The Hardness of Silicon Carbide: A Complete Technical Guide for Industrial Applications

Silicon carbide, or SiC, is an advanced ceramic with excellent hardness. Its excellent resistance to scratching, abrasion, and deformation is preferred for extremely harsh operations, like mining, chemical processing, or semiconductor manufacturing. Understanding SiC hardness helps you select the right material for long-lasting performance.

The following article discusses all you need to know about the hardness of silicon carbide, from the elements that affect it to comparisons with other materials and the benefits that silicon carbide hardness can bring in an industrial context.

Why is Silicon Carbide So Hard?

SiC consists of silicon and carbon. These atoms are bonded by strong covalent bonds in a 1:1 ratio in a tetrahedral pattern, forming a rigid three-dimensional crystal lattice.

Such bonds share electrons between adjacent atoms to create a stable connection. It can resist plastic deformation under pressure, making SiC maintain its shape until the stress exceeds its fracture threshold. In contrast, metals will deform through dislocation motion.

Further Reading: Which Ceramics Have the Highest Hardness? – A Guide to Selecting Industrial-Grade Wear-Resistant Ceramics

What Determines the Hardness of Silicon Carbide?

There is not necessarily uniform hardness among silicon carbide ceramics. The manufacturing process and material can determine hardness. Knowing it will help you select the correct grade.

Material Purity

Higher purity silicon carbide consistently delivers higher hardness. Impurities such as iron, aluminum, and free silicon can weaken the structure.

Technical-grade SiC (98-99% purity) works well for standard wear parts. High-purity grades (99.5%+) achieve maximum hardness for the most demanding environments.

Grain Size

Finer-grain structures produce harder ceramics.^[1] Most high-performance SiC ceramics use starting powders in the 0.5-5 micron range to achieve a fine, uniform microstructure after sintering.^[4]

Density and Porosity

Porosity dramatically reduces effective hardness by creating stress concentrations and weak points. Fully dense sintered SiC (above 98% theoretical density) delivers the highest hardness values.

Reaction-bonded SiC contains residual silicon and some porosity. It generally shows lower hardness than pressureless or hot-pressed sintered grades.^[2]

Sintering Method

The manufacturing procedure affects the hardness of materials.

• SSiC sintered with the addition of boron and carbon shows the best results in terms of density and hardness.
• Hot-pressed SiC is characterized by near-theoretical density and hardness.
• RBSiC material shows quite good hardness, though it is somewhat low owing to free silicon.
• Si₃N₄-bonded SiC shows good high-temperature hardness properties for fire-resistant applications.

Crystal Polytype

Silicon carbide has over 250 polytypes. 6H-α and 4H-α are the most common in industrial ceramics. While hardness differences between polytypes are relatively small, α-phase SiC generally exhibits slightly higher hardness than β-phase material at room temperature.

Silicon Carbide Hardness vs Other Engineering Materials

To better understand SiC hardness, this table compares it against materials commonly used in similar industries.

Silicon carbide is significantly harder than alumina and tungsten carbide, yet more affordable and less brittle than boron carbide. These balanced properties make it cost-effective for most heavy-duty wear applications.

In testing, SiC components typically last 3-5 times longer than equivalent alumina parts. It is up to 100 times longer than hardened steel. This helps to reduce replacement frequency and maintenance downtime for your equipment.

Advantages of Hardness on the Performance of Silicon Carbide

Hardness can directly translate into functional advantages that will enhance your manufacturing processes.

Excellent Wear Resistance

One of the greatest advantages of silicon carbide is wear resistance. The hardness allows SiC materials to hold their accuracy and surface finish for longer than metals or softer ceramics. For instance, in applications such as mechanical seals, any wear could lead to failures due to leaks.

Extended Service Life

Harder materials last longer in harsh environments. For example, SiC sandblasting nozzles typically outperform tungsten carbide nozzles by 2-3 times in life. In mining and mineral processing equipment, employing SiC liners reduces replacement intervals from weeks to months.

Surface Finish

High hardness means that SiC components can maintain precise polishing surfaces over a long period of time. It is very important in applications such as sealing surfaces, races of bearings, and metering devices where surface finish plays a key role.

High-Temperature Hardness Retention

Unlike metals that soften significantly at elevated temperatures, silicon carbide retains most of its hardness well above 1,000℃. This makes it suitable for furnace components, hot gas path parts, and high-temperature processing equipment where other materials lose their wear resistance.^[2]

Silicon Carbide Industrial Applications Where Hardness Matters

The excellent hardness of silicon carbide brings many advantages to diverse industries.

