The precipitate morphology and lattice mismatch of ternary (Pt)/Pt₃Al alloys

The effects of some ternary alloying additions (Ti, Cr, Ru, Ta and Ir) on the phase relations and properties of two-phase (Pt)/∼Pt₃Al alloys were investigated. The crystal structure and morphology of the ∼Pt₃Al phase were examined, and the compressive strengths and melting temperatures of the alloys were determined. It was found that Ti, Cr and Ta partitioned to ∼Pt₃Al and stabilised the Ll₂ form of this phase. The ∼Pt₃Al phase in these alloys had cuboidal morphologies and a small lattice misfit with the matrix (about -0.7%). The tetragonal D0′_C form of ∼Pt₃Al was observed in the alloys containing Ru and Ir. The ∼Pt₃Al in these alloys formed in groupings shaped somewhat like a Maltese cross, which may result from the higher lattice misfit in these alloys (-1 to -1.2%) or the D0′_C crystal structure of the ∼Pt₃Al. The compressive strengths of the alloys were found to depend on the proportion of ∼Pt₃Al in the microstructures; higher strengths being recorded for alloys containing larger proportions of ∼Pt₃Al.