Volume 100, Issue 1

Bibliometric methods, in particular citation analysis, are used to evaluate the International Journal of Materials Research (IJMR) and its two predecessor journals Zeitschrift für Metallkunde (ZfM) and Internationale Zeitschrift für Metallographie (IZfM). Firstly, the coverage of the journals by the various literature databases is discussed and the number of articles per year is determined. The time evolution of the publications with respect to German and English as original languages is established and the language dependent impact is analyzed. A ranking of the most important countries of authors is given. Furthermore, the ensemble of ZfM and IJMR articles is analyzed with respect to the occurrence of substances (metals, alloys, compounds) and some subject specific terms (diffusion, microstructure, recrystallization, mechanical properties). A listing of the twenty most frequently cited articles and the citation time evolution (citation history) of the top three articles are presented. Moreover, the distribution of the citations on the articles is determined and the amount of simultaneous citations with other journals (co-citations) is given. The citing papers of the IJMR and ZfM articles are analyzed with respect to the most frequently appearing countries of authors and journals. Finally, the Journal Impact Factor (JIF), the Cited Half-Life and the Citing Half-Life as bibliometric indicators of a journal as a whole are analyzed. The meaning of the widely used JIF is discussed and hints for its careful and cautious use are given.

The paper retraces, from a personal viewpoint, the development of atomistic models of dislocations in crystals from the model of Prandtl, Dehlinger, Frenkel, and Kontorova, first conceived in 1912, to recent work on kinks in dislocations. Among the topics discussed in some detail are the emergence of the theory of solitons, the rate theory of kink-pair generation, and the interplay of experiment and theory in the quantitative investigation of kinks by mechanical relaxation and flow-stress measurements. An outcome of this interplay, the determination of the planes of the elementary slip steps of screw dislocations in refractory body-centred cubic metals, has become the ‘open sesame!’ of quite a number of puzzling phenomena in which the plastic deformation of bcc metals differs from that of fcc metals and alloys. These phenomena include non-uniformities in the flow-stress – temperature relationship, anomalous slip, tension – compression asymmetry in uniaxial straining tests, alloy softening, and the enigma of ‘reversible’ vs. ‘irreversible’ γ-relaxation. The key for their understanding is a first-order transition transforming the cores of a 0 <111>/2 screw dislocations from a low-temperature configuration capable of slipping on {110} planes to a configuration with a {112} slip plane at elevated temperatures. Various problems needing further research are pointed out.

Experiments have been conducted to see whether specific crystallographic variants of bainite form in polycrystalline steel when transformation occurs from plastically deformed austenite which is otherwise free from externally applied stress. It is demonstrated by studying both overall and microtexture that there is no perceptible variant selection as bainite forms. Indeed, the texture is found to weaken on transformation.

The kinetic details of the microstructure evolution during a liquid – liquid phase transformation under the common action of the nucleation, diffusional growth and Ostwald ripening of the minority phase droplets are investigated numerically. The results demonstrate that the cooling rate during the nucleation period of the minority phase droplets has an overwhelmingly strong effect on the microstructure formation compared with the cooling rate after the nucleation period. Generally, the effect of the Ostwald ripening of the minority phase droplets is weak in an alloy cooled continuously all through the miscibility gap and the average radius of the minority phase particles shows an inverse square root dependence on cooling rate. An obvious coarsening of the minority phase droplets occurs and the exponential varies towards – 1/3 only when the cooling rate decreases by more than two orders of magnitude after the nucleation of the precipitated droplets.

In the present study, we compare available experimental surface tension data with two theoretical concepts: the Butler equation and a multilayer model in which the surface is described as a stacking of atomic layers. The experimental data were measured systematically over a wide temperature and concentration range using electromagnetic levitation and the oscillating drop technique. Three classes of alloys are studied: alloys with rather weak or no segregation, alloys with strong segregation, and associate forming alloys.

The Ni – B system is reassessed based on critical literature review and the results of key experiments and first-principles calculation. Eight Ni – B alloys are prepared by arc melting the pure elements. The samples are analyzed by means of chemical analysis, X-ray diffraction and differential thermal analysis. NiB 12 and NiB 2 are not found in the equilibrium condition. Four invariant temperatures are measured: 1098 ± 2 °C for L ↔ fcc(Ni) + Ni 3 B, 1114 ± 2 °C for L ↔ Ni 3 B + Ni 2 B, 1025 ± 2 °C for L ↔ Ni 2 B + orthorhombic-Ni 4 B 3 and 1044 ± 2 °C for L + βB ↔ NiB. The heat capacity of NiB is determined to be 58.46092 + 0.0012 · T – 1 597 915.59793 · T – 2 (J mol – 1 K – 1 , T in Kelvin) in the temperature range from 40 to 950 °C by differential scanning calorimetry. First-principles calculation indicates that the energy of inserting a B atom into the interstitial site of the lattice for Ni atoms is lower than that of substituting for an Ni atom with a B atom. Consequently, the sublattice model (Ni) (B, Va) in which B atoms occupy the interstitial sites is employed for the fcc(Ni) phase rather than the model (Ni, B) (Va) in which B atoms substitute for Ni atoms. In addition, the enthalpies of formation for the five compounds are obtained via first-principles calculation to supplement the modeling. A self-consistent set of thermodynamic parameters for the Ni – B system is finally obtained and the calculated results show good agreement with the experimental data.

