Volume 92, Issue 4

Results of investigations on the determination of properties of 〈100〉-split interstitials and vacancies in many different model stainless steels, in 316L, in Ni–Cr and Fe–Ni alloys and in pure Ni are reported. Results obtained recently in our laboratory and in many different laboratories all over the world during the last 35 years are presented and discussed. It is shown that many different microstructures can develop in all the investigated alloy materials, which are formed by migrating 〈100〉-split interstitials and vacancies after plastic deformation, after quenching, and after and during irradiation with high energy particles. The microstructure was determined by various diffraction experiments and the kinetics of the evolution of the microstructure was determined by electrical resistivity techniques. The self-diffusion coefficients in model stainless steels and in Ni were determined by means of radio-active tracers. It was found that 〈100〉-split interstitials and vacancies migrate in all the investigated materials in recovery stages III and IV, respectively, and that the activation energies of migration of 〈100〉-split interstitials and vacancies in these steels are E1IM=(0.9±0.1) eV$E_{1I}^M = (0.9 \pm 0.1)\,{\rm{eV}}$ and E1VM=(1.15±0.1) eV$E_{1V}^M = (1.15 \pm 0.1)\,{\rm{eV}}$, varying slightly from material to material.

A consistent thermodynamic data set for the Ru–Si system is obtained by a computer-aided least-squares method applied to the experimental phase diagram and thermodynamic data. The liquid phase is described by the Redlich-Kister formula. All of the compounds, Ru 2 Si, Ru 4 Si 3 , RuSi, and Ru 2 Si 3 , are treated as stoichiometric phases. Comparisons between the calculated and measured phase diagram and thermodynamic quantities show that all of the accurate experimental information is well accounted for by the thermodynamic description.

The phase diagram of the In–Sb–Sn ternary system was studied by X-ray powder diffraction analysis and differential scanning calorimetry. 123 alloys were elaborated on 9 vertical sections. Four transition peritectic reactions (U-type), one peritectic ternary reaction (P-type), one ternary eutectoid reaction (E-type) and one ternary eutectic reaction (E-type) were characterized.

The excess enthalpies of liquid alloys in the ternary systems Ag–Ge–Te and Ag–Sn–Te have been determined in a heat flow calorimeter for three sections Ag–Ge–Te with y = 0.2, 0.5, and 0.8 at 1213 K and for the section Ag 0.5 Sn 0.5 –Te at 973, 1073, and 1173 K to complete recent measurements. The excess enthalpies of both systems are exothermic and decrease with increasing temperature by the dissociation of telluride associates. The enthalpy surface of both systems is determined by a valley of minima from Ag 2 Te to GeTe and SnTe, respectively. Preceding the analyses of the ternary excess enthalpies the thermody-namic functions of the systems Ag–Ge and Ag–Sn were reoptimized with the Lukas program using the association model of Sommer for the description of the melt. Ternary interactions were taken into account for the analyses of the excess enthalpies of the liquid Ag–Ge–Te and Ag–Sn–Te alloys.

The development of a method for determining phase transformation kinetics for a multistep solid-state transformation from a dilatation curve is described. The dilatation of steels during a continuous cooling or an isothermal holding of an austenite is analyzed. A model is proposed in which the transient dilatation is calculated based on the fraction of the phases present. The model can be applied to calculate the phase transformation kinetics from a dilatation curve of a hypo-eutectoid steel. After verification by comparison with experimental results for an interstitial-free steel, the model is used to calculate the transformation kinetics indicated by the dilatation curves of a bainitic grade steel. Excellent agreement between the model and experiments has been obtained.

