Question

Creep resistance can be improved by allowing the

• A. Fine grains to grow
• B. Soft particles to precipitate along grain boundaries
• C. Directional solidification of alloys
• D. Uniformly dispersed coarse particles precipitation in the metal matrix

Hint:

Creep-resistant alloys often employ \textbf{directional solidification} or even \textbf{single crystal structures} to reduce grain boundary sliding.

Answer 1

The Correct Option is C

Step 1: Understanding creep resistance Creep resistance refers to a material's ability to resist deformation under prolonged exposure to high temperatures and stress. Materials intended for such applications require a microstructure that impedes dislocation movement and diffusion. Step 2: Role of directional solidification Directional solidification aligns grains in a preferred direction, typically parallel to the loading axis. This reduces the number of grain boundaries transverse to the applied stress, thus minimizing pathways for creep deformation (especially grain boundary sliding). Step 3: Why other options are incorrect - \textit{Option A:} Fine grains promote creep due to increased grain boundary area. - \textit{Option B:} Soft particles are ineffective at blocking dislocation motion. - \textit{Option D:} Coarse particles may not efficiently hinder creep, especially if not finely dispersed or coherent. Conclusion: Among the options, directional solidification of alloys is the most effective method to enhance creep resistance.