5. The graph pictured to the right is sample data from a copper labbefore and after cold work. Consult it for the followingmultiple-choice questions.(4 noints)Write the letter on the line. i) The increase in hardness with increasing cold work isseen because: A) Cold working the material makes the grainssignificantly smaller thus blocking dislocation motion. 20B) Extra thermal energy is stored in the material makingit more resistant to further deformation. C) Dislocation density is increasing due to dislocation multiplication mechanisms. D) The act of deforming the material shifts the preferred slip systems making the resolved shear stress on those slip systems decrease. ii) The hardness levels-off in the post-cold-work data because: A) Dislocations escape to the grain boundaries at the same rate they are formed. B) At a certain point, a grain can no longer allow more dislocations to form. C) The heat generated during large amounts of cold work allows for the material to enter the recovery phase of annealing. D) The Rockwell F scale is not accurate above a certain value and thus cannot measure a higher hardness making it only appear that there is a leveling off.

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