Creep of the lameller AlCuAl2 composite I. Microstructural observations

Abstract

To study the respective deformation modes of the Al and CuAl2 lamellae as well as the interface properties (phase boundaries, lamellar faults) in lamellar eutectic monograins, in situ creep experiments are performed in a high voltage electron microscope between 270 and 350 °C. They are completed by conventional observations of crept samples. At 300 °C a transition occurs: at lower temperatures the CuAl2 phase is brittel by lack of dislocations while above 300 °C dislocation multiplication and movement are possible, involving high friction forces. Outlines for two corresponding deformation models are proposed, involving the observed interface sliding, dislocation sources in volume or at the phase boundaries, shearing of the Al lamellae, and a heterogeneous deformation. These models are discussed in terms of the activation parameters measured in macroscopic creep tests presented in another article.

Crystalline Defects in a B.C.T. Al2Cu(?) Single Crystal Obtained by Unidirectional Solidification along [001]

“…In the literature, possible Burgers vectors attached to perfect dislocations in a C16 lattice were only mentioned for q and Zr 2 Ni. They were proposed from five different experiments: (i) from analyses of low angle tilt boundaries with axes close to [100] present in deformed q lamellae of the eutectic [3]; (ii) by the application of the invisibility criterion in polycrystalline q [11] and in Zr 2 Ni deformed at room temperature by indentation [36]; (iii) optical analysis of slip lines on flat faces of q single crystals plastically deformed above 400 C [23]; (iv) analysis of slip lines on the free surfaces of thin foils in the Al-q lamellar eutectic deformed by in situ TEM experiments at 320 C [6]; (v) from recent HRTEM images of q/q low angle tilt boundaries with the axis h113i, formed at lamellar faults of the eutectic [10].…”

“…The structural and mechanical properties of the Al(a)-Al 2 Cu(q) lamellar eutectic have been largely studied in the past by conventional transmission electron microscopy (TEM) at room and high temperature [1][2][3][4][5][6][7][8][9][10]. Most of these studies involved specimens taken from a unidirectionaly solidified ingot.…”

“…Most of these studies involved specimens taken from a unidirectionaly solidified ingot. They were aimed to understand the relationships between the macroscopic properties of such composites and the nature of their microstructural defects: crystalline defects inside each phase [3,[6][7][8], defects along the heterointerfaces [4,7], defects related to the mosaic substructure of a single grain eutectic [1,[7][8][9][10]. However, if the defects present in the face-centred cubic Al(a) phase are fairly well understood, the Burgers vectors of the dislocations present in the bodycentred tetragonal (b.c.t.)…”

Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure

“…Thus, further study focusing not only on the stress exponent but also on other factors is required to confidently conclude the creep deformation mechanism of them. As one of the possibilities, in addition to the diffusion-controlled grain-boundary sliding, the occurrence of localized deformation governed by the dislocation glide and climb in the vicinity of the C40/C11 b lamellar interface 38, 39 is also suspected, since it may occur more easily and generate larger strain in the Cr-added and Ir-added crystals in which the lamellar interfaces are much flatter than that in the nonadded crystal owing to the disappearance of coarse C11 b -phase grains.…”

HRTEM Observation of a ?113?? Low Angle Tilt Boundary in the Al-Al2Cu(?) Eutectic Composite

“…For experimental simplification, an Al 2 Cu thin foil containing a (random) low angle boundary was prepared in the goal to observe the evolution of the boundary structure when the temperature is maintained at about 300 C. Initially, the examined boundary contained several types of dislocations and was inclined in the foil. In [33], long dislocation segments were observed to interact with the q/q low angle boundaries at lamellar faults, as well as active cross slip in the adjacent q crystals. 13 represents the approximate projection of the initial boundary as the corridor limited by the two long straight, skew, black lines.…”