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Grain boundary is one of the most important interfaces that hinder dislocation motion in polycrystalline materials. Knowledge of how grain boundary affects plastic deformation is crucial for both the material design and manufacturing. Grain boundary has the multi-dimensional features, i.e. the grain boundary network topography (~microns) and grain boundary interfacial properties (~nm). Those features can dramatically influence the mechanical properties of material. In this work, the gradient nanocrystalline material and electro-plasticity are investigated, and the effects of grain boundary characteristics on these plasticity phenomena were studied. In the first part of the dissertation, the gradient nanocrystalline (GNC) coppers were produced by Ultrasonic Nanocrystallization Surface Modification (UNSM), and their mechanical properties were measured using tensile tests. It shows that the GNC copper possesses better yield strength and decent ductility compared with the homogeneous polycrystalline copper. A theoretic model, which considers the dislocation interactions in the heterogeneous grain boundary network, was proposed to analyze and explain the superior mechanical properties of GNC material. Our model shows that the yield strength of GNC material can be estimated using the root mean square (RMS), instead of rule of mixture (ROM), of the yield strengths of coarse-grained (CG) layer and gradient-structure (GS) layer. The higher yield strength in GNC material is a result of the dislocation interaction between CG layer and GS layer. On the other hand, the dislocation interaction also induces the dislocation migration from CG layer to GS layer, leading to a transition from dislocation-starvation to dislocation-strengthening. As a result, the dislocation accumulation capacity can be recovered and provide extra strengthening hardening to accommodate large deformation. Our work provides new physical understandings to the unique strengthening mechanisms of GNC materials.In the second part of the dissertation, the electro-plasticity in electric-assisted formation was investigated and the role of grain boundary was examined. During electric-assisted formation (EAF), grain boundary interacts with both electric flows and dislocations. The interaction between grain boundary and dislocation, under the effect of electric current, is important to the physical understanding of electro-plasticity. To simplify this question, we have decomposed the work into two steps. Firstly, a multi-scale numerical model was proposed to simulate the current density distribution in a nanocrystalline metal subjected to electropulsing. The electric current density obtained from the macro scale model was used as the boundary condition for the nano/micro scale model. The electric current density distribution, considering the material heterogeneity of grain boundaries, was predicted by solving the Maxwell’s electromagnetic equations. The simulation results suggested that heterogeneous current density rises as a result of the heterogeneity in the electromagnetic properties at grain boundaries. Due to this current density heterogeneity, grain rotation and selective heating may occur under the effect of electric current. In the second step, enlightened by our simulation work, the electric assisted tensile tests, which have the similar root mean square current densities and, thus, the same temperature rises, were investigated by conducting electric-assisted tensile test. The short duration (100 µs) and high frequency (120 to 800 Hz) pulsed current were used. It shows that, there exists a threshold value of the peak current density, where the electro-pulsing with higher peak current density can reduce more flow stress than direct current. The electric-induced grain rotation, which was suggested in our simulation works, was proved by our experiments as well. The electric-induced grain rotation can reduce the dislocation accumulation around grain boundary and reduce the flow stress eventually. The threshold peak current density is closely related to the electric-induced grain rotation. The results can shed some lights on process design of EAF for an optimized efficiency in reducing the flow stress.This dissertation gives two specific examples of how grain boundary characteristics affect the polycrystalline plasticity. New physical understanding of the grain boundary effects on plastic deformation can be attained, providing fundamental principles for material design and advanced manufacturing.

This paper describes the development of an 8-bit SCL 8051 ALU with two versions: SCL 8051 ALU with nsleep and sleep signals and SCL 8051 ALU without nsleep. Both versions have combinational logic (C/L), registers, and completion components, which all utilize slept gates. Both three-stage pipelined and non-pipelined designs were examined for both versions. The four designs were compared in terms of area, speed, leakage power, average power and energy per operation. The SCL 8051 ALU without nsleep is smaller and faster, but it has greater leakage power. It also has lower average power, and less energy consumption than the SCL 8051 ALU with both nsleep and sleep signals. The pipelined SCL 8051 ALU is bigger, slower, and has larger leakage power, average power and energy consumption than the non-pipelined SCL 8051 ALU.