]B2 and (1-10)P || (1-41)B2.\

Guinier-Preston Platelets Interaction with Dislocations: Study at the Atomic Level

Guinier-Preston zones, in Al-1.7 at % Cu, have been studied by means of high resolution electron microscopy. Most of the zones are atomic monolayers. Bilayers have been also observed. Observations have been carried out under $\langle100\rangle$ and $\langle110\rangle$ orientations. The shearing of a GP zone by an edge dislocation is reported. It is corresponding to one out of the three possible shearing geometries for a given glide plane. It is the one which is essentially at the origin of the chemical hardening of this kind of alloy. The other two variants for a given gliding plane seem to be soft obstacles. It is shown that the sheared GP zone which has been observed is very rich in Cu (close to 100%). We know from our other results that the content in Cu can be included in a range from less than 50% to 100%.Les amas de Guinier-Preston ont été étudiés dans un alliage Al-Cu 1,7 % at. à l'aide de la microscopie électronique à haute résolution. La plupart de ces amas sont des monocouches atomiques. Les échantillons ont été observés selon deux orientations $\langle100\rangle$ et $\langle110\rangle$. Le cisaillement d'un amas par une dislocation coin a été observé. Il correspond à une des trois géométriques possibles. Celle-ci à l'origine du durcissement chimique de cet alliage. Les deux autres familles d'amas pour un même plan de glissement ne semblent pas, ou peu pour l'un d'entre eux, participer au durcissement. À partir de simulations du contraste de cette intersection, on peut déterminer que l'amas cisaillé est très riche en cuivre (près de 100 %). De nos résultats précédents, on peut déduire que la concentration de cuivre dans les amas varie de moins de 50 % à 100 % environ

Effect of Si and Fe on the Recrystallization Response of Al-Mn Alloys with Zr Addition

Al-Mn alloys are often used for the production of automotive heat exchanger fins. During brazing at about 600°C, recrystallization and grain coarsening resulting in the reduction of the strength and possible buckling of the fin can occur. In order to obtain a good recrystallization resistance, the alloy should contain a dense and homogeneous distribution of second phase particles. The effect of Si and Fe addition on the recrystallization response of Al-Mn-Zr alloys direct-chill cast in the laboratory conditions and twin-roll cast in the industrial conditions was examined. Microstructure of the alloys was characterized during downstream processing. The particles were analyzed by light metallography, energy dispersive X-ray spectroscopy and by means of electron backscattering diffraction. Computer assisted quantitative particle analysis was carried out on field emission gun-scanning electron microscope micrographs. Vickers hardness and electrical conductivity were measured at thicker sheets, while at the final gauge of 65 μm the 0.2% proof stress was evaluated. The best recrystallization resistance had twin-roll cast alloy containing 0.5 wt% Si and 0.2 wt% Fe

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)