Introduction
Traditional metal materials fail quickly when facing erosion, extreme pressure, or highly abrasive media. High-hardness ceramics have become important to industrial upgrades. But which ceramic is actually the hardest? What are the differences between ceramics with different hardness levels? This article will provide an analysis of the hardness rankings and application of mainstream advanced ceramics. The article will help you in choosing the right wear-resistant ceramic materials for your requirements.
Key Metrics for Measuring Ceramic Hardness
In the advanced ceramics field, we primarily refer to two values.
The first one is Vickers Hardness (HV). This is the most accurate standard in the industry. It is measured using a precision diamond indenter. A higher value means the material has a stronger ability to resist local plastic deformation.
Another is Mohs Hardness. The Mohs scale is relatively simple, ranging from 1 to 10. Diamond is the highest, at level 10. The Mohs hardness of high-performance industrial ceramics is usually concentrated at level 9 or above.
Comparison of Representative Industrial High-Hardness Ceramics
Alumina, silicon nitride, silicon carbide, and boron carbide make up the first tier of high-hardness materials. The table below summarizes the hardness of these ceramic materials.
| Material Name | Vickers Hardness (GPa) | Mohs Hardness |
| Alumina (Al2O3) | 15 – 18 | 9 |
| Silicon Nitride (Si3N4) | 18 – 22 | 9 |
| Silicon Carbide (SiC) | 22 – 28 | 9.5 |
| Boron Carbide (B4C) | 30 – 35 | 9.7 |
Alumina Ceramics: Economical Wear-Resistant Solution
Vickers Hardness: 15 – 18 GPa
Mohs Hardness: 9.0
Although it ranks lower among advanced ceramics, alumina still possesses a hardness far exceeds quenched steel.
Wear-resistant alumina liners utilize this hardness to handle low-speed erosion from pulverized coal in power plants or ores in mines. It can protect steel equipment from wearing. Alumina ceramic valve cores also ensure no scratches during frequent opening and closing friction, maintaining tight seal.
However, when facing strong erosion from harder particles like quartz, the wear rate of Al2O3 increases significantly.
Silicon Nitride Ceramics with Well-Balanced Performance
Vickers Hardness: 18 – 22 GPa
Mohs Hardness: 9.0
Silicon nitride possesses higher hardness than that of alumina. It has both high hardness and impact resistance. Unlike other ceramics, Si3N4 is not prone to chipping.
High-speed bearing balls utilize its high hardness property to reduce deformation during rolling friction. Additionally, its high-hardness surface can crush tiny impurities in the lubricant, without sustaining damage.
While its hardness is superior, its surface scratch resistance is lower than that of silicon carbide in extreme high-pressure cutting or sandblasting environments.
Silicon Carbide Ceramics for Harsh Wear Conditions
Vickers Hardness: 22 – 28 GPa
Mohs Hardness: 9.5
Among non-oxide ceramics, silicon carbide possesses a hardness second only to boron carbide. It effectively resists cutting and wear from the vast majority of natural substances. Even at high temperatures of 1400°C, its hardness hardly degrades. For 90% of extreme environments, silicon carbide is the optimal solution.
SiC high-pressure nozzles are specifically designed to handle fluid jets containing hard solid particles, like sandblasting or desulfurization. Only silicon carbide can ensure the nozzle orifice is not rapidly eroded. Mechanical seal rings with high hardness of SiC ensures the mating faces remain as flat as a mirror even under high-speed rotation, achieving zero leakage.
However, extreme hardness comes with extreme brittleness. Due to its extreme hardness, the cost and difficulty of precision post-processing are much higher than those for alumina.
Silicon Carbide Ceramic Tiles That Shatter Due to Strong ImpactBoron Carbide Ceramics with Extreme Hardness: Specialty Choice
Vickers Hardness: 30 – 35 GPa
Mohs Hardness: 9.7
Boron carbide is also called “Black Diamond”. Its hardness in nature is second to diamond and cubic boron nitride. It also features low density, making it lightweight.
Ballistic armor plates utilize its extreme hardness. It can instantly shatter high-velocity projectiles upon contact and absorb their energy. Used as an abrasive, it leverages the hardness differential to process and polish other hard alloys or ceramics.
Its excessive hardness results in extremely high processing costs. As a result, BN is typically used only in specialized fields that demand the absolute limits of weight reduction and hardness.
Why Should be Cautious with Higher Hardness Materials?
Ceramics possess high hardness because of their strong internal covalent bonds. This structure makes its atoms difficult to displace. But it also means the material lacks ductility. Materials with higher hardness are generally more sensitive to impact. You should try your best to avoid subjecting these ceramic materials to physical shocks.
Furthermore, the higher the ceramic’s hardness, the higher the cost for post-processing and finishing. Machining SiC requires expensive diamond tools and places extremely high demands on the manufacturer’s equipment and technical processes.
How to Choose the Right Solution Based on Hardness Needs?
To optimize production costs and extend equipment life, we recommend selecting ceramic materials based on your specific engineering requirements.
Mild Wear & Budget Sensitive: First choice should be 92/95/99 Alumina ceramics.
High-Speed Operation & Impact Environments: Silicon Nitride. Its toughness helps prevent parts from chipping or cracking.
Extreme Erosion & High-Temperature Corrosion: Silicon Carbide ceramics. Its ultra-long service life reduces your total cost of ownership.
Maximum Hardness Regardless of Cost: Choose Boron Carbide.
Hardness is the most fascinating characteristic of advanced ceramics. Matching them to the right working conditions can deliver the greatest value. So choosing the right one is a key step in improving your industrial quality and efficiency.
NKM Wear-Resistant Silicon Carbide Bushing DrawingsIf you are facing wear issues or need high-hardness materials, feel free to consult us. Newthink New Materials has been deeply involved in the R&D and production of advanced ceramic materials for 14 years. We specialize in the custom processing of high-performance Silicon Carbide and Silicon Nitride parts. Our engineers will provide you with free, full-process support from material selection to after-sales service.
Reference
[4] Kato, K., & Adachi, K. (2002). Wear of advanced ceramics. Wear, 253(11-12), 1097-1104.
