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MM: Metall- und Materialphysik

MM 45: Mechanical Properties III

MM 45.2: Vortrag

Freitag, 31. März 2006, 12:45–13:00, IFW A

Strain rate effects of nano- and microcrystalline nickel measured form the macro- to the nanoscale — •Horst Vehoff, Delphine Lemaire, Bo Yang, and Michael Marx — Saarland University, Department of Materials Science, Building D23, D-66041 Saarbrücken, Germany

Understanding the macroscopic deformation behaviour of metals based on the microscopic mechanisms like grain rotation, grain boundary- and volume diffusion, emission and motion of dislocations and the interaction of dislocations with microstructure elements is one of the main objectives of modern materials science. Due to the different length scales of the deformation mechanisms the active mechanisms change with the grain size. Therefore the grain size dependent deformation behaviour was investigated locally by nanoindentation and macroscopically by incremental strain rate tests with nanocrystalline and microcrystalline nickel. The nanoindentation measurements probe the interaction of dislocations and grain boundaries locally during plastic deformation. It will be shown that with decreasing grain size the pile up of dislocations at grain boundaries as the dominant mechanism of the deformation process which leads to hardening is changed to grain boundary sliding and grain rotation as active mechanisms which leads to softening. The measurements were completed by macroscopic measurement of the strain rate sensitivity as function of the grain size. It will be shown that nanocrystalline materials have a higher strain rate sensitivity and smaller activation volumes than microcrystalline materials which indicates a continuous change of deformation mechanisms with the grain size.