Band 92, Heft 12

The decomposition at 628 K of a Pd(B) solid solution containing 6 at.% boron was analyzed by use of, primarily, X-ray diffraction. A structure model was used to simulate the X-ray diffraction-line profiles. The decomposition is described as the precipitation of a boron-poor face-centered cubic (fcc) phase in the parent fcc phase gradually enriching in boron. The experimentally determined width of the miscibility gap is different from previous experimental results, but agrees with theoretical data obtained on the basis of the quasi-chemical approximation. Further, the micro-strain in the decomposed state was measured and compared with that of the initial, quenched supersaturated solid solution; good agreement is observed between results obtained from X-ray diffractometry and transmission electron microscopy.

To clarify the effect of Mg content on annealing textures developed in Al–Mg alloys during high temperature annealing, Al–Mg alloys containing up to 9 wt.% Mg in supersaturated solid solution were cold rolled 95% and isothermally annealed at 450 °C. Their textures were investigated with the orientation distribution function analysis. It was found that, in the recrystallization textures observed at complete recrystallization, addition of more than 1 wt.% Mg was sufficient to suppress the development of {100}<001>. With increasing Mg content, {100}<001> decreased remarkably, whereas {100}<013> and {103}<321> increased. Thus, {100}<013> and {103}<321> were found to be the main orientations of the recrystallization textures of Al–Mg alloys annealed at high temperatures. {100}<013> developed most remarkably at 4 wt.% Mg, while {103}<321> showed the maximum development at 7 wt.% Mg. During subsequent grain growth at 450 °C, remarkable texture changes were observed only in the alloys containing Mg in the range between 2 and 4 wt.%. In these alloys, {100}<013> developed at the expense of {100}<001> at earlier stages of grain growth, whereas {103}<321> increased independently of these two orientations at later stages of grain growth. Reflecting these texture changes, grain growth occurred in these alloys discontinuously. Such a discontinuous grain growth with large texture changes is expected, if strong textures are already present before grain growth, and if recrystallized grains having similar orientations are distributed by forming large clusters before grain growth.

A method was developed allowing the reconstruction of the form of the weld pool after laser beam welding, using texture measuring. The effects of the process parameters (laser power and welding velocity) on the formation of the solidification front could be determined. The method was applied to aluminium, steel and titanium; the influences of the type of solidification, the amount of alloying additions and the number of transformations in the solid state being equally subject of the analysis. Additional metallographic examinations indicated the microstructure formation and grain orientation. The results of the practical examinations formed the basis of a subsequent, more detailed theoretical simulation.

The electrical resistance of Ag-10, 17, 26 and 50 at.% Ge alloys is measured as a function of temperature in various isobaric pressures up to 7 GPa. Pressure dependence of the eutectic, peritectic, eutectoid and liquidus temperatures has been observed in the electrical resistance – temperature curves. The phase identification of the alloys is carried out by means of X-ray diffraction. Isobaric phase diagrams at 2, 3, 5 and 7 GPa are constructed. A three-dimensional phase diagram is constructed from the isobaric phase diagrams. It is shown that an intermediate phase (ζ-phase) appearing under high pressure is stable down to 1.2 GPa. Pressure – temperature sections at the germanium contents of 10, 17, 26 and 50 at.% and isothermal sections at 500 and 700 °C are given from the three-dimensional phase diagram.

This article deals with the composition design of a novel P-containing transformation-induced plasticity (TRIP) steel grade on basis of the thorough thermodynamic analysis. The influence of P on the equilibrium phases and phase transformations in a potential TRIP steel grade Fe-0.2 C-(0.0–0.8) P-1.5 Mn-0.4 Si (mass %) has been investigated by assuming that a full thermodynamic equilibrium can be reached in the system. The phases involved are liquid, δ-fer-rite, austenite, α-ferrite, θ-carbide and phosphide (Fe 3 P), and the phase transformations discussed include solidification, properitectic, peritectic, proeutectoid, eutectoid, θ-carbide and phosphide precipitation from both ferrite and austenite. It is shown that P promotes the precipitation of phosphide within austenite or ferrite. The former is regarded as a limitation on the intercritical annealing while the later is thought to be beneficial to the strength of the ferritic component of the microstructure. The effects of P on other phase transitions in this system are more complicated and most of the effects are detrimental. Thus, it is better to keep the P content as low as possible. Based on the analyses of the presence of various equilibrium phases and the occurrence of different phase transformations in the current system, it is concluded that the optimum P concentration for a prospective P-containing steel grade is about 0.2–0.25 mass %.

The procedures for producing a potential transformation induced plasticity (TRIP) steel grade with a composition of Fe-0.2 C-CO.15–0.25) P-1.5 Mn-0.4 Si (mass %) have been optimized and the amount of the TRIP effect of such a novel steel grade has been estimated. Based on thermodynamic calculations, the influence of P on the phase transformations in an Fe-0.2 C-(0.0–0.8) P-1.5 Mn-0.4 Si system have been investigated when different equilibrium conditions are assumed to exist. Analyses of the proeutectoid ferrite reaction and the effects of P on the partitioning of alloying elements indicate that the proper intercritical annealing temperature is around 1030 K. P is shown to decrease the maximum amount of proeutectoid ferrite prior to the precipitation of either carbide or phosphide. Hence, the total grain boundary area of the austenite after the ferrite reaction decreases, and this slows down the grain boundary nucleation of the upper bainite and increases the size of the bainitic sheaves. To compensate for this, a hot deformation before bainitic decomposition is suggested for the P containing steels. Note that the ability of P in retarding the carbide precipitation accompanying the bainitic reaction is not discussed. The martensite start (Ms) temperature of such Fe-0.2 C-1.5 Mn-0.4 Si–P steels has been estimated by considering the influences of the carbon enrichment of the austenite, the redistribution of substitutional alloying elements during the intercritical annealing, and of the fine grain size. The results show that the Ms temperature of the residual austenite can be controlled over wide range and extending even to a temperature below room temperature; implying that a sensitive and significant TRIP effect can be expected.

