- Email: [email protected]
Determination of phase equilibria in the systems YZrMo and YHfMo at 1273 K
Journal of the Less-Common
263
Metals, 163 (1990) 263-267
DETERMINATION OF PHASE EQUILIBRIA IN THE SYSTEMS Y-Zr-MO AND Y-HI-MO AT 1273 K DIN DAOYUN and ZHANG JIUXING Department of Materials Science and Engineering, (China)
Central South Universiry of Technology
Changsha
(Received March 10, 1990)
Summary The phase equilibria in the systems Y-Zr-Mo and Y-Hf-Mo at 1273 K were investigated by means of a diffusion triple technique and electron microprobe analysis. Four phases coexist in each ternary system and the experimental information obtained was used to construct the isothermal sections of the phase diagrams at 1273 K.
1. Introduction Many studies on the use of rare earth metals in non-ferrous alloys have been conducted. However, most of these have concentrated on rare earth magnetic materials or on the addition of rare earths to aluminium and copper alloys to improve their properties. Little is known about the effect of rare earths on refractory metals and their alloys, and therefore investigations of the phase equilibrium between rare earths and refractory metals are important. The information obtained from such studies will be very useful for the development and, use of refractory metals and their alloys. A diffusion triple technique [l, 21 is employed in the present work to determine the phase equilibria in the systems Y-Zr-Mo and Y-Hf-Mo, about which no information is currently available. This technique, which is based on the principle of inter-facial local equilibrium, is an effective method of determining ternary isothermal sections and has been applied successfully to several systems. The present work tends to verify the validity of the technique to ternary systems with rare earth components.
2. Experimental details The pure components zirconium (99.8 wt.%), hafnium (99.95 wt.%) and molybdenum (99.9 wt.%) were annealed in a furnace under a vacuum of better 0022-5088/9O/S3.50
0 Elsevier Sequoia/Printed
in The Netherlands
264
than 1O-3 Torr to remove gases and to increase their purity. The purity of the yttrium used was 99.95 wt.%. The pure components were used to make the Y-Zr-Mo and Y-Hf-Mo diffusion triples as described in ref. 1. To prevent oxidation and contamination, all of the grinding and polishing process was conducted in kerosene and the components were washed with water-free ethanol in an ultrasonic wash basin before assembly. The diffusion triples were wrapped in a molybdenum film and then sealed in a quartz capsule containing argon at a pressure of 380 mmHg. To purify the argon and absorb harmful gases remaining in the capsule, Zr-16Al alloy was placed at one end of the capsule to serve as a gas-absorbing agent. The sealed quartz capsule containing the triples was placed in a furnace to be diffusion annealed. The Zr-16Al end was placed inside the furnace while the specimen end remained outside, and the temperature was raised to 673-773 K to allow the gas-absorbing agent to do its job. Then the specimen end of the capsule was moved into the constant temperature zone of the furnace, and the temperature was increased to 1273 f 2 K. After 500 h the capsule was broken and the triples were quenched into liquid nitrogen. The diffusion triples were analysed with a Superprobeand a Camebaxmicro Cameca set with an accelerating voltage of 20 kV and an electrical current of
(c)
Y
Fig. 1. Phase distribution in the Y-Zr-Mo diffusion triple annealed at 1273 K for 500 h: (a) backscattered electron image (BEI); (b) BE1 and scanning curves of the zirconium and molybdenum content; (c) schematic diagram.
