Liquidus projection and reaction scheme of the Co-Al-Nb system

Abstract

By metallographic observation of the as-cast microstructures, determination of the liquidus temperatures and the temperatures of invariant reactions by differential thermal analysis, and measurement of the compositions of the primary phases and the eutectic residuals by electron probe miroanalysis, a liquidus projection for the Co-Al-Nb systemhas been established for the first time. The binary Co-Nb intermetallic phases have a large solid solubility for Al and their melting temperatures increase markedly by the addition of Al. The only ternary compound, the Heusler phase NbCo2Al, melts incongruently at about 1485 °C. ByCALPHADmodelling the consistency of the experimental data has been checked. Calculated and experimentally determined temperatures of the invariant reactions are in good agreement and are summarised within a reaction scheme. © ASM International.