What is the definition of hardness in materials?

The definition of hardness in materials primarily refers to the ability of a material to withstand surface indentation or penetration, which directly relates to its resistance to scratches and wear. Hardness is a crucial property in many engineering applications because it indicates how well a material can maintain its surface integrity under various conditions, especially those involving friction and contact with harder surfaces. This resistance to scratches and wear makes hard materials suitable for applications such as cutting tools, wear-resistant surfaces, and coatings where maintaining a smooth, undamaged finish is essential for functionality and longevity.

While there are other properties associated with materials that reflect their performance (such as resistance to chemicals or corrosion), these do not directly define hardness. Resistance to deformation highlights the ability of a material to retain its shape under stress but is distinct from hardness, which specifically concerns surface durability.