Hyper-Doping of Boron Carbide Ablators

Project Overview

The goals of this project were to (1) demonstrate the feasibility of doping boron carbide (B4C) using a co-sputter deposition method (2) and determine the effects on film growth modes and residual stress of B4C doped with silicon (Si) and molybdenum (Mo) dopants over a wide range of dopant concentration (exceeding 50 atomic (at.) %, i.e., hyper-doping) in the ultrathick regime (> 1 µm). This study included the use of Monte-Carlo method simulations to initially assess the angular and spatial distribution of B4C and dopant across a 3" substrate area in a co-sputtering configuration. This model-guided approach resulted in the synthesis of wide compositional ranges of Mo and Si hyper-doped B4C coatings. We demonstrated that the incorporation of Mo and Si into B4C can be achieved in concentrations exceeding 50 at.%. While the underlying surface microstructure of coatings is shown to be granular, the presence of these dopants may promote the growth of B3OH3 crystal growth on the surface of the coatings on films deposited at oblique angles. The evolution of residual stress as a function of dopant concentration has been determined for each dopant. The inclusion of both types of dopants is shown to reduce the compressive stress in films, however the concentrations needed to achieve this effect are understood to be dependent on the dopant type.

Mission Impact

This project supports the High Energy Density Science core competency area. It has clearly demonstrated the B4C can be effectively doped using magnetron sputter deposition over a wide concentration gradient with both Mo, and Si with residual stresses (< 1 GPa). This project focused on the development of new materials for future HED and ICF experiments that are beyond our current capabilities, as well as for future IFE applications.