Common Sintering Processes of Silicon Carbide (SiC) Ceramics

Silicon carbide (SiC) ceramics are premium industrial materials. It possesses excellent hardness, thermal stability, corrosion resistance and thermal conductivity. Therefore, SiC is indispensable for many industrial structural and functional components.

Sintering is an important step to govern the properties and final quality of SiC ceramics. Proper sintering process allows you to stabilize product performance and optimize production costs. This article covers 5 mainstream SiC sintering technologies, comparing their principles, strengths, and use cases to help you pick the ideal solution for your production needs.

Pressureless Sintering of SiC Ceramics (PSSiC)

Pressureless sintering is the most traditional and widely used sintering method. It proceeds under normal atmospheric pressure without external mechanical pressure. This process always needs to mix high-purity SiC powder with trace sintering additives before molding.

The sintering temperature ranges from 1,800℃ to 2,150℃ in an inert atmosphere. Additives solve the low self-diffusion problem of SiC covalent bonds. They promote particle bonding and body densification during heating.

Strength

This process has obvious practical strengths. It requires simple production equipment and low mold investment. It supports multiple molding methods for complex and large-sized SiC parts. Moreover, it enables large-scale continuous production to lower your unit costs.

Weakness

Its main weakness lies in the moderate densification effect. The finished product has tiny residual pores and slightly lower compactness. It suits standard industrial SiC parts with ordinary precision requirements.

Application

You can adopt PSSiC for the mass production of conventional SiC structural parts. It performs well for industrial kiln furniture and common heat exchange parts. Employing this process can balance production efficiency and cost control perfectly for your batch orders.

Hot Press Sintering of SiC Ceramics (HPSiC)

Hot press sintering is a high-precision sintering process for high-performance SiC ceramics. It applies 20MPa to 40MPa axial pressure while heating SiC raw materials in molds. The combination of high temperature and pressure accelerates particle rearrangement.

This dual action eliminates internal gaps effectively. It raises the product density to over 99.5% of the theoretical value. The finished SiC ceramics have ultra-low porosity and fine uniform grains.

Strength

Hot press sintering delivers superior mechanical properties. Its products boast high bending strength and strong corrosion resistance. It greatly improves the service life of precision components.

Weakness

This process also has noticeable limitations. It needs high-end customized molds and precise heating-pressure equipment. It only produces simple-shaped parts and has low single-batch output. Its overall production cost remains relatively high.

Application

You should choose hot press sintering for high-precision, high-strength SiC core components. It fits semiconductor equipment parts and high-end wear-resistant mechanical components. It meets your strict quality standards for high-performance industrial applications.

Reaction Sintering of SiC Ceramics (RBSiC/SiSiC)

Reaction sintering is a cost-effective process for complex SiC ceramic products. It mixes SiC powder with carbon sources to form pre-sintered green bodies. Then, infiltrate liquid silicon into the bodies at 1,500℃ to 1,700℃.

Liquid silicon reacts with internal carbon to generate new β-SiC phases. These new phases fill internal pores and bond original SiC particles tightly. The whole process brings nearly zero volume shrinkage.

Strength

Low sintering temperature cuts your energy consumption and equipment loss. Near net-shape molding reduces follow-up polishing and processing work. It greatly improves your material utilization rate.

Weakness

The main downside is residual silicon inside finished products. Excess silicon slightly reduces the material’s high-temperature oxidation resistance. It is not suitable for ultra-high temperature working environments.

Application

You can use reaction sintering for large-sized and irregular SiC ceramic parts. It is ideal for desulfurization nozzles, furnace radiation tubes and large heat exchanger components. It optimizes your production cost for large non-standard parts.

Liquid Phase Sintering of SiC Ceramics (LPSiC)

Liquid phase sintering relies on multi-component sintering additives. Additives form a uniform liquid phase at medium and high temperatures. The liquid phase wraps SiC particles and accelerates particle diffusion and sliding.

Strength

This process realizes rapid densification at lower temperatures. It avoids excessive grain growth caused by ultra-high temperature sintering. Finished products have balanced toughness and hardness.

Besides, liquid phase sintered SiC ceramics have good thermal shock resistance. They perform stably in environments with frequent temperature fluctuations.

