Metallographic｜Metallographic Preparation 2025

Last Updated：2025/01/09

Topics Covered:

4 Key Considerations

Item 1. Metallographic preparation involves a series of steps to prepare samples, aiming to reveal their microstructures and accurately evaluate the material's performance.
Item 2. The first step is to cut the sample into representative sizes and shapes. The second step involves mounting the sample to secure it and protect its edges and surfaces. In the third step, the sample undergoes grinding to remove surface defects and enhance smoothness. The fourth step is polishing, which removes surface scratches and achieves a highly reflective finish to ensure the microstructure is clearly visible.
Item3. Metallographic analysis examines the internal structure and performance of materials, covering applications such as coating inspection, corrosion analysis, weld assessment, and defect analysis. This process ensures material quality and defect prevention, with widespread applications in the electronics, mechanical, and construction industries.
Item4. Microscopy techniques help researchers observe and analyze the macro and microstructures of metal or non-metal materials. The two primary types of microscopes used are the optical microscope and the Scanning Electron Microscope (SEM).

Item 1.What is Metallographic Preparation

The History of Metallography

The history of metallography dates back to the 19th century, when advancements in metallurgy led scientists to recognize the importance of the internal structure of materials in determining their performance. Early scientists, such as Henry Clifton Sorby, studied the metallographic structures of steel and discovered the impact of grain size, phase distribution, and inclusions on material properties. His research emphasized the close relationship between microstructure and macroscopic performance, which was groundbreaking in the field of material science at the time.

Metallographic Scientist Henry Clifton Sorby

In modern material science, metallographic preparation techniques have become standardized procedures widely applied to the study of various metal and non-metal materials. These techniques are not only essential in quality control but also play a significant role in failure analysis and material development. Through metallographic analysis, researchers can assess the performance, quality, and suitability of materials, ensuring that products meet specified standards and regulations.

Definition and Importance of Metallographic Preparation

Metallographic preparation is a core technique in material science, primarily aimed at accurately observing the structures of metal and non-metal materials, which reveal their true properties. Material performance—including strength, toughness, and corrosion resistance—is closely linked to its internal microstructure. Therefore, proper preparation is crucial to ensuring the accuracy of the observation results.

The primary steps of metallographic preparation include metallographic cutting, metallographic mounting, grinding, and polishing. These steps ensure that samples are prepared for microscopic observation without altering the internal structures of metal and non-metal materials. Through these processes, the sample surface is refined to a smooth and flat state, making it suitable for detailed analysis using optical microscopes or scanning electron microscopes (SEM). These techniques are indispensable in quality control, failure analysis, and material research applications.

The primary steps of metallographic preparation include metallographic cutting, metallographic mounting, grinding, and polishing.

Item 2. Steps of Metallographic Preparation

Cutting

1. Purpose of Cutting

Metallographic Cutting is the first step in metallographic preparation and is essential for the preparation of both metal and non-metal materials. The primary purpose of this process is to cut the material sample into representative sizes and shapes for subsequent observation and analysis of its metallographic structure. The key to cutting lies in avoiding the introduction of heat-affected zones or mechanical deformation during the process, as these may alter the microstructure of the materials and affect the accuracy of the analysis.

2. Importance of Cutting

(1)Avoiding Heat-Affected Zones

Excessive heat generated during the cutting process can cause phase transformations or structural changes in metal and non-metal materials. To prevent this, coolants are typically used to lower the temperature during the cutting process, ensuring that the microstructure of the material remains unchanged.

Use coolant to reduce temperatures during cutting

(2)Minimizing Mechanical Deformation

<ㄘ>The pressure and speed during sectioning must also be controlled to avoid excessive mechanical stress on the metal and non-metal materials, which could result in deformation or cracking of the sample. Using precision cutting machines effectively mitigates these risks, ensuring smooth and defect-free cut surfaces.

