MECHANICAL-BEHAVIOR AND MICROSTRUCTURAL EVOLUTION IN THE SINGLE-CRYSTAL SUPERALLOY SC16

Mechanical testing at 1223 K and at constant strain rates (tensile tes ts) and constant loads (creep tests) of the single crystal nickel-base superalloy SC16 shows that after an initial hardening the alloy softe ns during deformation under all testing conditions. Within the testing range covered in the present study two different deformation mechanis ms are identified to occur in different regimes of resting. In the pre sent paper we analyse the softening behaviour observed in the low stra in rate regime. In this regime the softening is accompanied by a morph ological change in gamma' precipitates (rafting). We show that the obs erved microstructural instability leads to an increase in the spacing between the gamma' particles. This effect quantitatively accounts for the observed softening in this test regime. (C) 1997 Acta Metallurgica Inc.