Heat treatment and metallic materials
Which statement about substitutional solid-solution strengthening is correct?
- AThe larger the size difference between solute and solvent atoms, the more the lattice is disordered and the more easily dislocations move, so the smaller the strengthening effect
- BIncreasing the solute concentration generally lowers strength and raises ductility, so alloys become softer than the pure metal
- CThe lattice strain field around solute atoms interacts with dislocations and hinders their motion
Show answer and explanation
Answer: C. The lattice strain field around solute atoms interacts with dislocations and hinders their motion
Solute atoms differ from the host atoms in size and elastic modulus, so they create lattice strain fields around themselves. These strain fields interact with the strain fields of dislocations and pin them, so a larger stress is needed to move dislocations. This is solid-solution strengthening, and the effect is larger the greater the atomic size difference (size effect) and the modulus difference. Within the solubility limit, increasing the solute concentration generally raises strength and slightly lowers ductility. Brass (Cu-Zn), Al-Mg alloys, and Si and Mn in steel are typical examples of solid-solution strengthening.
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