Controlling the Microstructure of Arc Sprayed Shells

Techniques for controlling the microstructure of sprayed steel structures are discussed in this paper. Steel is arc sprayed onto shaped substrates to form tooling. The quality of the tool is greatly influenced by the microstructure of the material and the interlamella regions of the deposit. This work is focused on characterizing the microstructure, improving the state of the inter-lamella regions, and discusses our success in forming pseudo-alloys and graded shells by mixing sprayed materials. Microstructure control has interesting implications for other research as well, such as the MASK & DEPOSITS approach of forming objects.Mechanical Engineerin

Sprayed Metal Shells for Tooling: Improving the Mechanical Properties

Tbis work describes methods to improve the quality of the metal resulting from thermal spray deposition, including both the mechanical and metallurgical behavior. The engineering context is the production of sprayed metal shells suitable for tooling applications. The sprayed metal shells are mechanically dominated by interparticle interfaces; the particles are largely mechanically interlocked with very little metallurgical bonding. Based on these observations, improvements are made to these interfaces, and the measure of the improvement is shown in mechanical tests.Mechanical Engineerin

Keratin homogeneity in the tail feathers of Pavo cristatus and Pavo cristatus mut. alba

The keratin structure in the cortex of peacocks' feathers is studied by X-ray diffraction along the feather, from the calamus to the tip. It changes considerably over the first 5. cm close to the calamus and remains constant for about 1. m along the length of the feather. Close to the tip, the structure loses its high degree of order. We attribute the X-ray patterns to a shrinkage of a cylindrical arrangement of β-sheets, which is not fully formed initially. In the final structure, the crystalline beta-cores are fixed by the rest of the keratin molecule. The hydrophobic residues of the beta-core are locked into a zip-like arrangement. Structurally there is no difference between the blue and the white bird. © 2010 Elsevier Inc

Grain boundaries (moderator's comment)

Grain boundaries are an effective obstacle to dislocation motion. The resulting incompatibility stress causes multiple slip. Adjacent to the grain boundary the crystal is in an advanced stage of hardening. Transgranular slip is quantitatively unimportant.Les joints de grains sont des obstacles effectifs pour le mouvement des dislocations. Les contraintes d'incompatibilité associée causent du glissement multiple. Dans la vicinité du joint le cristal se trouve dans un état avancé du durcissement. Le cisaillement transgranulaire est quantitativement peu important

A calorimetric determination of the interfacial enthalpy of Cu-In and Cu-Al lamellar eutectoids

Differential Scanning Calorimetry has been used to measure the enthalpy of the pearlite transformation as a function of interlamellar spacing for the Cu-Al and Cu-In eutectiods. The interfacial enthalpies of Cu-Al and Cu-In lamellar pearlites were found to be 1183 mJ m and 1156 mJ m respectively, both associated with an error of ± 10%. Interfacial entropies were estimated for both these eutectoids and for Fe-C pearlite enabling the interfacial energies to be calculated as 764 ± 200, 360 ± 220 and 500 ± 360 mJ m for the Cu-Al, Cu-In, and Fe-C pearlites, respectively. These values were found to be in approximate agreement with those predicted by eutectoid growth theories provided that the alloy impurity element concentration was low. The enthalpies of formation of both Cu-Al and Cu-In eutectoids of infinite interlamellar spacing were also evaluated

INTERNAL FRICTION IN THE ALKALI METALS

Internal friction measurements in the alkali metals show that in Potassium there exists a γ-peak around 50K at about 10 kHz. It is due to the double kink formation in screw dislocation and has an activation enthalpy of ƉH=0.046 ± 0.003 eV. In Sodium and Lithium which undergo low temperature phase transformations there is no evidence of a similar peak above their resp. transformation temperature. This suggests in Sodium and Lithium a different structure of screw dislocations

Decomposition of the metastable phase in the silver-germanium system

The decomposition behaviour of the metastable h.c.p. phase in a splat- cooled silver-23 at. % germanium alloy was studied by differential thermal analysis, X-ray and electron metallographic techniques. A two-stage decomposition process was observed. The activation energies for the two stages were found to be 0·91±0·09 eV/atom and 1·95±0·19 eV/atom, respectively. The first stage is associated with the transformation from h.c.p. to metastable f.c.c. solid solution, the second stage represents the precipitation of germanium from this solid solution. The total enthalpy of transformation was found to be 2·21±0·22 meV/atom