Determination of phase relations in the Co–Cu–Ti system by the diffusion triple technique

Abstract

Two isothermal sections of the Co–Cu–Ti ternary system at 973 and 1123 K were experimentally determined using the diffusion triple technique together with scanning electron microscopy and electron probe microanalysis. The solubility of Cu (substituting Co) in CoTi increased from 22.8 at.% at 973 K to 28.1 at.% at 1123 K while that of Co (substituting Cu) in CuTi decreased from 11.1 to 8.8 at.% accordingly. In addition, the solubility limits of the third element in the binary compounds CoTi2, CuTi2, Cu4Ti3, and Cu3Ti2 were remarkable. Besides the solubility change, we found the Cu2Ti phase was stable at 1123 K but disappeared at 973 K. A ternary compound “m” with a composition range covering Co10Cu57Ti33 was detected at both isothermal sections. An invariant reaction Cu4Ti3 + CoTi ↔ CuTi + m at a temperature between 973 and 1023 K was deduced. Further investigations are necessary to confirm the reactions among Cu, Cu4Ti, Cu2Ti, Cu3Ti2, and “m” between 1023 and 1123 K.

The isothermal section at 923K of the Co–Cu–Ti ternary system measured by using diffusion triple

“…Note here that this deducibility is based on the assumption that there are no other new phases appearing within the temperature and composition range involved. Although, Ti 33 Co 10 Cu 57 was reported by Pfeifer et al [5] using X-ray diffraction, however, this ternary phase was not found in the present work and our previous experiments [6]. We cannot rule out the possibility that this reported ternary compound is real, but it did not form in our diffusion triples.…”

“…We shall now compare the observed phase relations in the isothermal section at 923 K with our previous work at 973 K [6] and see if any phase reactions can be identified in the Co-Cu-Ti system between 923 and 973 K. First, the three-phase equilibria #10, #11 and #12 in this isothermal section are consistent with our previous work at 973 and 1123 K. And this area including #10, #11 and #12 is wellinosculated with the work of Pfeifer et al [5] too. Second, there are several three-phase equilibria at both temperatures involving four phases: CoTi, CuTi, Cu 4 Ti 3 and Cu 3 Ti 2 .…”

“…Liu). sections of this system at 973 and 1123 K, respectively, and an invariant reaction has been deduced and two other invariant reactions suggested [6]. In order to further study the phase relations and possible reactions, other isothermal sections at different temperatures are necessary.…”

Phase equilibria of the Cu–Dy–Ti ternary system at 973 K

“…They suggested that the formation of the CuTi 3 phase was controlled by the annealing temperature and annealing time. At the same time, it should be a metastable phase in light of the works carried out by the other groups (Massalski et al, 1986;Xu et al, 2005;Liu et al, 2006a;Wang et al, 2006) a) Author to whom correspondence should be addressed. Electronic mail: zyzmatres@163.com…”

The 473K isothermal section of the Cu–Ti–Sn ternary system

“…Cu 4 Ti, Cu 3 Ti 2 , Cu 4 Ti 3 , CuTi and CuTi 2 . Although Canale and Servant [6] recently suggested that CuTi 3 is a stable phase on the basis of their experimental results, it should be a metastable phase in light of the works carried out subsequently by the other groups [7][8][9]. In the Ti-Sn phase diagram, four binary compounds, namely Ti 3 Sn, Ti 2 Sn, Ti 5 Sn 3 and Ti 6 Sn 5 , were reported in Ref.…”