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Environmentally enhanced crack growt...

Huang, Zhifan Frank.

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Environmentally enhanced crack growth in nickle-based superalloys.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Environmentally enhanced crack growth in nickle-based superalloys./
Author:	Huang, Zhifan Frank.
Description:	213 p.
Notes:	Adviser: Robert P. Wei.
Contained By:	Dissertation Abstracts International63-12B.
Subject:	Applied Mechanics. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3073976
ISBN:	0493937463

Environmentally enhanced crack growth in nickle-based superalloys.
Huang, Zhifan Frank.

Environmentally enhanced crack growth in nickle-based superalloys. - 213 p.

Adviser: Robert P. Wei.

Thesis (Ph.D.)--Lehigh University, 2003.

This dissertation research was designed to develop a better understand the role of niobium and other strengthening elements in enhancing crack growth by oxygen in nickel-based superalloys at high temperatures. It included modeling of diffusion controlled crack growth coupled with oxidation ahead of the crack tip, and an examination of the relationship between crack growth under sustained and fatigue loading. Three γ<super>′</super> strengthened powder metallurgy (P/M) alloys (having about 53 vol. pct of γ<super>′ </super> precipitates), with 0, 2.5 and 5 wt pct niobium and with the formation of γ<super>″</super> precipitates suppressed, were specially designed for this study. Crack growth and supporting microstructural studies were conducted on the alloys. They were complemented by a separate surface chemistry study of the alloys, key precipitates, fracture surfaces of interrupted crack growth specimens by x-ray photoelectron spectroscopy (XPS).

ISBN: 0493937463Subjects--Topical Terms:

1018410
Applied Mechanics.

Environmentally enhanced crack growth in nickle-based superalloys.
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005 20110511
008 110511s2003 eng d
020 $a 0493937463
035 $a (UnM)AAI3073976
035 $a AAI3073976
040 $a UnM $c UnM
100 1 $a Huang, Zhifan Frank. $3 1261090
245 1 0 $a Environmentally enhanced crack growth in nickle-based superalloys.
300 $a 213 p.
500 $a Adviser: Robert P. Wei.
500 $a Source: Dissertation Abstracts International, Volume: 63-12, Section: B, page: 6055.
502 $a Thesis (Ph.D.)--Lehigh University, 2003.
520 $a This dissertation research was designed to develop a better understand the role of niobium and other strengthening elements in enhancing crack growth by oxygen in nickel-based superalloys at high temperatures. It included modeling of diffusion controlled crack growth coupled with oxidation ahead of the crack tip, and an examination of the relationship between crack growth under sustained and fatigue loading. Three γ<super>′</super> strengthened powder metallurgy (P/M) alloys (having about 53 vol. pct of γ<super>′ </super> precipitates), with 0, 2.5 and 5 wt pct niobium and with the formation of γ<super>″</super> precipitates suppressed, were specially designed for this study. Crack growth and supporting microstructural studies were conducted on the alloys. They were complemented by a separate surface chemistry study of the alloys, key precipitates, fracture surfaces of interrupted crack growth specimens by x-ray photoelectron spectroscopy (XPS).
520 $a The results showed that sustained load and fatigue crack growth are directly related. Crack growth rates were significantly enhanced by oxygen, increasing by about 10<super>4</super> and 10<super>3</super> over those in argon (at 973 K) in the Nb containing and Nb free alloys, respectively. Crack growth was thermally activated, with an average apparent activation energy of about 250 kJ/mol; the actual values depended upon K and the alloys. The observed K dependence suggested oxygen diffusion control of crack growth, and was confirmed by results from the proposed model.
520 $a Microstructural analyses of grain boundaries demonstrated that the Nb-containing phases were oxidized. The presence of zone of an oxygen affected region (OAR), or embrittled zone, ahead of the growing crack was established mechanically, and confirmed by XPS analyses. The XPS analyses showed preferential oxidization of Nb along with Al and Ti (principally of Nb-rich carbides, Ni<sub>3</sub>Al and Ni<sub>3</sub>Ti), but not Ni within the OAR.
520 $a The results taken <italic>in toto</italic> show that embrittlement resulted from the formation and rupture of a brittle film of surface oxides of Nb, Ti and Al along grain boundaries and interfaces ahead of the crack tip; not from Fe and Ni as previously proposed. Crack growth is controlled by the rate of stress-enhanced diffusion of oxygen along the grain boundaries.
590 $a School code: 0105.
650 4 $a Applied Mechanics. $3 1018410
650 4 $a Engineering, Materials Science. $3 1017759
650 4 $a Engineering, Mechanical. $3 783786
690 $a 0346
690 $a 0548
690 $a 0794
710 2 0 $a Lehigh University. $3 515436
773 0 $t Dissertation Abstracts International $g 63-12B.
790 $a 0105
790 1 0 $a Wei, Robert P., $e advisor
791 $a Ph.D.
792 $a 2003
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3073976