Thermo Fisher highlights use of advanced SEM for metal quality control analysis

October 23, 2024

Copper-rich T1 (green) and Zircon-rich beta-prime (red) precipitates in the heat affected zone of an aluminium alloy friction-welded aerospace part, identified in the transmission electron microscope (Courtesy Thermo Fisher Scientific)
Copper-rich T1 (green) and Zircon-rich beta-prime (red) precipitates in the heat affected zone of an aluminium alloy friction-welded aerospace part, identified in the transmission electron microscope (Courtesy Thermo Fisher Scientific)

Thermo Fisher Scientific, headquartered in Waltham, Massachusetts, USA, has highlighted the ability of Scanning Electron Microscopy (SEM) to successfully capture defects when conducting failure analysis on metals. In the report, Dr Franz Kamutzki, Sales Account Manager at Thermo Fisher Scientific, explains how new elemental analysis approaches can help ensure the quality of metal components.

“In the metals industry, the difference between success and failure often hinges on microscopic details,” begins Dr Kamutzki. “Since component failure is often a direct result of microscopic defects, SEM helps establish metrics for quality control to help manufacturers get to the root cause of their material concerns.”

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With demand for steel expected to grow by 2030, there is an opportunity to reindustrialise and modernise production processes, the report adds. An increasingly popular method of regenerating production is engineering materials at the nanoscale; tailoring structures at this size can improve durability, reliability and cost.

“An example of this,” explains Dr Kamutzki, “is when engineering metals for the aerospace sector, reducing weight and increasing stiffness can help to improve performance and extend the working life of the component parts.”

Ternary diagrams representing particle size and chemical composition of inclusions as a function of laser speed in additively manufactured steel (Courtesy Thermo Fisher Scientific)
Ternary diagrams representing particle size and chemical composition of inclusions as a function of laser speed in additively manufactured steel (Courtesy Thermo Fisher Scientific)

Metals under the microscope

Even traditional processes now incorporate microscopic inspection to determine the material’s elemental and structural composition. Precise control of inclusions and precipitates is essential for effective metal production, but whether these additions strengthen the material or act as contaminants depends on their consistency and distribution.

Examples of these microscopic properties include nanoprecipitates, which form when the metal is rolled, annealed or hot pressed. Steel strengthened with nanoprecipitation offers good weldability and a high strength-to-weight ratio, making them ideal in aircraft structures.

“However, the presence of inclusions and precipitates can also have detrimental effects on material quality,” highlights Dr Kamutzki. “In the range of industries that use metal or steel, quality control measures are implemented to ensure material quality before it is used. For example, quality engineers must detect nanoscale morphological changes such as crack initiation sites, which can occur due to microstructural alternations during fatigue loading.”

Given that the metal used in demanding applications, such as aircraft frames, must withstand vibrations, pressure fluctuations and thermal stresses, accurately detecting crack initiation sites is an essential part of quality control.

Other nanoscale structural changes that require detection and control include grain boundaries, which are defects that can decrease the material’s electrical and thermal conductivity, as well as oxide inclusions that cause casting interruptions in steelmaking. Since steelmaking is a highly oxidising process, the quality is easily jeopardised by inclusions.

Here, Dr Kamutzki is keen to point out that microscopy can detect any major faults in the final product and help maintain compliance with industry standards. “For example, ASTM E45, which provides methods for microscopic examinations to evaluate non-metallic inclusions in steel, and E2283, which offers statistical methods for analysing the distribution of these inclusions.”

BSE image of a refractory oxides sample (L) and the determination of different phases from the detected elements using ChemiPhase (R) (Courtesy Thermo Fisher Scientific)
BSE image of a refractory oxides sample (L) and the determination of different phases from the detected elements using ChemiPhase (R) (Courtesy Thermo Fisher Scientific)

Simplifying microscopy with SEM

Scanning electron microscopy plays a vital role in characterising the composite materials employed in metal production. “Take for instance, refractories, which are commonly used in steel production as protection in extreme environments such as heating furnaces and refining vessels,” adds Dr Kamutzki. “Due to high temperatures and corrosive conditions, the physical and chemical properties of the refractories are hugely important for stability and wear resistance. Typically fabricated by combining material types such as ceramic (oxide) powders, reactive metals or carbides, the refractories may be employed in pressed bricks, monolithic linings and carbon-bonded products used in continuous steel casting.”

While conventional electron microscopy is useful, providing a backscattered or scattered electron (BSE and SE, respectively) image of materials distribution, the images can’t disclose grain composition or distinguish different phases and possible contaminations, explains Dr Kamutzki. “However, elemental analysis based on instantaneously displayed information from the SEM image is much quicker and more informative,” he says.

In the report, Thermo Fisher Scientific highlights its own ChemiSEM technology, which enables high-throughput chemical analysis with energy-dispersive X-ray spectroscopy (EDS) mapping. This allows for an overview of the elemental and structural composition of hundred, if not thousands, of inclusions to be given in hours, as opposed to the days it may take for manual analysis to achieve the same results, the company states.

Not only is statistical information on the bulk available, but individual precipitates can also be seen in the Transmission Electron Microscope (TEM) with high detail, providing a multi-scale overview of the metal. Within steel and aluminium production, where reducing weight is a priority, Thermo Fisher’s automated instruments can also carry out the critical task of nanoparticle counting.

“Since metal components are frequently used in demanding environments, detecting and controlling microscopic material defects is crucial. While this requires extensive structural analysis, advanced approaches to SEM can simplify the process and save time, without compromising quality testing standards,” concludes Dr Kamutzki.

www.thermofisher.com

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