Atomic site occupancy in D022and L12titanium trialuminides

Abstract

Abstract X-ray incoherent channelling patterns (ICPs) are generated by variations in characteristic X-ray emission rates induced by a systematic scan of incident fast electron beam orientation near low index zone axes. ICP contrast is used to derive relative sublattice site occupancies of alloyed atoms in Al3Ti and related intermetallics. Depending on composition and alloying atoms, these have crystal structures of type D022 or L12. When V is added to form the D022 intermetallic A13(V0.6Ti0.4), it is shown that Ti and V share the same sublattice site. The L12 structure is stabilized by additions of Cr (which induces the transformation from the D022 structure and stabilizes the L12 phase). Elements X = Hf, Zr and W were added at the 0.5at.% level to form separate quaternary alloys of overall composition A162Cr10.5Ti27X0.5 with the L12 crystal structure. The sublattice site partitioning of these minority atoms is investigated by the formation of X-ray ICPs and subsequent statistical analysis of these patterns, related to atom location by channelling enhanced microanalysis (or ALCHEMI). It is shown that Hf and Zr are accommodated exclusively on Ti sublattice sites whereas W favours the A1 sublattice site with about 10% of the alloyed W atoms accommodated on Ti sublattice sites. Cr is shown to partition exclusively onto the A1 sublattice site. Contrast from a 〈110〉 zone confirms that these minority atoms do not occupy the interstitial site at the body centre position of the L12 unit cell. Convergent beam electron diffraction data from the zero-order Laue zone and higher order Laue zone are shown and discussed for the 〈110〉 projection of the L12 structure.