Volume 93, Issue 2

The grain boundary diffusion of 32 P in a polycrystalline Fe – 2.2 wt.% Si alloy was measured with the radiotracer technique under the condition of the Harrison type-B regime (845 – 1173 K) and type-C regime (735 –830 K). The triple product P = sδD gb (s denotes the segregation factor, δ the grain boundary width and Dgb the grain boundary diffusion coefficient) was obtained in the B regime. The pre-exponential factor P0=(1.8−1.1+3.2) ${{P}_{0}}=\left( 1.8_{-1.1}^{+3.2} \right)$× 10 -10 m 3 s -1 and the activation enthalpy Q gb = 171:3 ± 8:3 kJ mol -1 were evaluated. The initial part of the penetration profiles measured in the B regime was used to calculate the volume diffusion coefficients D v. The resulting Arrhenius parameters of volume diffusion were D0=10−10+2600 ${{D}_{0}}=10_{-10}^{+2600}$m 2 s -1 and Q v = 320 ± 45 kJmol- 1 . The grain boundary diffusion coefficient Dgb was directly measured in experiments in the C regime. The temperature dependence is characterised by the Arrhenius parameters Dgb0= $D_{gb}^{0}=$ (7.9−6.2+28.2) $\left( 7.9_{-6.2}^{+28.2} \right)$× 10 -3 m 2 s -1 and Hgb = 201.5± 9:9 kJ mol -1 . Combining both series of measurements, the segregation coefficient s was determined, resulting in the segregation enthalpy H s = -30 ± 10 kJ mol -1 and the pre-exponential factor s0=47−35+159 ${{s}_{0}}=47_{-35}^{+159}$. The obtained results were compared with segregation data of P measured by Auger electron spectroscopy in a-Fe.

The efforts of this study aim to investigate the morphology and growth kinetics of the intermetallic compounds formed during the interfacial reactions of eutectic Sn–9Zn solders with Cu and Ni substrates at temperatures ranging from 250 to 350 °C. Experimental results show that the intermetallic growth rate at the Sn–9Zn/Cu interface is much higher than that at the Sn– 9Zn/Ni interface. Kinetics analyses indicate that both types of interfacial reactions are diffusion-controlled. The activation energies for the intermetallic growth at the Sn–9Zn/Cu and Sn– 9Zn/Ni interfaces are 8.2 and 68.9 kJ/mol, respectively. The formation mechanisms of the intermetallic compounds during the soldering reactions at both interfaces are clarified by using a Ta thin film as diffusion marker.

In a series of solidification experiments, the solidification morphology of 14 different solder alloys based on Pb–Sn2 with additions of 1 – 4 wt.% Ag and 0.3 – 1.2 wt.% Cu has been correlated with the cooling conditions through a quantification of microstructural features. Joints of these solders in assemblies similar to components in the electronics were exposed to thermal cycling. The damage in the solder material due to thermal fatigue has been quantified with the aid of a dye penetration test. Fracture surface analysis was used to evaluate the reliability of this test. The highest resistance against thermal fatigue was found in Pb–Sn2–Ag1– Cu0.3. The varying thermal fatigue resistance is attributed to a change of solidification morphology from columnar to equiaxed, which in turn is a consequence of changes in phase fraction and morphology of secondary phases due to slight variations in alloy composition.

By using the orientation distribution function analysis, rolling and recrystallization textures developed in Al –Mg alloys containing 6, 7 and 9 wt.% Mg were studied in detail. Also recrystallization behavior and precipitation of the β phase particles during annealing were investigated by using both optical and scanning electron microscopy. It turned out that cold rolling textures of these alloys were generally weak and random. The recrystallization textures of Al-6 wt.% Mg alloy annealed at 450 °C were found to be strongly dependent on the heating rate to the annealing temperature. Annealing by rapid heating enhanced the formation of {103}<321> and {100}<013>, suppressing the development of {100}<001> strongly. This is because {103}<321> and {100}<013> recrystallized grains were preferentially formed at shear bands and at peripheries of deformed cube bands, respectively. {100}<001> recrystallized grains were consumed during grain growth by grains of these orientations. In annealing by slow heating, precipitation of the β phase particles, which occurred preferentially at shear bands at low annealing temperatures, suppressed the nucleation of {103}<321> recrystallized grains. In this case, {100}<001> formed during recrystallization at low annealing temperatures, further developed during subsequent grain growth at higher annealing temperatures, yielding {100}<001> and {123}<634> recrystallization textures, which were commonly observed in Al alloys. Increase in the Mg content suppressed the development of all these texture components. In Al-9 wt.% Mg, the recrystallization textures were quite random. They were affected neither by the annealing temperature nor by the heating rate to the annealing temperature. This was ascribed to its random rolling texture, and also to a large amount of the β phase particles which precipitated homogeneously within grains at low annealing temperatures, suppressing nucleation of recrystallized grains of all orientations equally.

