A hypothetical metal alloy has a grain diameter of 2.4 × 10−2 mm. After a heat treatment at 575°C for 500 min, the grain diameter has increased to 5.6 × 10−2 mm. Compute the time required for a specimen of this same material (i.e., d0 = 2.4 × 10−2 mm) to achieve a grain diameter of 5.5 × 10−2 mm while being heated at 575°C. Assume the n grain diameter exponent has a value of 2.2.

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Answer:

The time to achieve a grain diameter of 5.5 × 10⁻² mm is 477 minutes

Explanation:

We need to first solve for K

Given that:

grain diameter exponent (n) = 2.2

grain diameter (d) = 5.6 × 10⁻² mm = 5.6 × 10⁻⁵ m

d₀ =  2.4 × 10⁻² mm =  5.6 × 10⁻⁵ m

t = 500 min

[tex]K=\frac{d^{n} -d_{o}^{n}}{t} = \frac{(5.6*10^{-5})^{2.2}-(2.4*10^{-5})^{2.2} }{500}[/tex] = 7.48 × 10⁻¹³ m/min

From K we can determine the time required based on the desired diameter

grain diameter (d) = 5.5 × 10⁻² mm = 5.5 × 10⁻⁵ m

[tex]t=\frac{d^{n} -d_{o}^{n}}{K} = \frac{(5.5*10^{-5})^{2.2}-(2.4*10^{-5})^{2.2} }{7.48*10^{-13} }[/tex] = 477 min