News

A step-by-step explanation of the core processes and technical points for polishing silicon nitride ceramics:

Pre-Polishing Pretreatment

Surface Cleaning

Use an ultrasonic cleaner or chemical solvents (e.g., acetone, alcohol) to remove oil, dust, and sintering residues from the silicon nitride ceramic surface, preventing impurities from affecting the polishing results.

Defect Inspection

Inspect the surface for cracks, pores, and other defects using a microscope or surface profilometer. Mark areas requiring special attention.

Rough Polishing (Macro-Defect Removal)

Mechanical Grinding

Tool Selection: Use diamond grinding wheels or silicon carbide abrasives (grit size 400-800 mesh) with high-precision surface grinders or ball mills.

Parameter Control: Rotational speed 800-1500 RPM, pressure controlled at 5-10 N/cm². Gradually reduce abrasive grit size in stages to eliminate scratches.

Ultrasonic-Assisted Polishing

For complex curved surfaces or miniature ceramic balls (e.g., bearing balls), use an ultrasonic vibration polisher. High-frequency vibration accelerates contact between the abrasive and the surface, reducing localized stress concentration.

Semi-Finish Polishing (Surface Texture Refinement)

Magnetic Float Polishing

Principle: Utilizes a magnetic field to levitate the polishing head, enabling uniform surface polishing in a non-contact manner to avoid mechanical damage.

Process Key Points: Use cerium oxide (CeO₂) or diamond suspension. Post-polishing roughness can be reduced to Ra 0.05-0.1 μm.

Chemical Mechanical Polishing (CMP)

Slurry Formulation: Alkaline solution (pH 9-11) containing nano-silica or alumina particles. Enhances efficiency through the synergistic effect of chemical corrosion and mechanical grinding.

Equipment Requirements: Dedicated CMP polishing machine, pressure 3-5 N/cm², temperature 20-30°C.

Fine Polishing (Achieving Mirror Finish)

Cluster Magnetorheological Finishing

Technical Principle: Under a magnetic field, abrasives within the magnetorheological (MR) fluid form a flexible “polishing blanket” that adaptively conforms to the ceramic surface, eliminating micro-ripples.

Result: After 3-5 hours of polishing, roughness can reach Ra ≤ 5 nm, with sphericity error ≤ 0.2 μm (suitable for high-precision bearing balls).

Ion Beam Figuring

For ultra-precision optical components (e.g., semiconductor equipment parts), use an ion beam to bombard the surface atomic layer, achieving atomic-level flatness.

Post-Processing and Inspection

Cleaning and Passivation

Rinse with deionized water, then immerse in a nitric acid passivation solution (concentration 5%-10%) to enhance surface oxidation resistance.

Quality Verification

Instrument Inspection: Measure roughness using white light interferometry; inspect spherical tolerance using a laser sphericity gauge.

Visual Standard: Mirror reflection should be free of haze or cloudiness, and visible scratches or orange peel effect.

Process Optimization Directions

Intelligent Parameter Adjustment

Use AI algorithms to adjust pressure, rotational speed, and slurry flow in real-time to improve consistency.

Composite Process Innovation

Combine Laser Assisted Machining (LAT) and chemical polishing to address challenges in polishing complex structures like deep holes and narrow grooves.

Environmental Upgrade

Develop water-based polishing slurries and abrasive recycling systems to reduce heavy metal pollution.

Application-Specific Variations

Aerospace Bearings: Require Ra ≤ 0.01 μm; employ composite polishing using Cluster MRF + Ion Beam Figuring.

Electronic Heat Spreaders: Focus on flatness; primarily use CMP.

Medical Devices: Incorporate biocompatible cleaning (e.g., plasma sterilization).

Through the combination of the above processes, the diverse surface precision requirements for silicon nitride ceramics—from industrial grade to optical grade—can be met. The specific workflow must be dynamically adjusted based on the workpiece shape (e.g., flat, spherical, complex geometries) and intended application.