Neutron and Synchrotron X-ray Studies of Recrystallization Kinetics
- PDF / 466,193 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 76 Downloads / 160 Views
ODUCTION
RECRYSTALLIZATION is a thermally activated process whereby new (almost) dislocation-free nuclei form in the deformed microstructure, and with time, they grow by boundary migration to finally occupy the entire sample volume. The driving force for recrystallization is the energy stored in the deformed microstructure. Generally, the recrystallization kinetics is described as the evolution in volume fraction of recrystallized material, Vv, as a function of time. An example is shown in Figure 1. Most of the analysis of recrystallization kinetics is even today based on the so-called JMAK (or KJMA) methodology, which was developed by Kolmogorov,[1] Johnson and Mehl,[2] and Avrami[3–5] in the late 1930s. This popularity is because the JMAK analysis is easy to understand and apply, and it results in parameters that directly describe the nucleation and growth processes of recrystallization. However, in most cases, JMAK does not give an adequate description of the observed recrystallization kinetics.[6,7] This is also the case for the data shown in Figure 1: If the JMAK should apply, the data should fit to one straight line when plotted in the way of Figure 1. As can be seen from the figure, at least two lines have to be used when fitting the data. The data of Figure 1 are measured by electron microscopy, and this method together with optical microscopy is by far the most used method for the study of recrystallization. By these methods, VV is measured for a series of partly recrystallized samples annealed for different times, t. The methods therefore D. JUUL JENSEN, Head of Department, is with the Center for Fundamental Research: Metal Structures in Four Dimensions, Materials Research Department, Risø DTU, DK-4000 Roskilde, Denmark. Contact e-mail: [email protected] R.B.N. GODIKSEN, Quantitative Analyst, is with Nordea Markets, DK-0900, Copenhagen, Denmark. This article is based on a presentation given in the symposium entitled ‘‘Neutron and X-Ray Studies for Probing Materials Behavior,’’ which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. Article published online August 7, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
give a statistical description of the recrystallization kinetics. Neutron and X-ray methods offer important complementary information to microscopy investigations. Of particular importance here is the possibility of in-situ bulk studies. By following texture changes, overall kinetics information may be achieved and synchrotron X-rays allow studies of the local kinetics of individual grains. In the present article, results obtained by these methods are overviewed. Implications for the modeling of recrystallization kinetics are discussed and an outlook is given.
II.
IN-SITU TEXTURE MEASUREMENTS
The crystallographic texture describes the crystallographic orientation distribution of the crystallite
Data Loading...
