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Recrystallization of deformed metals occurs in a lot of industrial processes, including the hot-deformation and heat treatment of metals and alloys. The onset of recrystallization has to be very accurately controlled since it dramatically affects the mechanical properties of the material. However the process is very difficult to observe in-situ. Scientists from Université de Nantes, France, have been using the HRPD instrument at ISIS to study nickel, with the aim of using the high penetrating, yet non-destructive, properties of neutrons to understand overall recrystallization kinetics on a bulk level.
All metals must be deformed in the fabrication process, creating a high density of dislocations. Recrystallization is triggered when the deformed metal is heated. Nucleation and the growth of new grains gradually “absorb” the deformed material. Understanding the recrystallization kinetics is important as the process impacts on the properties of the metal, including hardness, grain size and thermal and electrical conductivity.
A number of post mortem techniques have been used but this is time-consuming as many specimens need to be studied with different annealing times. In this experiment, samples of deformed nickel were annealed in the neutron beam using a furnace, so the recrystallization process could be studied in-situ on a single sample. Neutrons penetrate into the bulk of the material and allow the overall kinetics to be studied, not just particular components of the recrystallization texture.
Fred Christien from Université de Nantes , in collaboration with ISIS scientists Mark Telling and Kevin Knight, is leading the study. He says, “Here we are looking at nickel, which is a relatively simple metal. Industrial metals are very complex with a lot of processes going on at the same time. We are going back to the fundamentals, to a simple metal to see just one process and understand it. We’re using HRPD because the resolution is very high, and it is very sensitive to the presence of dislocations. This work has shown what the instrument can achieve and the prospects for metallurgy are very interesting."
Research date: July 2013
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