Metastable Phases in Fe75Sn25-Co75Sn25 Alloys
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Short Notes Kl15 phys. stat. sol. (a)?, Kl15 (1982) Subject classification: 1.3; 21.1.1 Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasil ) Metastable Phases in Fe75g25-C05gn25 Alloys BY V.K. SINGH, M. SINGH, and S. BHAN Bhan and Kudielka /1/ using a high temperature diffraction camera showed the existence of ordered high-temperature b. c. c. phases (B2, D028, B32) in a number of systems involving transition elements of group VIII and B-subgroup elements of groups LII, IV, and V. In the Ni-Si system, the authors reported a B2 structure in the composition range Ni75Si25 and in a narrow temperature range near the melting point. Since Ni-Si and Co-Sn are homologous systems it was natural to think that there should be a B2 phase in the other system also. Based on this reasoning, Schluckebier et al. /2/ obtained a metastable A2 phase at the composition C O,~S~~ by the splat cooling technique. In fact the A2 phase was appearing in Co75Sn12. 5Si12. alloy without application of extreme cooling rates /2/. The elements Fe and Co also come in the same category and the phase diagrams of Fe-Sn and Co-Sn are similar in many respects. Therefore, it was planned to subject the alloys in the composition range Fe,5S%5-Co,5S35 to rapid cooling from the melt by the given technique (splat cooling) /3/. The alloys were melted in evacuated and sealed silica tubes in a high fre- quency induction furnace. After melting, the alloys were homogenized for 12 h at 800 OC. The mortored powders were again annealed at different tem- peratures and water quenched. The results were found consistent with the existing literature as given in Table 1. The alloys subjected to splat cooling were analysed by X-ray diffraction and electron diffraction techniques. All the X-ray photographs showed a simple b.c.c. pattern with a (100) superlattice reflection. The X-ray dif- fraction data are given in Table 2. It is known that in NiAl the ordered B2 structure is stable upto the melting point. Also the calculations on interchange energies in b. c. c. ordered alloys in related systems show the stability of the ordered arrangement upto the melting point. 1) Varanasi 221 005, India.
Transcript of Metastable Phases in Fe75Sn25-Co75Sn25 Alloys
Short Notes Kl15
phys. stat. sol. (a)?, Kl15 (1982) Subject classification: 1.3; 21.1.1 Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasil ) Metastable Phases in Fe75g25-C05gn25 Alloys
BY V.K. SINGH, M. SINGH, and S. BHAN
Bhan and Kudielka /1/ using a high temperature diffraction camera showed the existence of ordered high-temperature b. c. c. phases (B2, D028, B32) in a number of systems involving transition elements of group VIII and B-subgroup elements of groups LII, IV, and V. In the Ni-Si system, the authors reported a B2 structure in the composition range Ni75Si25 and in a narrow temperature range near the melting point. Since Ni-Si and Co-Sn a re homologous systems it was natural to think that there should be a B2 phase in the other system also. Based on this reasoning, Schluckebier et al. /2/ obtained a metastable A2 phase at the composition C O , ~ S ~ ~ by the splat cooling technique. In fact the A2 phase was appearing in Co75Sn12. 5Si12. alloy without application of extreme cooling rates /2/. The elements F e and Co also come in the same category and the phase diagrams of Fe-Sn and Co-Sn a re similar in many respects. Therefore, it was planned to subject the alloys in the composition range Fe,5S%5-Co,5S35 to rapid cooling from the melt by the given technique (splat cooling) /3/.
The alloys were melted in evacuated and sealed silica tubes in a high fre- quency induction furnace. After melting, the alloys were homogenized f o r 1 2 h at 800 OC. The mortored powders were again annealed at different tem- peratures and water quenched. The results were found consistent with the existing literature as given in Table 1.
The alloys subjected to splat cooling were analysed by X-ray diffraction and electron diffraction techniques. All the X-ray photographs showed a simple b.c.c. pattern with a (100) superlattice reflection. The X-ray dif-
fraction data a re given in Table 2. It is known that in NiAl the ordered B2 structure is stable upto the melting point. Also the calculations on interchange energies in b. c. c. ordered alloys in related systems show the stability of
the ordered arrangement upto the melting point.
1) Varanasi 221 005, India.
Kl16 physica status solidi (a) 74
T a b l e 1
X-ray diffraction results on quenched powders
goo OC, 6 h, WQ
8o0°C, 12 h, WQ
alloy composition heat treatment
i) Fel. $n, B82-Ni21n type /4/
ii) Fe(Sn), A2
i) Fel. 3Sn, B82-Ni2In type
ii) Fe(Sn), A2
1 Fe75S%5
Fe65Col OSn25
Fe35C040Sn25
Fe5C 70'35
075Sn25
70c05s%? 5
8OO0C, 12 h, WQ i) Fel. 3Sn, B82-Ni21n type ii) Fe(Sn), A2
8o0°C, 12 h, WQ i) Co3Sn2, Bf$-NiAs type /5/ ii) Fe(Sn), A2
i) Cogs%, B81-NiAs type
ii) Co(Sn), Al
i) Cogs%, B81-NiAs type ii) Co(Sn), Al
8OO0C, 12 h, WQ
8OO0C, 12 h, WQ
alloy composition phases present (at%)
lattice constants (XI
Since there is a close relationship between CsCl(B2) and NiAs(B8) types of structures, it is easier for the transformation to yield the B2 structure instead of the disordered A2. Comparison of X-ray powder photographs of B2 and B8
indicates that (110) and (012) reflections of B8 merge to yield the (110) re-
flection of B2 while the (1 01 ) reflection of B8 becomes the (1 00) reflection of B2.
Fe 75sn2 5 Fe70C05S%5
Fe35C040Sn25
Fe65C01 OSn25
Fe5C070Sn25
Co75Sn25
T a b l e 2
b.c.c. B2 type 2.989 b.c.c. B2 type 2.980
b.c.c. B2 type 2.971
b.c.c. B2 type 2.934
b.c.c. B2 type 2.945
b.c.c. B2 type 2.939
Lattice constants of splat cooled alloys
-. 4 --__ --. Fig. 1 shows the variation of
l0lor5%5 lattice constants of splat cooled -
ameter with composition in splat cooled alloys
Fe75S%5-Co75S%5 alloys. There is no linear relationship between the lattice constants and the composition. The contraction of the lattice in the splat cooled ternary alloys indicates the exist- ence of ordering in the lattice.
References
/1/ S. BHAN and H. KUDIELKA, Z. Metallk. 9, 333 (1918).
/ 2 / G . SCHLUCKEBIER, E. WACHTEL, and B. PREDEL, Z. Metallk. 3
/3/ P. DUWEZ and R.E. WILLENS, Trans.MS AIME 22, 362 (1963).
/4/ M. ASANUMA, J. Phys. SOC. J a p a n s 1343 (1960).
/5/ M. ASANUMA, J. Phys. SOC. Japan -' 1 7 300 (1962).
456 (1980).
(Received September 22, 1982)
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