Atomistic simulations of hydrogen distribution in Fe-c steels

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Quantification of microdamage phenomena during tensile straining of high volume fraction particle reinforced aluminum

Particle reinforced composites are produced by infiltrating ceramic particle beds with 99.99% Al. Resulting materials feature a relatively high volume fraction (40-55 vol. pet) of homogeneously distributed reinforcement. The evolution of damage during tensile straining of these composites is monitored using two indirect methods; namely by tracking changes in density and in Young's modulus. Identification and quantification of the active damage mechanisms is conducted on polished sections of failed tensile specimens: particle fracture and void formation in the matrix are the predominant damage micromechanisms in these materials. The damage parameter derived from the change in density at a given strain is found to be one to two orders of magnitude smaller than the parameter based on changes in Young's modulus. A simple micromechanical analysis inspired by the observed damage micromechanisms is used to correlate the two indirect measurements of damage. The predictions of this analysis are in good agreement with experiment. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. AII rights reserved

LIGA microsystems aging : evaluation and mitigation.

The deployment of LIGA structures in DP applications requires a thorough understanding of potential long term physical and chemical changes that may occur during service. While these components are generally fabricated from simple metallic systems such as copper, nickel and nickel alloys, the electroplating process used to form them creates microstructural features which differ from those found in conventional (e.g. ingot metallurgy) processing of such materials. Physical changes in non-equilibrium microstructures may occur due to long term exposure to temperatures sufficient to permit atomic and vacancy mobility. Chemical changes, particularly at the surfaces of LIGA parts, may occur in the presence of gaseous chemical species (e.g. water vapor, HE off-gassing compounds) and contact with other metallic structures. In this study, we have characterized the baseline microstructure of several nickel-based materials that are used to fabricate LIGA structures. Solute content and distribution was found to have a major effect on the electroplated microstructures. Microstructural features were correlated to measurements of hardness and tensile strength. Dormancy testing was conducted on one of the baseline compositions, nickel-sulfamate. Groups of specimens were exposed to controlled thermal cycles; subsequent examinations compared properties of 'aged' specimens to the baseline conditions. Results of our testing indicate that exposure to ambient temperatures (-54 C to 71 C) do not result in microstructural changes that might be expected to significantly effect mechanical performance. Additionally, no localized changes in surface appearance were found as a result of contact between electroplated parts

Alumina-aluminum interpenetrating-phase composites with three-dimensional periodic architecture

Abstract Robotic deposition was used to create an alumina structure with three-dimensional periodicity and submillimeter feature size. Liquid metal infiltration of this structure resulted in an Al 2 O 3 -Al interpenetrating-phase composite exhibiting low thermal expansion and high compressive strength