Fracture toughness of 2090 Al–Li–Cu extrusions with high and low hydrogen contents

Bennett, Chris; Lynch, S.P.; Nethercott, R.B.; Kerr, Matthew; Sweet, E.

doi:10.1016/s0921-5093(98)00478-x

Cited by 15 publications

(6 citation statements)

References 18 publications

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“…Grain-Boundary Impurities Segregation of impurity atoms to grain boundaries promotes The presence of high levels of hydrogen has been suggested as a cause of embrittlement [20], but studies of 2090 alloys with high and low hydrogen levels suggest that there is little or no effect, possibly because hydrogen combines with lithium to produce small, innocuous lithiumhydride particles [21]. As mentioned above, there is no evidence of other impurity segregation at grain boundaries which could be responsible for embrittlement.…”

Section: 3mentioning

confidence: 99%

Challenges in Developing High Performance Al-Li Alloys

Pasang

Lynch

Moutsos

2006

Int. J. Soc. Mater. Eng. Resour

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The goal of replacing 'conventional' Al alloys with Al-Li alloys to reduce weight of aerospace structures has had only limited success to date, despite one of the largest alloy-development programs ever undertaken. One of the reasons being, for some product forms and crack-plane orientations, fracture toughness is lower compared with conventional Al alloys due to a greater propensity for low-energy intergranular fracture. Proposed explanations for brittle intergranular fracture include: (i) planar slip resulting in high stresses where slip bands impinge on grain-boundaries, (ii) embrittlement due to alkali-metal-impurity phases, and (iii) grain-boundary structural changes associated with segregation of lithium. The present paper reviews evidence for and against these proposed mechanisms based on (i) studies of 8090 and 2090 alloys, and the more recently developed 2297 alloy, and (ii) comparisons of fracture of these alloys with other materials that exhibit grain-boundary weakness. It appears that lithium segregation to grain boundaries is the prime cause of low-energy intergranular fracture in Al-Li alloys. Embrittlement by alkali-metal impurities is not important providing that impurity levels are less than about 5 ppm (as is the case for most commercially produced alloys). Planar slip and other factors probably play only a minor role.

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Section: 3mentioning

confidence: 99%

Challenges in Developing High Performance Al-Li Alloys

Pasang

Lynch

Moutsos

2006

Int. J. Soc. Mater. Eng. Resour

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“…Their fracture properties are their weak point and these have been reported on at length (for example Lynch 1991aLynch ,b, 1992Lynch , 1994Sweet et al 1996;Bennett et al 1998;Lynch et al 2001Lynch et al , 2002Lynch et al , 2003Lynch 2008). In particular, an important aspect that has restricted more widespread application of these alloys is their low ductility and fracture toughness in the short transverse (S-L) direction.…”

Section: Introductionmentioning

confidence: 95%

A study aimed at determining and understanding the fracture behaviour of an Al–Li–Cu–Mg–Zr alloy 8090

Bregianos¹,

Crosky

Munroe

et al. 2010

Int J Fract

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The S-L fracture toughness of aluminiumlithium based alloys is generally poor and this has limited their applicability, particularly in aerospace where good damage tolerance is required. The low S-L toughness has been attributed variously to grain boundary precipitation, planar slip and lithium segregation. This work examined the S-L fracture behaviour of an 8090 Al-Li-based alloy in 34-45 mm plate. The results confirmed that the S-L fracture toughness decreases from the centre to the surface of plate material and increases with double ageing. Fracture is principally intergranular, with both ductile and brittle components occurring, but some transgranular fracture also occurs and this produces steps in the fracture plane. Changes in the relative proportions of brittle and ductile intergranular fracture, as well as in the amount of transgranular fracture, accompany the changes in toughness. However, A. C. Bregianos the decrease in fracture toughness across the plate is accompanied principally by an increase in the relative proportion of brittle intergranular fracture, while the toughening produced by double ageing is accompanied principally by an increase in the amount of transgranular fracture. Evidence of coarse slip, indicative of slip planarity, was seen from slip steps and dislocation structures. However, planar slip was seen only towards the centre of the plate and not towards the surface. The level of planar slip was not reduced markedly by double ageing. Texture varied with position across the plate. There were also a larger number of low angle boundaries towards the centre of the plate than towards the surface. The hardness did not change across the plate. The results could not be explained fully in terms of either the grain boundary precipitate theory or the planar slip model, but were generally consistent with the lithium segregation model. However, the basic tenet of this model is that the level of embrittlement is influenced by the grain boundary structure, and the results did not indicate a substantial difference between the boundaries that failed in a ductile manner and those which failed by brittle fracture. This suggests that the factors which affect lithium segregation may be more complex than originally envisaged.Keywords Short transverse · S-L orientation · Fracture behaviour · Toughness · 8090 Aluminiumlithium based aerospace alloy 123 142 A. C. Bregianos et al.

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“…Environmental interactions, such as hydrogen embrittlement of the grain boundary and stress corrosion cracking processes: for the 2090 Al-Cu-Li alloy the effect of H content was shown to be very small however [38].…”

Section: Introductionmentioning

confidence: 99%

Assessment of mixed mode loading on macroscopic fatigue crack paths in thick section Al–Cu–Li alloy plate

2016

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High strength, wrought 7xxx (Al-Zn-Mg) and Al-Li based alloys show a propensity for fatigue macroscopic crack deflections aligned along grain boundaries. The present work reports a study on a 3 rd generation Al-Li based alloy in the form of a thick AA2297 (Al-Cu-Li alloy) plate, where it was found that although the lithium containing material may indeed be more susceptible to mixed mode grain boundary failure (and by implication crack deflection in conventional tests), the AA2297 alloy fatigue behaviour is mechanistically and functionally equivalent to 7xxx alloy behaviour. It is shown that crack paths are controlled by a combination of crack loading mixity (K II /K I ratio) and maximum strain energy release rates (expressed as K eq.max ). Increasing K II /K I ratio is seen to favour sustained grain boundary failure. Crack growth rate behaviour is discussed in terms of extrinsic and intrinsic components of crack growth resistance. It is shown that the present approach can be successfully applied to predict crack deflection / crack paths for a range of sample geometries and orientations on a range of high strength orthotropic aluminium alloys, including 3 rd generation Al-Li based alloys and well-established 7xxx alloys).

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Fracture toughness of 2090 Al–Li–Cu extrusions with high and low hydrogen contents

Cited by 15 publications

References 18 publications

Challenges in Developing High Performance Al-Li Alloys

Challenges in Developing High Performance Al-Li Alloys

A study aimed at determining and understanding the fracture behaviour of an Al–Li–Cu–Mg–Zr alloy 8090

Assessment of mixed mode loading on macroscopic fatigue crack paths in thick section Al–Cu–Li alloy plate

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