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The synthesis of nanocrystalline Ni75Nb12B13 alloys by high energy ball milling of elemental components
Journal of Alloys and Compounds 483 (2009) 86–88
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
The synthesis of nanocrystalline Ni75 Nb12 B13 alloys by high energy ball milling of elemental components L.M. Kubalova a,∗ , V.I. Fadeeva b , I.A. Sviridov c , S.A. Fedotov b a
K.L. Khetagurov North-Ossetian State University, 46 Vatutina Str., 362025 Vladikavkaz, Russia M.V. Lomonosov Moscow State University, Leninskie Gory, 119899 GSP, Moscow, Russia c All-Russia Research Institute of Automatics, Moscow, Russia b
a r t i c l e
i n f o
Article history: Received 30 August 2007 Received in revised form 18 July 2008 Accepted 29 July 2008 Available online 12 December 2008 Keywords: Nanostructured materials Mechanical alloying Phase transitions X-ray diffraction
a b s t r a c t Ni75 Nb12 B13 alloys were synthesized by mechanical alloying (MA) of individual Ni, Nb and B components. X-ray investigation showed the formation of Ni (Nb, B) solid solution and amorphous phase at the intermediate stage of milling. Metastable phases formed by MA turned into Ni (Nb), Ni21 Nb2 B6 and Ni3 Nb stable phases during heating up to 720 ◦ C. The exothermal effects on DSC curves were caused with these processes. The disintegration of Ni (Nb, B) solid solution and crystallization of an amorphous phase resulted in the stable phases formation during the milling prolongation as well as after thermal treatment. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Ni-based nanocrystalline alloys with the additives of Nb and B could have potential technological use as nanocomposits strengthened by boride phases. The ternary Ni–Nb–B alloys obtained by means of rapidly quenching (RQ) from the liquid state were studied in the papers [1,2]. It was noted that RQ-alloys containing 75–80 at.% of Ni with different correlation of Nb and B are lightly amorphized. The Ni75 Nb12 B13 alloy was obtained as an amorphous one at RQ of 106 К/s [3]. Researches connected with the mechanochemical synthesis and description of the structure of the Ni–Nb–B alloys is not found in literature. In the present paper we undertake the analysis of the structure of the Ni75 Nb12 B13 alloy obtained by mechanical alloying. Thermal stability of the phases formed by MA was also determined, as well as the final structure of the alloy after the thermal treatment. 2. Experimental procedures The mechanochemical synthesis was conducted by means of milling the mixtures powders of nickel (99.99%) with the size of the particles 70–100 mkm, of niobium (99.96%) with the size of the particles ∼100 mkm and amorphous boron (99.88%). Water-cooled planetary ball mill of the type MAPF-2M with the container and balls from hardened steel was used. Milling was conducted under the protection
∗ Corresponding author. Tel.: +7 867 2 53 10 93; fax: +7 867 2 53 10 93. E-mail address: [email protected] (L.M. Kubalova). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.07.167
atmosphere of argon. The mass of the mixture loaded was 9 g, the ratio of the mass of the balls to the mass of the powder was 6:1. The energy capacity of milling was 10 W/g that characterizes the mill as a high power one. Under such milling conditions the temperature fluctuation in the drum can be from 80 to 230 ◦ C [4], but at using the 3-min cycling time of this operation the temperature in the container does not exceed 80–100 ◦ C. The chemical analysis of the obtained powders was performed by means of an X-ray micro analyzer Camebax–Microbeam according to the characteristics spectra of К-series (˛ and ˇ) of Ni and Nb. The content of Ni and Nb in the mechanically synthesized alloys differed from the nominal one by ±1.1 mass.% Ni and 0.4–1.0 mass.% Nb according to the results of 7–10 measurements. After 3 h of milling presence of Fe about 1.8–2 mass.% was observed that caused by the abrasive friction of the drum and the balls. The alloys were investigated by the methods of X-ray diffraction analysis (DRON-4-07) with using Cu K␣-radiation and the differential scanning calorimetry (PerkinElmer DSC-7) with 40 K/min heating in the temperature region of 50–720 ◦ C. Processing of the diffractograms was made by means of X-rays program complex.
