Quality Control of Metals in the SEM Using AZtecWave

17^th August 2023 | Author: Dan Haspel

During the life of a production process, the metal supplier may change due to costs or maybe the original supplier ceased to supply. It would be expected that the new supplier is supplying the same metal with the same chemistry. However, this isn’t always the case, and this can cause problems during the processing of the metal or issues with it performing its end function. One quick method to ensure the quality of the newly supplied metal is to analyse the chemistry and check it against the specification sheet that should be supplied with the metal. However, most metal alloys contain trace levels of elements.

In most cases, a newly supplied metal comes with a specification data sheet (SDS) that also includes the chemistry, along with the tolerance of the concentration. One such chemistry table is shown below, which is for Kovar according to ASTM F15. It shows that there may be trace elements present in the alloy, but it also states the tolerances and nominals.

Chemistry	Composition %
Iron, nominal	53.00
Nickel, nominal	29.00
Cobalt, nominal	17.00
Manganese, max	0.50
Silicon, max	0.20
Carbon, max	0.04
Copper, max	0.20
Chromium, max	0.20
Molybdenum, max	0.20
Aluminium, max	0.10
Magnesium, max	0.10
Zirconium, max	0.10
Titanium, max	0.10

The iron, nickel and cobalt % listed are nominal. They shall be adjusted by the manufacturer so that the alloy meets the requirements for coefficient of thermal expansion

The total aluminium, magnesium, zirconium and titanium shall not exceed 0.20%

Can we accurately check the chemistry of a supplied metal in an SEM?

Generally, SEM-based microanalysis, such as Energy Dispersive X-ray Spectrometry (EDS/EDX) can’t detect trace elements that supplied metals can contain; in this case Wave Dispersive X-ray Spectrometry (WDS/WDX) is perfect, as this technique can detect elements low concentration or trace level, and quantitatively measure them more accurately. The AZtecWave software fully integrates WDS and EDS, enabling major elements to be quickly analysed using EDS and elements in low/trace concentrations to be measured using WDS.

This is done by combining both the WDS and EDS techniques together, with the EDS quantifying the major elements (Fe, Ni and Co) and the WDS quantifying the minor and trace elements. The analysis (below) was conducted on a FEG-SEM fitted with a fully focussing Rowland circle Wave spectrometer (i.e. EPMA-type) and an 170 mm² Ultim Max EDS detector. The beam condition used was 20 kV and ~20.8 nA at the microscope’s analytic working distance, which for this microscope is 10 mm. This was done.

Did the supplied metal fit within specification?

The results are shown in the following tables, with first table showing the measurement for each point and the second table showing the statistics for the five points analysed. The results show that the Kovar metal supplied does adhere to the ATM F15 specification.

In this sample, no Ti or Mg was identified, neither Al nor Zr had an individual concentration above 0.1%, and the combined concentration of these elements was not above 0.2%. The other minor elements were also within the specified standard.

Point	Al	Si	Cr	Mn	Fe	Co	Ni	Cu	Zr	Mo
1	0.0064	0.1174	0.0731	0.2785	53.4539	17.3234	28.1849	0.0944	0.0041	0.0179
2	0.0070	0.1685	0.0789	0.2780	54.1812	17.4930	28.8866	0.1067	0.0000	0.0366
3	0.0000	0.1703	0.0831	0.2638	53.9544	17.4732	28.7256	0.1005	0.0024	0.0405
4	0.0015	0.0662	0.0783	0.2497	53.2361	17.2725	27.909	0.0658	0.0027	0.0523
5	0.0000	0.1897	0.0898	0.2994	54.0326	17.4706	28.9471	0.0840	0.0012	0.0418

Statistic	Al	Si	Cr	Mn	Fe	Co	Ni	Cu	Zr	Mo
ASTM F15 standard	0.1 max	0.2 max	0.2 max	0.5 max	53nominal	17nominal	29nominal	0.2max	0.1 max	0.2 max
Technique	WDS	WDS	WDS	WDS	EDS	EDS	EDS	WDS	WDS	WDS
Max (wt.%)	0.0070	0.1897	0.0898	0.2994	54.1812	17.4930	28.9471	0.1067	0.0041	0.0523
Max (wt.%)	0.0000	0.0662	0.0731	0.2497	53.2361	17.2725	27.9090	0.0658	0.0000	0.0179
Average (wt. %)	0.0030	0.1424	0.0806	0.2739	53.7717	17.4065	28.5307	0.0903	0.0021	0.0378
Standard Deviation	0.0034	0.0503	0.0062	0.0185	0.4053	0.1011	0.4594	0.016	0.0016	0.0125

Take aways

WDS, combined with EDS in AZtecWave, can be effectively used to confidently assess a newly supplied metal against its specification sheet. The result showed that the newly supplied metal was within specification. If this hadn’t been the case and the newly supplied metal would not have adhered to the specification sheet, in which case the results could be used to go back to the supplier.

Dr Dan Haspel,
Product Scientist, Oxford Instruments

About the Author

Dr Dan Haspel graduated from Loughborough University with an MEng in Automotive Materials Engineering in 2014, during which he worked for Ross Ceramics and IHI in Japan. Dan then stayed at Loughborough Uni for his PhD, which focussed on utilising electrochemical methods to mitigate tin whisker growth. He then moved to the University of Plymouth where he managed their newly acquired FIB-SEM. During which he gained a wealth of knowledge in using Oxford kit and all things FIB and 3D reconstruction. Dan then joined Oxford Instruments June 2022 where he is a Product Scientist specialising in EBSD and FIB products.

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