• PDF / 298,772 Bytes
• 4 Pages / 593.972 x 792 pts Page_size
• 0 Downloads / 192 Views

DOWNLOAD

REPORT

---

Section II: Phase Diagram Evaluations

The Ni-Ti-Y (Nickel-Titanium-Yttrium) System K.P. Gupta, The Indian Institute of Metals, India

Introduction Very little work has been done in the Ni-Ti-Y system. An isothermal section at low temperature has been established and reported here.

Binary Systems The Ni-Ti system (Fig. 1) [1991Nas] has three intermediate phases, Ni3Ti (q), NiTi (b) and NiTi2 (p), of which the q and the b phases melt congruently at 1380 and 1310
C, respectively. The p phase forms through a peritectic reaction L + b M p at 984
C. Three eutectic and two eutectoid reactions occur: L M bTi + p at 742
C, L M b + q at 1118
C, L M q + c at 1304
C, bTi M aTi + p at 983
C, and b M p + q at 630
C. The Ni-Y system (Fig. 2) [1991Nas] has nine intermediate phases: Ni17Y2 (d), Ni5Y (g), Ni4Y (k), Ni7Y2 (h), Ni3Y (i), Ni2Y (s), NiY (m), Ni2Y3 (f), and NiY3 (n). All these phases are of invariant compositions at all temperatures. The g and m phases melt congruently at 1430 and 1070
C, respectively. All the other phases form through peritectic reactions: L + g M d at 1330
C, L + g M k at 1340
C, L + k M h at 1698
C, L + h M i at 1237
C,

L + i M s at 1100
C, L + m M f at 820
C, and L + aY M n at 902
C. Three eutectic reactions L M c + d, L M s + m, and L M f + n occur at 1285, 950, and 902
C, respectively. The Y-Ti [1987Mur] (Fig. 3) has been experimentally determined at the Ti side and Y side only. In the intermediate composition range between Ni and Y, the phase diagram has been predicted through thermodynamic calculations that indicate a probable liquid phase immiscibility in the composition range of 30 to 80 at.% Y. At the Ti side L1 M L2 + bTi occurs at 1370
C and at the Y side bY M L + aY occurs at 1440
C and L M bTi + aY occurs at 1355
C.

Binary and Ternary Phases The three binary systems Ni-Ti, Ni-Y, and Y-Ti have 12 binary intermediate phases. No ternary intermediate has been reported in the Ni-Ti-Y system. The binary phases and their structure data are given in Table 1.

Ternary System An isothermal section of the Ni-Ti-Y system has been established by [2000Zhu]. The alloys were prepared, using

Fig. 1 Binary Ni-Ti phase diagram [1991Nas]

402

Journal of Phase Equilibria and Diffusion Vol. 30 No. 4 2009

Phase Diagram Evaluations: Section II

Fig. 2 Binary Ni-Y phase diagram [1991Nas]

Fig. 3 Binary Ti-Y phase diagram [1987Mur]

Ni of 99.999 mass% purity and Ti and Y of 99.9 mass% purity, by arc melting. In all, 119 alloys were prepared for this investigation. The Ni-rich alloys were homogenized at

900
C for 30 days, the Y-rich alloys were homogenized at 720
C for 60 days, and the other alloys were homogenized at 800
C for 45 days. After homogenization the alloys were

Journal of Phase Equilibria and Diffusion Vol. 30 No. 4 2009

403

Section II: Phase Diagram Evaluations cooled to 500
C at the rate of 10
C/h and annealed for 10 days and quenched in ice water mixture. All heat treatment was carried out in vacuum. Phase analysis of Table 1

annealed alloys and the phase boundary