(3)Choosing the Right Cutting Tools

Different materials require specific cutting tools and methods. The choice of metallographic cutting consumables (such as grinding wheels or Diamond Blades) and cutting techniques (like Precision Cutting or Diamond Cutting) is critical to achieving high-quality sectioning. These tools are designed to minimize thermal and physical damage, maintaining the integrity of the sample.

It's important to choose the appropriate metallographic cutting consumables.

3. Precision Cutting

Precision Cutting uses abrasives such as Aluminum Oxide Blades and Silicon Carbide Blades to minimize deformation during the cutting process. The characteristics of precision cutting include:

(1) Accuracy

This technique can achieve micrometer-level precision, making it suitable for high-value or high-precision materials such as electronic components and medical devices.

(2) Diverse Cutting Tools

Commonly used cutting tools include Aluminum Oxide Blades and Silicon Carbide Blades, selected according to the properties of metal and non-metal materials to ensure optimal cutting quality.

(3) Broad Applications

Precision cutting is widely used in industries such as semiconductors, electronics, and metal and non-metal materials, particularly in scenarios requiring high precision and detailed processing.

4.Diamond Cutting

Diamond Cutting is designed for extremely hard materials, using Diamond Blades to achieve exceptional cutting precision. Its features include:

(1) High Cutting Precision

This technology offers excellent cutting results for brittle materials like hard alloys or ceramics, reducing material loss.

Counterweight rock arm cutting is suitable for cutting fine electronic parts.

(2) Suitable for High Hardness Materials

Given the hardness of diamonds, this cutting method is ideal for difficult-to-process metal or non-metal materials and enables the cutting of complex shapes.

(3) Various Fixtures for Different Shapes and Sizes

Fixtures can be easily changed to accommodate the shape, size, and properties of the sample, providing greater flexibility.

Clamps of various appearance sizes

▉▎Further reading: Understanding of Precision Cutting Machine- detailed types and functional specifications

▉▎Further reading: Understanding of Precision Diamond Saws- detailed types and functional specifications

Mounting

1.Functions of Mounting

Metallographic mounting involves encapsulating the cut metal or non-metal samples within a curing material to provide stability during subsequent grinding and polishing processes. This step protects the edges and surfaces of the sample, preventing damage during grinding and polishing, which is especially important for irregular or brittle samples.

Mounting encases the sample in a curing material.

Its main functions include:

(1) Providing Stability

The primary function of mounting is to encapsulate the cut metal or non-metal samples within a curing material to ensure stability during grinding and polishing. This process effectively secures the sample, preventing displacement or damage due to external forces, particularly for irregular or brittle samples.

(2) Protecting Edges and Surfaces

Metallographic mounting protects the edges and surfaces of metal and non-metal samples, preventing edge rounding or other defects during grinding and polishing. This is crucial for samples requiring edge observation, as unmounted samples are prone to damage during grinding, affecting subsequent analysis results.

Mounting protects the edges and surfaces of samples.

(3) Facilitating Handling

Mounted samples are easier to handle, especially during grinding and polishing. The cured material provides a smooth and stable surface, facilitating the polishing process and improving overall work efficiency.

(4) Standardizing Operations

Metallographic mounting also helps standardize workflows, ensuring consistent processing of different metal or non-metal samples. This is essential for laboratory quality control and ensuring data repeatability.

2. Hot Mounting

Metallographic mounting plays a critical role in metallographic preparation and can be divided into Hot Mounting and cold mounting. Hot Mounting uses thermosetting resins, such as acrylic or bakelite powders, to embed the sample through heating and pressure.

Hot mounting using bakelite powder.

Its features include:

(1) Stability

Hot mounting provides stable samples with clear edges, essential for subsequent grinding and polishing processes. Once secured in resin, the sample is protected from deformation or damage during processing.

(2) Wide Applicability

This method is suitable for most metal materials, particularly those not affected by heat. The high pressure and temperature conditions in Hot Mounting ensure that the resin penetrates into the micro-pores of the sample, enhancing its overall stability.

