Elastic and Plastic Deformation Behavior Studied by <i>In-Situ</i> Synchrotron X-ray Diffraction in Nanocrystalline Nickel

Abstract

In situ XRD measurements were conducted during the tensile deformation of both submicron-grained Ni specimens fabricated by accumulative roll bonding (having a grain size of 270 nm) and nanocrystalline Ni fabricated by electrodeposition (having a grain size of 52 nm). Variations in the dislocation density and the extent of elastic deformation could be determined with a time resolution of 1.0 s based on changes in the full width at half maximum of ten Bragg peaks and in the Bragg peak shifts, respectively. The dislocation density was found to vary in four different stages. Regions I and III were the elastic and plastic deformation regions, respectively, while Region II was the transition region. Here, the dislocation density rapidly increased to a value, ρ II , necessary for plastic deformation. Since the increase in ρ II was inversely proportional to grain size, it is evident that nanocrystalline materials require extremely high dislocation densities for deformation to progress solely by plastic deformation. In Region IV, the multiple dislocations were rapidly annihilated by unloading associated with fracture. In the case of the nanocrystalline Ni, there was little difference in the stress distribution in the grains depending on the crystal direction during plastic deformation and, accordingly, there was only minimal variation in the residual stress in the grain with different crystal directions after unloading.

Tensile Deformation of Ultrafine-Grained Fe-Mn-Al-Ni-C Alloy Studied by In Situ Synchrotron Radiation X-ray Diffraction

“…The estimated dislocation densities in austenite phase and B2 phase during tensile deformation are plotted in Figure 11. Before the tensile test, the dislocation densities in austenite phase and B2 phase were 6.0 × 10 13 m −2 and 4.5 × 10 13 m −2 , which were close to the values in fully recrystallized metals previously reported [21,45]. During the Lüders deformation, the dislocation densities in both phases rapidly increased, which was similar to the tendency of the The dislocation density of each constituent phase was estimated by the classical Williamson-Hall method [42] shown as:…”

“…After the tensile test, the diffraction peaks in a profile were fitted using the pseudo-Voigt function. For more details of the in situ XRD measurements in BL46XU, one can refer to References [19][20][21]. Figure 2 shows the EBSD grain boundary map superimposed on the phase map of the specimen.…”

Measurement of Dislocation Density Change during Tensile Deformation in Coarse-Grained Aluminum by <i>In-Situ</i> XRD Technique with Tester Oscillation

“…Figure 12 shows the change in the crystal grain size of µ II in the A1200 alloy and also shows the dependence of µ II on the grain size in nanocrystalline Ni. 4) This µ II is almost constant at ca. 10 14 m ¹2 when d > 3 µm, but increases in proportion to the particle size to the power of ¹1 when d < 3 µm.…”

“…The change in the dislocation density in region III was very gradual. In pure Ni with a grain size of 260 nm prepared by ARB processing, the dislocation density gradually increased in region III, 4) so that dislocation multiplication also occurred in this region; however, the melting points of Ni and Al are different, so that the dynamic recovery rate is different. It is considered that the dislocation density did not increase in region III, because pure aluminum the dynamic recovery is much faster and dislocation multiplication were balanced.…”

“…The measurement was performed with a time resolution of 2 s. The diffraction peak angle and full width at half maximum were calculated from the observed diffraction peak profiles from the (111), (200), (220), (311), (222), and (331) planes, and the dislocation density was calculated using the Williamson-Hall method. 4,8,9)…”