J. Phys. IV France 11 (2001) Pr8-493-Pr8-498
The effect of nickel on the martensitic-type transformations of Pt3Al and TiPtT. Biggs1, L.A. Cornish2, M.J. Witcomb3 and M.B. Cortie1
1 Physical Metallurgy Division, Mintek, Private Bag X3015, Randburg 2125, South Africa
2 School of Process Engineering, University of Witwatersrand, Private Bag 3, Wits 2050, South Africa
3 Electron Microscope Unit, University of Witwatersrand, Private Bag 3, Wits 2050, South Africa
The effect of nickel on two classes of martensitic-type transformations in platinum systems has been studied. The first transformation is Ll2 to DO'c in the Pt3Al system and the second is B2 to B19 in the TiPt system. The microstructures after transformation in the two systems are very different. The product of the Pt3Al transformation has a twinned microstructure, typical of cubic-to-tetragonal transformations. The product of the TiPt transformation is lath-like, although the morphology can be altered using heat treatments. The parent phase in the TiPt system is not retained at room temperature, whereas the parent phase in the Pt3Al transformation can be stabilised to room temperature. A great variation in hardness and transformation temperature is seen in each system as the composition is varied about the stoichiometric ratio, which has the lowest hardness. The Pt3Al transformation temperature has been reported to range from around room temperature to 1000°C. The TiPt transformation temperature can range from 1000 to 1080°C. The effect of nickel additions on these alloys also has a marked effect on the parent and product phase stability, and hence the microstructure and resulting hardness. The effect on the Pt3Al phase is complex, as nickel appears to stabilise the parent phase. The hardness varied in the region of 350 to 500 HV10. For the TiPt phase, the hardness values were generally found to increase with the nickel additions increasing from 250 to about 600 HV10. The addition of 20 at.% nickel decreases the transformation temperature from around 1000°C to about 600°C.
© EDP Sciences 2001