(3) Process Efficiency

Hot Mounting typically requires a short time to complete, achieving good molding results in a single operation, which improves laboratory efficiency.

3.Cold Mounting

Cold mounting, on the other hand, uses cold-setting resins, such as epoxy, suitable for heat-sensitive or irregularly shaped non-metal materials.

Cold mounting uses cold-setting resins.

Its features include:

(1) Avoiding Thermal Stress

Cold mounting does not require heating, avoiding thermal stress during the process and protecting the microstructure of non-metal samples, especially brittle materials.

(2) Easy Operation

The cold mounting process is relatively simple: the non-metal sample is placed in a mold, and mixed resin and hardener are poured in and left to cure. This makes cold mounting an efficient and user-friendly option.

(3) Wide Applicability

Cold mounting is suitable for various non-metal materials, particularly those prone to deformation or damage at high temperatures, such as electronic components or complex-shaped non-metal materials.

▉▎Further reading: Understanding of Metallographic Mounting-detailed types and functional specifications

Grinding

Metallographic grinding is a crucial step in metallographic preparation, primarily aimed at creating a flat and smooth surface on the mounted sample to prepare it for subsequent microscopic observation.

Grinding is to grind the surface of the mounting sample.

The metallographic grinding process typically consists of the following two stages:

1. Rough grinding

In the rough grinding stage of metallographic grinding, coarser abrasives are used to perform initial grinding, aiming to remove irregularities and significant defects from the surface of metal or non-metal samples. The characteristics of this stage include:

(1) Material removal

Rough grinding effectively removes excess material from the surface of metal or non-metal samples, laying the foundation for fine grinding.

(2) Tools used

Typically, coarser Silicon Carbide Grinding Papers or diamond abrasives are used. These abrasives have larger particles, enabling quick removal of uneven surface areas.

2. Fine grinding

In the fine grinding stage, the goal is to further smooth the sample surface, usually by using finer abrasives. The characteristics of this stage include:

(1) Smooth surface

Fine grinding removes the micro-scratches left from rough grinding, achieving a higher degree of flatness and smoothness on the surface of metal or non-metal samples.

Fine grinding can achieve higher flatness and smoothness on the sample surface.

(2)Choice of abrasives

Finer Silicon Carbide Grinding Papers or diamond abrasives are selected to provide a more precise grinding effect.

Polishing

Metallographic polishing is a critical step in the preparation of metallographic samples, aimed at achieving a highly reflective surface for metal samples or a scratch-free surface for non-metal samples, facilitating the clear observation of internal structures under a microscope.

Polishing gives the surface of a metal sample a mirror-like effect.

The key elements and materials used in metallographic polishing include:

1. Purpose of Metallographic Polishing

(1) Achieving a highly reflective surface

Metallographic polishing removes minor scratches and irregularities from the sample surface, making metal samples smooth and mirror-like. This is essential for the observation of metallographic structures, as the highly reflective surface clearly displays the sample's microstructure, aiding in the analysis of phase distribution, grain boundaries, and inclusions.

(2) Enhancing observation quality

Samples treated with metallographic polishing provide higher resolution under the microscope, enabling researchers to more accurately analyze material properties and structures.

2. Steps of Metallographic Polishing

Following the appropriate steps in metallographic polishing ensures that the surfaces of metal or non-metal samples achieve optimal smoothness and gloss. Typically, the polishing process consists of the following stages:

(1) Rough polishing

Coarser abrasives are used to remove significant defects and scratches on the surface.

(2) Fine polishing

Progressively finer abrasives are applied to further smooth the surface and eliminate scratches left by rough polishing.

(3) Final polishing

High-purity diamond or colloidal silica is used for the final polish to achieve a highly reflective surface.

