Cobalt - Niobium - Tantalum

Liya Dreval, Oleksandr Dovbenko

Introduction

The recent interest in the Co-Nb-Ta system is caused by the development of Co-based superalloys. Nb and Ta are particularly considered as the elements enhancing the stability of the γʹ phase in these multicomponent superalloys. [1984Ish] studied the phase equilibria in the system at 1100°C (Table 1). This article provided a summary of the main experimental findings and presented an isothermal section. However, the authors did not include primary experimental data, such as XRD patterns, composition of phases in equilibrium, micrographs etc., in their paper that prevents any possibility to evaluate their data critically. The most intriguing feature of the isothermal section provided by [1984Ish] is that the isostructural MgCu₂-type Laves phases NbCo₂ and TaCo₂ do not form a con...