Metallographic Analysis Methods and Processes【2025】

Metallographic analysis is one of the commonly used methods for studying the microstructure of metals and alloys, and it is also a key tool for determining phase diagrams. By cutting, embedding, grinding the sample, and selectively etching the grain boundaries on the polished cross-section, the material's section morphology, grain structure, phase composition, and defects can be observed under a microscope, thereby inferring its three-dimensional compositional structure.

With the development of innovative materials and the demand for advanced processing technologies, especially in semiconductor nanomaterials and angstrom materials, as well as composite materials, the methods of metallographic analysis must continue to advance.

Metallographic analysis is applied in advanced process technology development, including microstructural analysis, process parameter optimization, performance prediction, and failure analysis, making it an indispensable tool for optimizing advanced processing, not just a simple inspection process.

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Metallographic analysis is governed worldwide by several international organizations and standards. Here are some of the major ones:

1. International Organizations

(1)ASM International

One of the world’s largest associations of materials scientists and engineers, focusing on metallography and material property analysis.

(2)International Metallographic Society (IMS)

IMS is dedicated to promoting the art and science of metallography and enhancing the characterization of materials and their structures.

(3)ASTM International

ASTM is a international standards organization that has developed numerous standards related to metallography, such as sample preparation and hardness testing.

2. International Standards

(1)ISO 643

ISO 643 is a standard for the determination of the microstructure of steels, specifically for ferrite or austenite grain size measurement.

(2)ISO 945

ISO 945 is a standard involving microstructure analysis for cast iron.

(3)ISO/TR 20580

ISO/TR 20580 is a guideline on sample preparation for optical and scanning electron microscopy (SEM).

These organizations and standards are widely adopted globally, providing unified guidance and regulation for metallographic analysis to ensure the accuracy and consistency of analytical results.

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The mainstream method in metallographic analysis is Quantitative Metallography, which quantifies and statistically analyzes the microstructure of materials to describe material characteristics quantitatively. The purpose of this method is to transform microstructural observations into measurable data to predict or analyze the material's performance and behavior.

Compared to traditional qualitative observation, Quantitative Metallography provides more accurate and consistent data, which is of great value for material research and quality control. Quantitative Metallography includes various measurement and calculation methods, generally covering the following aspects:

• ● Grain Size Measurement
• ● Phase Content Measurement
• ● Porosity and Inclusion Content Measurement
• ● Morphological Measurement
• ● Grain Boundary Density and Distribution Measurement

1. Grain Size Measurement

Grain size is a key factor influencing material performance. Quantitative Metallography analyzes the mechanical properties of materials by measuring grain size, shape, and distribution. For example, small grains generally improve the strength of metals, a relationship expressed by the Hall-Petch equation. Common grain size measurement methods include the linear intercept method, cross-line method, and area method, which convert grain distribution into data for statistical analysis and comparison.

2. Phase Content Measurement

In alloy materials, different phases (such as ferrite, pearlite, and bainite) have varying impacts on material performance. Quantitative Metallography uses image analysis to measure the volume or area percentage of each phase within the material. For instance, in duplex steel, controlling the proportion of ferrite and martensite optimizes ductility and strength, and Quantitative Metallography provides an accurate method for measuring these phase ratios.

3. Porosity and Inclusion Content Measurement

Pores and inclusions are defects within materials that reduce strength and fatigue resistance. Quantitative Metallography measures porosity (the proportion of pores within the material) and inclusion content (such as the quantity and distribution of oxides, sulfides, etc.). This data helps researchers assess material purity and uniformity and provides a basis for quality control during the manufacturing process.

4. Morphological Measurement

Morphological (Morphology) analysis involves quantitatively describing the shape and arrangement of internal structures within materials, including grain shape, phase boundary distribution, and fiber orientation. For example, analyzing the grain shape factor (such as aspect ratio, roundness, etc.) can yield data on grain ductility, while the shape and distribution of phase boundaries influence crack propagation behavior within materials.

