Effect of Grain Size Distribution on Tensile Properties of Electrodeposited Nanocrystalline Nickel
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Effect of Grain Size Distribution on Tensile Properties of Electrodeposited Nanocrystalline Nickel Fereshteh Ebrahimi, Zunayed Ahmed and Kristin L. Morgan Materials Science and Engineering Department, University of Florida, Gainesville, FL 32611 ABSTRACT We have produced dense and ductile nanocrystalline nickel with various grain size distributions using electrodeposition techniques. The strength of the nickel deposits fell within the scatter band of the general Hall-Petch curve for nickel. However, large variations in yield strength, strain hardening rate and tensile elongation were associated with a relatively small change in the average grain size. The scatter in the elongation data has been attributed to the formation of nodules and the presence of voids. The variations in strength and strain hardening rate have been shown to be associated with the changes in the grain size distribution. A model based on confined dislocation motion and composite behavior has been developed for predicting the stress-strain behavior of the nanocrystalline nickel. INTRODUCTION Figure 1 shows the flow stress of nickel as a function of d-1/2, where d is the average grain size. A linear relationship indicative of the Hall-Petch relationship may be recognized in this plot (slope ≅ 7,000 MPa nm1/2). However, there is a large scatter in the data. Many sources contribute to this scatter. The flow stress values shown in 2500 Figure 1 represent hardness (flow stress = hardness/3), strength at 1% plastic strain and 2000 ultimate tensile strength (UTS) for specimens with a low ductility [1]. Since ultra-fine grained metals (d
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