P. Kratochvíl

The cellular substructure of zinc single crystals prepared by the Czochralski method

The dependence of the size of cellular substructure on the rate of growth and the temperature gradient of metal single crystals grown from the melt by the Czochralski or Bridgmann method are the same. The dependence of the size of elongated cells are of the same type as in the case of cells. A hypothesis on the mechanism of production of elongated cells is proposed regarding the influence of orientation of single crystals.

On solid solution hardening in crystals with randomly distributed solute atoms

The temperature dependence of the critical resolved shear stress (CRSS) of solid solution single crystals is explained on the basis of random distribution of solute atoms in the alloy. The calculated temperature dependence of CRSS in a crystal with both isolated solute atoms and their pairs is very similar to the experimentally observed one, i.e., the pronounced temperature independent region, so called “plateau”, appears.

FeAl-based alloys cast in an ultrasound field

Abstract An ultrasonic device was designed to fabricate relatively small (about 0.7 kg) vacuum chill castings of FeAl-based alloys with improved microstructure. The influence of ultrasound on the solidification microstructure of the Fe-40 at.% Al based castings was investigated. The subsequent hot-rolling of such an as-cast alloy was made using a special stainless steel bandage of the casting. This effectively prevents fraying and cracking caused by the thermal shock arising at the surface of the hot casting, when it comes in contact with a cold roller. The efficiency of ultrasonic vacuum casting, based on the influence of the acoustic cavitation on the solidification of the melt, is manifested by a refined microstructure of the prepared iron aluminides Fe-40 at.% Al with addition of C or Zr and B. First results of improved mechanical properties of these alloys are presented and discussed.

Tensile deformation and fracture micromorphology of an Fe–28Al–4Cr–0.1Ce alloy

Abstract Fracture and mechanical properties of a vacuum cast and hot extruded Fe–28Al–4Cr–0.1Ce (at.%) alloy were studied as a function of temperature and strain rate. The tensile deformation tests were carried out at temperatures ranging from 20 to 700°C, at strain rates of ∼10 −4 s −1 and ∼10 −2 s −1 . The effects of strain rate and testing temperature are well recognized in the fractographic features. At room temperature the main fracture mechanism is intergranular decohesion with a certain proportion of transgranular cleavage. With increasing temperature the proportion of transgranular cleavage and ductile dimple fracture gradually increase at the expense of intergranular decohesion. The plastic deformation at each testing temperature is more developed at lower strain rate. The changes in the micromorphology of fracture correlate better with reduction of area than with elongation to fracture. Room temperature ductility of 6.5 and 8.6%, was found for the strain rate of ∼10 −4 s −1 and ∼10 −2 s −1 , respectively.

Solid solution hardening in some copper base alloys

The increase of the critical resolved shear stress of cooper single crystals by additions of In and Co was studied in the temperature independent reagon. The results are explained on the basis of Labuschs theory (Labusch R.: Phys. stat. sol.41 (1970), 659) and are in agreement with measurements on other copper base alloys. The descrepancy between the redistribution of Cd during solidification and the data in the phase diagram ofCu-Cd alloy crystals was observed.

Ordering in the sublattices of Fe3Al during the phase transformation B2↔D03

Abstract The temperature dependence of the iron concentrations in the individual sublattices of hyperstoichiometric binary Fe72Al28 and ternary Fe68Al28Cr4 alloys were obtained from X-ray diffraction data measured in a high temperature vacuum chamber during linear heating around the phase transformation B2↔D03. A method for the processing of the diffraction pattern based on the splitting of the diffraction lines of the structure D03 into three groups is presented. Applying this method it was found that the structure B2 was not well developed in both samples. The maximum value of cC≈0.8 gives SB2 equal to 0.4 and 0.3 for binary and ternary alloy, respectively. The D03-order was not well developed too, because structure D03 arises from the structure B2. D03-ordering, i.e. redistribution of atoms within the sublattices A and B, is given only by the total number of iron atoms in these sublattices before the phase transformation B2↔D03.

The effect of annealing at temperatures near B2⇔D03 transformation in Fe3Al-type alloy on the yield stress

Abstract The changes of the yield stress during annealing at temperatures between 380 and 540°C were measured. These changes were related to the growth of D0 3 ordered domains by the in situ TEM observations. The yield stress is modified by low temperature annealing within the so called stress anomaly.

Dynamical phase analysis along pseudobinary line Ni2CuNi2CuSn

Abstract The ternary system NiCuSn includes some phases with interesting mechanical properties. The first group are the spinodal alloys in the ‘Cu corner’, the second is a group of intermetallics with large lattice parameters such as DO 3 , DO 19 and 2H. The investigation of the pseudobinary phase diagram Ni 2 CuNi 2 CuSn was undertaken to enable in future the preparation of samples with controlled phase composition for further study of mechanical properties of such intermetallics and of related two or, three phase composites. The solvus line and other boundaries were revealed with the help of the so-called dynamical methods based on the measurements of physical quantities during controlled linear change of temperature. The data are related to measurements after annealing at various temperatures and also to determination of the structure after cooling to room temperature. The main methods used were X-ray diffraction (XRD) and analytical electron microscopy (AEM). The results are related elsewhere to measurement of the electrical resistivity and to the determination of solidus and liquidus temperatures by means of differential thermal analysis (DTA).

On the effect of impurities on the critical resolved shear stress of zinc single crystals

The dependence of the critical resolved shear stress of zinc single crystals on the impurity content and the dislocation density is observed. It is shown that the effect of impurities on the critical resolved shear stress is indirect.AbstractИсследуется зависим ость критического на пряжения скольжения цинковых монокристаллов от содержания примес ей и плотности дислок аций. Указано, что влияние примесей на критичес кое напряжение сколь жения имеет косвенный характер.

Der Einfluss von Beimengungen auf die Fasersubstruktur von Zink-Einkristallen

ZusammenfassungAn Einkristallen von Zn mit Beimengungen von Cd oder Cu wurde experimentell die Abhä agigkeit der Größe des Durchmessers der Fasersubstruktur vom Gehalt der Beimengungen untersucht, die aus der Theorie von Rutter und Chalmers [1] hervorgeht. Es wird die Möglichkeit gezeigt, die Größe des Verteilungskoeffizientenk aus den erzielten Ergebnissen abzuschätzen.AbstractНа монокристаллах ци нка с примесью кадмия или меди эксперимент ально проверялась зависимость величин ы диаметра волокон су бструктуры от содерж ания примесей, вытекающая из теории Руттера и Чальмерса. П оказано, что из получе нных результатов можно оценить величи ну коэφφициента расп ределенияk.