Band 88, Heft 6

The intermetallic phases formed between solid nickel and molten aluminium have been studied under isothermal conditions. For temperatures ranging from 695 to 800 °C, the interfacial microstructure consisted of two phase layers, Al 3 Ni 2 and Al 3 Ni. It was found that the phase growth was diffusion controlled. The identified compounds, which coincide with the Al-rich phases of the Al –Ni phase diagram, have the highest interdiffusion coefficients. The observation of these phases was well linked with the thermodynamic behaviour of the melt, in agreement with the associate model applied to liquid alloys. The calorimetric experiments have indicated a negative curvature for the enthalpies of dissolution of Ni, which is consistent with the formation of transitory compound layers at the solid-liquid interface. Moreover, it was found that the dissolution time of Ni increased when interfacial compound layers were formed.

This is a comment on the recent paper “Phase Transformation in CuAu and Cu 3 Au: A Comparison between Calorimetric and Resistometric Measurements” published in this journal [1]. This is a careful study, but a few comments seem however to be in order, particularly concerning the structural states of the AuCu samples, which can present three phases. Use is made of some unpublished results of electron microscopy observations while temperature is varied in situ. The accent is put on the necessity of a precise characterisation of the structural state prior to any heating or cooling. Some possible bearings on the profile of transition peaks obtained in calorimetry or resistometry are investigated.

In diesem abschließenden Teil der Übersicht über die in den letzten drei Dekaden entwickelten numerischen Verfahren für die Simulation von Erstarrungsvorgängen werden Unterkühlungseffekte (Unterkühlung der Dendritenspitze und der eutektischen Reaktion) und ihr Einfluß auf die Vorhersage von Gefüge und Mikroseigerungen in metallischen Legierungen diskutiert. Die kinetischen Effekte, die bei hohen und sehr hohen Abkühlraten die Phasengleichgewichte beeinflussen, werden beschrieben. Die verschiedenen Ansätze werden im Hinblick auf ihre Verwendung in Simulationsprogrammen kritisch bewertet und offene Fragen definiert.

In this paper Redlich-Kister’s formalism and Darken’s formalism are used to describe the integral mixing enthalpy of the ternary system (In, Pb, Zn) at 756 K. The integral mixing enthalpy of the binary (Pb, Zn) system at 756 K is obtained over the whole composition range by extrapolation of the ternary function to the binary border.

Phase equilibria and extensions of solid solutions based on the binary La-phases of the NaZn 13 , ThMn 12 , and Th 2 Zn 17 structure types in several ternary systems are described. In the La–Fe –Al system, besides the ternary phases with the above given structure types, three other ternary phases of unresolved structures are obtained at compositions La 5 Fe 6 Al 4 , LaFe 2 Al 10 and La 2 Fe 2 Al 15 . The phase LaCo 13 (NaZn 13 ) dissolves up to 5.5 atoms of Fe per formula unit in place of Co leading to a steady increase of lattice parameter. Ternary phases with unresolved crystal structures are encountered in the La–Co –Fe alloys, one near LaCo 5 and another near the 2:17 stoichiometry. Likewise, LaCo 13 dissolves up to 3 atoms of Al per formula unit in place of Co. However, it dissolves very little, <1 atom each of Mn, Cu, or Ni. Possibly two different Th 2 Zn 17 - type phases, one on the Co-rich side and the other on the Mn-rich side, occur in the La–Co –Mn alloys. Addition of Fe to LaCu 13 (NaZn 13 ) possibly leads to structural distortions. LaFe 9 Al 4 (NaZn 13 ) is softly ferromagnetic at 77 K; its Curie temperature is around 170 K. The La (Co, X) 13 solid solution phases with Fe and Al have much stronger ferromagnetic moments even at room temperature. The ThMn 12 - type phase in the La–Fe –Al system and the Mn-rich Th 2 Zn 17 -type phase in the La–Co –Mn system are weakly paramagnetic at room temperature.

