Dense fine‐grained B4C was synthesized by the spark plasma sintering (SPS) method using mechanically activated elemental powders. Relative densities of up to 95% were achieved. When characterized by X‐ray line broadening methods, the grains of the resulting product were determined to be nanometric in scale. However, transmission electron microscopy (TEM) observations showed the product to be composed of a mixture of fine (nanometric) crystallites and grains in the micrometer range. The TEM images showed a highly defective structure containing a high density of twins. Their presence is the reason for the discrepancy between the X‐ray and TEM results.
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°C with minor amounts of -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°C, the solid solutions decomposed, precipitating a (W,Ti, Cr)B 2 phase in a spinodal form. In addition, -WB precipitates in the form of thin (0.4 -5.3 nm) layers were observed. They existed in a 60°/120°orientation to the (Ti,W,Cr)B 2 matrix, in agreement with previous observations. Highly faceted, small (nanosized) pores associated with the -WB precipitates were also observed.
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