▉▎Further reading: Understanding of Metallographic Grinding and Polishing-detailed types and functional specifications

Item 3. Sample Testing and Analysis in Metallographic Preparation

Metallographic Analysis

Metallographic analysis is mainly used to understand the internal structure, performance, and potential issues of metal materials or non-metal samples. The observation and testing objectives vary depending on the application fields, covering metallographic structure observation, coating inspection, corrosion evaluation, structural analysis, and weld point assessment.

1. Observation of Metallographic Structures

Observing the metallographic structure reveals the internal structure of metal or non-metal samples, helping determine the properties of the material. Different materials have distinct observation goals:

(1) Graphite

Observing the morphology and distribution of graphite provides insights into the material's properties and offers a basis for optimizing its performance in various applications.

Graphite 1000x optical microscope organizational structure observation

(2)Rocks

Analyzing mineral composition and structure is crucial in geology and building material applications.

Rock 500x optical microscope observation of organizational structure

(3)Aluminum

The metallographic structure of aluminum reveals its grain structure, which is especially critical for industries demanding high strength, such as aerospace and automotive.

Aluminum 50x optical microscope for observation of organizational structure

(4)Cast Iron

Observing the morphology and distribution of cast iron’s internal structure helps evaluate the toughness and strength of the metal.

Ductile iron 50 times optical microscope organizational structure observation

2. Coating Observation

Metallographic coating is an essential method to enhance the surface performance of metal or non-metal materials. Coating observations help evaluate the thickness, uniformity, and adhesion of coatings and understand the bonding between the coating material and the substrate.

For tools like sockets, the quality of the metallographic coating directly impacts their wear resistance and corrosion protection.

Sleeve 500x optical microscope Coating observation

3. Post-Corrosion Observation

The primary purpose of metallographic corrosion is to reveal the internal structure of the sample clearly, as untreated samples often have smooth, reflective surfaces that obscure microscopic details. The post-corrosion surface exposes the grain morphology, phase boundaries, and structural changes, which are essential for performance evaluation, process optimization, and defect analysis.

(1)Socket

Post-corrosion, the grain structure of the socket material is clearly visible, aiding in the analysis of its strength and toughness.

Sleeve 50 times optical microscope observation after corrosion

(2)Springs

Corrosion analysis helps explore the internal structure of spring materials.

Spring 500 times optical microscope observation after corrosion

4. Structural Analysis

Metallographic structural analysis evaluates both the internal and external structure of metal materials or non-metal samples, including:

(1) Passive Components and Inductors

Structural analysis of such electronic components ensures their stability and durability.

Passive components 500x optical microscope structural analysis

(2)Threads

Thread structure analysis ensures the strength and precision of connectors, preventing failures under high pressure.

Screw thread 200 times optical microscope structural analysis

5. R-curve Radius Analysis

The R-curve radius, or fillet radius, is crucial for connectors and other metal components. R-curve analysis optimizes structural design, ensuring adequate contact area and strength, enhancing reliability.

Connector 200 times optical microscope R angle angle analysis

6. Surface Contamination Testing

The cleanliness of a material's surface is a key factor influencing its performance, especially for high-performance metals like titanium. Surface contamination tests evaluate whether the material has been affected by environmental or processing pollutants, ensuring corrosion resistance and biocompatibility.

Titanium 100x optical microscope surface contamination test

7. Pin Contact Analysis

Pin contact analysis is crucial for electronic parts. Poor pin contact can lead to electrical performance degradation and even short circuits. This analysis observes whether the pin contact with the substrate is even and stable.

Electronic parts 100 times optical microscope Pin tightness analysis

8. Weld Joint Analysis and Weld Point Evaluation

The quality of weld joints directly impacts the lifespan and stability of electronic products. Metallographic weld joint analysis and circuit board weld point evaluations identify defects such as cracks or voids to ensure welding quality and prevent early failure.

Electronic parts 200x optical microscope welding joint analysis

9. Defect Analysis

Small defects in materials can cause significant failures, especially in high-precision applications. Metallographic defect analysis of components like resistors ensures their long-term stability.

