Synthesis of hard materials by field activation:: The synthesis of solid solutions and composites in the TiB2-WB2-CrB2 system

The synthesis of solid solutions of (Ti,W,Cr)B-2 from elemental reactants using the field-activated, pressure-assisted synthesis method and employing the SPS apparatus was investigated. The nature of the products depended on temperature; they were nearly pure solid solutions at 1900 degreesC with minor amounts of P-WB. The product density and microhardness depended on the temperature of synthesis for the same value of applied pressure (64 MPa). Samples with the highest density (94%) corresponded to a hardness of 22.7 GPa. When annealed at 1500 degreesC, the solid solutions decomposed, precipitating a (W,Ti, Cr)B-2 phase in a spinodal form. In addition, P-WB precipitates in the form of thin (0.4-5.3 nm) layers were observed. They existed in a 60 degrees /120 degrees orientation to the (Ti,W,Cr)B-2 matrix, in agreement with previous observations. Highly faceted, small (nanosized) pores associated with the P-WB precipitates were also observed.