An in situ synchrotron X-ray diffraction study of precipitation kinetics in a severely deformed Cu-Ni-Si alloy

In situ synchrotron X-ray diffraction was used to study the decomposition kinetics of a metastable Cu-2.5Ni-0.6Si (wt%) alloy after severe plastic deformation by equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). The measurements were performed at room temperature and also at high temperatures of 723, 823 and 973 K in order to determine the ageing effect after processing. Two forms of precipitates, namely δ-Ni2Si and γ-Ni5Si2, were identified and the sequence of their appearance was well established for ECAP processing and ageing. There was no detection of either a modulated structure resulting from spinodal decomposition or an ordered structure nucleated from the modulated structure. An X-ray hybrid pixel array detector (XPAD-S140 detector) permitted the detection of the nucleation stages of the δ-Ni2Si phase that began soon after 24 s of ageing at 723 K. There was also no trace of any amorphization of the matrix phase.