Journal of the Japan Institute of Metals and Materials

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The work-hardening phenomenon is one of the most well-known and utilized mechanical properties of crystalline materials. This paper overviews the history of the study of work hardening of face centered cubic (FCC) single crystals under monotonic and uniaxial loading and presents some of our work since the 1980s. Chapters 1 and 2 of this paper review the history of work hardening research beginning in the 19th century, and emphasize that the concept of dislocation was first presented by a Japanese researcher, Keiji Yamaguchi in 1929, prior to the work of Taylor, Orowan, and Polanyi. Progress of research in the mid-20th century, backed up by the invention of the transmission electron microscope is then briefly introduced. Chapter 3 discusses the most important question in the mechanism of work hardening, namely, what is the dislocation microstructure that causes work hardening? The role of deformation bands, i.e., kink bands and bands of secondary slip is accentuated from experimental approach. Chapter 4 describes the modeling and numerical approach to the work-hardening. Tensile deformation of numerical models for single crystals with initial inhomogeneities show subtle activity of secondary slip superimposed on the primary one and the formation of deformation bands. The important role of the mean free path of dislocations is emphasized. Finally, directions for future research on work-hardening behavior in face-centered cubic metals are outlined.

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A theorem of creep strengthening was derived from two axioms of creep for the polycrystalline Ni-20 mass％ Cr-X (X = Nb, Ta, Mo, W) solid solutions on the basis of internal stress concept. The general equation describing the minimum creep rate can be divided into two terms: one term is determined by the creep testing condition and the other term with no dimensions represents the creep strength. In the core-mantle model in dislocation creep, the central core region sustains the internal stress during creep and the peripheral mantle region along grain-boundaries is free from the internal stress. The creep strength for the polycrystalline solid solutions is improved by the enhancement of core intensity and core fraction. The strengthening techniques in high-temperature creep for the polycrystalline solid solutions rely on this simple principle: Enhancing core region renders a material stronger.

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