Lead induced intergranular fracture in aluminum alloy AA6262

The influence of lead on the fracture behavior of aluminum alloy AA6262 is investigated. Under certain conditions, the mode of fracture changes from transgranular microvoid coalescence to an intergranular mechanism. Three different intergranular fracture mechanisms are observed: liquid metal embrittlement, dynamic embrittlement at temperatures below the melting temperature of lead, and intergranular microvoid coalescence. An attempt is made to examine the dependence of these three mechanisms on temperature, strain rate, and stress state using in situ scanning electron microscopy (SEM). Liquid metal embrittlement occurs when the alloy is fractured at temperatures above the melting temperature of lead and at low strain rates. At lower temperatures, the occurrence of dynamic embrittlement depends largely on strain rate, stress state, and temperature. Intergranular microvoid coalescence is not often observed.

Competitive segregation of gallium and indium at heterophase Cu–MnO interfaces studied with transmission electron microscopy

This paper concentrates on the possible segregation of indium and gallium and competitive segregation of gallium and indium at atomically flat parallel {111}-oriented Cu–MnO interfaces. The segregation of gallium at Cu–MnO interfaces after introduction of gallium in the copper matrix of internally oxidized Cu–1 at.%Mn could be hardly detected with energy-dispersive spectrometry in a field emission gun transmission electron microscope. After a heat treatment to dissolve indium in the copper matrix, gallium has a weak tendency to segregate, that is 2.5 at.% Ga per monolayer at the interface compared with 2 at.% in the copper matrix. The striking result is that this gallium segregation is observable because it does not occur at the metal side of the interface but in the first two monolayers at the oxide side. Using the same heat treatment as for introducing indium in the sample, but without indium present, gallium segregates strongly at the oxide side of the Cu–MnO interface with a concentration of about 14.3 at.% in each monolayer of the two. In contrast, the presence of gallium has no influence on the segregation of indium towards Cu–MnO interfaces, because the outermost monolayer at the metal side of the interface contains 17.6 at.% In, that is similar to previously found results. This leads to the intriguing conclusions, firstly, that, in contrast with antimony and indium, gallium segregates at the oxide side of the interface and, secondly, that the presence of indium strongly hampers gallium segregation. The results from analytical transmission electron microscopy on gallium segregation are supported by high-resolution transmission electron microscopy observations.

Scattered wave functions of dislocated lattices

Using a Wannier function approach and a transformation of the coordinate system it is shown that a method can be set up to calculate the scattered wave function of a dislocated lattice

The i.r. spectra of several rare-earth formates

The i.r. spectra of some rare-earth formates are recorded in the range 4000-40 cm-1. The following compounds were studied: Ce(HCO2)3, Pr(HCO2)3, Nd(HCO2)3, Sm(HCO2)3, Eu(HCO2)3 and Gd(HCO2)3. Some compounds were also studied upon deuteration and at lowered temperature. Nearly all bands could be assigned and the expected factor group splitting was observed. A shift to higher frequencies was observed with increasing atomic number

Some aspects of nanocrystalline nickel and zinc ferrites processed using microemulsion technique

Nanocrystalline nickel and zinc ferrites synthesised using a microemulsion technique were characterised by high resolution transmission electron microscopy and vibrating sample magnetometry. A narrow and uniform distribution of crystals of size range 5 – 8 nm, distinguished by a clear lack of saturation magnetisation at 9 kOe, were obtained. Also, no coercivity or remanence was observed.

Surface Modification by Means of Laser Melting Combined with Shot Peening:A Novel Approach

Among the available laser applications laser surface melting has turned out to be a powerful technique for the production of wear-resistant layers. Despite the advantages of this process, laser surface melting results in tensile stresses which may assist crack propagation. In this paper it will be shown that shot peening can overcome this drawback effectively. It turned out that a preceding laser treatment of an euteetic aluminium-silicon alloy is able to amplify considerably the effectiveness of the shot peening treatment. In particular the maximum attainable hardness and compressive stress increase upon increasing the quench rate, i.e. upon increasing the laser scan velocity. The high concentration of silicon in solid solution turned out to be the main reason for the enhanced mechanical performance, not only directly through solid solution hardening, but also by precipitation hardening and by a higher dislocation density. The latter contribution is affected indirectly by a changed cross slip behaviour