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Jung, Hwan Gyo; Kim, Kyoo Young

doi:10.1023/a:1016024810408

Cited by 42 publications

(21 citation statements)

References 12 publications

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“…Microcracking was not observed. This might be associated with the low thickness of the coating and grain refinement by the alloying element Nb [21,23]. Similar results were found with TiAl 2 layers deposited on Ti-50Al alloy using magnetron sputtering [26].…”

Section: Introductionsupporting

confidence: 79%

“…Additions of Nb and Cr enhanced the aluminizing kinetics in comparison to unalloyed c-TiAl and increased the spallation resistance of the TiAl 3 layer formed on alloyed c-TiAl [25,45]. Both alloying elements had also a significant influence on the microstructure of the coating [21]. The grain size of the TiAl 3 coating decreased with increasing Nb and Cr content, with Nb exhibiting a more pronounced effect on the thickness, microstructure and stability of the coating.…”

Section: Discussionmentioning

confidence: 96%

“…16 Scanning electron micrographs of an aluminized Ti-45Al-8Nb sample coated with TBC, which was exposed to air at 950°C for 1,420 cycles: a continuous alumina scale underneath the thermal barrier coating, b cracks in the subsurface region below the alumina scale density of fast diffusion paths presented by the grain boundaries. The transformation of the TiAl 3 layer into TiAl 2 was retarded or even suppressed by the addition of ternary elements [21,45].…”

Section: Discussionmentioning

confidence: 99%

“…Thin coatings (B30 lm) were less prone to crack formation than thicker coatings [23]. Niobium was found to improve the toughness of the TiAl 3 layer and, thus, the cracking resistance, associated with grain refinement of the coating [21]. Furthermore, the aluminizing kinetic of alloys containing Nb and Cr was faster compared to that of unalloyed c-TiAl, and the formation of a TiAl 2 layer observed on binary c-TiAl was suppressed when alloyed with Cr and Nb [25].…”

Section: Introductionmentioning

confidence: 94%

“…Aluminizing of c-TiAl by pack-cementation produced an Al-rich intermetallic TiAl 3 coating [20][21][22][23]. Between the outer TiAl 3 layer and the c-TiAl substrate an inner TiAl 2 layer formed, increasing in thickness during a subsequent annealing treatment due to the rapid diffusion of aluminium into the substrate.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation Behaviour of TBC Systems on γ-TiAl Based Alloy Ti–45Al–8Nb

et al. 2009

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The lifetime of thermal barrier coating (TBC) systems on gamma titanium aluminides was determined in the temperature range between 850°C and 950°C under cyclic oxidation conditions in air. Coupons of the alloy Ti-45Al-8Nb (at.%) were coated by pack aluminizing. A subset of samples was subsequently annealed at 910°C for 312 h in argon. During this heat treatment, the two-phase (Nb,Ti)Al 3 plus TiAl 2 microstructure of the coating transformed into single phase c-TiAl. On pre-oxidised aluminized, annealed and bare samples, TBCs of yttria partially stabilized zirconia were deposited using electron-beam physical vapour deposition (EB-PVD). No spallation of the TBCs was observed in cyclic oxidation tests at 850°C for up to 3,000 cycles of 1 h dwell time at high temperature. The two-phase aluminide coating provided effective oxidation protection due to the formation of a continuous alumina scale. The lifetime of this TBC system exceeded 1,400 cycles at 950°C, whereas an aluminized and annealed sample failed after approximately 500 cycles. The TBC on bare substrate failed when thermally cycled at 900°C. In contrast, no spallation occurred with an aluminized and annealed specimen at this temperature during the maximum exposure length of 1,000 cycles, probably related to an increased aluminium concentration in the subsurface region.EB-PVD zirconia top coats were well adherent to the alumina scale and the thermally grown mixed oxides. Failure of the TBC systems observed with bare and annealed samples was associated with spalled oxide scales formed on c-TiAl.

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Section: Introductionsupporting

confidence: 79%