In Large Particle particle-reinforced composites, the particulate phase is...

• A. Ductile and soft compared to the matrix
• B. Harder and stiffer than the matrix
• C. Same hardness as the matrix
• D. Leads to ductility increase

Answer: (B)

The key idea is that the reinforcement phase in particle-reinforced composites is there to make the material stiffer and harder. In the case of large particle reinforcements, the particles themselves are much harder and stiffer than the surrounding ductile matrix, so they carry a larger portion of the applied load and resist deformation more effectively. This increases the composite’s stiffness (Young’s modulus) and hardness while the matrix remains to provide toughness and ductility.

If the particulate phase were ductile and soft, it wouldn’t boost stiffness or hardness as the matrix deforms similarly. If the particles had the same hardness as the matrix, there would be little improvement in stiffness or hardness. If the particles somehow increased ductility, that would oppose the typical strengthening effect of hard inclusions. Therefore, the particulate phase is harder and stiffer than the matrix.