AN X - R A Y D I F F R A C T I O N I N V E S T I G A T I O N

S Y S T E M S T i - N i - B , M o - N i - B , A N D W - N i - B

Y u . B. K u z ' m a a n d M. V. C h e p i g a

OF THE

Binary Systems. A detailed descr ipt ion of the Ti-B constitution diagram was given in [1]. According to the Mo-B constitution diagram, the following compounds form in this system: Mo2B-per i tec t ic react ion at ~2270~ CuA12 type s t ruc ture M o B - a n open maximum at 2550~ the polymorphic t ransformat ion of CrB type s t ruc ture into MoB type occurs at ~2000-1900~ MoB2-per i tec t ic react ion at .~2350~ eutectoid decomposit ion at ~1500~ A1B 2 type s t ructure ; Mo2Bs-per i tect ic react ion at ~2200~ homogeneity region ~69-75 at,% B at 1400~ a specific type of s t ructure; and MoB12-an open maximum at ,~2110~ [2]. The compound Mo3R 2 (U3Si 2 type), repor ted in [3], was not detected in [2]. In another work [4], it was found that the bo ron- r i ch compound has the approximate composit ion MoB 4 and a WB 4 type s t ruc ture (a = 5.22, c = 6.39 A). The sys tem W-B has been descr ibed by the present authors [5].

In recent years , three var iants of constitution d iagram have been reported for the sys tem Ni -B [6-9]. In the region up to 50 at.% B, all three d iagrams show the compounds Ni3B, Ni2B , p, m-Ni4B3, and NiB, the only differences being in the t empera tu res and modes of formation of the compounds. In a more bo ron- r i ch par t of the system, no compounds were discovered in [6], while in [7, 8] there was found the compound NiB12 with a cubic s t ruc ture (a = 7.377 kX) and in [9] the compound NiB 2 with an unknown s t ruc - ture. Data on the crysta l l ine s t ruc tures of nickel borides have been reported in [10].

In the sys tem Ti -Ni , the compounds TiNi 3 (hexagonal s t ructure , a = 5o1010, c = 8.3067 A) and TiNi (CsC1 type, a = 3.013-3.015 A) form with open maxima at 1380 and 1310~ respect ively, and the compound Ti2Ni (cubic s t ructure , a = 11.333 A) by per i tec t ic react ion at 984~ The solubility of Ti in Ni at 800~ is ~10 at.% and that of Ni in f l - T i is 4 at.% [11, 12].

The compounds MoNi 4 and MoNi 3 form by peri tectoid react ions at ~970 and ~860~ respect ively; the fo rmer has a te tragonal s t ruc ture (a = 5.683, c = 3.592 A) and the la t ter a TiCu 3 type s t ruc ture ( a = 5.064, b = 4.224, c = 4.448 A) [11-13]. A per i tect ic react ion at ~1350~ yields the compound MoNi [11-13] with a complex tetragonal s t ruc ture (a = 9.108, c = 8.852 A) [14, 15]. Nickel at 800~ dissolves 16 at.% Mo, while the solubility of Ni in Mo is negoligible [11-13]. In the sys tem W-Ni, only one compound, WNi 4 (MoNi 4 type s t ructure , a = 5.730, c = 3.553 A), forms by peri tectoid react ion at ~970~ at 800~ nickel dissolves 13 at.% W [11, 12].

In view of the d iscrepancies in data relating to the boron- r i ch par ts of the sys tems Ni -B, Mo-B, and W - B , in the present work we res t r i c ted ourse lves to studying the sys tems T i - N i - B , M o - N i - B , and W - N i - B at boron contents of up to 60-70 at.%.

EXPERIMENTAL PROCEDURE

Specimens for investigation were prepared from Ti (99.5%), Mo (99.98%), W (99.98%), Ni (99.99%), and B (99.3%) powders, which were pressed and melted in the required proportions in an arc furnace with an argon atmosphere. Specimens of the system Ti-Ni-B were annealed at 800~ in evacuated quartz am- poules for 670 h. The nickel-rich specimens of the systems Mo-Ni-B and W-Ni-B (containing up to 20 at.% Mo) were annealed in Al203 crucibles in a vacuum furnace at 1200~ for I0 h, after which the tempera- ture was slowly lowered to 800~ (cooling rate 50 deg C/h); the remaining specimens were annealed at 1400~ (20 h, vacuum, Al203 crucibles) and also cooled to 800~ Next, all the specimens were annealed in evacuated quartz ampoules at 800~ for 240-670 h (depending on the composition).

System Ti-Ni-Bo A partial investigation of the system Ti-Ni-B in a nickel-rich region (up to 25 at.% Ti and 37 at.% B) was conducted in [16] and the existence of the compound Ti2.TNi20.3B~ (~--phase) with

I. Franko Lenin Order L 'vov State University. Transla ted from Poroshkovaya Metallurgiya, No. 10 (82), pp. 71-75, October, 1969. Original ar t icle submitted Februa ry 28, 1968.

