The quasi ternary system TiB2-CrB2-WB2 between 1500 and 1900°C and the related quasi binary subsystems

Abstract

The quasi-ternary TiB2-CrB2-WB2 and the related quasi-binary subsystems were investigated by means of hot pressing and pressureless dilatometry in the temperature range between 1650 and 1900 °C. Long-term annealing up to 14 h was necessary for equilibration. Thus, samples were obtained first by densification and then by subsequent cooling to the respective temperature with continuous annealing for up to 16 h in some cases.In all binary subsystems the low-temperature range of the solidus and the liquidus lines could be determined. The CrB2-WB2 and the TiB2-WB2 systems are of eutectic type while the CrB2-TiB2 shows a continuous solid solubility.Furthermore, the miscibility gap proposed earlier for the CrB2-TiB2 could not be proven. The borders of the large homogeneity range of the AlB2-type (Ti,W,Cr)B2 solid solution were described. The presence of less than 5 mol% of CrB2 aids accommodating W into the AlB2-structure which agrees with previous sintering studies very well. Within the ternary composition range no indication for a ternary eutectic was found up to 1900 °C. Implications of impurities to the obtained phase diagrams are discussed.