Microstructure Evolution in Cold-Rolled Pure Titanium: Modeling by the Three-Scale Crystal Plasticity Approach Accountin
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and KATARZYNA KOWALCZYK-GAJEWSKA
A three-scale crystal plasticity model is applied to simulate microstructure evolution in hcp titanium subjected to cold rolling. Crystallographic texture and misorientation angle development, as an indicator of grain refinement, are studied. The impact of twinning activity on both phenomena is accounted for by combining the original three-scale formulation with the probabilistic twin-volume consistent (PTVC) reorientation scheme. The modeling results are compared with available experimental data. It is shown that the simulated textures are in accordance with the experimental measurements. The basic components of misorientation angle distribution, especially in the range of high angle boundaries, are also well reproduced. https://doi.org/10.1007/s11661-018-4676-2 Ó The Author(s) 2018
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INTRODUCTION
IT is well known that improvement of material properties can be achieved by tailoring the microstructure. The microstructure can be refined by advanced plastic deformation processes. The mechanisms leading to refinement are not yet fully described, in spite of the huge effort that has been put into modeling. While this statement is true in the case of face centered cubic (FCC) materials, it is even more relevant in the case of hexagonal close packed (HCP) materials. Mainly it is due to the fact that plastic deformation in HCP materials is usually more complicated than in FCC, because of the insufficient number of easy slip systems and the ease of twinning. Qualitative studies of the grain refinement phenomenon in FCC metals and alloys were reported in References 1 through 7. Based on the indicated mechanisms of microstructure evolution, a three-scale crystal plasticity (3SCP) model was built.[8] The model construction was motivated by the initially present deformation-induced cell substructure, schematically shown in Figure 1(a). Two types of grain boundaries can be recognized, namely geometrically necessary boundaries (GNBs) and incidental dislocation boundaries (IDBs). The new grains are formed by gradual increase of misorientation angles across the boundaries.
KAROL FRYDRYCH and KATARZYNA KOWALCZYKGAJEWSKA are with the Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences, Pawin nskiego 5B, 02-106 Warsaw, Poland. Contact e-mail: [email protected] Manuscript submitted January 11, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
The mechanisms governing the grain refinement in metals of hexagonal close packed (HCP) lattice experiencing large plastic strains, induced e.g., via severe plastic deformation (SPD) processes, are known to a much lesser extent. First of all, in those metals, the number of easy slip systems is in general less than in FCC metals, and twinning appears as an additional, complementary mode. Second, in spite of the many efforts to carry out cold SPD processes for commercially pure titanium (CP Ti)[9] and for AZ31b magnesium alloy,[10] they are usually performed at elevated temperatures, which promote discontinuous dynamic recrystallization
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