Dy-Ti (Dysprosium-Titanium)

Abstract

The Dy-Ti phase diagram shown in [Massalski2] was a monotectic type with the monotectic temperature at 1400 C. The miscibility gap in the liquid phase was speculated to be limited to a narrow range because a miscibility gap was observed in the Gd-Ti system and not in the Er-Ti system (atomic numbers of Gd, Dy, and Er are 64, 66, and 68, respectively). A eutectic reaction was shown at 1280 C. [2004Bul] doubted the monotectic type of this system because the Tb-Ti system is not a monotectic type (atomic number of Tb is 65). Figure 1 shows the Dy-Ti phase diagram proposed by [2004Bul], which was determined based on DTA data measured at 18 and 95 at.% Ti. The eutectic type was concluded because of the characteristic microstructure of the 18 at.% Ti alloy. According to the criteria given by [1991Oka], however, the opening angle of the L + (bTi) two-phase field at 100 at.% Ti in Fig. 1 is too broad. The initial slope of the liquidus is probably much steeper (the opening angle may be about a half). Then, it could be assumed that the phase diagram includes a monotectic reaction, as shown in [Massalski2]. This assumption does not contradict the result of [2004Bul] because a eutectic reaction also exists in the phase diagram. If the monotectic reaction does not exist, as concluded by [2004Bul], there would be a nearly horizontal section in the liquidus curve in the center region of the phase diagram. Further experimental data are needed to reach the conclusion.