Appl. Phys. A 74 [Suppl.], S1083–S1085 (2002) / Digital Object Identifier (DOI) 10.1007/s003390101195 Applied Physics A Materials Science & Processing SANS examination of precipitate microstructure in the creep-exposed single-crystal Ni-base superalloy SC16 P. Strunz 1,2, ∗ , G. Schumacher 1 , W. Chen 3 , D. Mukherji 4 , R. Gilles 5 , A. Wiedenmann 1 1 Hahn-Meitner-Institut (HMI), Glienicker-Str. 100, 14109 Berlin, Germany 2 Nuclear Physics Institute, 25068 ˇ Reˇ z near Prague, Czech Republic 3 Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, 12205 Berlin, Germany 4 Technische Universität Braunschweig, 38106 Braunschweig, Germany 5 Technische Universität Darmstadt, Petersenstr. 23, 64287 Darmstadt, Germany Received: 29 June 2001/Accepted: 24 October 2001 –  Springer-Verlag 2002 Abstract. The evolution of γ ′ -precipitate morphology in the creep-exposed, single-crystal, Ni-base superalloy SC16 was studied by small-angle neutron scattering (SANS). The scat- tering curves observed show that the originally cuboidal pre- cipitates become more rounded in the initial period. On fur- ther deformation, the increase in the proportion of the rafted (elongated shape) γ ′ -phase is observed at the expense of cuboidal precipitates, so that all the precipitates are rafted at a strain of 1.4%. PACS: 61.12.E; 81.40.C; 62.20.H High-temperature plus slow-strain-rate exposure is an im- portant regime of operation for components (usually tur- bine blades) made of Ni-base superalloys. In this regime, the γ ′ morphological change (the so-called rafting) oc- curs, which significantly influences the lifetime of the blades. During rafting, the initial cuboidal γ ′ precipitates coarsen to a plate-like or needle-like morphology (the rafts). This morphological change is a very complex phenomenon and de- pends on many factors, e.g. the γ/γ ′ lattice misfit, the rate and temperature of deformation, the initial microstructure, and the orientation of the crystal with respect to the load axis. Rafting occurs by simultaneous particle agglomeration and particle growth, but the mechanism of raft formation is not yet fully understood. Small-angle neutron scattering (SANS) [1] measurement of initial stages of the morphological changes in the bulk material can help to resolve some of the questions regard- ing the rafting phenomenon. The aim of the present SANS experiment was to study the initial stages of morphological changes during the formation of rafted γ ′ -precipitate struc- ture in the single-crystal Ni-base superalloy SC16 [2] after high-temperature creep. ∗ Corresponding author. (Fax: +420-2/2094-0141, E-mail: strunz@ujf.cas.cz) 1 Experiment The SC16 alloy (developed for application in land-based gas turbines) selected for this study was previously in- vestigated using SANS under various heat-treatment con- ditions [3]. The principal possibility of detecting mor- phological changes in creep-exposed specimens by SANS was proven in the past [4] as well. The original material contains cuboidal precipitates oriented with edges parallel to 〈001〉. Specimens of SC16 single-crystal bars were deformed at 950 ◦ C to different strains using a tensile stress of 150 MPa along [001]. The resulting strain rates were smaller than 10 -6 s -1 . The plate-like samples of thickness 1.5–2 mm for SANS were cut out of these bars after unloading and cooling to room temperature. The normal direction to the samples was parallel to [010]. Measurement was performed at the V4 facility [5] of BENSC at HMI Berlin. The data were collected with a sample-to-detector distance (SDD) equal to 16 m and a wavelength of λ = 19.4 Å (low- Q range; scattering vec- tor magnitude Q =| Q|=|k - k 0 |, |k|=|k 0 |= 2π/λ) and with a SDD equal to 16 m and λ = 6.0 Å (large- Q range). Due to the low neutron flux with the geometry and wave- length used for the low- Q range measurement, it was pos- sible to measure without the beamstop in front of the 2D detector. 2 Results Figure 1 displays some of the measured 2D scattering patterns after different deformations together with the fitted modeled ones in the low- Q range. The fit is discussed later in the text. The crystallographic direction [001] (i.e. the stress axis) was always vertical during the data collection. There were altogether three measurement for each individual sample at slightly differing orientations (ω-scan) and each fit was per- formed for all three sample orientations at once [6]. The data