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In-situ study of microscale fracture of diffusion aluminide bond coats: Effect of platinum

Published online by Cambridge University Press:  28 September 2015

Balila Nagamani Jaya ,
Sanjit Bhowmick ,
S.A. Syed Asif  and
Vikram Jayaram
Balila Nagamani Jaya*
Affiliation:
Department of Materials Engineering, Indian Institute of Science, Bangalore, Karnataka 560012, India
Sanjit Bhowmick
Affiliation:
Hysitron Inc., Minneapolis, Minnesota 55344, USA
S.A. Syed Asif
Affiliation:
Hysitron Inc., Minneapolis, Minnesota 55344, USA
Vikram Jayaram
Affiliation:
Department of Materials Engineering, Indian Institute of Science, Bangalore, Karnataka 560012, India
*
a)Address all correspondence to this author. e-mail: jaya86@gmail.com
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Abstract

The influence of Pt layer thickness on the fracture behavior of PtNiAl bond coats was studied in situ using clamped micro-beam bend tests inside a scanning electron microscope (SEM). Clamped beam bending is a fairly well established micro-scale fracture test geometry that has been previously used in determination of fracture toughness of Si and PtNiAl bond coats. The increasing amount of Pt in the bond coat matrix was accompanied by several other microstructural changes such as an increase in the volume fraction of α-Cr precipitate particles in the coating as well as a marginal decrease in the grain size of the matrix. In addition, Pt alters the defect chemistry of the B2-NiAl structure, directly affecting its elastic properties. A strong correlation was found between the fracture toughness and the initial Pt layer thickness associated with the bond coat. As the Pt layer thickness was increased from 0 to 5 µm, resulting in increasing Pt concentration from 0 to 14.2 at.% in the B2-NiAl matrix and changing α-Cr precipitate fraction, the initiation fracture toughness (KIC) was seen to rise from 6.4 to 8.5 MPa·m1/2. R-curve behavior was observed in these coatings, with KIC doubling for a crack propagation length of 2.5 µm. The reasons for the toughening are analyzed to be a combination of material's microstructure (crack kinking and bridging due to the precipitates) as well as size effects, as the crack approaches closer to the free surface in a micro-scale sample.

Keywords

aluminide bond coatsfracture toughnesscrack propagationfocused ion beam machiningnanoindentationaero-engine components
Type
Articles
Information
Journal of Materials Research , Volume 30 , Issue 21 , 13 November 2015 , pp. 3343 - 3353
Copyright
Copyright © Materials Research Society 2015 

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Footnotes

b)

Present address: Max Planck Institute for Iron Research, Max Planck Strasse-1, Duesseldorf 40237, Germany.

Contributing Editor: Yang-T. Cheng

References

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