The Role of Stacking Fault Energy on the Indentation Size Effect of FCC Pure Metals and Alloys
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The Role of Stacking Fault Energy on the Indentation Size Effect of FCC Pure Metals and Alloys D.E. Stegall, M.A. Mamun, A.A. Elmustafa Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, VA, 23529, United States ABSTRACT We investigated the effect of stacking fault free energy (SFE), on the magnitude of the indentation size effect (ISE) of several pure FCC metals using nanoindentation. The metals chosen were 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and 70/30 Copper Zinc (Įbrass). Aluminum has a high SFE of about 200 mJ/ m2, whereas Į -brass has a low SFE of less than 10 mJ/ m2. Nickel and Silver have intermediate SFE of about 128 mJ/ m2 and 22 mJ/m2 respectively. The SFE is an important interfacial characteristic and plays a significant role in the deformation of FCC metals due to its influence on dislocation movement and morphology. The SFE is a measure of the distance between partial dislocations and has a direct impact on the ability of dislocations to cross slip during plastic deformation. The lower the SFE the larger the separation between partial dislocations and thus cross slip and dynamic recovery are inhibited. The SFE impacts pure metals differently from alloys. It was discovered that the characteristic ISE behavior for the pure metals was different when compared to the Į-brass which is an alloy. Several additional alloys were chosen for comparison including 7075 Aluminum and 70/30 Nickel Copper. . INTRODUCTION We have investigated the influence of stacking fault energy (SFE) on the indentation size effect (ISE) for several metals using nanoindentation experiments. The formation of a stacking fault is an interruption of the normal stacking sequence for a given crystallographic structure and can be produced by plastic deformation in most metals. In particular, a stacking fault is formed when a perfect dislocation decomposes into two partial dislocations. The SFE is the energy associated with the separation distance between the partial dislocations that form the stacking fault. Metals having a low SFE, such as Į-brass, have a large separation between the partial dislocations. In contrast, metals having a high SFE, such as aluminum, have a very narrow separation between the partial dislocations. The SFE contributes to the mechanisms of work hardening and dynamic recovery by either assisting in dislocation cross slip in the case of high SFE metals or prohibiting dislocation cross slip in the case of low SFE metals. The effect of SFE on various parameters related to work hardening such as grain size dependence [1], tensile behavior [2], and size effects have been the subject of ongoing research for many years. Given that the SFE influences the movement of dislocations, several researchers postulated that indentation size effects (ISE) for different metals would be influenced greatly by their respective SFE [3,4]. The ISE of metals is commonly examined by using indentation experiments and is characterized by an increase in hardness (or flow stress) with decreasing indent
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