265
lo-* A. The yttrium, zirconium, hafnium and molybdenum standards taken from parts of the components far away from the diffusion region. 5 x
were
3. Results and discussion Since yttrium is very active physically and chemically and is rather different in terms of hardness from zirconium, hafnium and molybdenum, during preparation of the diffusion triples there were problems firstly of preventing contamination of the yttrium and secondly of having a tight contact between the components. To overcome these difficulties different grinding and coupling methods were tried. One method was to make the triples on the base of a binary diffusion couple. This method succeeded in making a diffusion triple with a rare earth metal component, but it had the disadvantages of consuming larger quantities of protecting materials and of requiring more working procedures and longer working cycles. We therefore made the Y-Zr-Mo and Y-Hf-MO diffusion triples directly in the present research. The phase distribution in the diffusion triple annealed at 1273 K for 500 h is shown in Figs. 1 and 2 for the Y-Zr-Mo and Y-Hf-Mo systems respectively. Four phases coexist in the Y-Zr-Mo system at 1273 K: a-yttrium, p-zirconium, b.c.c. molybdenum and a ,ul intermetallic phase. There are two three-
.--’ 1\ ----I
a -Hf:
MO : :
de_
Cc)
114
a
--Y
flf
Y -_I
_____
Y
Fig. 2. Phase distribution in the Y-Hf-Mo diffusion triple annealed at 1273 K for 500 h: (a) BEI; jb) BEI and scanning curves for the hafnium and molybdenum contents; (c) schematic diagram.
266
phase regions: a-yttrium + b.c.c. molybdenum + p1 and a-yttrium + p-zirconium, and five two-phase regions: b.c.c. molybdenum + p 1, p 1+ /?-zirconium, a-yttrium + /3-zirconium, a-yttrium + b.c.c. molybdenum and a-yttrium + ,~r. The ,uu,phase is a non-linear compound with a composition range around Mo2Zr, and the solubility of yttrium in this phase is very low. The exact composition range of the ,u1 phase will be determined in future work. Four phases also coexist in the Y-Hf-MO system at 1273 K: a-yttrium, a-hafnium, b.c.c. molybdenum and a y, phase. There are two three-phase regions: a-yttrium + b.c.c. molybdenum + pu2 and a-yttrium + a-hafnium + p,, and five two-phase regions: a-yttrium + b.c.c. molybdenum, b.c.c. molybdenum + ,u,, ayttrium+pu,, a-hafnium+pu, and a-yttrium+ a-hafnium. The ,u2 phase exists in the composition range 32.6-34.5 at.% hafnium. The solubility of yttrium in this phase is also very low. The isothermal sections of the Y-Zr-Mo and Y-IS-MO systems obtained by means of electron microprobe analysis are presented in Figs. 3 and 4. The phase boundaries, which were drawn by hand, are in general agreement with the wellknown binary phase diagrams which should hold on three sides of the ternary phase diagram [3].
Fig. 3. Isothermal section of the Y-Zr-Mo
system at 1273 K. The dots are the experimental points.
267
MO
10
20
30
40
50
60
70
80
90
.. --Ilf(at.K) Fig. 4. Isothermal section of the Y-Hf-Mo
system at 1273 K. The dots are the experimental points.
4. Conclusions
(1) The isothermal sections of the Y-Zr-Mo and Y-Hf-MO phase diagrams at 1273 K were surveyed by means of a diffusion triple technique. The results demonstrate that this technique is an effective means of determining ternary phase diagrams with rare earth metal components. However, special care must be taken in preparing the samples because of the active properties of rare earth metals. (2) Four phases coexist in both the Y-Zr-Mo and the Y-Hf-Mo systems at 1273 K: a-yttrium, /3-zirconium, b.c.c. molybdenum and p1 for the Y-Zr-Mo system, and a-yttrium, a-hafnium, b.c.c. molybdenum and ,u2 for the Y-Hf-Mo system. Both the p1 and ,L+phases are non-linear compounds.
References 1 Jin Zhanpeng, Stand. J. Metall., IO ( 198 1) 279. 2 M. Hasebe and T. Nishizawa, Application of Phase Diagrams in Metallurgy and Ceramics, NBS Special Pub. 4%, Vol. 2,1978, p. 911. 3 T. B. MassaIski, J. L. Murray, L. H. Bennett and H. Baker, Binary Alloy Phase Diagrams, ASM, Metals Park, OH, 1986.
