Group Members:Dr. Julia Ivanisenko (contact person), , (doctoral student)
Mechanical behaviour and properties of nanocrystalline (NC) and ultrafine grained (UFG) materials produced by inert gas condensation (IGC) and severe plastic deformation (SPD), such as high pressure torsion and equal angular channel pressing (ECAP). Strain induced microstructure- and phase transformations.
Current research projects:
1. Micro- and macromechanical properties of fully densified nanocrystalline metals and alloys.
In this project the fundamentals of plastic deformation in fully dense bulk NC metals and alloys with a mean grain size between 10 and 30 nm is being investigated. The experiments are focused on mechanical tests using new testing equipment for miniature specimens. The aim is to obtain a significantly improved database of mechanical behaviour for these materials at this very small grain size, and to elucidate the microscopic mechanisms that mediate the deformation. Special emphasis is addressed to in situ investigation of mesoscopic effects in plastic flow of nanocrystalline materials, such as formation of shear bands and/or cooperative grain boundary sliding.
2. Basic mechanisms of mechanical property enhancement for carbon steels through controlled nanostructure formation
Despite the progress achieved in the last fifty years in the development of new steel grades and thermal- and thermomechanical treatments, the quest for novel processing routes allowing further enhancement of the steel properties remains of great current interest and, in this respect, nanostructuring has not been extensively explored by the mainstream steel research. The aim of this project is to investigate:
(i) the coupled mechanisms of nanostructure formation and phase transformations (nanocrystallisation and concomitant carbide dissolution) in a number of Fe based alloys during severe plastic deformation using HPT and ECAP methods, and
(ii) the relationship between the nano-scale structure / local phase composition achieved and the resulting mechanical properties.
Tensile test machine for mini samples with a gage length of 2..5 mm and temperature control in the range between 20-600°C equipped with a Laser Extensometer Fiedler Optolektronik GmbH for precise strain measurement.
Set up for HPT deformation.
Microtensile stage MicroDAC by Kammrath and Weiss for in-situ tensile tests in SEM equipped with Gray Scale Correlation.