Optimisation of W2B-W composites for radiation attenuation and thermal-mechanical performance

The neutronics and engineering properties of a composite radiation shielding material, W2B-W, are systemati-cally investigated. Neutronics calculations using the MCNP code indicate that each additional 1 % volume fraction W2B reduces the neutron energy flux into the superconducting core by 0.4-0.9 %, and reduces the gamma flux by 1.0-2.2 %, depending on the shield thickness. Materials with W2B volume fractions of 43 and 89 % are fabricated by vacuum hot-pressing, resulting in a microstructure in which the dominant interpenetrating phase was W and W2B respectively. For the W2B-dominant material the thermophysical and mechanical prop-erties were inferior. For example, room temperature flexural strength, fracture toughness, and thermal con-ductivity were all lower (by-25%, 30% and 40% respectively). Also, the brittle to ductile transition temperature was-500 degrees C higher. The results indicate that when considering boride content there is an important trade-off between shielding performance and thermal stress resistance.