Weakness

The liquid phase formed by additives remains inside the ceramic matrix. It will slightly reduce the high-temperature oxidation resistance and structural stability above 1,400℃. LPSiC also has stricter requirements for additive purity and proportioning. Improper formula settings will easily cause internal impurities and affect product durability.

Application

You can employ LPSiC for medium-temperature industrial components with frequent thermal cycles. It is widely used for thermal cycling equipment parts and medium-temperature wear-resistant structural components. It is also ideal for industrial ceramic accessories that require both toughness and basic high-temperature performance.

Spark Plasma Sintering (SPS) of SiC Ceramics (SPSSiC)

Spark plasma sintering is an advanced rapid sintering technology. It uses pulsed current and micro-pressure to heat SiC raw materials instantly. It completes densification in a short time, far faster than traditional ones.

Rapid sintering restricts grain growth effectively. It prepares ultra-fine-grain SiC ceramics with excellent comprehensive performance. The product has high compactness and a uniform internal structure.

Strength

The biggest advantage is its short production cycle. This can greatly improve your prototype development and small-batch trial production efficiency.

Weakness

Relying on expensive professional SPS sintering equipment, the process can only support small-batch production. It cannot manufacture large-sized or ultra-complexly shaped parts.

Application

You can adopt SPSSiC for high-precision, high-value customized SiC components. It perfectly fits new material R&D trials and small-batch production of aerospace precision parts. It is also suitable for manufacturing high-performance semiconductor ceramic components that require an ultra-fine grain structure.

FAQs

Which SiC sintering process is best for mass production?

Pressureless sintering. It features low equipment costs, simple operation, and high batch output, fitting large-scale manufacturing of standard SiC ceramic parts.

Why do high-precision SiC parts adopt hot press sintering?

Hot press sintering achieves near-theoretical density with minimal pores. It produces uniform grains and stable mechanical properties. It meets strict precision and strength demands for core industrial components.

Can reaction sintered SiC ceramics work at ultra-high temperatures?

No. Residual free silicon exists in reaction sintered products, and it softens at ultra-high temperatures. This will reduces the material stability. RBSiC parts suit medium and conventional high-temperature scenarios only.

What factors affect the density of sintered SiC ceramics?

Sintering temperature, holding time and additive types. External pressure and raw material powder fineness also greatly impact final compactness.

Is SPS sintering suitable for large-scale industrial production?

Not currently. SPS equipment is costly with low single-batch output. It fits small-batch customization and R&D trials.

How to choose between liquid phase and solid phase pressureless sintering?

Choose liquid phase sintering for better toughness and thermal shock resistance.

Choose solid phase sintering for higher high-temperature purity and oxidation resistance.

How to reduce production defects in SiC sintering?

• Control raw material powder purity and additive dosage strictly.
• Stabilize sintering temperature, pressure, and atmosphere parameters.
• Optimize heating and cooling rates to avoid pores and cracks.

Conclusion

With continuous sintering technology upgrades, SiC ceramics gain wider applications in advanced industrial fields. Each SiC ceramic sintering process has unique technical characteristics and application boundaries. A reasonable process selection based on your product’s precision, usage environment, and production scale improves your product competitiveness and optimizes production cost.

Newthink New Materials is dedicated to providing high-quality silicon carbide ceramic products. Contact us for more information.

Reference

[1] Abderrazak, H., & Hmida, E. S. B. H. (2011). Silicon carbide: synthesis and properties. Properties and applications of Silicon Carbide, 361-388.

[2] Pawar, P., Ballav, R., & Kumar, A. (2017). Machining processes of silicon carbide: A review. Rev. Adv. Mater. Sci, 51(1), 62-76.

[3] Presser, V., & Nickel, K. G. (2008). Silica on silicon carbide. Critical reviews in solid state and materials sciences, 33(1), 1-99.

[4] Soltys, L. M., Mironyuk, I. F., Mykytyn, I. M., Hnylytsia, I. D., & Turovska, L. V. (2023). Synthesis and properties of silicon carbide. Physics and Chemistry of Solid State, 24(1), 5-16.