5. Grain Boundary Density and Distribution Measurement

Grain boundaries are regions between grains that affect material strain distribution and crack propagation paths. Quantitative Metallography measures the length, density, and distribution of grain boundaries, which is especially important for evaluating material toughness and crack resistance. Higher grain boundary density generally indicates improved crack resistance, making grain boundary density an essential analysis indicator for applications requiring high strength and durability.

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The metallographic preparation and inspection process in metallographic analysis is not just a physical operation; it also requires the experience and skill of technicians to ensure the quality of samples and the accuracy of analytical results.

A correct preparation and inspection process can reveal the true structure of materials and help predict their performance, which is of great significance for quality control, failure analysis, and the development of new materials.

The main steps in the preparation and inspection process in metallographic analysis include requirement assessment → vise selection → Precision Cutting or Precision Diamond Saw → Mounting (Hot Mounting or Cold Mounting) → Rough grinding → Fine grinding → General polishing → Final polishing → Etching → Microscopic analysis.

The importance of the preparation and inspection process in metallographic analysis lies in the detailed operations of each step and a deep understanding of material properties, ensuring that the final microscopic observation results are accurate and reliable.

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Metallographic analysis is primarily used to understand the internal structure, performance, and potential issues in both metal materials and non-metal samples. The objectives for observation and testing vary according to the application field. Below are common inspection items in metallographic analysis:

• ● Metallographic Structure Observation
• ● Coating Observation
• ● Post-Etching Observation
• ● Structural Analysis
• ● R-Angle Analysis
• ● Surface Contamination Testing
• ● Pin Contact Tightness Analysis
• ● Weld Joint Analysis and Solder Point Evaluation
• ● Defect Analysis
• ● Composite Material Inspection
• ● Inclusion Analysis
• ● Hardness Testing

1. Metallographic Structure Observation

Observing the metallographic structure reveals the internal configuration of metal materials or non-metal samples, allowing for the assessment of material properties. Different materials have different observation goals:

(1) Graphite

Observing the internal morphology and distribution of graphite helps in-depth understanding of its properties and provides a basis for performance optimization in various applications.

(2) Rock

Analyzing its mineral composition and structure is particularly important for applications in geology and construction materials.

(3) Aluminum

The metallographic structure of aluminum reveals its internal grain structure, which is essential in high-strength industries such as aerospace and automotive.

(4) Cast Iron

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

2. Coating Observation

Metallographic coating is an important method for enhancing the surface performance of metal or non-metal materials. Observing the metallographic coating helps evaluate the thickness, uniformity, and adhesion of the coating, as well as the bonding quality between the coating material and the substrate.

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

3. Post-Etching Observation

The primary purpose of metallographic etching is to clearly reveal the internal structure of the sample. In its unetched state, the sample surface is typically smooth and reflective, making it difficult to distinguish micro details. The etched surface can reveal grain morphology, phase boundaries, and structural changes, which are critical for performance evaluation, process optimization, and defect analysis.

(1) Socket

After etching, the grain structure of the socket material is clearly visible, which is essential for analyzing material strength and toughness.

(2) Spring

Metallographic etching observation provides insights into the internal structure of spring materials.

4. Structural Analysis

Structural analysis in metallography primarily assesses the internal and external structure of materials. Structural analysis of metal materials or non-metal samples includes:

(1) Passive Components and Inductors

Structural analysis of these electronic components helps ensure their stability and durability.

(2) Threaded Components

Thread structure analysis ensures the strength and accuracy of connectors, preventing failure under high pressure.

5. R-Angle Analysis

The R-angle, or corner radius, is crucial for metal components like connectors. Metallographic R-angle analysis aids in optimizing structural design, ensuring adequate contact area and strength, thus enhancing reliability.

6. Surface Contamination Testing

The cleanliness of a material’s surface is crucial to its performance, especially for high-performance metals like titanium. Metallographic surface contamination testing assesses whether the material’s surface is contaminated by environmental or processing factors, ensuring corrosion resistance and biocompatibility.