263
Metals, 163 (1990) 263-267
DETERMINATION OF PHASE EQUILIBRIA IN THE SYSTEMS Y-Zr-MO AND Y-HI-MO AT 1273 K DIN DAOYUN and ZHANG JIUXING Department of Materials Science and Engineering, (China)
Central South Universiry of Technology
Changsha
(Received March 10, 1990)
Summary The phase equilibria in the systems Y-Zr-Mo and Y-Hf-Mo at 1273 K were investigated by means of a diffusion triple technique and electron microprobe analysis. Four phases coexist in each ternary system and the experimental information obtained was used to construct the isothermal sections of the phase diagrams at 1273 K.
1. Introduction Many studies on the use of rare earth metals in non-ferrous alloys have been conducted. However, most of these have concentrated on rare earth magnetic materials or on the addition of rare earths to aluminium and copper alloys to improve their properties. Little is known about the effect of rare earths on refractory metals and their alloys, and therefore investigations of the phase equilibrium between rare earths and refractory metals are important. The information obtained from such studies will be very useful for the development and, use of refractory metals and their alloys. A diffusion triple technique [l, 21 is employed in the present work to determine the phase equilibria in the systems Y-Zr-Mo and Y-Hf-Mo, about which no information is currently available. This technique, which is based on the principle of inter-facial local equilibrium, is an effective method of determining ternary isothermal sections and has been applied successfully to several systems. The present work tends to verify the validity of the technique to ternary systems with rare earth components.
2. Experimental details The pure components zirconium (99.8 wt.%), hafnium (99.95 wt.%) and molybdenum (99.9 wt.%) were annealed in a furnace under a vacuum of better 0022-5088/9O/S3.50
0 Elsevier Sequoia/Printed
in The Netherlands
264
than 1O-3 Torr to remove gases and to increase their purity. The purity of the yttrium used was 99.95 wt.%. The pure components were used to make the Y-Zr-Mo and Y-Hf-Mo diffusion triples as described in ref. 1. To prevent oxidation and contamination, all of the grinding and polishing process was conducted in kerosene and the components were washed with water-free ethanol in an ultrasonic wash basin before assembly. The diffusion triples were wrapped in a molybdenum film and then sealed in a quartz capsule containing argon at a pressure of 380 mmHg. To purify the argon and absorb harmful gases remaining in the capsule, Zr-16Al alloy was placed at one end of the capsule to serve as a gas-absorbing agent. The sealed quartz capsule containing the triples was placed in a furnace to be diffusion annealed. The Zr-16Al end was placed inside the furnace while the specimen end remained outside, and the temperature was raised to 673-773 K to allow the gas-absorbing agent to do its job. Then the specimen end of the capsule was moved into the constant temperature zone of the furnace, and the temperature was increased to 1273 f 2 K. After 500 h the capsule was broken and the triples were quenched into liquid nitrogen. The diffusion triples were analysed with a Superprobeand a Camebaxmicro Cameca set with an accelerating voltage of 20 kV and an electrical current of
(c)
Y
Fig. 1. Phase distribution in the Y-Zr-Mo diffusion triple annealed at 1273 K for 500 h: (a) backscattered electron image (BEI); (b) BE1 and scanning curves of the zirconium and molybdenum content; (c) schematic diagram.
