How to solve the problem of fragile ceramic parts?

2025-09-01

The Fundamental Reasons for the Fragility of Ceramic Materials

1. Atomic Bonding Characteristics

Ceramics are mainly composed of ionic bonds/covalent bonds (accounting for over 80%), with high bond energy but lacking the electron delocalization of metallic bonds. When subjected to external forces, atoms are difficult to slide, and stress concentration directly leads to crack propagation. For example, the fracture toughness of alumina (Al₂O₃) is only 3-4 MPa·m¹/², which is much lower than that of steel (about 50 MPa·m¹/²).

2. Microscopic Structural Defects

Defects formed during sintering are the cause of brittleness:

- Porosity: The porosity of traditional sintered ceramics ranges from 5% to 10%, becoming a source of stress concentration;

- Grain Boundary Impurities: For example, SiO₂ forms a glass phase at the Al₂O₃ grain boundaries, reducing the high-temperature strength.

3. Phase Transformation Stress Sensitivity

Some ceramics (such as ZrO₂) have a phase transformation volume effect, and temperature fluctuations are prone to trigger microcracks. Unstabilized 3Y-ZrO₂ has a 300% increased risk of cracking at a 200°C temperature difference.

Understanding the reasons for the fragility of ceramics

The reasons for the fragility of ceramic products are numerous and mainly include the following points:

1. Inadequate manufacturing process: If the manufacturing process of ceramic products is improper, such as insufficient temperature or insufficient firing time, it can easily lead to internal defects in the products, thereby affecting their compressive strength and making them prone to breakage.

2. Improper maintenance: During the use and maintenance of ceramic products, if incorrect methods are not adopted, it can easily increase their fragility and make them more prone to breakage.

3. External force collision: During transportation, storage, and use of ceramic products, if they are subjected to external force collisions, drops, etc., it may cause the ceramic products to break.

Main reasons for the fragmentation of parts during ceramic milling machine processing

1. Inappropriate tool selection

Inappropriate tool material: The high hardness of ceramic materials requires the use of ultra-hard materials such as diamond tools. If the selected tool material is inappropriate, the tool will be prone to wear or breakage, leading to the fragmentation of the workpiece.

Inappropriate tool geometric parameters: The geometric parameters of the tool (such as rake angle, clearance angle, inclination angle, etc.) have a significant impact on the cutting force and stress distribution during the processing. If the tool geometric parameters are not reasonably selected, it will increase the cutting force and stress, leading to the fragmentation of the workpiece.

2. Unreasonable cutting parameters

Excessive cutting speed: Excessive cutting speed will increase the cutting force and cutting heat, leading to increased tool wear and stress on the workpiece, thereby causing the workpiece to fragment.

Excessive feed rate: Excessive feed rate will increase the cutting force, and the stress on the workpiece will also increase, making it prone to fragmentation.

3. Machine vibration

Insufficient machine rigidity: Insufficient rigidity of the machine will cause vibration during processing, increasing the stress concentration on the workpiece, and making it prone to fragmentation.

Insecure tool fixation: Insecure tool fixation will cause the tool to vibrate during processing, increasing the cutting force and stress, leading to the fragmentation of the workpiece.

4. Improper workpiece clamping

Excessive clamping force: Excessive clamping force will cause the workpiece to deform or have stress concentration, making it prone to fragmentation.

Inappropriate clamping position: Inappropriate clamping position will cause the workpiece to be subjected to uneven stress during processing, increasing stress concentration and making it prone to fragmentation.

5. Insufficient cooling and lubrication

Insufficient coolant supply: During the processing of ceramic materials, a large amount of cutting heat is generated. If the coolant supply is insufficient, the tool temperature will be too high, accelerating tool wear and even causing tool fracture, thereby leading to the fragmentation of the workpiece.

Poor lubrication effect: Poor lubrication effect will increase the friction force between the tool and the workpiece, increasing the cutting force and stress, and making it prone to fragmentation.

Improvement Methods and Practical Cases

1. Structural Toughening Technology

- Fiber/Whisker Composites: SiC whiskers reinforcing Al₂O₃ ceramics, with fracture toughness increased to 8.5 MPa·m¹/²;

- Phase Transformation Toughening: Adding 3 mol% Y₂O₃ to ZrO₂ (3Y-TZP) through stress-induced phase transformation absorbs energy, with fracture toughness reaching 12-15 MPa·m¹/²;

- Nanocomposites: Al₂O₃/SiC nanocomposite ceramics (particle size < 100 nm) increase strength to 1.2 GPa.

2. Process Optimization

- Hot Isostatic Pressing (HIP): Processing at 1500°C/200 MPa in argon atmosphere, porosity can be < 0.1% (technology report from Kyocera Japan);

- Discharge Plasma Sintering (SPS): Rapid sintering of nano-ZrO₂ in 5 minutes, with grain size controlled below 200 nm, strength increased by 40%.

3. Material System Innovation

- Functionally Graded Materials (FGM): Such as ZrO₂/Ni multilayer ceramics for aerospace applications, thermal shock resistance increased by 5 times;

- Self-Repairing Ceramics: Si₃N₄ ceramics containing microcapsule healing agents, with cracks releasing liquid SiO₂ at high temperature, achieving strength recovery rate > 90%.

Solutions for reducing part fragmentation during ceramic milling machine processing

1. Select appropriate tools

Use tools made of super-hard materials, such as diamond tools, to enhance the wear resistance and impact resistance of the tools.

Optimize tool geometric parameters: Based on the characteristics of the ceramic material, select appropriate geometric parameters such as the rake angle, clearance angle, and edge inclination of the tool to reduce cutting force and stress.

2. Set cutting parameters reasonably

Reduce cutting speed appropriately: According to the hardness and brittleness of the ceramic material, select an appropriate cutting speed to reduce cutting force and heat.

Control feed rate: Based on the characteristics of the ceramic material, select an appropriate feed rate to reduce cutting force and stress.

3. Improve machine rigidity and stability

Strengthen machine rigidity: Improve the machine structure to enhance its rigidity and stability, reducing vibrations.

Securely fix the tool: Ensure the tool is stable during processing to reduce vibrations.

4. Reasonably clamp the workpiece

Control clamping force: Select appropriate clamping force based on the strength and rigidity of the workpiece to avoid excessive clamping force that causes deformation or stress concentration of the workpiece.

Choose a reasonable clamping position: Select a reasonable clamping position based on the shape and processing requirements of the workpiece to ensure uniform force on the workpiece during processing.