Boris StraumalInstitute of Solid State Physics RASDiffusive And Displacive Phase Transformations Driven By High Pressure Torsion Zehetbauer International Symposium on Science of Intelligent and Sustainable Advanced Materials (4th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM)) Back to Plenary Lectures » | |
Abstract:The influence of high pressure torsion (HPT) on the diffusive and displacive phase transformations in sustainable advanced materials has been studied. In diluted Cu-based binary alloys the HPT drives the competition between deformation-driven precipitation and dissolution of precipitates. The dynamic equilibrium between these two processes is reached already after 1.5-2 anvil rotations. The composition of Cu-matrix in this equifinal state is equal to that which can be reached in equilibrium after long annealing at a certain temperature T<sub><i>eff</i></sub>. T<sub><i>eff</i></sub> in diluted Cu-based binary alloys increases with increasing activation enthalpy of diffusion of a second component and its melting temperature Tm [1, 2]. In Cu-Al-Ni shape memory alloys, HPT leads to the combination of displacive (austenite-martensite) and diffusive (decomposition of supersaturated solid solution) phase transitions. On the one hand, the HPT of these alloys led to the precipitation of α1-phase in the Al-pure alloy and to the precipitation of γ1-phase in the Al-rich one (as if they were annealed at an effective temperature T<sub><i>eff</i></sub> = 620-20°C). As a result of this precipitation, the matrix in the first alloy was enriched and in the second one depleted in Al. The resultant composition change in the Cu-rich matrix changed also the route for the martensitic transformations. After HPT, both alloys contained mainly β'3 martensite with a certain amount of γ'3 martensite. Thus, the HPT-driven diffusive transformations (precipitation of α1- and γ1-phase) influence the followed displacive (martensitic) transformation [3]. The combination of displacive and diffusive phase transitions has been observed also under HPT of Ti-Fe and Ti-Co alloys [4]. |