Solid solution strengthening

Résumé

In metallurgy, solid solution strengthening is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal), forming a solid solution. The local nonuniformity in the lattice due to the alloying element makes plastic deformation more difficult by impeding dislocation motion through stress fields. In contrast, alloying beyond the solubility limit can form a second phase, leading to strengthening via other mechanisms (e.g. the precipitation of intermetallic compounds). Types Depending on the size of the alloying element, a substitutional solid solution or an interstitial solid solution can form. In both cases, atoms are visualised as rigid spheres where the overall crystal structure is essentially unchanged. The rationale of crystal geometry to atom solubility prediction is summarized in the Hume-Rothery rules and Pauling's

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https://en.wikipedia.org/wiki/Solid_solution_strengthening

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This course covers the metallurgy, processing and properties of modern high-performance metals and alloys (e.g. advanced steels, Ni-base, Ti-base, High Entropy Alloys etc.). In addition, the principles of computational alloy design as well as approaches for a sustainable metallurgy will be addressed

Ce cours est une introduction au comportement mécanique, à l'élaboration, à la structure et au cycle de vie des grandes classes de matériaux de structure (métaux, polymères, céramiques et composites)

Présentation des mécanismes de déformation des matériaux inorganiques: élasticité, plasticité, fluage.

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Elastic, dielectric, and piezoelectric anomalies and Raman spectroscopy of 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3

Leili Batooli, Alberto Biancoli, Dragan Damjanovic, Amirhossein Vahabzadeh

The solid solution 0.5Ba(Ti0.8Zr0.2)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising lead-free piezoelectric material with exceptionally high piezoelectric coefficients. The strong response is related to structural instabilities close to ambient temperature. We report here on temperature-induced anomalies in the dielectric, piezoelectric, and elastic coefficients and Raman spectroscopy of ceramic BCZT. The data indicate ferroelectric-ferroelectric structural phase transitions in this material in addition to those previously reported. An anomaly is also observed above the Curie temperature T-C and is associated with the loss of polar structure that persists thirty degrees above T-C. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714703]

American Institute of Physics2012

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Finite Element Analysis for Fatigue Damage Reduction in Metallic Riveted Bridges Using Pre-Stressed CFRP Plates

Mario Fontana, Elyas Ghafoori, Andrin Herwig, Emmanuel Mayor, Masoud Motavalli, Alain Nussbaumer, Gary Scott Prinz

Many old riveted steel bridges remain operational and require retrofit to accommodate ever increasing demands. Complicating retrofit efforts, riveted steel bridges are often considered historical structures where structural modifications that affect the original construction are to be avoided. The presence of rivets along with preservation requirements often prevent the use of traditional retrofit methods, such as bonding of fiber reinforced composites, or the addition of supplementary steel elements. In this paper, an un-bonded post-tensioning retrofit method is numerically investigated using an existing railway riveted bridge geometry in Switzerland. The finite element (FE) model consists of a global dynamic model for the whole bridge and a more refined sub-model for a riveted joint. The FE model results include dynamic effects from axle loads and are compared with field measurements. Pre-stressed un-bonded carbon fiber reinforced plastic (CFRP) plates will be considered for the strengthening elements. Fatigue critical regions of the bridge are identified, and the effects of the un-bonded post-tensioning method with different prestress levels on fatigue susceptibility are explored. With an applied 40% CFRP pre-stress, fatigue damage reductions of more than 87% and 85% are achieved at the longitudinal-to-cross beam connections and cross-beam bottom flanges respectively.

Mdpi Ag2014

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Thermodynamic study and re-assessment of the Ge-Ni system

Shan Jin, Christian Leinenbach, Andrew Watson

The enthalpies of formation of the intermetallic compounds in the Ge-Ni binary system have been determined by calorimetric measurement and first-principles calculations. Based on the results obtained and information available in the literature, the phase diagram and thermodynamic properties of the Ge-Ni system have been re-assessed using the CALPHAD approach [L Kaufman, H. Bernstein, Computer Calculation of Phase Diagrams, Academic Press, New York (1970)], applying appropriate thermodynamic models for the phases. The liquid phase and the Ni-based solid solution (Ni) were modeled as substitutional solutions using the Redlich-Kister equation to represent the excess Gibbs energy. The B8-type intermediate phases epsilon Ni5Ge3, Ni19Ge12 and Ni3Ge2 were treated as a single phase, designated as Ni5Ge3. A three-sublattice model with stoichiometry (Ge)(Ni)(Va,Ni) was used to describe the B8-type Ni5Ge3-phase based on its crystal structure. The order-disorder transformation between disordered FCC_Al and the ordered L1(2)-type phase, beta Ni3Ge, was treated using a two-sublattice model. The other five intermetallic compounds were treated as stoichiometric compounds. The phase diagram and the thermodynamic properties calculated from the optimized model parameters are in good agreement with most of the experimental data. (C) 2012 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2012

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