Core-multishell globular oxidation in a new TiAlNbCr alloy at high temperatures

S Q Tang,C Feng,A H Feng,J Shen,D L Chen,S J Qu

doi:10.1038/s41598-017-03690-0

S Q Tang, C Feng + Show 4 more

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https://doi.org/10.1038/s41598-017-03690-0

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Abstract

Oxidation resistance is one of key properties of titanium aluminide (TiAl) based alloys for high-temperature applications such as in advanced aero-engines and gas turbines. A new TiAlNbCr alloy with micro-addition of yttrium has been developed, but its oxidation behavior is unknown. To provide some fundamental insights, high-temperature oxidation characteristics of this alloy are examined via scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, and X-ray diffraction. We show that distinctive core-multishell globular oxidation and “daisy” flower-like oxidation occur exclusively around Y2O3 particles. Globular oxides exhibit multi-layered Y2O3/TiO2/Al2O3-rich/TiO2-rich shell structures from the inside to outside. Flower-like inner oxides consist of core Y2O3 particles surrounded by divergent Al2O3 and oxygen-rich α2-Ti3Al in the near-scale substrate. As the scale-substrate interface moves inward, the inner oxide structures suffer deeper oxidation and transform into the globular oxide structures. Our results demonstrate that the unique oxidation characteristics and the understanding of formation mechanisms pave the way for the exploration and development of advanced oxidation-resistant TiAl-based materials.

Highlights

Titanium aluminide (TiAl) based alloys are considered to be a new class of promising advanced high-temperature structural materials in the aerospace, gas turbine and automotive industries, because of their lightweighting with a low density (3.9–4.2 g/cm3), high specific yield strength and stiffness, and superior creep resistance at elevated temperatures[1,2,3,4,5,6]
Oxide pegs protruding into the substrate[26] and convex-shaped nail-like oxides[25] were observed at the scale-substrate interface, which play an important role in anchoring the oxide scale and improving anti-spalling ability of the scale on the surface of titanium aluminide alloys with an addition of yttrium
Back-scattered electron (BSE) scanning electron microscope (SEM) micrograph, TEM bright field image along with the relevant selected area diffraction (SAD) patterns, and X-ray diffraction (XRD) pattern of as-cast TiAlNbCr alloy are shown in Fig. 1(a) through (d)

Summary

Introduction

Titanium aluminide (TiAl) based alloys are considered to be a new class of promising advanced high-temperature structural materials in the aerospace, gas turbine and automotive industries, because of their lightweighting with a low density (3.9–4.2 g/cm3), high specific yield strength and stiffness, and superior creep resistance at elevated temperatures[1,2,3,4,5,6] This is highly inspired by the recent successful application of a TiAl-based alloy in General Electric’s high-thrust GEnex jet engines for powering Boeing 747-8 and 787 Dreamliner, to substitute Ni-based superalloys in the temperature range of 650–750 °C with the benefit of a weight reduction of ~50%1–3. Special attention is paid to the formation and growth mechanism of this unique type of globular oxides to give underlying insights about the effect of yttrium on the oxidation process of titanium aluminide alloys

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