Manufacturing failure analysis
Failure analysis is a crucial process in various industries used to identify the root causes of failures and ultimately help improve material selection, reliability, and lifespan. While visual examination, microscopy, and physical analysis provide important insights, chemical analysis techniques are often essential in determining the chemical composition of materials. These techniques complement other methods and help address questions related to material selection, contamination sources, the presence of volatile compounds, and environmental factors. Energy-dispersive X-ray spectroscopy is one of the most used chemical analysis techniques thanks to several benefits that will be discussed in this article. However, while EDS has several advantages for failure analysis, it is worth noting that no single technique can address all aspects of failure analysis.
In this article, we will discuss the role of EDS in failure analysis, exploring both the advantages and limitations of the technique. Additionally, we will present case studies that highlight its practical relevance in the field.
The role of energy-dispersive spectroscopy in materials failure analysis
One of the main roles of EDS is, generally speaking, to provide the composition of a material. EDS not only identifies but also quantifies the elements in a material. By analyzing the characteristic X-rays emitted, EDS can detect a full range of elements. In failure analysis, understanding the composition of the material around a failure, how it has changed, and if undesired elements contributed to the failure itself are the starting points to assessing the integrity of the materials involved and eventually taking action to prevent future failures.
Locating the presence of impurities and contaminants is important in failure analysis. While there are several possible causes of failures depending on the industry, corrosion is one of the most common across several fields. EDS can be employed to analyze the elemental composition of corroded products and corrosion deposits. By identifying the specific elements involved in the corrosion process, such as oxygen, sulfur, or chlorides, EDS can help you understand the causes of corrosion and select appropriate prevention strategies.
EDS is integrated in scanning electron microscopes, and it works in combination with microscopic inspections of fracture surfaces. EDS provides valuable information about the elemental composition and chemical states of these regions. It can identify the presence of thin layers, coatings, or oxides that may contribute to failures. Coatings, in fact, are often applied to materials on purpose to enhance their performance or protect the coated material. EDS plays an important role both as a preventive control of thickness, uniformity, and adhesion to the substrate material and as a way to identify possible coating defects, such as pinholes, delamination, or improper composition, hence linking them to early failures.
EDS failure analysis advantages and limitations
As mentioned above, EDS provides the chemical composition of areas of interest, helping to discover possibly unknown materials. However, EDS is not limited to qualitative analysis. It also offers quantitative capabilities, providing relative concentrations of elements within a sample. It provides these results within minutes, highlighting one of the main benefits of this technique: quick answers that can guide changes to the manufacturing process.
Within production, one advantage of EDS is that it’s non-destructive and requires only minimal sample preparation. This makes it possible to perform analysis without wasting any piece of the product, which is particularly valuable when working with irreplaceable samples or when performing quality control in the production process. It also makes it possible to combine EDS with other analytical techniques, enabling more robust and accurate failure analysis.
However, there are some limitations that can make EDS a secondary choice for some specific applications. EDS primarily analyzes the surface of a sample, typically only penetrating a few micrometers into the material. In the case of subsurface defects, EDS might not reveal the right answer without sample preparation techniques like cross-sectioning or polishing.
EDS is less sensitive to detecting light elements compared to heavier elements. The low X-ray emission and difficulties in detecting low atomic number elements can limit the capability of EDS to analyze certain types of materials or failure modes.
Lastly, EDS data and results can become less intuitive when characterization is conducted on materials with complex chemistries or mixtures of different materials. This is because there might be overlapping peaks or spectral artifacts from neighboring elements that change the accuracy and reliability of the results. Alternative ways to make use of the EDS signal, such as phase analysis rather than just the elemental maps and spectra, can overcome this limitation by providing clear results about the different materials without the need for manually interpreting the results.
Despite these limitations, EDS remains a widely used and valuable technique in failure analysis due to its ability to provide rapid and informative elemental analysis.
EDS failure analysis applications and case studies
Corrosion failure analysis
Pickling is a crucial steel surface treatment, especially when the steel must be uniform and free of surface stains or oxides. The process uses an acid solution followed by a proper washing step to eliminate acid contamination on the steel surface. In the following link you'll read about a case study where stains were found on structural steel after pickling, and SEM-EDS was used to identify the root cause of the contamination. EDS was used to examine the surface morphology and chemical constituents of the defect. This showed that the surface stain was rich in chlorides and had a higher oxygen content, suggesting that a drop of hydrochloric acid contacted the surface after cleaning.
Steel failure analysis
Bend testing is commonly used to test the ductility of steel and other materials and to check their resistance to fracture. When fractures or cracks occur, SEM and EDS can be used to characterize the failure and quickly determine its root cause. The link will redirect you to a case of a HSLA (high-strength, low-alloy) steel failed bend test. SEM imaging and EDS chemical information were used to examine the split and ultimately locate a stringer. EDS provided compositional information about inclusions in the stringer. It was then determined that a cluster of non-metallic inclusions had spread into a linear defect during the hot rolling process, which caused the failure in the bend test.
Automotive parts coating defects
As mentioned above, SEM/EDS can be used to examine defects in layers of protective coatings to understand the root cause of a defect and prevent it in the future. Characterizing coatings is especially useful in the automotive industry, where the quality of exposed steel panels such as doors or roofs is important to their resistance to atmospheric corrosion. In the example presented in the application note in the link below, EDS was used to find the presence of foreign particles and quickly assess their composition. The study identified a foreign particle with elements suggesting mold powder residue. Mold powder is used for heat control, lubrication, and to prevent oxidation. This prevented the protective coating from adhering to the steel, leading to corrosion.
Failure analysis of composite materials
Composite materials, and in this specific case polymer composites, are widely used in various industries. They can be susceptible to failures due to factors such as delamination, fiber breakage, or resin degradation. The example presented in the application note in the following link, is a glass fiber-reinforced polymer (GFRP), which consists of a polymer matrix mixed with one or more types of glass fiber. This combines the strength and stiffness of glass fibers with the elasticity, light weight, and durability of polymers. EDS was used to find and characterize unknown and unexpected materials. The presence of a contaminant can lead to degraded product performance, compromised electrical insulation, mechanical failure, or reduced chemical resistance.
Battery manufacturing materials contamination
Contamination is a major issue at every stage of battery manufacturing, causing problems such as lower efficiency, cell degradation, and even internal shorts. Combined SEM and EDS can help you understand contaminants that enter the battery manufacturing process. SEM and EDS can be used to analyze the structure and elemental information of contaminants, which provides insights on their possible cause and helps manufacturers prevent unexpected materials from entering the production process.The example presented in the following application note shows the characterization of a LiCoO2 cell. EDS was used to discover the presence of Al, Mg, and Ti in the electrode, which was unexpected. These contaminants may have been introduced during the cathode materials synthesis, mixing, or coating processes.
Advanced failure analysis for industrial manufacturing
Failure analysis is the best way to improve product performance, quality, development, and reliability. Commonly employed in engineering, manufacturing, and QC processes, failure analysis is also a critical tool for enabling continuous improvements. Depending on the nature of the failure and the specific industry, it makes use of different techniques that are often used in combination to provide a complete understanding of the failure mechanism. In most cases, however, the chemical information is an important factor. EDS is one of the easiest and fastest analytical techniques available for collecting this information. Its ability to detect and quantify contaminants, examine fracture surfaces, and correlate microstructural characteristics with elemental composition makes EDS an indispensable technique in failure analysis.
For Research Use Only. Not for use in diagnostic procedures.