In this work, we studied nanocrystalline LIGA Ni-2.6 at.% Fe and Ni-5.6 at.% Fe with an average grain size of 10 nm. Microtensile samples were produced by the LIGA process including direct current electrodeposition. Microstructures and mechanical properties were investigated in the as-deposited state as well as after annealing at different temperatures. Results from tensile testing were compared to nanoindentation experiments with a particular emphasis on the strain rate sensitivity of the alloys. The Ni – Fe alloys were confirmed to be suitable LIGA materials for applications that require high hardness combined with microstructural stability and low internal stresses. For both alloys with 10 nm grain size, tensile yield strength and corresponding hardness values of the order of 2 GPa and 6 GPa, respectively, were found. After annealing at moderate temperatures (200 °C), strength and hardness increased although some grain growth was observed.

Short DC pulses (∼10 – 4 s duration with a maximum electric field strength of 2.0 – 9.3 kV cm – 1 ) applied continuously at a frequency of 10 Hz reduced the tensile flow stress of ultrafine-grained 3Y-TZP at 1400 °C. The decrease in flow stress was attributed to a retardation of dynamic grain growth by the average electric field. The degree of retardation decreased with strain, which correlated with the calculated reduction in electric field strength due to the change in dimensions of the specimen as it elongates. Considering the present electropulsing results along with those obtained previously employing DC and 60 Hz AC fields, it was found that the ratio of the decrease in grain size with field to the grain size without field, was proportional to the average effective electric field strength, relatively independent of test temperature in the range of 1400 – 1500 °C. The proportionality constant increased in the order DC, AC, EP, indicating that a varying field has a greater effect on retarding dynamic grain growth than a constant DC field.

The paper tries to show the essential role played by a brazing process in the manufacturing of filigree and granulation decorated ancient jewels. A purely experimental framework is proposed. Reasons for such a methodological choice are outlined and general protocols for a standard experiment are provided. Specific advantages for the accomplishment of the manufacturing process in all its stages are shown to be related to the employment of a fluid brazing solution. The concordance of the few available ancient sources, the simplicity of technique's application, as well as the jewels concretely produced during years of research in the field, highlight the plausibility of the adopted approach.

The mechanical properties of the hot-worked and tempered tool steel grade X37CrMoV5-1 were studied as a function of the heat treatment and, thus, microstructure. Based on the continuous cooling transformation diagram, different hardening processes had been chosen to achieve fully martensitic and mixed martensitic-bainitic microstructures with different amounts of bainite. Mechanical tests demonstrate that the fully martensitic microstructure exhibits the highest toughness and ductility over the entire temperature range, whereas the strength remains constant. Microstructural investigations, performed using scanning and transmission electron microscopy, show that the degraded mechanical properties are related to the presence of the bainitic microstructure as well as carbides at former austenite grain boundaries.

Full tetragonal 3 mol.% Y 2 O 3 doped zirconia has been subjected to hydrothermal ageing in water at 131 °C in order to study the change in microstructure just below the surface. The degraded layer was examined by scanning and transmission electron microscopy in a section perpendicular to the surface which was prepared by focus ion beam machining. The existence of microcracks and transformed grains in a thin surface layer of the hydrothermal degraded specimens is shown. Scratch damage in annealed and in thermally degraded specimens is compared.

At the Institute of Materials Science of the Leibniz University of Hannover, investigations were carried out to better understand the crystallisation processes of the cast alloy AlSi12. Here, the influence of different cooling rates was investigated in-situ and ex-situ. The temperatures of the geometric specimens were determined during the experiment with the aid of a near-infrared camera and thermocouples. The aim was to both determine a function between the specimen' cooling rate and the speed of the solid – liquid interface as well as establish a relationship between the thermographic images and the solidification' morphology.

The oxidation behaviour of experimental Co – Re-based alloy at 1000 °C was studied. A set of binary, ternary and quaternary alloys from the Co – Re – Cr – C system was used as model alloys to understand the role each alloying element plays on oxidation. The morphology and composition of the oxide scale that formed was analysed by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. It was found that the present Co – Re alloys with 23 at.% and 30 at.% Cr additions behaved very similarly to Co – Cr binary alloys with equivalent Cr content. The oxide scale was multilayered, consisting of a dense CoO outer layer, a porous mixed oxide layer containing Co-oxide and Co – Cr spinel, and a discontinuous and non-protective Cr 3 O 2 layer. The binary Co – Re alloy behaved differently in oxidation, and it formed only a monolithic CoO scale. However, Re in combination with Cr promotes Cr – Re-rich phase formation, which oxidises preferentially compared to the Co matrix. Carbon ties up part of the Cr to form Cr 23 C 6 type carbides. However, these carbides are not stable at 1000 °C and dissolved with time, therefore C had only a minor role in the oxidation behaviour. In general, increasing Cr content in the alloy improved oxidation resistance.