- The characteristic of a material that defines its resistance to surface deformation such as scratching or indentation is Hardness.

- Hardness measures how well a material can withstand localized plastic deformation, which occurs when the surface is subjected to mechanical forces.
- This property is crucial in applications where materials are exposed to wear and abrasion.
- For example, harder materials are less likely to be scratched or indented compared to softer materials.

- In contrast, Toughness refers to the ability of a material to absorb energy and plastically deform without fracturing, which relates to overall durability rather than surface resistance.
- Ductility measures a material’s ability to undergo significant plastic deformation before rupture, typically associated with stretching or bending rather than surface resistance.
- Elasticity is the ability of a material to return to its original shape after deformation, reflecting reversible deformation rather than permanent surface damage resistance.

Understanding hardness is essential in selecting materials for surgical instruments, implants, or other medical devices where resistance to surface wear is imperative.

Reference: Materials Science and Engineering: An Introduction, 10th Edition, Chapter 5 / Page 150