Thermodynamic, Kinetic and Structural Study of Pt_42.5Cu_xNi_36.5-xP₂₁ Alloy Variations

Pt-P based alloy is one of the best glass-forming systems, in recent years, Pt-Cu-Ni-P alloys have drawn much attention due to its industrial potential. Their high glass forming ability (GFA) and remarkable thermal stability also predestinates them for thermophysical characterization. In a study by Neuber et.al, Pt_42.5Cu₂₇Ni_9.5P₂₁ was developed from the well-known glass former composition Pd₄₃Cu₂₇Ni₁₀P₂₁ and was shown that despite the topological similarities between Pt and Pd, the supercooled liquids of these two alloys are stabilized by different mechanisms. Compared to the low driving force of Pd-P system, in Pt-P system, large interfacial energy is considered to compensate the high driving force for crystallization. Moreover, an interesting pre-peak at low-Q value was observed in structural data of Pt_42.5Cu₂₇Ni_9.5P₂₁ during synchrotron measurement, which is argued to be a signature of medium range order (MRO) and arise from Pt-Pt or Pt-Cu correlations. <br/>In this work, four alloy variations based on the composition Pt_42.5Cu₂₇Ni_9.5P₂₁ with fixed atomic contents of Pt and P (42.5 and 21) were developed and studied via different methodologies in differential scanning calorimetry (DSC) and flash DSC (FDSC) and by high-energy synchrotron X-ray diffraction. Focus is laid on the influence of compositional changes on thermodynamic and crystallization behavior of the alloy liquids. In addition, an attempt is made to build connections between thermodynamic fragility and structural signature. <br/>Firstly, the thermophysical properties were obtained by standard scan in DSC, then Tg shift method and step method were applied to attain the relaxation time and specific heat capacity (Cp) evolution with Cu substituted by Ni, from which fragility parameters are calculated. By measuring the critical cooling rates and TTT-diagrams of the selected compositions in FDSC, the GFA and interfacial free energy of each alloy liquid is evaluated. Furthermore, the structural data during heating from room temperature to crystallization of amorphous alloys were investigated via high-energy synchrotron diffraction experiments (HEXRD) at DESY. <br/>Due to the dominant Pt-Pt partial scattering function, the respective role of Cu and Ni in the formation of the medium range order is still not fully revealed. In the next step efforts will be made to trace the single element behavior in the alloy, to achieve a deeper understanding of the influence of compositional change on the atomic packing scheme within the supercooled liquid.