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'v'B/l~/~'/ .~' / / / l / / .11. '~T,~ M-,,v4z~ t~f../~//,~/" .~ /~ II I1\\ ~ - - ~ B . ~ / / / j - / / / // 11 II \ \

Y" fl II ~ \\

N ~ TI TiNi 3 TiN/ Ti 2 NJ

Fig. 1. I so thermal section of par t of sys - tem T i - N i - B at 800~

lished of the compound Mo2NiB 2 with an unknown

a W2Cr21C 6 type s t ruc ture (a = 10.507-10.538 A) was es tab- lished. The T -phase is in equilibrium with a N i -ba se solid solution and the binary compounds TiNi3, Ni3B , and TiB2, while the binary compound TiB 2 is in equil ibrium with TiNi 3 and Ni2B. The existence of T -phase in the sys tem T i - N i - B was confirmed independently in [17, 18].

The resul ts of our investigation of the sys tem T i - N i - B in the range up to 60 at.% B at 800~ are presented in Fig. 1. The homogeneity region of ~--phase extends f rom 6.9 to 10 at.% Ti (boron content 20.6 at.%) and is bounded by the composit ion Ti2Ni21B6 and Ti3Ni20B 6, the lattice constants a varying from 10.524 to 10.533A, r e - spectively. The compound TiB 2 is in equilibrium with all nickel borides, T-phase , and all compounds in the sys tem Ti -Ni . In nickel borides, t i tanium is vir tual ly insoluble. Boron shows negligible solubility in the compounds of the sys tem T i - N i and has little effect on their lat t ice constants .

System M o - N i - B . In [19], the existence was es tab- crys ta l l ine s t ructure . A study of phase equil ibrium in the

sys tem M o - N i - B at up to 50 at.% B was ca r r i ed out in [20] and the compound MoNiB with a unknown s t ruc - ture (M-phase) was discovered; la ter [21], the composit ion of this compound was changed to Mo2NiB 2 and the s t ruc ture of this compound was found to be te t ragonal (a = 10o036, c = 11.952 A). One of the present authors, in collaborat ion with Kripyakevich and Skolozdra, determined the crys ta l l ine s t ruc ture of the com- pound Mo2NiB 2 (rhombic crys ta l lographic sys tem, specific type of s t ructure, a = 4.55, b = 7.07, c = 3.18 /~) [22]; s imi la r data onthe s t ructure of Mo2NiB 2 were obtained in [23]. Another x - r a y diffract ion invest igation of the sys tem M o - N i - B confirmed the existence of the compound Mo2NiB 2 and d iscovered new compounds with unknown crysta l l ine s t ruc tures : a) at the composit ion 15 ato% Mo, 30 at.% Ni, and 55 at.% B; b) Mo 3 NiB G (it was found impossible to obtain this compound in a pure form); in addition, it is noted that nickel s tabil izes the h igh- tempera ture modification f i-MoB [24].

| �9 0 0 �9 �9 �9 @ �9

�9 �9 �9 ~ M O B

O 0 Q

O 0

0

�9 �9

0

�9 �9

iVJ MoN,, MoN5 MoNi ~

Fig. 2. I so thermal section of par t of sys tem M o ' N i - B at 800~

833

This rev iew of l i t e r a tu re data on the s y s t e m M o - N i - B demons t r a t e s the need for fu r the r study of the s y s t e m M o - N i - B in a region containing m o r e than 33 at.% B.

Phase equi l ibr ia in the s y s t e m M o - N i - B were studied by us at 800~ (Fig. 2). We were able to con- f i r m the exis tence of the compound Mo2NiB 2 and es tab l i sh the p r e sence of another compound (Y-phase) with an unknown crys ta l l ine s t ruc tu re and a homogenei ty region bounded by the composi t ion 40-42.5 at.% Mo, 15-12.5 at.% Ni, and 45 at.% B. As can be seen f rom Fig. 2, the phase equi l ibr ia in the sy s t em M o - N i - B signif icantly d i f fe r f rom those repor ted in [20, 21]. According to our data, the compound Mo2Nit~ 2 (w-phase) is not in equi l ibr ium with Ni4I ~ and NiB, while for the compound a - M o B an equi l ibr ium with Ni4B 3 and Ni2B is observed . No b o r o n - r i c h compounds, noted in [24], were found by us at 800~ all spec imens in this pa r t of the s y s t e m have a t h r e e - p h a s e s t ruc tu re (Mo2B 5 + s - M o B + m-Ni4B3}. It cannot be ruled out that the d i f fe rences between our data and those repor ted in [20, 21, 24] a r e at l eas t pa r t ly due to the dif- ferent annealing t e m p e r a t u r e s employed. A detai led invest igat ion of n i cke l - r i ch spec imens of the s y s t e m M o - N i - B has conf i rmed our conclusion that a compound with a W2Cr2tC 6 type s t ruc tu re (T-phase) does not exis t [25]~

Sys tem W - N i - B . E a r l i e r invest igat ions [22, 23] have es tabl ished the exis tence of the compound o

W2NiB 2 with a rhombic , Mo2NiB 2 type s t ruc tu re (a = 4.55, b = 7.07, c = 3.17 A). An x - r a y dif f ract ion study of spec imens of this s y s t e m d i scovered two compounds with the approx imate composi t ions W3NiB 2 (this compound was not obtained in a pure form) and WNi4Bt5 [24]. Up to now, the const i tut ion d i a g r a m of the s y s t e m W - N i - B has not been examined.

