Depth profiling of Hf-doped aluminide coating by glow-discharge mass spectrometry
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Depth Profiling of Hf-Doped Aluminide Coating by GlowDischarge Mass Spectrometry L.M. HE, K. PUTYERA, J.D. MEYER, L.R. WALKER, and W.Y. LEE
element (e.g., Hf ) via proactive control of the gas-phase concentration of a dopant precursor (HfCl4) as a function of time. Prior studies have certainly shown that, in order for its beneficial effects to be operative, a reactive element must be present at a well-controlled characteristic level and distribution in the matrix material.[2,3,4] In our recent studies,[5,6] a laboratory-scale CVD reactor was used to study the effects of a “continuous” Hf doping procedure, in which HfCl4 and AlCl3 were simultaneously introduced with H2, on the Hf incorporation behavior. Measuring Hf concentration and distribution was a major challenge for these investigations due to their low Hf concentration (0.01 to 0.6 wt pct as measured locally), which was mostly below the detection limit of electron microprobe analysis (EMPA) for Hf (⬃0.15 wt pct). With its ability to detect major, minor, trace, and ultratrace elements (i.e., parts per million to percent) in the same analytical cycle at a rapid sputtering rate, glow discharge mass spectroscopy (GDMS) was selected as a depth profiling tool for Hf concentrations below ⬃0.2 wt pct. However, analysis and interpretation of the GDMS data were not straightforward due to some generic issues associated with the GDMS technique such as nonuniform sputtering and phase inhomogeniety in the coating samples.[7] The objective of this article is to assess the advantages and limitations of the GDMS technique as a depthprofiling technique in terms of analyzing the concentration and distribution of Hf in the coating matrix and in comparison to traditional metallography and EMPA characterization. A “melt-desulfurized” single-crystal Ni superalloy RENE´* N5 and a pure Ni (99.99 pct purity and polycrystal*RENE´ is a trademark of General Electric Company, Fairfield, CT
line) were used as the substrate materials as described elsewhere.[5] Three coating samples from our previous studies were select
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