TEM investigations of the early stages of TiAl oxidation

Lång, Christian; Schütze, M.

doi:10.1007/bf01050799

Cited by 113 publications

(46 citation statements)

References 15 publications

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“…4. Scanning electron micrograph (a) and EDS analysis (b) of a cross-section of an alloy 98G sample pre-oxidised in air and coated with TBC which was exposed to air at 850 8C for 1100 cycles sample oxidised at 900 8C in air [35]. With increase in the partial pressure of oxygen, TiN was oxidised to titanium oxide, thus limiting the presence of the nitride layer to a narrow zone adjacent to the substrate [36].…”

Section: Resultsmentioning

confidence: 99%

Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatings

Braun

Fröhlich

Ebach-Stahl

et al. 2008

Materials & Corrosion

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In the present study, the applicability of thermal barrier coatings (TBCs) on g-TiAl alloys was investigated. Two alloys with the chemical compositions of Ti-45Al-8Nb-0.2B-0.15C and Ti-45Al-1Cr-6Nb-0.4W-0.2B-0.5C-0.2Si were used. Before TBC deposition, the specimens were pre-oxidised in laboratory air or low partial pressure oxygen atmosphere. Yttria partially stabilised zirconia top coats were then deposited using electron-beam physical vapour deposition (EB-PVD). The oxidation behaviour of the g-TiAl specimens with TBC was studied by cyclic oxidation testing in air at 850 and 900 8C. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). No spallation of the TBC was observed for pre-oxidised specimens of both alloys when exposed to air at 850 8C for 1100 cycles of 1 h dwell time at high temperature. SEM micrographs of the thermally grown oxide scale revealed outer mixed TiO 2 /Al 2 O 3 protrusions with a columnar structure. The protrusions contained small particles of zirconia and a low amount of about 0.5 at% zirconium was measured by EDS analysis throughout this outer oxide mixture. The TBCs exhibited excellent adherence on the oxide scale. Intercolumnar gaps and pores in the root area of the TBC were filled with titania and alumina. Below the outer columnar oxide scale, a broad porous zone of predominant titania was observed. The transition region between the oxide scale and substrate consisted of a discontinuous nitride layer intermixed with alumina particles and intermetallic phases rich in niobium formed at the nitride layer/substrate interface. When thermally cycled at 900 8C, the oxide scales on the alloy Ti-45Al-8Nb-0.2B-0.15C pre-oxidised in low partial pressure oxygen spalled off after 540 cycles. For the sample with TBC, spallation was observed after 810 cycles. Failure occurred in the thermally grown oxide near the oxide/nitride layer interface. Microstructural examinations revealed again oxide scales with columnar structure beneath the zirconia top coat and good adherence of the TBC on the thermally grown oxides formed at 900 8C.

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Section: Resultsmentioning

confidence: 99%

Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatings

Braun

Fröhlich

Ebach-Stahl

et al. 2008

Materials & Corrosion

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“…41,42 Rakowski et al 43 observed TiN on Ti-50 at.%Al after oxidation for only 1 h at 900°C in air. Lang and Schu¨tze 44 found that TiN and Ti 2 AlN formed at the interface beneath a mixture of Al 2 O 3 +TiO 2 . Chu and Wu 45 found that TiN formed during the initial oxidation stage and a Ti 2 AlN layer formed at the later stage through the combination of TiN initially formed on the surface with Al left behind the layer.…”

Section: Discussionmentioning

confidence: 99%

Isothermal Oxidation Behavior of Ti-50Al Alloy with Y Additions at 800 and 900°C

Umakoshi

et al. 2006

Oxid Met

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The isothermal-oxidation behavior of Al-rich TiAl alloys containing Y up to 1.0 at.% was studied in synthetic air with a flow of 200-250 mL/min at 800 and 900°C. Oxidation kinetics and scale adherence were studied in terms of the morphological features and microstructural evolution of the oxide scale. In the specimens oxidized at 800°C, all alloys containing 0.3-1.0 at.%Y showed reduced mass gain compared to the Y-free alloy, especially for the 0.3 at.%Y alloy. Under isothermal exposure at 900°C, the addition of small amounts of Y (0.1 and 0.3 at.%) was effective in enhancing the oxidation resistance. The alloys with higher Y contents (0.6 and 1.0 at.%), on the contrary, had a reverse effect on the oxidation resistance by providing rapid diffusion paths in the form of coarse Y 2 O 3 particles close to the substrate. The improvement of oxidation resistance of the alloy with Y additions was due partly to the improved adhesion of the scale and due partly to the formation of a continuous a-Al 2 O 3 layer in the outer scale. Y segregation and/or Y 2 O 3 precipitation at the oxide grain boundaries was effective in decreasing the oxidation rate and refining the oxide grains. The thinner scale was responsible for relaxing the thermal stress and, thus the cohesion between the scale and substrate was greatly improved in Y-containing alloys.

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“…The oxide scales formed on c-TiAl are a rather complex mixture of fast-growing TiO 2 and discontinuous, slow-growing Al 2 O 3. 33,34 The volume expansion of the fast-growing TiO 2 may have a great effect on the cracking of the macroparticles. After prolonged oxidation at 600°C, the macroparticles cracked completely (Fig.…”

Section: Morphologies and Reasons For Crackingmentioning

confidence: 99%

Mechanical Properties and Oxidation Behavior of a Graded (Ti,Al)N Coating Deposited by Arc-Ion Plating

Chi

et al. 2006

Oxid Met

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A graded (Ti,Al)N coating was deposited on 1Cr-11Ni-2W-2Mo-V stainless steel for aero-engine compressor blades by arc-ion plating(AIP). The microstructure and the morphology of the graded coating were investigated using electron-probe microanalysis (EPMA), X-ray diffraction and scanningelectron microscopy. The mechanical properties of the graded coating were investigated and it was found that the microhardness and the wear resistance were similar to those of the monolithic (Ti,Al)N coating, but much better than those of a homogenous TiN coating. In addition, the adhesive strength and the thermal-shock resistance of the graded (Ti,Al)N coating were much better than those of the monolithic TiN and (Ti,Al)N coatings. The oxidation tests were performed at 600 and 700°C in air for 500 hr, and corrosion tests were carried out at 600°C under the synergistic effect of water vapor and NaCl for 20 hr. Compared to pure TiN, it was found that due to the incorporation of aluminum, a protective layer rich in alumina was formed on top of the graded (Ti,Al)N coating, which greatly improved the oxidation resistance and corrosion resistance of the coating.

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TEM investigations of the early stages of TiAl oxidation

Cited by 113 publications

References 15 publications

Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatings

Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatings

Isothermal Oxidation Behavior of Ti-50Al Alloy with Y Additions at 800 and 900°C

Mechanical Properties and Oxidation Behavior of a Graded (Ti,Al)N Coating Deposited by Arc-Ion Plating

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