265
lo-* A. The yttrium, zirconium, hafnium and molybdenum standards taken from parts of the components far away from the diffusion region. 5 x
were
3. Results and discussion Since yttrium is very active physically and chemically and is rather different in terms of hardness from zirconium, hafnium and molybdenum, during preparation of the diffusion triples there were problems firstly of preventing contamination of the yttrium and secondly of having a tight contact between the components. To overcome these difficulties different grinding and coupling methods were tried. One method was to make the triples on the base of a binary diffusion couple. This method succeeded in making a diffusion triple with a rare earth metal component, but it had the disadvantages of consuming larger quantities of protecting materials and of requiring more working procedures and longer working cycles. We therefore made the Y-Zr-Mo and Y-Hf-MO diffusion triples directly in the present research. The phase distribution in the diffusion triple annealed at 1273 K for 500 h is shown in Figs. 1 and 2 for the Y-Zr-Mo and Y-Hf-Mo systems respectively. Four phases coexist in the Y-Zr-Mo system at 1273 K: a-yttrium, p-zirconium, b.c.c. molybdenum and a ,ul intermetallic phase. There are two three-
.--’ 1\ ----I
a -Hf:
MO : :
de_
Cc)
114
a
--Y
flf
Y -_I
_____
Y
Fig. 2. Phase distribution in the Y-Hf-Mo diffusion triple annealed at 1273 K for 500 h: (a) BEI; jb) BEI and scanning curves for the hafnium and molybdenum contents; (c) schematic diagram.
266
phase regions: a-yttrium + b.c.c. molybdenum + p1 and a-yttrium + p-zirconium, and five two-phase regions: b.c.c. molybdenum + p 1, p 1+ /?-zirconium, a-yttrium + /3-zirconium, a-yttrium + b.c.c. molybdenum and a-yttrium + ,~r. The ,uu,phase is a non-linear compound with a composition range around Mo2Zr, and the solubility of yttrium in this phase is very low. The exact composition range of the ,u1 phase will be determined in future work. Four phases also coexist in the Y-Hf-MO system at 1273 K: a-yttrium, a-hafnium, b.c.c. molybdenum and a y, phase. There are two three-phase regions: a-yttrium + b.c.c. molybdenum + pu2 and a-yttrium + a-hafnium + p,, and five two-phase regions: a-yttrium + b.c.c. molybdenum, b.c.c. molybdenum + ,u,, ayttrium+pu,, a-hafnium+pu, and a-yttrium+ a-hafnium. The ,u2 phase exists in the composition range 32.6-34.5 at.% hafnium. The solubility of yttrium in this phase is also very low. The isothermal sections of the Y-Zr-Mo and Y-IS-MO systems obtained by means of electron microprobe analysis are presented in Figs. 3 and 4. The phase boundaries, which were drawn by hand, are in general agreement with the wellknown binary phase diagrams which should hold on three sides of the ternary phase diagram [3].
Fig. 3. Isothermal section of the Y-Zr-Mo
system at 1273 K. The dots are the experimental points.
267
MO
10
20
30
40
50
60
70
80
90
.. --Ilf(at.K) Fig. 4. Isothermal section of the Y-Hf-Mo
system at 1273 K. The dots are the experimental points.
4. Conclusions
(1) The isothermal sections of the Y-Zr-Mo and Y-Hf-MO phase diagrams at 1273 K were surveyed by means of a diffusion triple technique. The results demonstrate that this technique is an effective means of determining ternary phase diagrams with rare earth metal components. However, special care must be taken in preparing the samples because of the active properties of rare earth metals. (2) Four phases coexist in both the Y-Zr-Mo and the Y-Hf-Mo systems at 1273 K: a-yttrium, /3-zirconium, b.c.c. molybdenum and p1 for the Y-Zr-Mo system, and a-yttrium, a-hafnium, b.c.c. molybdenum and ,u2 for the Y-Hf-Mo system. Both the p1 and ,L+phases are non-linear compounds.
References 1 Jin Zhanpeng, Stand. J. Metall., IO ( 198 1) 279. 2 M. Hasebe and T. Nishizawa, Application of Phase Diagrams in Metallurgy and Ceramics, NBS Special Pub. 4%, Vol. 2,1978, p. 911. 3 T. B. MassaIski, J. L. Murray, L. H. Bennett and H. Baker, Binary Alloy Phase Diagrams, ASM, Metals Park, OH, 1986.