Resistor 500x optical microscope Defect analysis

10. Composite Material Testing

Testing techniques for composite materials are becoming increasingly important, particularly for new materials like carbon fiber. Metallographic composite material testing reveals layered structures and interfaces, ensuring strength and durability.

Carbon fiber 500x optical microscope composite material detection

11. Inclusion Analysis

Inclusions are potential contaminants during the manufacturing process, particularly for metals like copper used in high-conductivity applications. Metallographic inclusion analysis identifies foreign matter introduced during processing, ensuring the purity and performance of the metal.

Copper 50x Optical Microscope Intrusion Analysis

12. Hardness Testing

Metallographic hardness testing is a key method for evaluating the mechanical performance of metal materials. Hardness testing of steel balls helps determine wear resistance and load-bearing capacity, essential for assessing the performance of high-precision mechanical components.

Steel ball hardness test

Item 4. Observation Instruments for Metallographic Preparation

In metallographic analysis, microscopy techniques enable researchers to observe and analyze the macro and microstructures of metal or non-metal materials. Depending on the observation needs and sample characteristics, commonly used microscope tools mainly include optical microscopes and Scanning Electron Microscopes (SEM).

These two types of microscopes each have unique features, briefly described below:

Optical Microscope

The optical microscope is the fundamental tool for observing metal and alloy samples, with the following features:

1. Macroscopic Structure Observation

At low magnification, the optical microscope reveals the macroscopic metallographic structure of the metal sample, helping researchers quickly grasp the overall characteristics of the metal material.

2. Metallographic Structure Analysis

At high magnification, the optical microscope can observe fine metallographic structures, which is crucial for analyzing metal grains, phase structures, cracks, and inclusions.

3. Reflected Light Observation

The optical microscope primarily uses reflected light to observe the surface of polished and corroded metal samples, making it highly effective in metallographic analysis, as it clearly displays surface features and defects of the sample.

The optical microscope is relatively easy to operate and cost-effective, suitable for the observation and analysis of a variety of materials. It is widely used in fields such as material science, engineering, and biology.

Scanning Electron Microscope (SEM)

The Scanning Electron Microscope (SEM) is a high-resolution microscope suitable for observing the microstructural details of metal or non-metal samples. Its features include:

1. High Resolution

The SEM offers higher resolution than optical microscopes, enabling the clear display of the material's micro-morphology and structural characteristics. It is particularly suitable for analyzing very small metallographic structures, such as sub-micron-level inclusions, pores, and grain boundaries.

2. Electron Beam Scanning

The SEM scans the surface of metal or non-metal materials using an electron beam, generating high-resolution images. This process reveals the surface characteristics and internal metallographic structure of the sample, providing rich morphological information.

3. Versatility

In addition to morphological observation, the SEM can also perform elemental analysis, making it valuable in material science and failure analysis.

Item 5. Conclusion

Metallographic preparation and metallographic analysis have become integral to many industrial sectors, including the evaluation of materials for extreme environments in aerospace, fatigue life analysis in the automotive industry, weld quality control for electronic components, and corrosion resistance testing for building materials. In these high-precision applications, the in-depth observation of microstructures through optical microscopes and Scanning Electron Microscopes (SEM) allows for the accurate analysis of grain interfaces, inclusions, and welding defects. Every minor flaw identified can prevent product failures and even avert catastrophic consequences that could endanger lives.

The profound significance of metallographic techniques lies not only in ensuring product quality but also in laying the foundation for industrial competitiveness. With continuous innovations in manufacturing processes—ranging from Precision Cutting with high-hardness diamonds to Hot Mounting Press and cold mounting processes—each technological breakthrough expands the boundaries of material analysis, allowing the once-inaccessible microscopic world to come to light. This not only advances failure analysis and new material development but also grants scientists greater freedom, paving the way for future material innovations.