X-ray diffraction studies of the decomposition and microstructural characterization of cold-worked powders of Cu-15Ni-Sn alloys by Rietveld analysis

The present work concerns study of the precipitation sequence due to aging below the critical aging temperature of cold-worked powder samples of industrially important Cu-Ni-Sn alloys with compositions, Cu-15 wt.% Ni-(5, 8, 13) wt.% Sn. The analysis adopts a recently developed JAVA based software Materials Analysis Using Diffraction (MAUD), based on Rietveld's whole X-ray pattern fitting methodology. The evoluted phases have been characterized microstructurally in terms of different defect parameters, namely, stacking, twin and compound fault probabilities, crystallite (domain) sizes, microstrains (root mean square, rms strains), dislocation densities, preferred orientation parameters, etc. The analysis also includes quantitative estimation of phase abundances of the precipitating phases. The decomposition due to aging with varying Sn composition and aging period has been critically studied and the percentage of volume fraction of the evoluted phases has been evaluated and compared. The results depict, for the three different alloy compositions, three distinct different types of precipitation sequence comprising α, γ and δ phases with continuously varying volume fractions with aging time. The size-strain-shape analysis adopting the Popa model reveals almost isotropic values of both the crystallite sizes and rms strains in all [h k l] directions for the evoluted phases. The values of all the above defect parameters have been evaluated and compared for elucidating a better structure-property relationship