Berlin 2012 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 29: Topical Session Bulk Nanostrucured Materials VI - Mechanical Properties I

MM 29.4: Talk

Wednesday, March 28, 2012, 11:15–11:30, H 0107

Thermal stability and strain-rate sensitivity of nanocrystalline Ni and a Ni/Al2O3 nanocomposite — •Michaela Prell¹, Karsten Durst¹, Harald Natter², Anne Jung², and Mathias Goeken¹ — ¹Institute of General Materials Properties, Department of Materials Science and Engineering, University of Erlangen-Nürnberg — ²Physical Chemistry, Saarland University, Saarbruecken, Germany

The thermal stability and strain-rate sensitivity of a nickel-alumina nanocomposite and nanocrystalline Ni with different amount of grain refiner has been studied using compression tests up to 300°C and microstructural investigations with scanning and transmission electron microscopy. It is found that during deposition, the Al2O3 particles form clusters, which are evenly distributed in the nc-Ni microstructure. The initial hardness and flow stress of the nc-Ni/Al2O3 is smaller compared to nc-Ni, but with heat treatment or testing at higher temperatures, nc-Ni/Al2O3 shows a higher strength and higher strain rate sensitivity. For nc-Ni, even at an annealing temperature of 250°C strong grain coarsening has been found, where initially large grains are embedded in a nanocrystalline matrix. For longer annealing times, a stable ultrafine grain size of ~1 micron was observed. During compression test at 250°C however, homogenuous grain coarsening is observed. The stability of the microstructure against coarsening due to the Al2O3 particles is discussed as one of the main reasons for the enhanced properties of the nanocomposite.