Experimental reinvestigation of the Co–Nb phase diagram

High-temperature mechanical properties of Zr alloyed Fe3Al-type iron aluminide

“…Similar results were also found by Prahl et al [9]. Very recently two papers have appeared dealing with the structure and mechanical properties of the alloys within the FeeAleZr ternary system [10,11]. Unfortunately, most of the information presented there is related to the compositions very different from that tested in this paper.…”

Liquidus Projection and Reaction Scheme of the Co-Al-Nb System

“…For the Co-Al system the data of McAllister [16] are accepted except that the current DTA data show that the melting point of CoAl is at 1675°C. The Al-Nb system is adopted from Ref 17 except for the melting point of NbAl 3 and the temperature and the composition of the eutectic L M NbAl 3 + Nb 2 Al which have been recently experimentally measured and assessed, respectively, by Witusiewicz et al [13] The Co-Nb system has been re-investigated within the scope of the present project [2,15] except for the Nb-rich part which is adopted from the assessment by Hari Kumar et al [1] The compositions of the investigated alloys, of the primary phase, i.e., the phase that formed first from the melt, and of the eutectics measured by SEM-EDS and electron probe miroanalysis (EPMA), as well as liquidus temperatures and temperatures of the invariant reactions determined by DTA are summarised in Table 2. Figure 1 shows a number of micrographs of samples which are decisive for establishing the liquidus projection.…”

“…Hunt and Raman [7] reported a phase at a composition of about 26 Co, 20 Al, 54 Nb whose structure they could not identify exactly but as the x-ray diffraction (XRD) pattern was closely related to that of Co 7 Nb 6 (l phase; Fe 7 W 6 -type) they termed the phase l¢. The phase was also reported by Burnashova et al [5] The hexagonal C14 Laves phase, which is only stable above about 1250°C in the binary Co-Nb system, [2] exists in the ternary system within an extended homogeneity range even at much lower temperatures, e.g., at 800°C. [5,6] Above 1250°C the single-phase field of C14 extends from the binary system to an Al content of 55 at.%.…”

“…[1,2] A list of phases that are stable in the Co-Al-Nb system and the binary subsystems at the liquidus together with the invariant reactions involving the liquid is compiled in Table 1. Besides the binary phases a number of ternary compounds have been reported.…”

Solidification Reaction Sequence of Co-Rich Nb-Al-Co Alloys

“…This is because all three types of Laves phase, hexagonal C14 and C36 as well as cubic C15, are stable in the binary Co-Nb system. [18,19] It is this alloy system that is the subject of investigation in the current study.…”