3. Results and discussion The changes of X-ray spectra, shown in Fig. 1, indicate the sequence of structural transformations during milling of the Ni, Nb and B powder mixture. Thus, after 2 h of MA there is already no line of Nb in the diffractogram. The presence of boron in the MA alloy as an individual phase is impossible to detect because of amorphous boron was deliberately used in the powder mixtures. The diffractogram shown in Fig. 1b contains only the strongly widened reflections of fcc phase that are shifted to the minor angles as compared to the position of the Ni lines. This fact indicates that the mechanochemical reaction between components of the mixture
L.M. Kubalova et al. / Journal of Alloys and Compounds 483 (2009) 86–88
87
Fig. 2. The isolation the scattering component of an amorphous phase from experimental diffractogram: (1) XRD of the alloy after 2 h of milling; (2) calculated diffractogram of nanocrystalline fcc phase; (3) a scattering of an amorphous phase.
Fig. 1. Diffractograms of Ni75 Nb12 B13 alloys obtained after different milling time: initial mixture of the components (a); 2 h of MA (b); 4 h of MA (c); 8 h of MA (d).
resulted in the formation of the solid solution of Nb and partially of B in fcc lattice of Ni. The substructure of fcc phase is characterized by the domain size of about 7 nm and the medium lattice microdeformation ε2 1/2 ≈ 1.3%. The lattice parameter of Ni (Nb, B) solid solution is equal to 0.3568 nm (аNi = 0.3524 nm). If we assume that only Nb dissolves into the Ni lattice during the chemical interaction of the components and B remains as the second amorphous phase, then according to [5] the lattice parameter of Ni (Nb) should be equal to 0.3575 nm. The lesser value of the lattice parameter of fcc phase may be explained by the supplementary dissolution of B in Ni. The formation of Ni (Nb, B) solid solution occurs by means of the substitution of Ni positions by Nb and B (rNb = 0.146 nm [6], rB = 0.086 nm [7]). In Fig. 2 one can see the higher background of X-ray noncoherent scattering in the region of (1 1 1) and (2 0 0) lines. Using the Lorenz function, we modeled the diffraction spectrum of the nanocrystalline fcc phase with the lattice parameter of a = 0.3568 nm. This calculated spectrum was subtracted from the experimental one. Residual part of the spectrum contains the “amorphous halo” in the region 2 = 35–50◦ (Cu K␣-radiation). Similar halo was observed in the diffractogram of the fully amorphous RQ-alloy of the same composition [3]. Therefore one can conclude that the amorphous phase is presented in the mechanically synthesized alloy. The further milling of Ni (Nb, B) solid solutions resulted in their partial dissociation. Thus, in the diffractogram of the Ni75 Nb12 B13 alloy after 4 h of MA (Fig. 1c and d) one can see Ni (Nb, B) lines and the weak reflections of the cubic phase (Ni21 Nb2 B6 ). Prolongation of milling up to 8 h leaded to the increasing of the line intensity of phase and the appearance of Ni3 B lines. Both formed phases are stable. These phases are characteristic for the equilibrium alloy of this composition according to the data of the Ni–Nb–B diagram [8,9].
Calorimetric measurements of MA alloys during the continuous heating in 80–720 ◦ C temperature range revealed the presence of exothermal effects on DSC curves (Fig. 3). One can see two exothermal peaks with Tmax (1) = 483 ◦ C and Tmax (2) = 630 ◦ C on DSC curve of the alloy obtained after 2 h of MA. The temperature region of the first exothermal peak corresponds to 450–518 ◦ C (H = −2.3 J/g). The second more expressed exothermal effect starts from 530 ◦ C and extends up to the final heating point in the calorimeter. The first exothermal effect is caused by the process of an amorphous phase crystallization that was formed during MA. The same temperature range and Tmax were observed in DSC experiment [3] for an amorphous RQ-alloy of the Ni75 Nb12 B13 composition. Two exothermal effects on DSC curve of the alloy obtained after 4 h of MA there are also present, however the value of the first peak has become
Fig. 3. DSC curves of Ni75 Nb12 B13 alloys synthesized at different time of milling: 2 h of MA (a); 4 h of MA (b); 8 h of MA (c).
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Fig. 5. Fragment of the phase fields of Ni–Nb–B equilibrium diagram [9] and the position of stable (1) and metastable (2) Ni75 Nb12 B13 alloy.
