A SMALL-ANGLE NEUTRON-SCATTERING AND TRANSMISSION ELECTRON-MICROSCOPYSTUDY OF KRYPTON PRECIPITATES IN COPPER

The annealing behaviour of bulk copper containing 2.6 at.% krypton has been studied by small-angle neutron scattering (SANS) and transmissio n electron microscopy (TEM). In addition positron annihilation spectro scopy (PAS) and mass-density measurements (MDM) were made. In the as-p repared and annealed material a high density of krypton precipitates ( 'bubbles') exists. Special emphasis is put on different approaches to the analysis of the SANS data. Differences between the results from th e various analyses are pointed out and discussed. Polydisperse models clearly give the most extensive information, i.e. the size distributio n of the Kr bubbles and integral parameters derived from it (i.e. bubb le volume, total surface area and average radius). It is demonstrated that a correct choice of form factor is important for the reliability of the derived size distribution. In TEM a high degree of overlap of b ubble images is observed and corrected for. Good agreement between the shapes of SANS and TEM size distributions is found, while differences in amplitude are ascribed to experimental uncertainties. Average kryp ton densities in the bubbles as well as fractional cavity volumes deri ved from PAS and MDM are found to be in good agreement, but the cavity volumes are clearly larger than the total bubble volumes obtained fro m the SANS and TEM size distributions. Above roughly 300 degrees C bub ble growth takes place. Two different mechanisms for the initiation of growth are discussed. At the higher annealing temperatures the growth in bubble size and total volume fraction is explained by bubble migra tion and coalescence followed by absorption of thermal vacancies.