Mechanical Seal Faces

If you deal with designing or specifying pumping systems in chemical processing, you may be well aware of how important the reliability of the seals is. SiC seal faces combine high hardness with chemical inertness to withstand aggressive liquids and abrasive suspensions. Its high hardness ensures no grooves form on the contact surfaces.^[5]

Abrasive Blasting Nozzles

The deterioration of the nozzle has an effect on both the uniformity of the pattern and the operating costs. Silicon carbide nozzles resist the constant erosion of high-velocity abrasive media. They stand out well above the steel and tungsten carbide. It means that you can get more consistent blast patterns over longer production runs and fewer changeovers.

Wear Liners & Pipeline Components

Material transport will lead to constant abrasive wear on chutes, pipes and cyclones in mining and mineral processing. SiC liners protect equipment surfaces from the impact and sliding action of ores, coal, and ash. Compared to steel or rubber linings, SiC ones extend equipment service life several times. They are helpful for you to schedule shutdowns and replacement part costs.

Ceramic Bearings & Rolling Elements

If your equipment works in corrosive or high-temperature environments, standard steel bearings fail quickly. Silicon carbide ceramic bearings deliver exceptional hardness along with corrosion resistance and low friction. They perform reliably in chemical pumps and high-temperature conveyors where lubrication is difficult or impossible.

Semiconductor Processing

Exactness and purity are key requirements of semiconductor production. Silicon carbide products, such as wafers handling tools, liners for process chambers, and gas distribution plates, preserve their exactness through thousands of processing cycles.^[3] Silicon carbide’s hardness allows it to prevent plasma and corrosive gases from eroding the material. Using them can keep your equipment running within tight tolerances.

FAQs

Does silicon carbide’s hardness change at high temperatures?

Silicon carbide retains most of its room-temperature hardness up to approximately 1,200-1,400℃. Above this range, hardness gradually decreases. But it still outperforms most other materials at equivalent temperatures.

Can you increase the hardness of an existing SiC component?

No. However, surface treatments such as diamond polishing can improve surface hardness by creating a densified outer layer.

Can silicon carbide scratch hardened steel?

Yes. With a Mohs rating of 9.2-9.5 compared to 7.5-8.0 for hardened steel, SiC will abrade steel surfaces rapidly. This is why it works so effectively as an abrasive and cutting tool.

What hardness grade should I specify for slurry pump parts?

For most slurry applications, a standard sintered SiC grade with 2,500-2,600 HV provides the best balance of hardness, toughness and cost.

Consider a higher-density hot-pressed grade approaching 2,800 HV for extremely abrasive slurries with large particle sizes. It provides maximum service life.

Conclusion

Compared to alumina, tungsten carbide, and steel, silicon carbide offers significantly greater hardness, along with increased resistance to wear, at a comparable price point. Whether you need long-lasting mechanical seals, durable blasting nozzles, or reliable wear protection for equipment, the hardness of silicon carbide translates directly into longer life and lower total operating cost.

Newthink New Materials aims to provide high-quality hard SiC ceramic components to your most demanding industries. Contact us for more information.

Reference

[1] Hansen, N. (2004). Hall–Petch relation and boundary strengthening. Scripta materialia, 51(8), 801-806.

[2] Milman, Y. V., Chugunova, S. I., Goncharova, I. V., Chudoba, T., Lojkowski, W., & Gooch, W. (1999). Temperature dependence of hardness in silicon–carbide ceramics with different porosity. International Journal of Refractory Metals and Hard Materials, 17(5)

[3] Neudeck, P. G. (2006). Silicon carbide technology. The VLSI handbook, 20061800.

[4] Pan, C., Zhang, L., Jiang, W., Setyawan, W., Chen, L., Li, Z., … & Wang, T. (2020). Grain size dependence of hardness in nanocrystalline silicon carbide. Journal of the European Ceramic Society, 40(13), 4396-4402.

[5] Xia, Y., Wang, B., Du, Y., Lu, Y., Yang, M., Yang, G., … & Li, H. (2024). Superior tribological and sealing performance of micro-crystalline diamond coated silicon carbide seals under dry friction and high load. Diamond and Related Materials, 144, 111039