The formation of ordered δ′-phase in AlLi alloys by diffuse and small angle neutron scattering

Kinetics of joint ordering and decomposition in binary alloys

“…At this stage, the ordering (as characterized by the short-range order parameter η sr , eq.3) has reached its maximum value and the further development corresponds to the coarsening of domains by long-range diffusion, much like in a situation where decomposition into two pure (or disordered) phases occurs. The fact that ordering appears prior to decomposition has been observed experimentally [29,30,[11][12][13][14][15] and can be explained by the fact that the diffusion of B-atoms is required only over short distances for the development of atomic order but needs to cover long distances for the decomposition into phases with different amounts of B-atoms.…”

“…We also find, in the case of high volume fraction of ordered precipitates, clear evidence of the wetting of APB's. This may explain some of the results in Al-Li systems [29,30] where ordered domains with little lattice mismatch are formed and supports the interpretation of non-merging precipitates given in [29,30]. We plan to extend our work to include elastic interactions, present in Ni-based alloys [11][12][13][14][15], mentioned earlier.…”

“…In particular, the lack in symmetry between the case c = 0.15 (with volume fraction f ≈ 0.3) and c = 0.35 (with volume fraction f ≈ 0.7) may be related to the presence of ordered domains of two kinds (on the two sublattices) with some additional positive energy appearing (as pointed out, e.g., in [29,30,34]) on their interface when they are coming in contact due to their growth (anti-phase boundary). These anti-phase boundaries (APB's) appear to be wetted by the disordered phase which reduces the overall energy of the system.…”

Small-angle scattering studies of phase separation and defects in inorganic materials

“…Under these conditions, the system may follow stable trajectories in (L,C) space where L is the scaling parameter and C is the volume fraction (Fratzl & Blaschko, 1987) and scaling holds even for a changing integrated intensity. A growth rate proportional to t ~'3 has been observed in all investigations on A I-Li, essentially without any incubation time (Blaschko et al, 1990 and earlier work quoted therein; Pike, Messoloras & Stewart, 1989;Abis, Caciuffo, Carsughi, Coppola, Magnani, Rustichelli & Stefanon, 1990). For an Al-10.7at.% Li alloy aged at 463 K, Abis et al (1990) find coarsening with an essentially constant volume fraction of about 24% and particle growth proportional to t I/3.…”

“…Komura, Takeda, Osamura & Okuda (1988) report a width of about 2.3 for a volume fraction of 2.8% in AI-4at.% Zn-0.1 at.% Mg (aged at 313 K). The AI-8-0, -10.7 at.% Li alloys investigated by Blaschko, Glas & Weinzierl (1990) at temperatures from 373 to 453 K show scaling even for very small precipitate sizes, independent of temperature for both concentrations, and also a narrower width of s(LQ) for the larger volume fraction. The mismatch of A13Li in the AI matrix is very small, and this may be a system where the interfacial energy term becomes effective even while the matrix is still supersaturated.…”