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MM: Fachverband Metall- und Materialphysik

MM 12: Growth

MM 12.2: Talk

Monday, March 26, 2007, 16:30–16:45, H6

Abnormal grain growth of nanocrystalline materials: In situ investigation in the SEM — •Michael Marx, Andreas Noll, and Horst Vehoff — Saarland University, Materials Science, Building D22, 66041 Saarbrücken, Germany

To develop nanocrystalline (NC) and ultra fine grained (UFG) materials to secure operating construction materials, it is essential to stabilize the microctructure. So far the different mechanisms of grain growth and recrystallization were often investigated however a final description through all stages of grain growth is missing. Therefore in this work NC und UFG materials which were produced by different procedures were imaged in a SEM during heat treatment. The materials investigated were pulse electro deposited (PED) nickel, severe plastic deformed (SPD) aluminium by equal channel angular pressing for 2 and for 8 passes and an AlMgSi-alloy produced by accumulative roll bonding also for 2 and for 8 passes. No significant difference in the development of the microstructure between PED and SPD materials was found. In every case there is abnormal grain growth which results in an UFG matrix with some large grains of more than 100 um, the ratio of matrix grains and larger grains varies with the heat treatment. The growth of the large grains was monitored and the growth kinetics measured. By focused ion beam combined with orientation imaging microscopy, the growing grain boundaries could be identified as (100)-planes. So far the investigations are not finished however it will not be easy to find a heat treatment to produce a mono-modal ultra fine grained microstructure which is stable at moderate temperatures.