The Effects of Straining on Copper-Silver Hardness By: Dhanvir Aujla Advisor: Dr. Anthony Rollett Graduate Student: Samuel Lim

Background To advance the development of magnets, new composites consisting of high strength, and high electrical conductivity properties are needed. To increase the strength of a material, temperature, impurities, and plastic deformation, are used to influence the materials strength. These influences also create an increase in resistivity by increasing the number of electron scattering centers, the result can be illustrated by the Mathiessen’s rule as shown below:

Background Cont’d The samples used in the following research were comprised of 40% copper and 60% silver. Copper and silver are the two most conductive metals. There are two sets of samples, one, which is cold-worked by a method known as swaging, and the other which is first swaged down to the desired diameter, and then annealed.

Goals Improving the current magnets by testing potential composites will lead to creating higher magnetic fields. Some applications for the higher generated magnetic fields include, efficient power generation, improved magnetic resonance imaging (MRI), and breakthroughs in disease treatments. My Goals for this summer were to test whether the copper-silver composites will become harder when strained and reduced to a smaller diameters. The results of this research will enable one to determine if a silver enriched copper-silver composite is suitable for creating the next generation magnets.

Approach Preparing the samples The nano-indenter allowed me to test the hardness across a sample. The SEM pictures were used to calculate the lamellae thickness. Secondary electrons (2.63mm)Backscattering electrons (2.63mm)

Results SEM pictures were taken at different magnitudes and were then used to measure the lamellae thickness using the line intercept method. As the diameter of the samples decrease, so does the thickness, which contributes to the yield stress of the material, illustrated by the Hall-Petch equation.

Hall-Petch equation: Where: = yield stress= friction stress= locking parameter D = grain diameter Taking the experimental Young’s modulus of Copper-Silver to be 88 GPa, and solving for the stress using: One is able to graph the calculated stress vs. the diameter of the grains (D^1/2), to yield the theoretical friction stress and locking parameter, which correspond to the intercept and slope respectively.

The friction stress and locking parameter for the annealed samples are GPa and (N/m) (3/2) respectively. The friction stress and locking parameter for the as swaged samples are GPa and (N/m) (3/2) respectively.

As the diameter of the material increases, the yield stress decreases. This correlation can also conclude that if the yield stress decreases as the diameter increases, the hardness must also decrease as the diameter increases.

The hardness for the annealed and as swaged values are relatively the same, and show a trend to increase in hardness as the diameters decrease. However, at larger diameters the values are quite different.

References Callister, William D. Jr. Material Science and Engineering an Introduction sixth edition, Wiley Inc. Dieter, George E. Mechanical Metallurgy third edition, McGraw-Hill Inc Heringhaus, Frank. “Quantitative Analysis of the Influence of the Microstructure onStrength, Resistivity, and Magnetoresistance of Eutectic Silver-Copper.” Shaker Verlag, Aachen, 1998 National High Magnetic Field Laboratory (NHMFL)

Acknowledgements Dr. Rollett Samuel Lim Charney Davy Dr. Kalu Questions?

Lamellae thickness Annealed (mm) Thickness (microns) As Swaged (mm) Thickness (microns)

Mean Hardness Values DiameterAs SwagedStd. Dev.AnnealedStd. Dev mm2.154 GPa GPa mm1.784 GPa GPa mm2.24 GPa GPa mm2.15 GPa GPa0.1863