How is "hardness" best defined in metallurgy?

Hardness in metallurgy is best defined as the degree to which a metal can resist penetration. This definition highlights the property of materials that determines how well they can withstand local deformation under an applied force. The measurement of hardness typically involves assessing how difficult it is to make an indentation or groove in a material with a specific indenter, which gives insights into the material's resistance to wear and scratching.

Understanding hardness is crucial in various applications, especially in aerospace, where materials are often subjected to extreme conditions and need to exhibit a certain level of durability and wear resistance. The specific methods for measuring hardness, such as Rockwell, Brinell, or Vickers tests, all relate back to the material's resistance to penetration.

Other options focus on different material properties: the ability to withstand pressure is more related to strength characteristics, the property of conducting heat pertains to thermal conductivity, and the weight-bearing capacity directly relates to a metal's structural capabilities. Each of these attributes plays a role in material selection for specific applications, but they do not specifically define hardness as effectively as the resistance to penetration.