Metallographic Preparation Steps 2025｜Got it in 3 minutes!

Metallographic preparation steps, including requirement assessment, vise design, cutting, cold mounting or hot mounting, rough grinding, fine grinding, rough polishing, final polishing, etching, and microscopic analysis, reveal the microstructure of materials to assist in quality control and failure analysis, enhancing product reliability.

Metallographic preparation steps, including cutting, mounting, grinding, polishing, etching, and microscopic analysis.

▉▎Further reading: Understanding of Detailed Information on Metallographic Cutting, Mounting, Grinding, and Polishing Equipment

In metallographic preparation material testing, precise needs assessment is crucial for improving process efficiency and reducing errors. The characteristics of different materials and their testing requirements will impact the preparation methods. Through these assessments, businesses can effectively select suitable materials and the appropriate metallographic preparation testing methods, thus enhancing production efficiency and product quality.

Metallographic Preparation Requirement Assessment Table 1

Metallographic Preparation Requirement Assessment Table 2

The following is a detailed analysis of the metallographic preparation requirements for various materials:

1. Types of Materials

(1) Metal Materials

Including steel, copper alloys, and aluminum alloys. When testing these materials, particular attention is needed regarding their hardness and ductility. Hardness testing evaluates the material's wear resistance and strength, which is essential to ensure its performance in practical applications.

(2) Non-Metal Materials

Such as ceramics and plastics. In the metallographic preparation process, it is critical to avoid cracks or deformation. Brittle materials like ceramics or quartz require careful handling during sectioning and testing to prevent fracturing.

2. Analysis Objectives

(1) Metallographic Structure Observation

Primarily used to examine grain size, grain boundaries, and phase transformations, which are crucial for understanding the material’s physical properties and predicting its performance.

(2) Metallographic Defect Detection

Includes inspecting for pores, inclusions, and cracks, which can affect the material’s overall performance and reliability.

(3) Evaluation of Heat Treatment Effects

Assesses changes in the metallographic structure after heat treatment, ensuring the material meets required performance standards.

(4) Hardness Testing

Measures the hardness of specific sample regions, a fundamental method for evaluating wear resistance and strength in metallographic preparation.

(5) Structural Analysis

Includes coating analysis and weld inspection, serving as the basis for material acceptance and process control to ensure compliance with specifications and performance requirements.

Choosing the appropriate vise depends on the sample’s shape, size, and material properties, which are critical factors in metallographic preparation. Below is a detailed evaluation based on these factors:

1. Sample Shape and Size

(1) Standard Vises

Most samples can be held using standard vises, designed for common shapes and sizes. For instance, standard vises can securely hold regular geometries like cylinders or square objects.

(2) Special Shapes

For irregular or uniquely shaped samples, custom-designed vises may be necessary. These vises are tailored to the sample's specific shape to ensure stable clamping and safety. Some vises can adjust to fit various sample profiles.

For metallographic preparation irregularly shaped or special samples may require customized vises.

2. Material Properties

(1) Material Impact

The material characteristics (e.g., hardness, brittleness, and elasticity) of metallographic preparation samples will influence the choice of vise. For softer materials like rubber or certain plastics, the vise must prevent damage. Conversely, brittle materials like ceramics or quartz require protective measures, such as silicone padding, to prevent fractures from excessive clamping force.

(2) The Need for Customized Vises

In some cases, the sample may be too small or complex for standard vises to provide adequate support. Custom vises designed for the sample's specific needs ensure stability during sectioning, grinding, or testing.

▉▎Further reading: Understanding of Metallographic accessories – Various vises

Metallographic sectioning is the first step in metallographic preparation. The primary goal is to cut material samples to representative sizes and shapes for subsequent metallographic structure observation and analysis. A key consideration in this process is avoiding thermal or mechanical deformation, which can alter the microstructure of both metallic and non-metal materials. Therefore, selecting an appropriate metallographic cutting machine and metallographic cutting blade is essential.

Adding coolant in metallographic cutting is to prevent thermal effects or mechanical deformation during the process.

1. Metallographic Cutting Machine Operation Steps

(1) Open the top cover.

(2) Clamp the sample securely. If the sample is not held tightly, the electrical current may become unstable, potentially causing the metallographic cutting blade to break.

(3) Close the top cover and activate the coolant switch. The coolant serves two purposes: lubricating the sample to prevent overheating and protecting the machine from rust.

(4) Perform the sectioning process while monitoring the current. Unstable current indicates that the sample is not clamped properly, or the blade is unsuitable for the material.

(5) Once cutting is complete, retract the blade. Most automatic machines will stop and shut off the coolant automatically.

(6) Ensure the machine and coolant are turned off before opening the top cover to remove the sample.

