November AMP_Digital

iTSSe TSS A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 9 4 3 iTSSe TSS FEATURE ly poorer coatings, despite optimized parameters, espec- ially because adsorbed moisture can lead to significant powder-feeding issues and thus premature degradation of the formed coating. In this application, XRF can pro- vide precise information about the starting powder chem- istry. Figure 2 is an example of using XRF to characterize the amount of copper in a mixture of copper-chromium powders taken at different ratios, as a function of the coat- ing thickness. Auger electron spectroscopy (AES) is a surface charac- terization technique that enables determination of the el- emental composition and chemistry of sample surfaces. It uses a focused electron beam to create secondary electrons near the surface of a solid sample. Some of these have ener- gies characteristic of the elements and, in many cases, of the chemical bonding of the atoms from which they are released. Typically used in combination with ion sputtering to gradually remove the surface, AES can be used to characterize sample through-thickness and therefore the chemistry and bonding through the sample depth. The high spatial resolution of the process allows micro- analysis of high lateral resolution (300 Å), semiquantitative el- emental analysis, and accurate chemical bonding information, including standardless semiquantitative analysis. It is useful in analyzing fractured cold-sprayed samples to evaluate the oxygen levels across the coating fracture surface, as shown in Fig. 3a, which indicates peaks of aluminum, carbon, and O 2 . After removal of a surface layer using ion beammilling, the Au- ger spectrum was devoid of oxygen and carbon, as shown in Fig. 3b, which confirms the presence of an oxide layer of 31-nm thickness in the as-deposited condition. ~iTSSe For more information: This article series is adapted from Chapter 5, Cold Spray—Advanced Characterization authored by Dheepa Srinivasan in High Pressure Cold Spray—Principles and Applications, edited by Charles M. Kay and J. Karthikeyan (ASM, 2016). Complete references are included in this volume. The author may be reached at dheepasrinivasan6@gmail.com . Fig. 2 — Relationship between the chromium content of mixed powders and coating thickness, as evaluated by x-ray fluorescence spectroscopy. Fig. 3 — Auger electron spectroscopy of the fracture surface of an aluminum cold-sprayed coating (a) in the as-sprayed condition and (b) after ion beammilling, revealing the surface layer chemistry. 9