High Temperature Plastic Behaviour of Icosahedral AlCuFe Quasicrystals
- PDF / 104,495 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 223 Views
High temperature plastic behaviour of icosahedral AlCuFe quasicrystals. Jan Fikar1, Joël Bonneville, Nadine Baluc2 and Pierre Guyot3 1 Ecole Polytechnique Fédérale de Lausanne, DP, CH-1015 Lausanne, SWITZERLAND. 2 Université de Poitiers, LMP, UMR-CNRS 6630, SP2MI, F-86962 Futuroscope Cedex, FRANCE. 3 Fusion Technology, CRPP-EPFL , CH-5232 Villigen PSI, SWITZERLAND. 4 Institut National Polytechnique de Grenoble, UMR CNRS 5614, LTPCM, F-38042 St Martin d'Hères, FRANCE. ABSTRACT Icosahedral AlCuFe poly-quasicrystalline specimens were deformed in constant strain rate compression tests at temperatures ranging between 300K - 1020K. Below nearly 0.7 Tm (Tm is the melting temperature) the specimens were brittle. Above the brittle-to-ductile transition temperature, after the elastic stage the stress-strain curves exhibit a marked yield-point followed by a stage of strain softening only. Transient creep tests were performed at different given stress/strain levels after interrupting the constant strain-rate deformation tests. After the transient tests, the flow strength of the specimens was investigated anew at constant strain rate. The results are interpreted in the framework of a dislocation model, where two effects opposing dislocation movement are considered: firstly, the usual elastic dislocation interaction, yielding a work-hardening contribution, and, secondly, a friction stress specific to the quasiperiodic lattice, leading to a softening effect. INTRODUCTION Among all the quasicrystalline phases, which have now been produced, the icosahedral phase is certainly the most widely investigated. Up until now, it has been well-established that icosahedral quasicrystals are brittle at low and intermediate temperatures and plastic deformation only takes place at temperatures above nearly 0.7 Tm (Tm is the melting temperature). The stress-strain curves are atypical and, after an elastic stage, exhibit a marked yield-point that is followed by a stage of strain softening only. Direct proof of dislocation activity has not yet been established for all icosahedral quasicrystalline compounds [1, 2], but it is now well-accepted that their plastic deformation certainly results from dislocation movement [3]. However, it is not yet clear whether yielding is controlled by nucleation or propagation of dislocations [4]. In addition, the mechanism by which dislocations move, i.e., glide or climb, remains controversial, as recently emphasised in [5]. Guyot and Canova [6,7] have shown that unusual shape in icosahedral quasicrystals deformation curves can be theoretically well-reproduced by considering a strain decreasing friction stress opposing dislocation movement. Combining this friction stress with the usual elastic dislocation hardening leads to a yield-point followed by strain-softening only, as observed on the stress-strain curves obtained at constant strain-rate. Originally developed to account for the plasticity of AlPdMn, this model was recently successfully applied to describe the stress-strain curves of AlCuFe poly-quasicrystals [8
Data Loading...
