Nt1310 Unit 6 Lab

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Discussion
1. What causes the increase in hardness when brass undergoes cold work?
Hardness increases as cold working occurs because the dislocation density increases. Dislocations generate a repulsive stress field and result in a repulsive force to dislocation incident. Thus increasing amount of applied stress is necessary to move a dislocation and allowing for a higher yield strength. This is why the resistance value or the hardness value towards deformation is increasing.

2. What is “stored energy” and where is it stored in the structure?
The stored energy of a material is its internal strain energy or residual stress within the structure as a tangled network of dislocation and crystal distortion. This energy can also be referred to as …show more content…
Calculate and solve for the activation energy, Q, and the material constant, A using R is equal to 8.314 J/(mol K).
The following calculations is very similar to problem 3 under the deliverable section. ln⁡(1/τ_50 )=ln⁡(A)-Q/RT
The Q and A are obtain with different R given in this problem, calculation can be seen below.
Q=3628.8*8.314 J/(mole*k)=30169.8 J/(mole*k) ln⁡(A)=3.778=y-intercept, A=e^3.778=43.729
8. Would a component made by cold forging be stronger than the same component made by casting?
A component made by cold forging would be stronger than the same component made by casting. This is because cold forged components undergo work hardening, which results in the increasing of dislocation density which increases the material’s strength.

9. What microstructural effect does cold working produce that causes an increase in strength and residual stress?
During the cold working, the number of dislocations increases and dislocation motion decrease, causing the metal to be strengthened as its shape is changed. Nevertheless, an increase in cold working also increases the level of total internal energy of the material, which results in residual stress as a tangled network of …show more content…
From the annealing part of lab, I was expose to heating up brass at three different temperatures and measuring the harness value of each sample under different time intervals. The result show reduction trend in hardness value of material as annealing time increase. This makes sense because the dislocation density decrease and ductility of material increase. Thus, it result decrease in harness value. Also in figure 1, the four samples show an increase in hardness value for a little bit prior to quickly dropping. This matches with the beginning of the annealing process where hardness increase a bit then decreases all due to the recovery, recrystallization, then grain growth which causes the decrease. For the cold working lab, brass was rolled to reduce the thickness and increase the strength of material. The samples experienced 30% and 60% total reduction. I also learn that recrystallization temperature (which is the temperature at which a microstructure of new grains that have very low dislocation density appear) decrease when amount of cold work increase, this is because greater amounts of cold work make the metal less stable and encourage nucleation of recrystallized grain. Nevertheless, recrystallization temperature will reduce as annealing temperature increase because it allows more time for nucleating and growth of the new recrystallized
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