Lawrence Berkeley National Laboratory
An In-situ method for the study of strain broadening using synchrotronx-ray
- Author(s): Tang, Chiu C.
- Lynch, Peter A.
- Cheary, Robert W.
- Clark, Simon M.
- et al.
A tensonometer for stretching metal foils has been constructed for the study of strain broadening in x-ray diffraction line profiles. This device, which is designed for use on the powder diffractometer in Station 2.3 at Daresbury Laboratory, allows in-situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on a 18mum thick copper foil experiencing strain levels of up to 5 percent using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental parameters approach using the TOPAS peak fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile pre-determined using high quality LaB6 reference powder. The de-convolution process yielded "pure" sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from fcc a/2 111 dislocations, we have extracted the variation of mechanic al property with strain. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities.