Diamond Strength

Diamond strength consists of two key metrics: static compressive strength and impact toughness.

  1. Core Indicators  

Static compressive strength: The load (measured in Newtons) at which a single synthetic diamond or CBN grain fractures under static pressure.

Impact toughness: The primary parameter used for quality grading of diamonds today. It refers to the number of impacts required for a 50% unbroken rate under specified impact conditions. Two common values are reported: TI (Toughness Index)​ measured at room temperature, and TTI (Thermal Toughness Index)​ measured after cooling from a 15-minute heat treatment at 1100°C in pure argon. A third variant, thermal impact toughness tested after a 15-minute treatment at 900°C (simulating sintering temperatures, also in pure argon), better reflects real-world application performance.

 

  2. Performance Correlations of Impact Toughness  

• Higher impact toughness corresponds to better overall diamond quality, higher compressive strength, and superior thermal and impact resistance. Diamonds containing magnetic inclusions may retain acceptable compressive strength, but will always exhibit lower impact toughness and poor thermal stability.
• For diamonds of the same grade, finer particle sizes yield higher impact toughness; for diamonds of the same particle size, higher grades correspond to greater impact toughness. Notably, impact toughness values are not comparable across different particle sizes or grades.

 

  3. Supplementary Evaluation for Coarse High-Grade Diamonds  

For high-grade diamonds coarser than 35/40 mesh, the difference in impact toughness between adjacent grades is negligible. In these cases, static compressive strength and thermal stability must be used as auxiliary criteria for quality differentiation.