2. Precision Cutting

Precision cutting uses aluminum oxide blades and silicon carbide blades to minimize deformation during the sectioning process. The characteristics of precision cutting include:

(1) Accuracy

Achieving micron-level cutting precision, suitable for high-value or high-precision materials such as electronic components and medical instruments.

(2) Variety of Cutting Tools

Common tools include aluminum oxide blades and silicon carbide blades, selected based on the properties of metallic and non-metal materials to ensure quality cuts.

Metallographic cutting requires selecting suitable blades based on the characteristics of metal and non-metal materials.

(3) Broad Applications

Precision cutting is widely used across industries such as semiconductors, electronics, and both metallic and non-metal materials, especially in scenarios requiring high precision and fine processing.

3. Diamond Cutting

Diamond cutting is designed for very hard materials, using diamond as the cutting material to achieve high metallographic sectioning precision. Key features include:

(1) Exceptional Cutting Precision

Diamond cutting offers excellent results when processing brittle materials such as hard alloys or ceramics, minimizing material loss.

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

(2) Suitable for High-Hardness Materials

The hardness of diamonds makes this sectioning process ideal for challenging metals or non-metals, facilitating complex shape cutting.

(3) Diverse Vise Options

Vises are easy to replace, allowing selection of the appropriate vise based on the sample’s shape, size, and characteristics, increasing flexibility in metallographic preparation.

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

Metallographic mounting techniques mainly include hot mounting and cold mounting methods. These techniques involve encapsulating sectioned metal or non-metal metallographic preparation samples in curing materials to provide stability during subsequent grinding and polishing processes. This step protects the edges and surfaces of the metallographic preparation samples from damage during grinding and polishing, especially for irregularly shaped or brittle samples. Metallographic mounting is crucial in such cases.

Metallographic mounting encases the sample in a curing material.

1. Characteristics of Hot Mounting

Hot mounting uses thermosetting resins, such as acrylic or phenolic powder, to embed metal metallographic preparation samples by applying heat and pressure.

Metallographic hot mounting using bakelite powder.

The features of hot mounting include:

(1) Stability

Hot mounting provides stable and clearly defined edges for metallographic preparation samples. Once the samples are fixed in the resin, they are effectively protected from deformation or damage during metallographic preparation.

(2) Application Range

Hot mounting is suitable for most metal materials, especially those unaffected by heat. The high-pressure and high-temperature environment ensures the resin fully penetrates the sample’s micropores, enhancing stability. It is essential to monitor the quality of the resin or phenolic powder, as degradation may result in hot mounting failure.

It is essential to ensure that phenolic powder has not deteriorated; otherwise, it may cause hot mounting failure in metallographic preparation.

(3) Process Efficiency

Hot mounting typically completes quickly, achieving good molding results in one operation, which significantly improves laboratory efficiency.

2. Steps for Operating Hot Mounting Press

(1) Clean the metallographic preparation sample to avoid oil stains or impurities on the surface.

(2) Open the machine’s lock cover and ensure it is fully rotated to the end.

(3) Raise the lower mold head.

(4) Place the metallographic preparation sample, ensuring a gap between the sample and the mold tube. A tight fit may cause incomplete edge encapsulation and scratch the mold tube.

(5) Lower the lower mold head.

(6) Slowly pour in phenolic or acrylic powder.

(7) Close the machine’s lock cover and confirm it is fully secured.

(8) Start the hot mounting process. Most machines feature automatic heating and cooling functions, though some require manual control.

(9) Ensure the sample is fully cooled after hot mounting to prevent burns from residual heat if the cooling system is not activated.

(10) Remove the hot mounted sample.

3. Characteristics of Cold Mounting

Cold mounting in metallographic preparation uses cold-setting resins, such as epoxy resin, ideal for heat-sensitive or irregularly shaped non-metal materials.

Metallographic Cold mounting uses cold-setting resins.

Features of cold mounting include:

(1) Avoidance of Thermal Stress

Since cold mounting does not require heating, it prevents thermal stress from affecting the microstructure of non-metal samples, especially brittle ones.

(2) Ease of Operation

The cold mounting process is relatively simple. Place the non-metal sample in a mold, pour in the mixed resin and hardener, and allow it to harden. This makes cold mounting an efficient and user-friendly option.

(3) Wide Applicability

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

4. Steps for Operating Cold Mounting Mold

(1) Clean the metallographic preparation sample to avoid oil stains or impurities on the surface.

(2) Place the sample into a silicone mold.

(3) Slowly pour the epoxy resin and hardener along the edge of a paper cup. Pouring too quickly may introduce air bubbles.

(4) Stir the epoxy resin and hardener consistently to prevent excessive bubbles. Maintain a uniform stirring direction and speed.

(5) Slowly pour the mixed resin into the silicone mold, ensuring minimal air bubbles. For high-flow epoxy resin, use a vacuum impregnation machine to extract resin into the mold gradually.

