Alloying and microstructural changes in platinum–titanium milled and annealed powders

Equiatomic platinum–titanium powder mixtures were processed by high energy ball milling under argon atmosphere and sintered under vacuum. Evolution of the crystal structures and microstructures of the products formed were investigated by XRD and SEM techniques, respectively. The HCP crystals of Ti were first deformed and then a disordered metastable FCC Pt(Ti) solid solution was formed during milling due to semi-coherency of FCC lattices. A nanostructured Pt(Ti) product was formed after long milling time, which contained 44–47 at.% Ti and 53–56 at.% Pt.An ordered PtTi intermetallic was formed by annealing the metastable Pt(Ti) at temperature above 1300 °C. The crystal structure and microstructure of the TiPt phase depended on the milling time, annealing temperature and the cooling rate. The B19 PtTi plate martensite was formed after annealing at 1500 °C and quenching at a cooling rate of 23 °C/min to 200 °C/min for short time milled products. The width of martensite features was smaller at high cooling rate. In PtTi products milled for longer time, no martensitic transformation was observed on cooling the annealed samples. Small amounts of Pt5Ti3 were formed in the powders milled for 16 h or more, followed by annealing at 1500 °C and furnace cooling at ∼2 °C/min.

(a) SE-SEM micrographs of PtTi martensite formed in powder milled for short time annealed at 1500 °C and quenched in helium gas flow (b) BSE-SEM of structure formed after slow cooling.Figure optionsDownload as PowerPoint slideHighlights
► A disordered metastable FCC Pt(Ti) solid solution was formed after longer milling period.
► HCP Ti crystals were first deformed and then the atoms were dissolved in strained FCC Pt lattices.
► Longer milling time suppressed the occurrence of martensitic transformation after annealing.
► Martensite phase was formed in products that went through a short milling time then annealed and quenched.
► The width of the martensite features formed was smaller at higher cooling rates.