Laves phases in the ternary systems Ti–{Pd, Pt}–Al

Formation and crystal structure of Laves phases in the systems Ti–{Pd,Pt}–Al were investigated employing XPD (X-ray powder diffraction), XSCD (X-ray single crystal diffraction) and EPMA (electron probe microanalysis) techniques. Laves phases with MgZn2 type (space group: P63/mmc) and its variant with the Nb(Ir,Al)2-type (a√3 × a√3 × c supercell of MgZn2-type, space group: P63/mcm) were found in both systems. Formation of a particular structure type is dependent on temperature and composition. Laves phases with the Nb(Ir,Al)2-type form around 25 at.% of Pd,Pt at 950 °C. The MgZn2-type Laves phase Ti(Pt,Al)2 was not observed at 950 °C, but it forms in as-cast alloys at a slightly lower Pt content, Ti37.8Pt19.0Al43.2. In the Ti–Pd–Al system at 950 °C the MgZn2-type phase exists at the Pd-poor side of the homogeneity region whilst the Nb(Ir,Al)2-type phase is slightly richer in Pd. Phase relations associated with the Ti–Pt–Al Laves phase were established at 950 °C and reveal a new compound TiPtAl that derives from hexagonal ZrBeSi-type (ordered Ni2In-type, a = 0.43925(4) nm, c = 0.54844(5); space group P63/mmc; RF2 = 0.015 from single crystal data). Atom distribution in the compound shows a slight deviation from full atom order Ti(Pt0.97Al0.03)(Al0.98Pt0.02).