A processing route for freeze-casting of particle suspensions is presented, where the microstructure development during the solidification process can be controlled precisely. For this purpose, the single-side cooling and double-side cooling methods are compared. A procedure will be shown to control the freezing process using the double-side cooling method. Our approach was to determine the freezing conditions in order to forecast the freezing velocity and to carry out an advanced directional solidification setup for the experimental realization. Using this setup and the theoretical knowledge, the microstructure development can be controlled during the whole freezing process over a length of several centimeters.

No abstract

The effect of grain size on strain rate sensitivity and activation volume -from nano to ufg nickel The strain rate sensitivity of nanocrystalline nickel was studied at different temperatures in tensile tests and with a nanoindenter in order to examine the effect of grain size on the different deformation mechanisms of nanocrystalline materials. The experiments yielded, depending on temperature and strain rate, the strain rate sensitivity, the activation volume and the creep exponents as a function of stress and grain size. From the creep experiments the transition between grain boundary sliding and dislocation climb as a function of temperature was obtained. The strain rate jump tests gave extremely small activation volumes, nearly a factor of 100 smaller than in conventional nickel as a function of grain size. To help in understanding this behaviour the strain rate sensitivity of single grains was tested with a nanoindenter. The results clearly showed that the primary interaction of dislocations with grain boundaries is the reason for the strong rate effects and small activation volumes observed.

No abstract