Low Temperature Plastic Behaviour of Icosahedral AlCuFe Quasicrystals
- PDF / 634,573 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 269 Views
Low temperature plastic behaviour of icosahedral AlCuFe quasicrystals Jan Fikar1, Joël Bonneville2, Jacques Rabier2, Nadine Baluc3, Anne Proult2, Patrick Cordier4 and Iona Stretton5 1 Ecole Polytechnique Fédérale de Lausanne, DP, CH-1015 Lausanne, SWITZERLAND. 2 Université de Poitiers, LMP, UMR-CNRS 6630, SP2MI, BP 30179 F-86962 Chasseneuil Futuroscope Cedex, FRANCE. 3 Fusion Technology Materials, CRPP - EPFL CH - 5232 Villigen PSI, SWITZERLAND. 4 Université des Sciences et Techniques de Lille, LSPEA, ESA CNRS 8008, Bât. C6 F-59655 Villeneuve d'Ascq Cedex, FRANCE 5 Bayerisches Geoinstitut (BGI), Universität Bayreuth D -95440 GERMANY ABSTRACT The mechanism by which dislocations move in the icosahedral quasicrystalline structure, i.e., glide or climb, is still an open question. In order to check whether pure dislocation glide occurs in this quasi-periodic structure, low temperature deformation tests have been performed under confining pressure conditions. These experimental techniques, which superimpose a shear stress on an isostatic component, enable the brittle-to-ductile transition temperature to be shifted to temperatures at which diffusion processes can be assumed to be negligible. Such techniques have been applied to deform plastically AlCuFe poly-quasicrystals at low and intermediate temperatures, using both gas and solid-confining media. Mechanical data as well as microstructural observations associated with this low temperature deformation range are reported. The first results provide new insights into the deformation mechanisms that control plasticity in the icosahedral quasicrystalline phase. INTRODUCTION Quasicrystalline compounds are recent in the field of physical metallurgy. Initially produced by rapid solidification techniques, such as melt-spinning, only metastable phases were produced. Hence, the first studies were restricted to describing the crystallography of these new nonperiodic structures. A renewal of interest concerning their mechanical properties has arisen over the last ten years from the discovery of thermodynamically stable quasicrystal alloys, which has allowed the growth of specimens with sizes suitable for investigation by conventional deformation techniques. It has now been established that icosahedral quasicrystals are brittle at low and intermediate temperatures, when deformed in compression under constant strain-rate conditions and atmospheric pressure. Plastic deformation only takes place at temperatures above nearly 0.7 Tm (Tm is the melting temperature). Above 0.7 Tm, the stress-strain curves exhibit a peculiar shape that consists, after an elastic stage, of a marked yield-point followed by a stage of strain softening. Plastic flow is considered to be intimately correlated with dislocation activity [1, 2]. However, it is not yet clear if, in this quasi-periodic structure, the dislocations move either by glide or by climb, as recently emphasised in [3, 4]. The very high brittle-to-ductile transition temperature (BDTT) of icosahedral quasicrystals strongly suggests that diffusion
Data Loading...
