Experimental investigation of isothermal sections at 1373 and 1473 K in the Co–Nb–Ti system

Abstract The isothermal sections at 1373 and 1473 K in the Co–Nb–Ti system were constructed using annealed diffusion couples and equilibrated alloys by using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), electron probe microanalysis (EPMA), and X-ray diffraction (XRD) techniques. Three three-phase regions, Co2(Nb,Ti) + Co7Nb6 + CoTi, Co7Nb6 + CoTi + bcc(Nb,Ti), and CoTi + liquid + bcc(Nb,Ti) were determined. Co3Nb and α-Co2Ti with a C36 crystal structure, and Co2Nb and β-Co2Ti with a C15 crystal structure at 1373 and 1473 K formed continuous solid solutions Co3(Nb,Ti) and Co2(Nb,Ti), respectively. The solubilities of Ti in Co7Nb6 and Nb in CoTi are determined to be ~11.4 at.% and ~22.3 at.% at 1373 K, and ~12.5 at.% and ~24.8 at.% at 1473 K, respectively. No ternary compounds were observed.