Controlled precipitation of W2B4 platelets and of β-WB nanolaminates for the in situ reinforcement of ternary TiB2–W2B4–CrB2 ceramics

Mechanical reinforcement of hard ultrahigh-temperature materials often requires complex processing techniques involving the mixing of platelet-shaped particles into the matrix – ultimately leading to inhomogeneities that compromise strength and fracture toughness. Thus, this paper investigates in situ reinforcement of a TiB2 ceramic matrix by controlled precipitation of W2B4 platelets and β-WB nanolaminates. The results showed successful precipitation of: (i) W2B4 platelets according to the phase diagram, (ii) epitaxial β-WB lamellas, and (iii) spinodal, i.e. fully coherent W-rich lamellas which change to either W2B4 platelets or β-WB during ageing. The study of phase amount and microstructure as a function of homogenization temperature and annealing temperature/time regimes allows one to control the volume fraction, size as well as aspect ratio of precipitates. This enables the control of fracture toughness affected by crack deflection, particle pull-out, crack bridging and crack branching. Composition and milling treatment most affect microstructure. Successful precipitation is possible at 1650 °C.