Figure 12. Typical micrographs of the six samples examined in the Inter-Laboratory Study (ILS). Table 7. Parameters Studied in the ILS
Performing the analysis at 200x and using a 5µm trap size resulted in larger fluctuations in the nodule count results, even though 25 fields of view were used (Figures 13 and 14).
Such a larger fluctuation was expected since at 200x, the use of the same number of fields of view represent roughly a quarter of the area examined; the results obtained are there- fore more susceptible to the nature of the local area being analyzed.
When assessing the nodularity in % Number of particles, looking at only 500 particles as opposed to 25 fields of view tended also to negatively impact the repeatability of the re- sults (Figures 17 and 18).
The comparison between Figures 10 and 11 seemed to in- dicate that the nodularity values expressed in % Number of particles were less repeatable than those expressed in % Area. However, the ILS results (Figures 16 and 17) indicate that nodularity values expressed in %Number obtained by the participating laboratories were more reproducible than those expressed in %Area.
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It is also interesting to note the difference in the spread of values obtained when the shape factor was varied from 0,5 to 0,6 depending on the laboratory performing the analysis. For example, when looking at the nodule count data for sam- ple 12-103-J2 (Figure 13), changing the roundness shape factor from 0,5 to 0,6 resulted in a nodule count variation of 40 Nod/mm2
for Laboratory B, as opposed to a 10 Nod/mm2 variation for Laboratory E. Conclusions and Recommendations
This paper showed that the IA parameters greatly influence the nodularity and the nodule count values obtained. Presently, IA results of nodule count and nodularity are often published, or given to customers, without specifying the trap size used, the number of fields examined, the magnification, as well as the shape factor and its magnitude. In order for the industry to share or publish IA results which are both meaningful and reproducible, it is important for the IA users to specify the analysis parameters used and avoid selecting parameters, such as 500 particles minimum or examination at 200x with a 5µm trap size, which inherently lead to less repeatable results.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
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