Small-angle neutron scattering investigation of the early stages of decomposition in Ni-rich Ni-Ti

Abstract

In-situ small-angle neutron scattering was performed on polycrystals and single crystals of Ni-10 to 12 at.% Ti at temperatures between 900 and 1240 K. A plateau in the integrated intensity as a function of aging time for polycrystalline Ni-11.3 at.% Ti at 900 K indicates the presence of a precursor state γ" preceding the formation of the metastable γ' state, with a Ti concentration of 16.5(1.0) at.% in the particles. In the scattering patterns of a Ni-12.0 at.% Ti single crystal aged at 1200 and 1240 K, strong scattering intensities along <100> related to the coherent γ"/γ' states, and sharp streaks along <111> related to plates of the stable η phase appear successively. At 1240 K, the presence of the L1 2 -related intensities along <100> is unexpected, as this temperature lies above the metastable miscibility gap suggested in the literature.

Small-angle scattering in materials science - a short review of applications in alloys, ceramics and composite materials

“…Fig. 4 shows in-situ SANS data from Ni-Ti, a different model system for nickel-base superalloys, treated at a temperature of 1240 K (Kompatscher et al, 2000). Two types of streaks are seen to develop successively.…”

“…Data were taken for ~ 5 min in each case. These streaks indicate the formation of the hexagonal η phase in lamellae parallel to the cubic {111} planes (from Kompatscher et al, 2000).…”

The asymptotic leading term of anisotropic small-angle scattering intensities. II. Non-convex particles

“…Along other directions of reciprocal space, the decrease will be faster than q À4 and this fact explains the origin of the streaks often observed in anisotropic SAS intensities (see e.g. Kompatscher et al, 2000). In conclusion, the generalization of Porod's law to anisotropic samples formed by particles of arbitrary shapes follows from (43) after dividing this equation by Á q 0 and reads…”

Short-Range Order in Ni-Rich Ni–Ti Studied by Diffuse Neutron Scattering

“…4) or in the line widths. A recent transmission electron microscopy and small-angle neutron scattering study [4,27] at similar temperatures showed that the h phase is not yet formed, i.e. a long incubation time is necessary to transform cuboidal precipitates of the g H state to plates of the h phase.…”

“…After more extended aging, a second metastable state, g H , with 22 AE 2 at% Ti was observed at 850 K [1]. While the precipitates of the g HH and g H states are of cuboidal or`brick' shape [4] and aligned along an elastically soft h100i direction, the stable h phase forms large plates on f111g planes.…”