(6) Use a vacuum impregnation machine to reduce air bubbles when using high-flow epoxy resin.

(7) Once the epoxy resin hardens, remove the sample from the mold.

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

The primary goal of metallographic grinding is to smooth the surface of the mounted metallographic preparation sample to prepare it for microscopic observation.

Metallographic grinding is to grind the surface of the mounting sample.

The grinding process generally involves two stages: rough grinding and fine grinding.

1. Rough Grinding

Rough grinding uses coarser abrasives to remove surface irregularities and large defects from metal or non-metal samples. Features of rough grinding:

(1) Material Removal

Rough grinding effectively removes excess material from the surface, setting the foundation for fine grinding.

(2) Tools Used

Coarse-grit silicon carbide blades or diamond abrasives are typically used, offering fast removal of surface irregularities.

2. Fine Grinding

Fine grinding enhances the smoothness of the sample surface, typically using finer abrasives. Features of fine grinding:

(1) Smooth Surface

Fine grinding eliminates scratches left by rough grinding, achieving a higher degree of flatness and smoothness.

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

(2) Abrasive Selection

Finer-grit silicon carbide blades or diamond abrasives provide precise metallographic preparation grinding results.

3. Steps for Operating Automatic Grinding & Polishing Equipment

The key is to select appropriate silicon carbide grinding papers according to the sample’s material properties, starting from coarse to fine grit sequentially.

(1) Begin with rough grinding by wetting the grinding disc and attaching silicon carbide grinding papers securely by spinning the disc to remove excess water.

(2) Use an O-ring to secure the silicon carbide grinding papers and moisten the surface.

(3) Lift the polishing head holding the metallographic preparation sample.

(4) Place the mounted sample on the support plate and lower the polishing head.

(5) Start the machine from 0 rpm and gradually increase to the desired speed.

(6) After grinding, raise the polishing head.

(7) Remove the sample and clean it with water, then dry it with a blower to avoid cross-contamination between different grits.

(8) Repeat the process for fine grinding, changing only the grit of the silicon carbide grinding papers, while keeping other steps consistent.

1. Purpose of Metallographic Polishing

The goal of metallographic polishing is to remove fine scratches and irregularities from the surface of the metallographic preparation sample, leaving it smooth and highly reflective like a mirror. This mirror-like effect clearly reveals the microstructure of the sample, facilitating analysis of phase distribution, grain boundaries, and inclusions.

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

2. General Polishing Steps

Following proper metallographic polishing steps ensures that both metal and non-metal samples achieve optimal smoothness and gloss. General polishing typically starts with coarser abrasives to remove larger defects and scratches. The main steps in metallographic preparation are as follows:

(1) Select the appropriate Polishing Cloth based on the specific polishing requirements.

(2) Lift the polishing head holding the metallographic preparation sample.

(3) Spray a suitable polishing liquid onto the Polishing Cloth.

(4) Place the ground sample on the support plate and lower the polishing head.

(5) Start the machine at 0 rpm and gradually adjust the speed to the specified level.

(6) During polishing, monitor the moisture of the Polishing Cloth. If it becomes too dry, add more polishing liquid promptly.

(7) After polishing, lift the polishing head and clean the surface of the Polishing Cloth.

(8) Remove the sample, rinse it with water, and dry it with a blower. Proper cleaning is essential to prevent cross-contamination between polishing liquids, which could affect observation results.

During metallographic polishing, spray suitable polishing liquid onto the Polishing Cloth.

1. Key Points of Final Polishing

In the final polishing step of metallographic preparation, porous polishing pads and silica are commonly used. The porous structure of the pads absorbs polishing liquids and abrasives, ensuring proper lubrication on the sample’s surface. These pores also help distribute abrasives evenly, preventing over-polishing in localized areas.

Colloidal silica suspension is a very fine polishing material with a particle size of about 0.04 μm. Due to the nearly spherical shape and lower hardness of silica compared to aluminum oxide, it is ideal for final polishing of soft and ductile materials.

In chemical mechanical polishing (CMP), the pH of the silica suspension usually ranges between 8.5 and 11, facilitating chemical removal during the final polishing process. This combination of chemical and mechanical methods is especially suitable for silicon wafers and metal/ceramic composites, enhancing polishing performance while minimizing surface deformation.

When using silica suspension during the final polishing, it is crucial to maintain the cleanliness of the polishing pads to prevent drying of the suspension, which can cause crystallization on the pad surface, leading to scratches on the sample. Rinsing the polishing pads with water after use helps prevent such issues.

2. Steps for Operating Final Polishing Equipment

(1) Replace the Polishing Cloth with a polishing pad.

(2) Lift the polishing head holding the metallographic preparation sample.

