The earliest alloys used by humans were meteoric irons, natural combinations of iron and nickel found in meteorites. With the advancement of smelting technologies, humans began producing alloys like bronze and brass, which allowed for adjustable properties based on their constituent ratios.
The discovery of most metals occurred in the 19th century, paving the way for the creation of numerous new alloys, including those based on aluminum.
Initially regarded as a novelty, aluminum alloys demonstrated their practical value when the Wright brothers incorporated them into their first airplane engine. Since then, alloys have been integral to engineering progress, with the development of superalloys enabling technologies that operate at extremely high temperatures.
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Superalloys
Superalloys represent a significant improvement on standard alloys because these advanced alloys continue to operate as normal at high temperatures, even when close to their specific melting point.
Superalloys boast excellent mechanical strength, robust surface stability, and resistance to thermal creep. The latter of these benefits is especially important in turbine engines used in marine and aerospace operations, where deformation from thermal creep tends to be the primary reason for the replacement or retirement of components.
It is important to note, however, that superalloys are vulnerable to oxidation. This can result in degradation of the alloy over time, potentially resulting in embrittling, cracking, or elemental depletion.
Selective oxidation continues to be the best means of protecting against this negative oxidation.
Alloys can be designed to oxidize in a very specific way, creating a protective layer of already-oxidized material over the alloy and protecting the rest of the alloy’s structure from oxygen. However, that protective layer needs to remain intact and stable. Any weakness where oxygen can reach the rest of the superalloy means that negative oxidation can resume.
Sulfur can interfere with the selective oxidation process, even when this element is present at ultra-low levels. Sulfur determination is, therefore, critical to quality assurance when working with superalloys.
The 844 Series Combustion Analyzer
Glow Discharge Mass Spectrometry (GD-MS) instruments were historically the only means of accurately determining ultra-low levels of sulfur, with these instruments offering detection limits of approximately 0.1 μg.
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LECO has developed an instrument able to reach these detection limits using a combustion technique. The 844 Series combustion analyzer is just a fraction of the cost of a GD-MS instrument.
When equipped with the ES option, the 844 series of sulfur determinators can be used to accurately detect ultra-low levels of sulfur in a range of steels, alloys, and superalloys.
Acknowledgments
Produced from materials originally authored by LECO.
This information has been sourced, reviewed and adapted from materials provided by LECO Corporation.
For more information on this source, please visit LECO Corporation.