High-resolution synchrotron X-ray diffraction studies of size and strain effects in a complex Al–Fe–Cr–Ti alloy

Abstract

We present a study of a complex ultra-high-strength Al alloy containing ~40 volume per cent of second-phase particles, ranging in size from nanometres to a few microns. The microstructure has been investigated using scanning electron microscopy and high-resolution synchrotron X-ray diffraction using the I11 beam line at the Diamond Light Source, UK. Powder diffraction was carried out to (i) determine phases present, (ii) quantify the weight per cent of each phase and (iii) quantify size and strain effects in the Al matrix. The high beam quality (i.e. low divergence and wavelength purity) and multi-analysing crystal detectors makes this an ideal instrument to resolve the high peak density and determine the contribution of sample broadening in the complex alloy. Using Pawley and Rietveld full pattern fitting, the intermetallic phases present were determined to be Al3Ti, Al13Cr2 and Al13Fe4. The weight fraction of each phase was calculated from the Rietveld refinements and correlated well with thermodynamic calculations assuming an equilibrium microstructure. Size and strain in the Al matrix was measured from peak broadening using a Double Voigt analysis and showed significant physical broadening due to both size and strain.