Amorphization‐induced volume change and residual stresses in boron carbide

Abstract

The residual pressure surrounding quasistatic and dynamic Vickers indentations in boron carbide was quantitatively mapped in 3 dimensions using Raman spectroscopy. These maps were compared against similar maps of amorphization intensity and optical micrographs of deformed regions to determine the roles of amorphization and damage upon indentation‐induced residual stress. Stress relaxation was observed near radial cracks, spalled regions, and graphitic inclusions. A positive correlation was found between high levels of residual stress and the number of amorphized sites detected. Finite element simulations were conducted to model the indentation‐induced residual stress fields in the absence of amorphization and cracking. The simulations underpredicted the average residual pressure observed through Raman spectroscopy, implying that amorphization contributes to increased pressure in the material. This pressure is interpreted as potential evidence of volumetric expansion of the amorphized material which is less ordered and hence exerts compressive forces on the surrounding crystalline matrix.

Tuning the deformation mechanisms of boron carbide via silicon doping

“…Having both the undoped and Si-doped regions in the same boron carbide grain, we then used Vickers indentation and Raman mapping to assess whether Si doping could mitigate amorphization. Indentation with sharp indenter tips (such as Vickers and Berkovich) is a common technique to impose large shear stress and to trigger stress-induced amorphization in boron carbide (15,(21)(22)(23)(24)(25). Raman spectroscopy was then performed on the residual imprints.…”

Experimental observations of amorphization in multiple generations of boron carbide

“…The prepregged fabric was next cut Raman microscope, 3) normalizing all Raman spectra with respect to each spectra's maximum peak intensity, and 4) displaying the intensity and distribution of the ~1810 cm −1 peak as a 2D heat map. 21,22,42 A typical 2D heat map derived from a 4.9N Vickers residual impression is illustrated in Figure 5. The relative intensity of the ~1810 cm −1 peak is represented by a color scale, where red and blue mean the high and low intensity, respectively.…”

“…Shearing with and without F I G U R E 1 3 Proposed crystal structure of B-rich boron carbide based on the descriptions of Kuhlmann et al 32 A survey of the published literature modeling of CMCs has been studied by a n ers. Processes that have been modeled CVD, 17,18 CVI, [19][20][21][22] and Sol-Gel Infiltrat of alumina matrix in eight-harness satin has been studied numerically in Ref. [ proaches used in the above work general ing the flow of a high viscosity resin thr and modeling the chemical reactions and during processing.…”

“…Overall, while amorphous bands were observed in fragments, this latter analysis indicates that amorphization, A survey of the published literature shows that process modeling of CMCs has been studied by a number of researchers. Processes that have been modeled include RMI, 15,16 CVD, 17,18 CVI, [19][20][21][22] and Sol-Gel Infiltration. 23 Impregnation of alumina matrix in eight-harness satin Nextel 610 fabric has been studied numerically in Ref.…”

“…Realizing the significance of amorphization on the ballistic performance of boron carbide, numerous efforts have been devoted to understand fundamental mechanisms that activate amorphization 4,13,14,16–24 and to design strategies to mitigate amorphization. One potential mechanism that explains the detailed sequences of the amorphization process in perfect boron carbide crystals with the B 4 C stoichiometry was suggested by An et al 16,17 The authors used density functional theory (DFT) and large‐scale reactive dynamics simulations to examine simple shear deformation along multiple crystallographic orientations and found the slip system to have the lowest shear strength.…”