Theory for plasticity of face-centered cubic metals

Abstract

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control.planar fault | twinning | slip | molecular dynamics E lastic deformation of metals is fully described by Hooke's law, connecting stress and strain via the usual elastic parameters. In contrast, plasticity is a property that originates from dislocations and involves transitions over various competing energy barriers. A phenomenological description of the plastic regime based merely on the stacking fault energy (SFE) has been widely used by material scientists (1-11), even though it is not at all clear whether such an equilibrium property can really capture the complexity of plastic deformation. To try to mend this situation, researchers have introduced the so-called generalized planar fault (GPF) energy, which comprises several intrinsic energy barriers (IEBs) and thus provides detailed information on the deformation process itself (12, 13). Nevertheless, the GPF energy has not yet been fully recognized because of its inherent difficulty in experimental validation (14). In the present paper we solve this and introduce an approach that is fully transparent, where there are no such ambiguities.Face-centered cubic (fcc) metals possess three distinct deformation mechanisms: stacking fault (SF), twinning (TW), and full slip (SL) (2,(5)(6)(7)15). Many studies tried to relate the deformation of fcc metals to the GPF energy. For example, the competition between TW and SL was explained by a relative change between the intrinsic energy barriers, assuming the activation of the lowest barrier mode (16)(17)(18). However, such a simplified picture was found to be inadequate to elucidate the simultaneous activation of different modes seen in experiments (2,5,6,15). It has emerged that additional factors should be taken into account in conjunction with the GPF energy for describing the deformation behavior.The microstructure of materials, such as grain size and orientation, is known to in...

Impurity effect of Mg on the generalized planar fault energy of Al

“…Besides, the different pseudopotentials as used in the calculations (cf. [20,38]. Instead, several features of the full GPFE curves are needed to determine the plastic deformation mechanisms of materials, and to predict the propensity for formation of stacking faults, nucleation of dislocations and deformation twins.…”

“…Instead, several features of the full GPFE curves are needed to determine the plastic deformation mechanisms of materials, and to predict the propensity for formation of stacking faults, nucleation of dislocations and deformation twins. It is generally believed that three distinct deformation mechanisms exist in fcc metals: twinning (TW), stacking faults (SF), and full slip (FS) [38]. To compare the deformation mechanism in Al and Cu, their GPFE curves, including TW, SF and FS, are shown in Fig.…”

“…Cu is on the other hand displaying a much smaller  UTFE - USFE , so that deformation twinning is much more energetically probable. Recently, Jo et al [38] proposed the intrinsic slip barrier, defined as  d = ISFE /( USFE - ISFE ), to classify the deformation characteristics of materials. For fcc metals having 0< d <2, both twinning and FS can be activated during plastic deformation, while for metals possessing  d >2, deformation will be governed by FS.…”

First-principles prediction of the deformation modes in austenitic Fe-Cr-Ni alloys

“…Note that twinning always occurs together with the slip mechanism. [13] It is interesting that the upper limit for the stacking fault mode at 300 K locates at 8 c Ni 11 (at.%). These alloys have SFE around 10-14 mJm −2 (see Fig.2 (a)).…”

“…[19] On the other hand, δγ utf /δT increases slightly from ∼0.019 mJm Utilizing the calculated GSF energies, we may discuss the favorable plastic deformation modes in Fe-Cr-Ni alloys with respect to composition and temperature according to the recently developed plasticity theory for fcc metals and alloys. [13] It was proposed that the preferred plastic deformation is decided by the competition between the three effective deformation energy barriers defined as…”