Intrinsic fatigue crack growth rates for Al-Li-Cu-Mg alloys in vacuum

Journal Article · Sun Aug 01 00:00:00 EDT 1993 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02657855· OSTI ID:5729737

Slavik, D C; Gangloff, R P; Starke, Jr, E A ^[1]; Blankenship, Jr, C P ^[2]

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1. Univ. of Virginia, Charlottesville, VA (United States)
2. General Electric Corp. R and D, Schenectady, NY (United States)

The influences of microstructure and deformation mode on inert environment intrinsic fatigue crack propagation were investigated for Al-Li-Cu-Mg alloys AA2090, AA8090, and X2095 compared to AA2024. The amount of coherent shearable [delta][prime] (Al[sub 3]Li) precipitates and extent of localized planar slip deformation were reduced by composition (increased Cu/Li in X2095) and heat treatment (double aging of AA8090). Intrinsic growth rates, obtained at high constant K[sub max] to minimize crack closure and in vacuum to eliminate any environmental effect, were alloy dependent; da/dN varied up to tenfold based on applied [Delta]K or [Delta]K/E. When compared based on a crack tip cyclic strain or opening displacement parameter ([Delta]K/([sigma][sub ys]E)[sup 1/2]), growth rates were equivalent for alloys except X2095-T8 which exhibited unique fatigue crack growth resistance. Tortuous fatigue crack profiles and large fracture surface facets were observed for each Al-Li alloy independent of the precipitates present, particularly [sigma][prime], and the localized slip deformation structure. Reduced fatigue crack propagation rates for X2095 in vacuum are not explained by either residual crack closure or slip reversibility arguments; the origin of apparent slip band facets in a homogeneous slip alloy is unclear. Better understanding of crack tip damage accumulation and fracture surface facet crystallography is required for Al-Li alloys with varying slip localization.

• OSTI ID: 5729737
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Vol. 24:8; ISSN 0360-2133
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM BASE ALLOYS
CRACK PROPAGATION
COPPER ALLOYS
LITHIUM ALLOYS
MAGNESIUM ALLOYS
CRYSTALLOGRAPHY
DEFORMATION
FATIGUE
FRACTURE MECHANICS
MICROSTRUCTURE
STRAINS
SURFACE PROPERTIES
ALLOYS
ALUMINIUM ALLOYS
MECHANICAL PROPERTIES
MECHANICS
360103* - Metals & Alloys- Mechanical Properties