(3) Place the sample, previously polished with general polishing, on the support plate and lower the polishing head.

(4) Start the machine at 0 rpm and gradually adjust the speed to the specified level.

(5) During the final polishing process, monitor the moisture of the polishing pad. If it becomes too dry, add more polishing liquid promptly.

(6) After polishing, activate the cooling water and rotate the polishing disc slowly to clean both the sample and the polishing pad surfaces. At the end of the final polishing process, rinse the polishing pad with water to prevent crystallization of dried silica, which could affect the next polishing result.

(7) Remove the sample and dry it with a blower for subsequent observation.

Specifications related to polishing pads for final polishing.

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

In metallographic preparation, Etching is an essential step to reveal the internal structure of the sample, allowing clearer observation of different phases or microstructures under a microscope. After the final polishing, an etchant is applied to the sample to make it observable.

There are three key steps to focus on during Etching: selecting the etching method, controlling etching time, and observing the etching process to respond appropriately.

1. Selecting the Etching Method – Chemical Etchant and Electrolytic Etching

Each metal or alloy requires a different etchant to highlight its microstructure. The appropriate etchant (e.g., nitric acid-alcohol solution, hydrochloric acid solution) must be chosen based on the material of the sample.

Common etchants include:

• Low-carbon steel, carbon steel: Nitric acid + alcohol mixture (Nital), picric acid + alcohol mixture (Picral).

• Stainless steel: Oxalic acid or sulfuric acid.

• Copper alloys: Ferric chloride solution.

For materials that are difficult to process with chemical etching, electrolytic Etching can be used.

This method applies a weak current to cause differential etching between phases, making the metallographic structure visible.

2. Controlling Etching Time

Immerse the final polished sample into the etchant for a short period (ranging from seconds to minutes).

There is no fixed standard for etching time. As the sample begins to etch, it should be checked periodically, every few seconds to minutes, to see if the desired grain structure has become visible.

3. Observing the Etching Process and Taking Action

The depth of etching should align with the magnification level of the microscope and the characteristics of the material. Shallow etching is preferable for high magnification, while deeper etching can be used for low magnification.

If the sample turns rainbow-colored or dark gray, stop the etching immediately and rinse the sample with distilled water or alcohol to halt the action of residual etchant.

If the grain structure is clear, cease etching and dry the sample with a blower or oil-free compressed air to avoid water stains.

If immediate observation is not possible, apply a protective agent to reduce the risk of oxidation or contamination.

Microscopic techniques in metallographic preparation allow researchers to observe and analyze both the macroscopic and microscopic structures of metal or Non-Metal materials. Depending on the observation needs and sample characteristics, the most commonly used microscopes are optical microscopes and scanning electron microscopes (SEM).

Metallographic preparation optical microscope

Below is a brief overview of these two tools:

1. Optical Microscope

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

(1) Macroscopic Structure Observation

At low magnification, an optical microscope displays the metallographic macroscopic structure of metal samples, helping researchers quickly understand the material’s overall characteristics.

(2) Metallographic Structure Analysis

At high magnification, it can reveal fine metallographic structures, crucial for analyzing grain structures, phases, cracks, and inclusions.

(3) Reflected Light Observation

Optical microscopes primarily use reflected light to observe polished and etched metal samples, making them effective for metallographic analysis by clearly showing surface features and defects.

Optical microscopes are relatively simple to operate, cost-effective, and widely used across fields such as material science, engineering, and biology.

2. Scanning Electron Microscope (SEM)

The SEM is a high-resolution microscope suitable for observing detailed microstructures of metal and Non-Metal samples processed through metallographic preparation. Its features include:

(1) High Resolution

SEM offers higher resolution than optical microscopes, clearly displaying the microstructure and morphology of the sample. It is particularly useful for analyzing submicron-level inclusions, pores, and grain boundaries.

(2) Electron Beam Scanning

The SEM scans the sample’s surface with an electron beam to generate high-resolution images, revealing surface features and internal structures.

(3) Versatility

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

Metallographic preparation and analysis are integral to many industries, such as evaluating materials for extreme environments in aerospace, fatigue life analysis in automotive applications, welding quality control for electronic components, and corrosion resistance testing for building materials. In these precision applications, metallographic preparation provides deep insights into grain boundaries, inclusions, and welding defects, where even minor flaws can prevent product failure and avert catastrophic safety risks.

The significance of metallographic techniques goes beyond product quality assurance; they are fundamental to industrial competitiveness. With ongoing innovations in manufacturing processes—ranging from high-hardness precision diamond cutting to advanced hot and cold mounting techniques—each breakthrough expands the boundaries of material analysis, enabling previously unobservable microstructures to be explored. This accelerates the development of new materials and gives scientists more freedom to innovate, paving the way for future material advancements.