Response by M.A. Kaplan and G.E. Fuchs
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In his letter, Professor Campbell comments on Kaplan and Fuchs papers ‘‘Oxides Bifilms in Superalloy: IN100, Parts I and II and provides some very interesting thoughts on the impact of casting procedures on the formation of defects referred to as bifilms. Campbell also notes that these papers are the first reports of the use of powerful characterization techniques such as high resolution TEM and Auger microscopy. The vast majority of Campbell’s comments are re-interpretation of the photomicrographs and the data reported by Kaplan and Fuchs, which Campbell claims to be proof of the presence of bifilms throughout the test material examined. However, Campbell appears to ignore the extensive surface characterization results reported that clearly indicate that there are no oxide films or bifilms on the fractures surfaces examined. In a similar manner to Prof. Campbell, each of the comments will be addressed from each paper in order.
PART I Prof. Campbell states that the master alloy utilized in the Kaplan and Fuchs studies would be expected to contain a high proportion of bifilms and that the current melting and casting processes would only add to the ‘‘massive’’ population. However, again, Prof. Campbell does not provide any direct evidence for the existence of the bifilms and all of the results reported by Kaplan and Fuchs did not indicate the presence of bifilms. In addition, since the bifilms are reported to be predominantly Al2O3 in Ni-base superalloys, the presence of a massive population of bifilms, whose density is approximately 3.95 g/cc, would be expected to result in a significant reduction in the density of the alloy (IN100 density reported to be 7.75 g/cc). However, there is no reported density reduction in any of the materials if GERHARD E. FUCHS, Associate Professor, and MAX A. KAPLAN, Graduate Student, are with the Department of Materials Science & Engineering, University of Florida, Gainesville, FL. Contact e-mail: [email protected]fl.edu Manuscript submitted May 5, 2016. Article published online June 15, 2016 3806—VOLUME 47A, AUGUST 2016
massive populations of bifilms were present as reported by Prof. Campbell. It was clearly stated in the Kaplan and Fuchs manuscripts that the test materials were not heat treated to produce materials with mechanical properties comparable to the literature. Instead, heat treatments, HIP cycles, etc, were only performed in order to help identify or ‘‘thicken’’ bifilms, if they were present. However, Prof. Campbell states that the materials in the Kaplan and Fuchs studies exhibited very poor properties and appears to ignore the statement regarding the heat treatment selection. In addition, it appears that Prof. Campbell is reporting that bifilms strengthen the material since he claims that the lack of differences in yield strength is due to the work strengthening of the region surrounding the defects, even though the bifilms, if present, would reduce the cross-sectional area of the material. Again, Prof. Campbell does not provide any evidence or data to support his claims. In the Kaplan and Fu
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