Already during solidification of the melt, in the aluminum alloy AA 6013 occur precipitates, which are a part of a very complex microstructure and have a significant influence on the recrystallization and fracture behaviour. The chemical composition as well as the high value of microhardness suggest that it is a quasicrystal or crystalline approximant. Convergent beam electron diffraction (CBED) and selected area diffraction (SAD) investigations in combination with the interpretation of electron backscatter diffraction (EBSD) patterns led to the conclusion that the precipitates are crystalline approximants. Their chemical composition can bedescribed with the formula Al 19 Fe 4 MnSi 2 and their crystallographic point group is 2 m 3 ¯ . $\frac{2}{m}\,\bar{3}.$

The hot working characteristics of hot rolled Mg– 11.5Li – 1.5Al (wt.%) alloy have been studied using hot compression tests in the temperature range 200 –450°C and strain rate range of 0.001 – 100 s –1 . Using the principles of dynamic material model and on the basis of the hot compression data, a processing map has been developed for this alloy. The map exhibited two domains: (i) with a peak efficiency of about 62% occurring at 450 °C and 0.001 s –1 (ii) with a peak efficiency of about 58% occurring at 300 °C and 0.001 s –1 . On the basis of microstructural features, the apparent activation energy for hot deformation (110 kJ/mol) and very high tensile ductilities, the second domain has been identified to represent superplastic deformation. In the first domain, the microstructure of the specimen revealed intergranular cracking and it is therefore not a safe domain for processing.

The major tools used in applying computational thermodynamics to various problems in materials science are briefly presented and several practical examples are given as illustrations. Solutions to industrial problems, pertaining to the processing of and microstructure development in several different materials, are shown with answers given in graphical form. Solutions to kinetic problems linked with diffusion are also treated. The last section is devoted to the problem of interfacing between thermodynamic computations and applications oriented software.

Phase equilibria of the Fe –Co –R system with R ⩽ 33.3 at.% Sm 0.5 Nd 0.5 were determined in an isothermal section at 1073 K and a vertical section RFe 2 –RCo 2 by using optical microscopy, X-ray diffraction analysis, electron probe microanalysis, and differential thermal analysis techniques. There are seven intermetallic phases: (Sm, Nd) (Fe, Co) 2 , (Sm, Nd)(Fe, Co) 3 , (Sm, Nd) 5 (Fe, Co) 17 , (Sm, Nd) 2 (Fe, Co) 7 , (Sm, Nd) 5 (Fe, Co) 19 , (Sm, Nd)(Fe, Co) 5 , and (Sm, Nd) 2 (Fe, Co) 17 . The (Sm, Nd) 5 (Fe, Co) 17 phase dissolves less than 4 at.% Co at 1073 K. However, the (Sm, Nd) 2 (Fe, Co) 7 phase in R 2 (Fe 1– xCox) 7 alloys dissolves about 15 at.% Fe at 1073 K.

Plastic deformations of materials generally originate macrostresses as well as microstresses between the constituents of the material. Both parts may contribute to the results of stress determinations. Their influence on the material behaviour, however, is different. Therefore, a detailed assessment requires the separation of the stress kinds. The present paper deals with the portions and the depth profiles of macro- and micro-residual stresses after uniaxial elongation and after mechanical surface treatments. The possibilities to separate stresses are discussed. It will be distinguished between one-phase, quasi-one-phase, two-phase and multi-phase materials. The measurement techniques include X-ray and neutron diffraction and mechanical methods. The paper reviews the published results and reports on recent studies.

The effects of the type of electrode coating – basic or rutile – on the composition of a welded structure made of duplex stainless steel UNS-S31803 have been investigated. It was found that when welding with an electrode having a basic coating (“basic electrode”) the covering of the slags affords better protection of the melt against the entrapment of air but is less effective in de-oxidizing it. There is, therefore, more dissolved oxygen when welding with a basic electrode, and consequently more ε-Fe 2 O 3 is created. On the other hand, the entrapment of air when a rutile-coated electrode (“rutile electrode”) is used leads to considerable porosity and a higher nitrogen content.

The effect of mixed mode I/III loading on the fracture toughness of Armco iron at 77 K was studied. The results showed that the mixed mode I/III fracture toughness increases with increasing loading angle or mode III loading contribution. This behaviour was in contrast to the behaviour of Armco iron at room temperature wherein the fracture toughness was found to decrease significantly with increasing mode III loading contribution. The difference in behaviour was explained on the basis of the difference in the fracture mechanisms at the two temperatures as well as on the nature of the deformation fields ahead of mixed mode I/III crack.

The paper deals with the results of measurement of mechanical properties of maraging steel Thyssen 1.2799 after precipitation annealing with a wide spectrum of temperature/time conditions. The purpose of the investigation conducted on the material for die-casting tools was to find out how the tool life could be extended depending on the heattreatment conditions and the microstructure of the steel. Thus the influence of temperature/time conditions of precipitation annealing on tensile strength, hardness, and impact toughness of the steel was studied. The Charpy impact toughness test was carried out at a temperature of 200 °C, which is, according to our assessment, an average operating temperature of the observed tool surface in die casting of aluminium alloys. Measurements of the mechanical properties were accomplished on three test pieces under each combination of annealing conditions. Special attention was paid to the correlation of the mechanical properties measured under individual precipitation annealing conditions.

A study of the properties of maraging steel Thyssen 1.2799 in the production of die-casting tools for aluminium alloys has been undertaken. Beside the study of the mechanical properties described in Part I of the paper, analyses of the microstructure by means of optical microscopy and scanning electron microscopy were made, too. The precipitates having a size of the order of a few 10 nm and more could be identified. Relating of the mechanical properties to the microstructure analyses supported by a micro chemical analysis, the suitability of the maraging steel concerned for the production of die-casting tools for aluminium alloys was proved.