7. Pin Contact Tightness Analysis

The tightness of pin contacts is crucial for electronic components. Poor pin contact tightness can lead to reduced electrical performance or even short circuits. Metallographic pin contact tightness analysis observes the contact surface between the pin and the substrate to ensure it is uniform and stable.

8. Weld Joint Analysis and Solder Point Evaluation

The quality of weld joints in electronic products directly affects their longevity and stability. Metallographic analysis of weld joints and solder point evaluation in circuit boards detects cracks, voids, or other defects in solder points, ensuring weld quality and preventing early failures.

9. Defect Analysis

Small defects within materials can lead to significant failures, particularly in high-precision applications. Metallographic defect analysis of components such as resistors helps ensure their stability during prolonged use.

10. Composite Material Inspection

Inspection techniques for composite materials are increasingly important, especially for advanced materials like carbon fiber. Metallographic composite material inspection reveals the layered structure and interface conditions within composites, ensuring their strength and durability.

11. Inclusion Analysis

Inclusions are potential contaminants introduced during material processing. For metals like copper, used in high conductivity applications, metallographic inclusion analysis detects foreign substances introduced during the process, ensuring material purity and performance.

12. Hardness Testing

Metallographic hardness testing is a critical method for evaluating the mechanical properties of metal materials. Hardness testing of steel balls helps determine wear resistance and load-bearing capacity, suitable for performance assessment in high-precision mechanical components.

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In the development of advanced technology products, metallographic analysis through metallographic preparation and inspection processes enables in-depth microstructural analysis, helping technicians ensure material integrity and long-term stability of products. These metallographic preparation devices and inspection processes allow detailed structural observation, aiding in process control and material selection precision, thus enhancing product reliability and performance. Below are applications of metallographic analysis in industries such as semiconductors, IC design, packaging and testing, thermal management, networking, electric vehicles, and smartphones:

1. Wafer Sectioning and Interlayer Defect Analysis

In semiconductor wafer metallographic analysis, maintaining the integrity of the wafer's internal structure is essential for metallographic failure analysis. Metallographic preparation uses precision tools (such as diamond blades) combined with low-speed cutting, aided by a cooling system, to prevent thermal damage. After cutting, mounting is performed, followed by multi-stage grinding and polishing to reveal copper wiring, dielectric layers, and semiconductor material interfaces between layers, assisting in the inspection for delamination, microcracks, or abnormal oxide layers.

2. Feature Size and Microstructure Analysis

After grinding and polishing, samples observed under an electron microscope reveal fine particles and grain boundaries, especially suitable for studying the microfeatures of nano-scale materials, helping improve the performance and stability of IC conductors within wafers.

3. Metal Wire Bonding Examination

Metal wires in IC components require stable bonding. After cutting, cold mounting is performed to secure the sample, followed by fine grinding to minimize surface deformation. Polishing then reveals bonding strength, boundary integrity, and signs of metal fatigue, facilitating contact reliability evaluation.

4. Stability of Thin Film and Dielectric Layers

The thin film structure in IC design and manufacturing requires high signal stability. Grinding and polishing are performed with controlled pressure and grinding speed, gradually removing surface layers, achieving a smooth, undamaged observation surface, which reveals the continuity and thickness distribution of thin films and dielectric layers, preventing signal interference.

5. Interface Bonding in Multilayer Chips

Multilayer chip stacking in semiconductor packaging and testing requires tight bonding to avoid signal attenuation. Precision cutting in metallography ensures complete separation of each layer, and after mounting, polishing allows observation of bonding points between layers. This helps detect pores, delamination, or poor contact, particularly for analyzing connectivity at interfaces of different materials.

6. Heat Dissipation Material Particle Structure Inspection

The internal uniformity of heat dissipation materials (such as metal alloys and ceramics) directly affects thermal conductivity. After cutting and securely mounting, grinding and polishing reveal particle distribution and size, assessing their uniformity and particle connectivity to prevent uneven heat conduction.

7. Conductor Stability Under Current Overload Conditions

Conductor materials in power sources must withstand high current overloads. After grinding and polishing, it is possible to observe whether microcracks exist within the conductor structure, preventing material failure under high current load conditions.

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