Elemental Composition Analysis of Ti Alloy Turbine Blades

In the aerospace industry and associated materials research, microanalysis plays an important role in the investigation of their advanced technical products, which have to meet the highest demands in terms of performance and durability.

Here we show results from combined EDS and WDS microanalysis of a jet engine turbine blade made of titanium alloy. The localized element analysis as well as element distribution mapping by EDS (Fig. 2) is convenient and fast. Mappings show µm-sized Ti-Al-rich grains and interstices composed of Mo-Zr-rich alloy. The small diameter of the interstices (ca. 100 nm) requires application of low kV for discrete analysis.

EDS peak deconvolution in Bruker ESPRIT software allows most element identification and quantification based on least squares fitting of X-ray line series (Fig. 3). However, when reliable material characterization is required for elements with severe EDS peak overlaps, like Zr L lines with Pt M lines, Mo L lines with S K lines or Pb M lines, WDS is the only analytical technique that can confirm the presence or absence of these respective elements.

QUANTAX WDS achieves distinctly higher spectral resolution and energy range scans, necessary to confirm the presence of Zr and rule out any Pt for both grains and interstices (Fig. 4). QUANTAX WDS proves the presence of Mo and absence of any S or Pb in interstices and detect trace elements of a few 100 ppm of Si, which is not visible in the EDS dataset because it is hidden by the Zr-Ll line.

Figure 1: Turbine of an aircraft. The materials used must fulfill the highest requirements in terms of resilience and durability.

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Figure 2: Composite element distribution map showing the major elements detected by EDS. Ti-, Al-rich grains are surrounded by Mo-, Zr-rich interstitial fillings. Note the fine diameter of the interstices.

Figure 3a and 3b: Devonvoluted EDS spectra of the grains (left) and interstices (right) acquired at 5 kV. Deconvolution suggests the presence of Zr and Mo, however, contributions of traces of Pt, S or Pb cannot be ruled out due to severe peak overlaps at these low X-ray energies.

Figure 4a and 4b: Complementary WDS analyses reliably confirm the presence of Zr and Zr plus Mo, respectively, while they can rule out any presence of Pt, S or Pb. Furthermore, WDS is able to find and determine traces of Si.

Sample courtesy of Michael Ude, University of Jena, Germany