Determination Approach of Dislocation Density and Crystallite Size Using a Convolutional Multiple Whole Profile Software

Abstract

Neutron diffraction profile analysis using the whole profile fitting method is useful for obtaining microscopic information on metallic materials. To determine an appropriate fitting approach for obtaining reasonable and non-arbitrary results, we applied diffraction line profile analyses using the Convolutional Multiple Whole Profile (CMWP) method to diffraction patterns obtained using the Engineering Materials Diffractometer (TAKUMI, BL19) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The tensile specimens of 780 MPa grade bainitic steel were uniaxially stretched until the plastic strain reached a value of 0.05. We performed CMWP analyses on the obtained diffraction patterns during tensile test with various initial parameters of dislocation density and crystallite size. These parameters were optimized in the fitting procedures to minimize the weighted sums of squared residuals (WSSRs). Following this approach, we found that unsuitable initial parameter values resulted in unreasonable convergence. Therefore, initial fitting parameters should be chosen to ensure that the initial profiles are as broad as possible. Reasonable results were obtained following this suggestive approach even when the strain anisotropy parameter is set to arbitrary values.

Effect of Hydrogen on Evolution of Deformation Microstructure in Low-Carbon Steel with Ferrite Microstructure

“…The fractions of screw and edge dislocations were determined from pa-rameter q obtained from CMWP fitting. Parameter q has to be in between 1.29 (for 100% edge) and 2.64 (for 100% screw) in BCC steels [27] . The microscopic dislocation morphologies were characterized using STEM at an acceleration voltage of 200 kV.…”

Inhomogeneous Strains and Dislocation Evolution in Surface-Treated Ni-Base Superalloys

“…A number of reports are available in recent literature [35][36][37][38] that demonstrate the application of the CMWP method to determine dislocation density and planar defects in a wide range of plastically deformed structural alloys.…”

Convergence Behavior in Line Profile Analysis Using Convolutional Multiple Whole-Profile Software

“…The measured diffraction line profile for 780-MPa-grade steel [7] was used in this study. The profiles covering the scattering vector region from 3.75 to 12.5 nm −1 , which includes six peaks ( Fig.…”

“…Thus, the optimum values are reasonably expected to coincide with these values. [7]. In that study, e was set to 0.1 (R e * = 38.9 nm) because the value is reasonable as effective radius for a dislocation.…”