Atomic site occupancy in D0(22) and L1(2) titanium trialuminides

X-ray incoherent channelling patterns (ICPs) are generated by variations in characteristic X-ray emission rates induced by a systematic scan of incide nt fast electron beam orientation near low index zone axes. ICP contrast is used to derive relative sublattice site occupancies of alloyed atoms in Al 3Ti and related intermetallics. Depending on composition and alloying atoms , these have crystal structures of type D0(22) or Ll(2). When V is added to form the D0(22) intermetallic Al-3(V0.6Ti0.4), it is shown that Ti and V s hare the same sublattice site. The Lit structure is stabilized by additions of Cr (which induces the transformation from the D0(22) structure and stab ilizes the Ll(2) phase). Elements X = Hf, Zr and W were added at the 0.5 at .% level to form separate quaternary alloys of overall composition Al62Cr10 .5Ti27X0.5 With the Lit 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 locatio n by channelling enhanced microanalysis (or ALCHEMI). It is shown that Elf and Zr are accommodated exclusively on Ti sublattice sites whereas W favour s the Al sublattice site with about 10% of the alloyed W atoms accommodated on Ti sublattice sites. Cr is shown to partition exclusively onto the Al s ublattice site. Contrast from a [110] zone confirms that these minority ato ms do not occupy the interstitial site at the body centre position of the L l(2) unit cell. Convergent beam electron diffraction data from the zero-ord er Laue zone and higher order Laue zone are shown and discussed for the [10 0] projection of the Ll(2) structure.