Metallic state Plastic deformation of metals

When subjected to stress, a crystalline solid, such as a metal, deforms reversibly as long as the applied stress is below a critical value, known as the elastic limit. Beyond this critical stress, deformation ceases to be reversible: a deformation, known as plastic deformation, remains after the stress has been removed. If deformation continues, the solid will eventually break.

Ductility defines the ability to tolerate significant plastic deformation, and depends on both the nature of the material and the type of test. For example, by rolling in several passes, it is possible to reduce a metal block whose dimensions are of the order of a metre to a plate whose thickness is of the order of a fraction of a millimetre, i.e. a deformation of the order of 10 ³ , whereas in uniaxial tension, it is difficult to achieve a deformation at break greater than 1.

The study of plastic deformation undoubtedly had its origins in the desire to control the forming and use of metals, and more generally of materials. As a result, it has long been empirical, and it is only in the last few decades that the concepts needed to understand the physical phenomena involved in plastic flow have been developed. For crystalline solids, to which we shall confine ourselves in this presentation, the basic mechanisms are fairly well understood, but the dynamics of flows are poorly understood, and currently constitute a very active area of research.

In this article, we aim to describe as simply as possible the mechanisms involved in the plastic deformation of metals, and more generally of crystalline solids.

In paragraph 2 , we analyze deformation mechanisms from a structural point of view; paragraph 3 describes general aspects of plastic flows. Specific examples are given in paragraph