Mechanism of failure in a free-standing Pt–aluminide bond coat during tensile testing at room temperature

Das

2011

DSJ

Microstructural aspects and cyclic oxidation behaviour of plain aluminide and Pt-aluminide coatings on the near-a Ti-alloy IMI-834 have been studied. Both the coatings provide good oxidation resistance to the above alloy at 650 °C, 750 °C, and 850 °C. However, significant cracking develops in the coatings during coating formation as well as during cyclic oxidation exposure. The extent of cracking during oxidation is found to increase with the exposure temperature. Presence of through-thickness cracks in the coatings leads to localised oxidation damage of the underlying substrate at all the three temperatures. At 850 °C, such localised oxidation generates enough TiO 2 so that this oxide phase grows through the cracks and emerges at the sample surface forming a clearly identifiable mud-crack pattern. The extent of such oxidation damage is comparatively much lower at 750 °C and 650 °C.

“…Further, unlike the precipitate-rich IDZ typically found in aluminide coatings on superalloys (see Fig. 3) 16,17 , both plain aluminide ( Fig. 2(a)) and PtAl [ Fig.…”

Section: As-formed Coating Microstructuresmentioning

confidence: 98%

Section: As-formed Coating Microstructuresmentioning

confidence: 99%

Aluminide Coatings on Titanium-based Alloy IMI-834 for High Temperature Oxidation Protection

Das

2011

DSJ

“…The plated strips were subjected to a diffusion heat treatment in vacuum, followed by a two-step high activity pack aluminization treatment, as described elsewhere. [7,9,10] Microtensile samples having dimensions as shown in Figure 1(a) were cut out from the coated strips by electrodischarge machining. The dimensions of the microsamples were established by a finite element method-based study.…”

mentioning

confidence: 99%

“…The dimensions of the microsamples were established by a finite element method-based study. [10,11] The gage length (GL), gage width (GW), and fillet radius (R) of the cutout samples were 2, 0.5, and 0.5 mm, respectively, while their overall length was 8 mm, as shown in Figure 1(a). A holding length (HL) of 1 mm was provided in order to arrest the sample within slotted grips during testing.…”

mentioning

confidence: 99%

“…A holding length (HL) of 1 mm was provided in order to arrest the sample within slotted grips during testing. [7,10,11] The free-standing coating samples were prepared by precision polishing of the cut-out samples from one side until the substrate was completely removed and the sample thickness became equal to the thickness of bond coat, which was approximately 100 lm (Figures 1(a) and (b)). The flatness of the surface and uniformity in thickness reduction during polishing were ensured by the use of a Tripod Polisher.…”

mentioning

confidence: 99%

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Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

Chatterjee

Muraleedharan

et al. 2011

Metall Mater Trans A

Self Cite

The ductile-to-brittle transition temperature (DBTT) of a free-standing Pt-aluminide (PtAl) bondcoat was determined using the microtensile testing method and the effect of strain rate variation, in the range 10 À5 to 10 À1 s À1 , on the DBTT studied. The DBTT increased appreciably with the increase in strain rate. The activation energy determined for brittle-to-ductile transition, suggested that such transition is most likely associated with vacancy diffusion. Climb of h100i dislocations observed in analysis of dislocation structure using a transmission electron microscope (TEM) supported the preceding mechanism.

Effect of Cyclic Oxidation Exposure on Tensile Properties of a Pt-Aluminide Bond-Coated Ni-Base Superalloy

Hazari

Varma

et al. 2011

Metall Mater Trans A

Self Cite

The tensile behavior of a directionally solidified (DS) Ni-base superalloy, namely, CM-247LC, was evaluated in the presence of a Pt-aluminide bond coat. The effect of the thermal cycling exposure of the coated alloy at 1373 K (1100°C) on its tensile properties was examined. The tensile properties were evaluated at a temperature of 1143 K (870°C). The presence of the bond coating caused an approximately 8 pct drop in the strength of the alloy in the as-coated condition. However, the coating did not appreciably affect the tensile ductility of the substrate alloy. The bond coat prevented oxidation-related surface damage to the superalloy during thermal cycling exposure in air at 1373 K (1100°C). Such cyclic oxidation exposure (up to 750 hours) did not cause any further reduction in yield strength (YS) of the coated alloy. There was a marginal decrease in the ultimate tensile strength (UTS) with increased exposure duration. Because of the oxidation protection provided by the bond coat, the drastic loss in ductility of the alloy, which would have happened in the absence of the coating, was prevented.