Creep of platinum alloys at extremely high temperatures

Extremely high temperatures, mechanical stresses and severe corrosion conditions act in combination in equipment for the production of optical glasses. Common solid solution platinum base alloys such as Pt-10%Rh or Pt-5%Au often cannot be used because they can cause a detrimental discoloration of the glass. The materials selection is therefore limited to pure platinum or a dispersion hardened pure platinum matrix. However, compared to conventional alloys, dispersion hardened alloys are usually less ductile. In the present investigation creep tests have been carried out on pure Pt (99.95 weight%) and the oxide dispersion hardened alloy Pt DPH in the temperature range between 1473 K and 1873 K, The specimens were heated directly by an alternating electric current in specially designed creep test facilities. Strain was measured with a video extensometer. The measurements confirm, much better creep rupture strength and lower stationary creep rates at high temperatures for the oxide dispersion hardened alloy Pt DPH compared to pure Pt. Activation energies and stress exponents are given. The hardening effect in Pt DPH is achieved by finely dispersed zirconium and yttrium oxides, which are formed during an internal oxidation heat treatment of the alloy in a compact state. Oxide particles can be found both inside grains and at grain boundaries. SEM and TEM investigations of the microstructure were performed in order to discuss the mechanical properties of the alloy at high temperatures.