Ein Vergleich von Reaktionskinetik und Ausscheidungsmodus der σ-Phasenbildung im Ferrit von zwei rostfreien Stählen, und zwar einem rein ferritischen (W.-Nr. 1.4575) und einem ferritisch-austentitischen Duplex-Stahl (W.-Nr. 1.4462) mit nahezu gleicher chemischer Zusammensetzung der Ferritphase wurde durchgeführt. Während im Duplex-Stahl eine eutektoide Umwandlung der Ferritphase in σ-Phase und Austenit auftrat, erfolgte im Superferrit eine traditionelle Ausscheidung der σ-Phase. Es wurden Zeit-Temperatur-Umwandlungs(ZTU)-Schaubilder für den Beginn der σ-Phasenbildung in den Ferritphasen beider Stähle bestimmt. Die σ-Phasenausscheidung verlief um etwa zwei Größenordnungen schneller im Duplex-Stahl als im Superferrit. Die Ausscheidungsnasen der ZTU-Kurven waren gleichzeitig zu höheren Temperaturen verschoben; ebenso lagen die oberen Ausscheidungstemperaturen höher als im Superferrit. Durch Kaltumformung wurde in beiden Stählen der Ausscheidungsbeginn beschleunigt.

The application of microalloying, controlled rolling and controlled cooling has been the most important achievements in the metallurgical industry in the last 30 years. Microstructure and mechanical properties of steels are greatly improved by applying these technologies. This application resulted in significant progress in the production and application of high-strength low-alloy steel. In the present investigation, the effect of different rolling schedules on the microstructure and mechanical properties of grade X60 API steel has been studied. The tensile and impact properties of this steel are related to the microstructure introduced by various rolling schedules. It has been found that it is possible to obtain a steel with 25 % elongation to fracture, 560 MPa yield strength, 650 MPa tensile strength, and an impact transition temperature of -35°C through thermomechanical rolling process.

Depending on the chemical make-up of the waste stream and operational parameters, a variety of high temperature corrosive environments are generated in the incinerator. As corrosion of industrial equipments is essentially due to high content of sulfur and chlorine in the combustion gas, this study is focused on the interpretation of degradations of pure iron in experimental air environment containing 1000 ppm of HCl and 100 ppm of SO 2 . Thermochemical calculations were used to estimate the role of these corrosive elements considering chemical potential diagrams and stability paths in pseudo-binary diagrams involving iron and the corrosive atmosphere. The influence of chlorine has been described by the “active corrosion” mechanism proposed by Grabke and confirmed by our calculations. The role of sulfur has been pointed by its “cycle” leading to the formation of eutectic metallic tri-sulfates, promoting a liquid phase corrosion type in the range of the industrial temperatures.

This paper reports a Mössbauer spectroscopic study of Fe 80 – x Ni x Cr 20 [19 ≤ x (at.%) ≤ 30] alloys in the temperature range 10–295 K. From the temperature variation of the center shift, the Debye temperatures of different alloys have been calculated and the lattice dynamics of the system has been discussed. From the temperature dependence of the relative broadening of the full-width-at-half-maximum, the relaxation nature of the system has also been discussed.

A polluted Zn–22 wt.% Al surface layer was found to turn out to be clean and lustrous after superplastic blowing, which has never been observed in the other superplastic alloys. From the results of thermal and chemical analyses, an explanation for such a self-cleaning effect is proposed, which is based on the evaporation phenomenon of zinc as corroborated by various accommodation theories on grain boundary sliding, such as subsurface grain emergence, sliding interface explosion, and grain separation and rotation. The submicron grain size in this superplastic alloy should also play an important role for such a self-cleaning effect to take place.

The acoustic emission (AE) method has been applied for the first time in the investigations of the strain localization phenomena (shear banding) occurring in copper and silver as well as in copper-aluminium alloy single crystals under channel-die compression in plane state of strain at liquid nitrogen temperature (77 K). It has been found that the rate of AE events is correlated with the transition from the twinning mode to the shear band mode of the deformation process. Moreover, it has been observed that pronounced correlations between the AE behaviour and the nearly periodic drops of the external force are related with the beginning of shear bands formation. The presented results are discussed in terms of both dislocation acceleration and annihilation processes accompanied by the operation of the Frank-Read sources as well as accompanied by the escape of dislocations from the crystal to a free surface, including the partial dislocations engaged during the operation of the pole mechanism of twinning. Moreover, it has been pointed out that the dislocation annihilation and the step formation on a free surface can be also considered in terms of the dynamics of dislocation kinks treated as the solitary wave processes.

