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Chapter 6: Problem 42

An undeformed specimen of some alloy has an average grain diameter of \(0.050 \mathrm{~mm}\). You are asked to reduce its average grain diameter to \(0.020 \mathrm{~mm}\). Is this possible? If so, explain the procedures you would use and name the processes involved. If it is not possible, explain why.

Short Answer

Expert verified
If so, what are the procedures and processes involved? Answer: Yes, it is possible to reduce the average grain diameter from 0.050 mm to 0.020 mm. The procedures and processes involved include cold working techniques (rolling, extrusion, forging), recrystallization annealing (a heat treatment), and controlling the conditions of subsequent heat treatments to avoid excessive grain growth.

Step by step solution

01

Determine the possibility of grain reduction

In order to reduce the average grain diameter of an undeformed alloy specimen, certain metalworking processes, such as cold working (deformation at temperatures below the recrystallization temperature) and heat treatments (e.g., annealing), can be employed. So, yes, it is possible to reduce the average grain diameter from \(0.050 \mathrm{~mm}\) to \(0.020 \mathrm{~mm}\).
02

Cold working and annealing

The first procedure to reduce the grain size is cold working, which involves deforming the material at a temperature below its recrystallization temperature. Popular cold working techniques include rolling, extrusion, and forging. Cold working induces plastic deformation in the material, resulting in an increase in dislocation density and a decrease in grain size.
03

Heat treatment (recrystallization annealing)

After cold working, the material will have an increased dislocation density and a reduced grain size. At this point, a heat treatment called recrystallization annealing can be performed to obtain a finer grain size. In recrystallization annealing, the material is heated to a temperature just below its melting point and then slowly cooled down to room temperature. Recrystallization occurs, and the high dislocation density is relieved, forming new, smaller, and more equiaxed grains. The final grain size can be controlled by adjusting the annealing temperature and time.
04

Grain growth control

If further grain size reduction below the achieved level after the recrystallization annealing is required, additional cold working followed by annealing might be performed. However, if the target grain size is already reached, subsequent heat treatments must be controlled carefully to avoid excessive grain growth. This can be achieved by optimizing the temperature and the duration of the heat treatment. In conclusion, it is possible to reduce the average grain diameter of an undeformed alloy specimen from \(0.050 \mathrm{~mm}\) to \(0.020 \mathrm{~mm}\) through a combination of cold working, recrystallization annealing, and controlling the conditions of subsequent heat treatments.

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Most popular questions from this chapter

(a) What is the driving force for recrystallization? (b) What is the driving force for grain growth?

An aluminum bar \(125 \mathrm{~mm}\) (5.0 in.) long and having a square cross section \(16.5 \mathrm{~mm}(0.65 \mathrm{in}\).) on an edge is pulled in tension with a load of 66,700 \(\mathrm{N}\left(15,000 \mathrm{lb}_{\mathrm{f}}\right)\) and experiences an elongation of \(0.43 \mathrm{~mm}\left(1.7 \times 10^{-2}\right.\) in.). Assuming that the deformation is entirely elastic, calculate the modulus of elasticity of the aluminum.

Two previously undeformed cylindrical specimens of an alloy are to be strain hardened by reducing their cross-sectional areas (while maintaining their circular cross sections). For one specimen, the initial and deformed radii are 15 and \(12 \mathrm{~mm}\), respectively. The second specimen, with an initial radius of \(11 \mathrm{~mm}\), must have the same deformed hardness as the first specimen; compute the second specimen's radius after deformation

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