Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy

We investigate early stages of spinodal decomposition in a melt. spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 min indicate the presence of a modulated structure (lambda= 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt. spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5 degrees)C/s).