Our invest igat ion of the s y s t e m W - N i - B covered composi t ions up to 67 at.% B at a t e m p e r a t u r e of 800~ and yielded the resu l t s shown i~ Fig. 3. In addition to the p rev ious ly known compound W2NiB 2 (w- phase) , we found the p r e s e n c e of another compound at the composi t ion 42.5 ato% W, 12.5 at.% Ni, and 45 at.% B (Y-phase), in equi l ibr ium with the compounds W2NiB2, W2Bs, and (~-WB. The Y-phase of the s y s t e m W - N i - B is i s o s t r u c t u r ~ with the Y-phase of the s y s t e m M o - N i - B ; the c rys ta l l ine s t ruc tu re of the Y-phase will be the subject of a subsequent invest igat ion, because up to now it has been found imposs ib le to p r e p a r e single c r y s t a l s of these compounds. It. the s y s t e m s M o - N i - B and W - N i - B , no compounds with a W2Cr2iC 6 type s t ruc tu re (~ -phase) have been detected; in this r e spec t , these s y s t e m s dif fer f rom the s y s t e m s M o - C o - B and W - C o - B [25], as well as f rom other R - N i - B s y s t e m s (where R is Sc, Ti, V, Mn, Zr, Nb, Hf,

B

S O �9 ~

: . .

P-N/483 B ~ ` ~ " " " " "

WB

�9 �9 0 �9 �9 �9

Ni WN~ w

Fig. 3. Isothermal section of part of system W-Ni-B at 800~

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Ta, or Re) [18]. Bear ing in mind the favorable volume fac tor , the absence of ~ - p h a s e in the s y s t e m s M o - N i - B and W - N i - B may be at t r ibuted to a change in e lec t ronic concentra t ion.

LITERATURE CITED

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(1967). 5. Yu. B. KuzTma and M. V. Chepiga, Neorgan. Mater ia ly , 5, 49 (1969). 6. J . D . Schobel and H. H, S tade lmaier , Z. Metallk~ 56, 856 (1965). 7. K . I . Por tnoi , V. M. Chubarov, et al. , Dold. Alad. Nauk SSSR, 169, 1104 (1966). 8. K. I~ Por tnoi , V. M. Romashov, et al., Po roshkovaya Met., No. 2, 15 (1967). 9~ A . S . Sobolev and T. F, Fedorov, Neorgan. Mater ia ly , 3, 723 (1967).

10. Yu. B. K u z ' m a and V. P. Koval ' , Neorgan. Mater ia ly , 4, 450 (1968). 11. M. Hansen and K. P. Anderko, Constitution of Binary Alloys, McGraw-Hil l , New York (1957). 12. I . I . Korni lov, N. Mo Matveeva, L. N. Pryakhina , and R. S~ Polyakova, Meta l loehemica l P r o p e r t i e s

of the E lements of the Per iod ic Sys tem [in Russian], Izd-vo Nauka, Moscow (1966). 13. R. Casse l ton and W. Hume-Rothery , J: L e s s - C o m m o n Metals , 7, 212 (1964). 14. C . B . Shoemaker , A. H. Fox, and D. P~ Shoemaker , Acta Crys t . , 1_33, 585 (1960). 15. C . B . Shoemaker and D. P. Shoemaker , Acta Cryst~ 1.~6, 997 (1963). 16. J . D . Seh5bel and H. H. S tade lmaier , Metall , 19, 715 (1965). 17. E. Ganglberger , H. Nowotny, and F. Benesovsky, Monatsh. Chem., 96, 1144 (1965). 18. Yu. B. K u z ' m a and Yu. V. Voroshi lov, Kr i s t a l log ra f iya , 1_22, 353 (1967). 19. R. Steinitz and Io Binder, Powder Met~ Bullo, 6, 123 (1953). 20. P . T . Kolomytsev and N. V. Moskaleva, Dokl. Akad. Nauk SSSR, 154, 1120 (1964)o 21~ P . T . Ko lomytsev and N. V. Moskaleva, Po roshkovaya Met., No~ 8, 86 (1966). 22. YUo B. K u z ' m a , P. I. Kr ipyakevich , and R. V. Skolozdra, Dopovidi Akad. Nauk UkrRSR, No~ 10, 1290

(1966). 23~ W. Rieger , H. Nowotny, and F. Benesovsky, Monatsh. Chem., 97, 378 (1966). 24. H. Haschke, H. Nowotny, and F. Benesovsky, Monatsh. Chem., 97, 1459 (1966). 25. Yu. V. Voroshi lov and Yu. B~ KuzTma, Neorgan. Mater ia ly , 2, 764 (1966).

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