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Experimental Observations And Theoretical Modelling Of Equilibrium Quasicrystalline Phase In A Commercial Maraging Steel
Published online by Cambridge University Press: 10 February 2011
Abstract
A recently developed maraging steel of type 12%Cr-9%Ni-4%Mo-2%Cu-l%Ti in which precipitation strengthening is caused by quasicrystalline precipitates is presented. The steel is used in its tempered condition as surgical instruments such as surgical needles and dental reamers. The high strength and the resistance to tempering induced softening is in part attributable to the formation of quasicrystalline precipitates of icosahedral symmetry. Profuse nucleation in combination with slow coarsening of precipitates are explicable in terms of a low surface energy associated with quasicrystallinity. There is experimental evidence supporting the conclusion that the quasicrystalline precipitates in the present material are formed under thermal equilibrium conditions. To rationalise this conclusion, we compare it with the thermodynamics and kinetic properties of an equilibrium quasicrystalline phase simulated by molecular dynamics. The simulation has demonstrated that the stability of this quasicrystal with respect to the crystalline ground state may be attributed to the large configurational entropy arising from the thermally activated phason dynamics. We argue that this mechanism, suggested by the random tiling model, may account for the observed equilibrium quasicrystalline precipitates in metallic alloys.
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- Copyright © Materials Research Society 1999
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