This paper reports the room temperature monotonie and cyclic stress–strain (CSS) response, the low and high cycle fatigue behaviour of a medium carbon microalloyed (MA) steel in different microstructural conditions obtained by isothermal transformation at 973, 773 and 573 K following austenitizing at 1123 K. The isothermal transformations resulted in coarse pearlite (CP), fine pearlite (FP), and acicular ferrite/bainite (AF/B microstores, respectively. In low cycle fatigue, the CP and FP microstructures exhibited cyclic softening at low total strain amplitudes (<0.6%) and cyclic hardening at higher total strain amplitudes The AF/B microstructure exhibited cyclic softening in the whole range of total strain amplitudes employed. In the FP microstructure similar CSS curves were obtained in both constant total strain amplitude and multiple step tests. In the AF/B microstructure, however, the CSS curve depended on the test procedure. Fatigue life in the LCF regime was greater (135%) for the CP microstructure compared with the FP and AF/B microstructures. Fatigue crack propagation in the pearlitic microstructures was through void growth and coalescence. In the AF/B microstructure it was by transgranular cleavage. The high cycle fatigue resistance (fatigue limit) of the FP structure was greatest (400 MPa) while that of the CP microstructure was the least (245 MPa). The fatigue limit correlated well with the cyclic yield strength ( σ cys ) of the material and was approximately equal to 0.7 σ cys .

The temperature dependence of the dynamic viscosity of Al-Sr alloy melts has been investigated using a torsional oscillation viscometer. It has been found that the viscosity of the Al–Sr alloy melts decreases with increasing temperature, as well as the absolute value of the first derivative of viscosity with respect to temperature. Furthermore, an anomalous change occurs at about 1250 °C, indicating the occurrence of a change in the melt structure. The temperature dependence of the viscosity exhibits an exponential correlation and can be well fitted by an exponential decay equation. The comparison of the model predictions and experimental viscosities has also been made, and the model parameters are renewedly determined in the light of the present experimental results. The pertinent mechanisms are also discussed.

Molten salts electrolysis has been used for the preparation of an Al–Sr master alloy. The effect of the parameters, including cell current, SrCl 2 concentration and electrolysis time on the electrolysis process, was investigated in a laboratoryscale electrolysis cell. A polynomial regression analysis was carried out on the experimental data and showed a good agreement. In addition, the results from scanning electron microscopy showed that the microstructure of an Al-10 wt.% Sr alloy produced by electrolysis is quite different from that one prepared by a direct mixing process.

Microstracture and phase transformation of a cast Zn–Albased alloy (ZnAl11Cu3) are studied during ageing using X-ray diffraction and back-scattered scanning electron microscopy techniques. Decomposition of a zinc-rich ηs′$\mathrm \eta _{\rm{s}}^\prime $ phase is observed to take place in the way of continuous precipitation. A four-phase transformation, α + ε → T′ + η, occurs during prolonged ageing. It is found that the phases involved in the phase transformation can be distinctly identified by using different atomic contrasts in the back-scattered scanning electron image of precipitates.

Crystallographic analysis has been carried out on the serrated grain boundaries, which can be frequently observed at the early stage of M 23 C 6 precipitation in an AISI 316 stainless steel. Microstructural observation reveals that the serrated grain boundaries, which were formerly planar in shape before aging treatment, are produced by the serration during aging treatment. Crystallographic features of the serrated grain boundaries were obtained through transmission electron microscopy. Moreover, atomistic approach to the serrated grain boundary was applied to calculate the coincidence points between the two neighboring grains. Both investigations indicate that by serration at the incipient stage of M 23 C 6 precipitation, the interfacial free energy of the grain boundary can be lowered even though the grain boundary area is increased.

Nach ca. einem Betriebsjahr wurde in der Antriebswelle der Umlenkradlagerung eines Sessellifts ein ungewöhnlicher Bruch festgestellt. Die Bruchfläche war durch drei, etwa gleich grosse Ermüdungsflächen gekennzeichnet, wobei der Restbruch nur ca. 5 % der Gesamtbruchfläche einnahm. Umfangreiche fraktographische, metallographische, mikroanalytische sowie mechanische Untersuchungen zeigten, dass die Rissinitiierung massgeblich von Korrosionsprozessen bestimmt wurde. Dafür verantwortlich war eine äusserst ungünstige Konstruktion der Welle. Im Bereich der aufgeschrumpften Seilscheibe kam es aufgrund von Spaltkorrosion zur interkristallinen Rissbildung und mit zunehmender Risstiefe zum Ermüdungsbruch.