Mechanical Behavior and Fracture of Engineering Materials by Jorge Luis González-Velázquez

Author:Jorge Luis González-Velázquez
Language: eng
Format: epub, pdf
ISBN: 9783030292416
Publisher: Springer International Publishing

The precipitates are classified depending on the coincidence of their crystalline planes with those of the matrix, as depicted in Fig. 4.27, as follows:(a)Coherent. The matrix planes match in all directions with those of the particle.

(b)Semi-coherent. The plane matching is partial.

(c)Incoherent. There is no plane match.

Fig. 4.27Schematic representation of precipitate coherency

As observed in Fig. 4.27, in coherency, the differences of lattice parameters between the particle and the matrix introduces an elastic deformation field around the particles. Such stress field difficult the dislocation movement by the attraction and repulsion forces between the dislocation and the particle stress fields.

The mechanism of fine particle strengthening depends on whether the particles can be cut by dislocations or not. When particles are cut by dislocations, a shear deformation, along with a step in each side of the particle are produced, as illustrated in Fig. 4.28. The deformation strains the surrounding matrix and the new surfaces created by the steps increase the work demand to produce the corresponding surface energy. Since the work is supplied by the load, the result is an increment on the stress required to plastically deform the material.

Fig. 4.28Mechanism of fine particle dislocation cutting

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