An approach was developed for observation of the wetting behavior of molten magnesium on solid substrates by pre-filling magnesium vapor in the reaction chamber from a special magnesium evaporation source to control its evaporation from the sessile drop. Based on this approach, the wetting behavior of four kinds of substrates (alumina, iron, SUS316 and SUS430 stainless steel) by molten magnesium was investigated. The results showed that the molten magnesium drop revealed a spreading tendency during the initial wetting process stages on alumina and SUS316 stainless steel solid substrate and gave a good wettability of 89° and 71°, respectively, for the initial contact angle at 973 K. In these wetting processes, there were two distinct behaviors of the advancing wetting because of the good wettability of molten magnesium and the subsequent drop-receding, resulting from the evaporation of magnesium. Furthermore, the interfacial reaction products that induce good wettablity could be observed in other specimens obtained under higher reactive conditions, although they were hardly detected at the interface between molten magnesium and the substrate at the end of the wetting experiment. On the contrary, the molten magnesium drop did not advance on the surface of iron and SUS430 substrates because of the poor wettability at 115° and 116°, respectively, for the initial contact angle at 973 K.

Commercial K–Si–Al-doped tungsten wires, selected by different splitting properties, are investigated by torsion. During deformation the “as-drawn” wires deform in visible Lüders bands (LBs), while no LBs appear after stress-relieve annealing (at 1700 K). This change in the properties corresponds to a transition annealing temperature of T ≈ 1200 K, which can hardly be seen in wires with splits or latent splits. The first LB usually appears at low surface strains ( γ ≤ 0.04) and coincides with the yield point phenomenon. At higher strains new LBs appear and propagate axially till they all meet at γ ≈ 0.7 to 1. In some respect axially split wires resemble to a cable, represented now by a stranded copper cable (10 mm × 0.1 mm).

Amorphous quaternary Ni–Fe–P–B alloy deposits have been first and successfully made by electroless plating. It was found that the deposits show an amorphous structure when the reductant NaH 2 PO 2 concentration ranges from 23 to 38 g/l. The crystallization processes of the alloys have been studied by X-ray diffraction. The crystallization processes of different alloys vary with composition, which is determined by the prepared conditions. A two-step process of crystallization was observed for the amorphous alloys. At first, the crystalline phases are Fe 2 B, γ-(Fe, Ni) solid solution and Ni 3 Fe, then Ni 3 P, Fe 3 P and (Ni, Fe) solid solution appear at high temperatures. The lattice spacing first decreases then increases with heating temperature for the γ-(Fe, Ni) solid solution.

The morphology and size characteristics of the population of AIP particles produced by treatment of a pure aluminium melt with an Al-Fe-P inoculant addition have been determined. The particles are shown to be polyhedral like the primary silicon they nucleate in hypereutectic Al-Si alloy melts and to be prone to clustering at increased phosphorus addition levels. The number of AIP particles per unit area is shown to be comparable with the corresponding number density of polyhedral primary silicon in Al-20wt.%Si treated in the same way under identical conditions which is consistent with earlier conclusions that AIP acts as a nucleation catalyst for primary silicon in hypereutectic Al-Si casting alloys.

An earlier proposed method for the estimation of critical data of metals with extrapolated vapor pressure curves does not work with uranium. This strongly indicates the problems of such high-temperature extrapolations with the available vapor pressure data. Thus, various similarity relations for the critical data have been discussed. As most reliable values the critical temperature T c = 9 000 K and pressure p c = 5000 bar have been chosen. With these values a two-term vapor pressure equation has been constructed.