1. M ATERIALS E NGINEERING – D AY 8 Review of Cold Work and Annealing Demonstration Metal Processing Examples

2. R EVIEW Q UESTIONS What is cold work (CW) and how is it used in metal processing? What is annealing and how is it used in metal processing? Name three phenomena associated with the annealing process. Describe what happens to the Cold Worked metal as each occurs.

3. S AMPLE C OLD W ORK C ALCULATION Can you calculate the cold work associated with cold rolling a 0.25 inch thick plate down to a thickness of 0.15 inches?

4. E XAMPLE P ROBLEM – B ASED ON F IGURE 7.19 A copper wire must be drawn to a diameter of 1/8 inches. We are starting with stock having diameter of 1.0 inches. The wire’s final %EL ductility must be greater than 20%. The yield strength must exceed 30 ksi. Describe the processing of this wire. (Maybe multiple steps?)

5. E XAMPLE P ROBLEM – B ASED ON F IGURE 7.19 – F INAL S TEP OF CW Observe that 10% < %CW < 16%. Settle on 13%. Calculate the diameter at the start of the final step.

6. E XERCISE C ONTINUED. We can see that a number of steps of cold work followed by annealing must be carried out. The %CW is arbitrary excep in the last step, in which we have to go with 13% CW

7. A N EW I DEA : A MORPHOUS M ETALS (G LASSY M ETALS ) Glass means that there is no recognizable crystallinity. Glasses are made when liquids solidify rapidly enough so that the amorphous liquid structure is “frozen” into place. We will be talking about glasses from time to time in ME328. First metallic glass: 1957, Pol Duwez at Caltech. (See Wikipedia) 1. 80% Gold – 20%Si 2. Needed cooling rates of 1,000,000K/sec.

8. P ROPERTIES AND P ROBLEMS Imagine a metal with no grains! And no dislocations! What would the properties be like? It turns out that amorphous metals have much better mechanical properties than ceramic or polymeric glasses. The problem lies in the extreme cooling rate. It is hard to get very large bulk pieces. Need to work with filaments, sheets and ribbons.

9. R ECENT D EVELOPMENTS BMG, bulk metallic glasses with thicknesses on the order of centimeters can be produced. These are alloy systems with many different components. There is a “confusion effect” due to the need for many different types of crystals to form at once. Therefore, slower cooling rates are now possible. Glassy steel. Ductile BMG