In situ SHS-pseudo-HIP as an effective method to develop neutron shielding ceramic matrix composites from quaternary Ti-B-Cr-C system

Abstract

Highly refractory composites with predominant volume fraction of TiB 2 , were “in situ” synthesized and consolidated. The production process was carried out using elemental powders by means of self-propagating high-temperature synthesis under pseudo-hot isostatic pressure (SHS-pseudo-HIP). The Ti:B atomic ratio corresponded to TiB 2 formation, and Cr:C atomic ratio has been established in (3:2) molar ratio. Based on scanning electron images (SEI), very high relative density was obtained with nearly full densification in composite with intended 85vol.% of TiB 2 , which is sufficiently high concentration of boron from the perspective of neutron shielding. However XRD results indicated formation of CrB and TiC, next to TiB 2 . This clearly indicates no equilibrium in pseudo-binary TiB 2 -Cr 3 C 2 system. Besides, broadened peaks in XRD patterns as well as gradient of composition in EDS maps may indicate solid solutions, especially (Ti,Cr)C. The existence of (Ti,Cr) solid solutions and ternary compounds is possible, considering Hume-Rothery rules for hypothetical mutual solubility.