Discrete obstacles, particularly in the form of precipitates of second phases with coherent or incoherent interfaces, dispersed crystalline or glassy nano-scale particles, and aggregates of point defects of various types and even nano-scale cavities can all interact with dislocations to act as slip obstacles that can significantly increase the plastic shear resistance of a metal or alloy. Since the strength of many precipitates can increase with size by aging the alloy at some elevated temperature, precipitate strengthening is a very flexible and powerful industrial process. The chapter explains the precipitation process to develop insight into the factors controlling discrete precipitate formation and decomposition of alloys in unstable regions of equilibrium into different domains by spinodal decomposition. This provides guidance into the factors that control the strengthening mechanisms associated with precipitate coarsening. The chapter also considers the development of a number of prominent mechanisms by which precipitates of various different types and other discrete nano-scale heterogeneities affect the plastic resistance of alloys. The discussion begins with a brief catalogue of the principal forms of interaction between discrete particles and dislocations, as well as of other heterogeneities acting as particles, including an assessment of the possible extent of thermal activation in overcoming such obstacles. There follows a presentation of the various ways in which glide dislocations sample discrete obstacles ranging from the more embryonic forms of clusters to eventually fully mature dispersoids. Relevant theoretical details of specific individual interaction mechanisms of precipitates with dislocations are presented to develop models for plastic resistance, that are compared with corresponding experimental results.
Keywords: precipitation of particles, coarsening of precipitates, spinodal decomposition, dislocation, Friedel-Fleischer sampling, Mott-Labusch sampling, Schwartz-Labusch sampling, peak aging, force-distance curves, strenghening
Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.
If you think you should have access to this title, please contact your librarian.