The quasi chemical approximation (QCA) which hitherto is used for the calculations of thermodynamic properties of binary alloys have been applied to the study of Bi–As 2 Te 3 and Tl–As 2 Te 3 ternary systems by assuming a pseudo binary configuration for the systems. The calculated values of the activity ( a m ) and free energy of mixing G m / RT show good agreement with experiment. The concentration fluctuation in the long wavelength limit S cc (0) and the Warren-Cowley short range order parameter for the first neighbour shell (a 1 ) have been studied as a function of composition in the ternary alloys. The results indicate that the Tl–As 2 Te 3 ternary alloy is more stable than the Bi–As 2 Te 3 alloys. S cc (0) computed from the model are in good agreement with experimental values for the systems investigated and for both systems indicate that they are compound forming. In addition for the Bi–As 2 Te 3 , the concentration dependence of the concentration-concentration fluctuations shows a regular solution behaviour while that of Tl–As 2 Te 3 manifests its highest tendency for compound formation in the range C Tl > 0:5454.

A new method for the calculation of Fe, Cr, Ni, Co, Ti, Nb, Mo, V, Cu, Pd, Ag, Pt, Au solubility in Bi, Pb, Na, Li, Al, Sn melts is proposed using the ideal solution approximation. The thermodynamic parameters of the solubility of metals are determined. The possibility to employ different metals for metallic coatings by the hot-metallization method is shown.

Samples of polycrystalline pure cobalt were treated by spark erosion in distilled water and in oil and investigated by X-ray diffraction. After cutting in oil a Co –C fcc solid solution and an unidentified phase are formed. Concentration of carbon in the Co–C solid solution and positions and intensity of reflections of the unknown phase are found to have spark energy dependence. Decomposition of the solid solution after subsequent heating of the samples to up to 500 °C is studied.

In this paper we propose a test method for the evaluation of the fracture thoughness of metal coatings. The fracture thoughness of supported amorphous and crystalline Ni–P (P 9%) layers plated onto nitriding steel was determined using a Vickers indentation technique. With this testing technique, Palmqvist cracks were induced by indenting the sample in the plane of the deposit. The as-deposited metastable amorphous structure shows a tougher behaviour ( K Ic0 = 7:4 MN/m 3/2 ), the equilibrium two-phase (Ni–Ni 3 P) system obtained by heat-treating the deposit, is more brittle ( K Ic0 = 1:1 MN/m 3/2 ).

The electroless nickel-phosphorus process was used for the deposition of Ni –P–MoS 2 composite coatings containing about 3 wt.% MoS 2 . The effect of the heat treatment on the wear resistance of composite coatings was studied. The tribological behaviour of the electroless Ni –P– 3 %MoS 2 composite coatings was assessed by comparison with electroless Ni –P coatings. The block on ring test was used to evaluate frictional and wear characteristics of coatings produced under different conditions such as load, duration, heat treatment, substrate and counterface material. It was concluded that the presence of MoS 2 particles within the Ni –P matrix improved the wear resistance and reduced the coefficient of friction when the electroless Ni –P– 3 %MoS 2 coating runs against itself, an electroless Ni –P coating and carburized steel.

Three different austenitization treatments were applied to high strength 34CrNiMo6 steel: conventional austenitization (CAT), high temperature austenitization (HTA) and duplex treatment (DT). It was found that DT structure has finer prior austenite grain size (30 μm) than those of HTA (200 μm) and CAT (70 μm) structures. DT and HTA structures have coarser lath size for martensite than CAT structure. DT results in higher room temperature impact toughness than HTA and CAT structures and shifts the ductile –brittle transition to lower temperatures by 14 K and 32 K in comparison with HTA and CAT structures, respectively. However, DT structure has intermediate values of room temperature yield stress and ultimate tensile strength between those of CAT and HTA structures. When this steel was tempered at 300 and 400 °C it underwent tempered martensite embrittlement associated with intergranular fracture.

Auf Grundlage der strukturanalytischen Theorie wird ein mathematisches Modell aufgestellt, das die mechanischen Eigenschaften von Metallen mit Formgedächtniseffekt beschreibt. Es wird die Frage untersucht, wie das Versetzungsgleiten die Entwicklung von Erscheinungen der martensitischen Inelastizität beeinflußt. Die Ergebnisse der numerischen Simulation zeigen, daß im Rahmen des Modells solche Erscheinungen wie Pseudoelastizität in Austenit und Martensit, Deformations-Zyklen in beschränkten Temperaturintervallen oder der Zweiweg-Effekt gut beschrieben werden. Der Zweiweg-Effekt wurde unter Annahme der Vererbung der effektiven Spannungsfelder in Martensit und Austenit modelliert.