Structure and Mechanical Properties of Thick Metal Condensates Strengthened by Dispersed Particles of Various Types.
II. Strengthening Mechanism of Dispersion Strengthened Metals

V.A. Yavor

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Omeliana Pritsaka str.,3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2021, #03/04


Following the experimental data in Part I of this article, the present paper considers existing strengthening mechanisms of dispersion strengthened alloys, including Ansell–Lenel and Orowan–Ashby models, to explain yield strength increase after inserting incoherent and undeformable second-phase particles into a metal matrix. The influence of the particle type on the structure and flow stress under Ansell–Lenel model was evaluated using iron condensates, which contain the most significant number of combinations within the ‘matrix – neutral particle’ system. It was assumed that the shear modulus values for bulk materials are applicable for dispersed particles of the same composition when a yield strength increase was determined. An increase in yield strength after inserting oxides, carbides, and borides into the metal matrix was inconsistent with the Ansell–Lenel model. Therefore, Ansell defines a distance between particles using the volumetric approach to consider the second phase distribution within the matrix. According to the Orowan model modified by Ashby, the yield strength of the matrix with dispersed particles is calculated considering that a planar approach is used to define distance between particles. This parameter is calculated as a mean value of the shortest distances between surfaces of neighboring particles in a sliding plane. It is shown that a distance between particles determined using a volumetric approach displays lower absolute values at the given volumetric content of the second phase compared to the planar approach. Consequently, the first approach (volumetric) suggests larger incremental values of the yield strength. In this study, a planar approach was applied as more realistic to evaluate the distance between reinforcing particles when estimating an incremental yield strength following Orowan–Ashby model. A model proposed in this work as a prototype of the Orowan analysis addresses distance between dislocation clusters generated due to a blocking effect of the second phase, as well as dislocation generation by interphase ‘particle–matrix,’ taking into account a dispersed particle type and a size of an interphase surface.