Different Deformation Behaviour Between Zirconia And Yttria Particles In Dispersion Strengthened Platinum-20% Rhodium Alloys

Platinum-20% rhodium strengthened by oxides of zirconium and yttrium were prepared by solidification of platinum-rhodium-(zirconium)-yttrium powder which had been internally oxidised. After forging, rolling and annealing, 1 mm plates were obtained. Then the plates were mechanically ground to 50-70 mu m from rolling-normal direction, followed by argon ion milling until a hole appeared on the centre of the foil to obtain samples which were characterised by transmission electron microscopy (TEM), combined with thermodynamic analysis. The existence of spherical ZrO2 and Y2O3 particles was verified with platinum and rhodium present as pure metals at the same time. It was found that the deformation behaviour of ZrO2 and Y2O3 particles was quite different during processing, where the former basically maintain their spherical shape and were bonded tightly to matrix, while the latter were compressed along normal direction and form two cracks on both sides of Y2O3 particles along the rolling direction. The differences in hardness and interface bonding properties of these two types of particles are supposed to be the main causes of different deformation behaviour during hot forging and cold rolling.