3Ti Alloys Research Articles

Microstructure, deformation, and fracture characteristics of an Al67Pd8Ti25 intermetallic alloy

Microstructure, indentation, and fracture characteristics of an intermetallic alloy with nominal composition Al67Pd8Ti25 have been investigated. Following a homogenization anneal at 1323 K, the material consists primarily of a phase having the Ll2 crystal structure. This phase is analogous to the π phase previously reported in (Al,X)3Ti alloys, where X represents Ni, Cu, Zn, or Fe substituted for Al in Al3Ti. The deformation and fracture characteristics of Al67Pd8Ti25 are similar to those previously reported for Al67Ni8Ti25: Vickers hardness is moderate, plastic deformation occurs by a0 «110» 111 slip, and fracture in bending occurs by transgranular cleavage with no evidence of associated plasticity.

CO adsorption on (111) and (100) surfaces of the Pt 3Ti alloy: Evidence for parallel binding and strong activation of CO

An atom superposition and electron delocalization molecular orbital (ASED-MO) study has been made of CO adsorption on a 40-atom cluster model of the (111) surface and a 36-atom cluster model of the (100) surface of the Pt 3Ti alloy. Parallel binding to high-coordinate sites associated with Ti and low CO bond scission barriers are predicted for both surfaces. The preference for parallel adsorption is a consequence of the nature of the CO π-to-surface donation interactions. On Ti sites the π orbitals donate to the nearly empty Ti 3 d band and the antibonding counterpart orbitals are empty. Thus the π donation makes substantial contributions to the adsorption bond order that are in addition to the contributions from 5σ donation and metal backbonding to the π ∗ orbitals. Altogether these bonding interactions favor the lying down orientation. On Pt sites, on the other hand, the π donation antibonding counterpart orbitals are occupied so that the net interaction with Pt is a closed-shell repulsion. CO bonds upright in order to minimize the π interaction and, concomitantly, the closed-shell repulsion, while maintaining 5σ donation and π ∗ backbonding stabilizations. Comparisons are made with the results for a 40-atom cluster model of the unalloyed Pt(111) surface. It is shown that the extended Hückel parameterization is inappropriate for studying CO adsorption to Pt with the ASED-MO theory because it incorrectly favors adsorption bonding through the oxygen end.