4. Conclusions
Fig. 4. Diffractograms of Ni75 Nb12 B13 alloys obtained at different milling time and annealed at 720 ◦ C: 2 h of MA (a); 4 h of MA (b); 8 h of MA (c).
much more (H = −36 J/g) and the second one is shifted to lower temperature values. The second exothermal effect is caused, in both cases, by the partial disintegration of Ni (Nb, B) solid solution and the phase formation. Noticeable exothermal effects are not observed on the curve (Fig. 3c) for the Ni75 Nb12 B13 alloy obtained after 8 h of MA since the stable and Ni3 B phases were already formed under the deformation action. Total thermal effect during heating of this sample caused evidently by the relaxation processes that take place during the transition from the non-equilibrium alloy to the equilibrium one. Diffractograms in Fig. 4 are shown the phase composition of the alloys after 2 and 8 h of MA and annealing in the calorimeter up to 720 ◦ C. A partial disintegration of the solid solution and formation of only phase one can see from the diffractogram of the alloy after 2 h of MA and following heating up to 720 ◦ C (Fig. 4a). The lattice parameter of fcc phase increased up to 0.3585 nm since boron contained in the solid solution was spent on the phase formation and the solid solution was enriched by niobium. Such value of the lattice parameter corresponds the solid solution containing up to 11–12 at.% Nb and it is supersaturated and metastable. The diffractogram in Fig. 4b for the annealed alloy obtained after 8 h of MA shows the presence of three phases – Ni (Nb), Ni21 Nb2 B6 and Ni3 Nb. According to the equilibrium phase diagram [9] (see Fig. 5) just these phases have to contain in the alloy of Ni75 Nb12 B13 composition. Therefore the alloy becomes equilibrium already at 720 ◦ C.
The mechanochemical synthesis of the Ni75 Nb12 B13 alloy by high energy milling of individual components at the intermediate stage resulted in the formation of the Ni (Nb, B) solid solution and an amorphous phase. But completely amorphous alloy is not formed because of the prolonged deformation action resulted in the disintegration of the supersaturated solid solution and crystallization of an amorphous phase. The formation of Ni21 Nb2 B6 () and Ni3 Nb phases with the stable chemical bond of the metals with boron interrupts the amorphization process. In this case the influence of deformation promotes the transition of the metastable phases in the MA alloy to the stable phases that is analogous to the thermal treatment. Acknowledgments This research was supported by Russian Foundation for Basic Research (Projects no. 06-03-96651 and 08-02-00392) and by the Federal Agency of Science and Innovations (FASI) of Russian Federation under contract #02.552.11.7035 using equipment of joint research center of North-Ossetian State University. References [1] I.W. Donald, K.D. Ward, H.A. Davies, Proceedings of the 4th International Conference on Rapidly Quenched Metals, Sendai, 1981, pp. 597–600. [2] J. Reeve, H.A. Davies, I.W. Donald, Proceedings of the 4th International Conference on Rapidly Quenched Metals, Sendai, 1981, pp. 815–818. [3] V.I. Fadeeva, L.M. Kubalova, D.V. Varganov, I.N. Shabanova, in: P. Duhaj, P. Mrafko, P. Svec (Eds.), Proceedings of the Second International Conference on Amorphous Metallic Materials, Smolenice, CSSR, May 22–26, Trans Tech Publications, Switzerland/Germany/UK/USA, 1989, pp. 113–118. [4] L.Yu. Pustov, S.D. Kaloshkin, V.V. Tcherdyntsev, I.A. Tomilin, J. Metastable Nanocryst. Mater. 360–362 (2001) 373–378. [5] S. Arajs, H. Chessin, R.V. Colvin, Phys. Status Solidi 3 (1963) 2337–2346. [6] H.J. Goldschmidt, Interstitial Alloys, Butterworth’s, London, 1967. [7] W.B. Pearson, The Crystal Chemistry and Physics of Metals and Alloys, WileyInterscience, New York, 1972. [8] J.D. Schöbel, H.H. Stadelmaich, Metallkunde 18 (1964) 1285–1287. [9] A.S. Sobolev, Y.B. Kuzma, T.F. Fedorov, Izv. AN USSR Neorg. Mater. 3 (1967) 638–643 (in Russian).
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
The synthesis of nanocrystalline Ni75 Nb12 B13 alloys by high energy ball milling of elemental components L.M. Kubalova a,∗ , V.I. Fadeeva b , I.A. Sviridov c , S.A. Fedotov b a
K.L. Khetagurov North-Ossetian State University, 46 Vatutina Str., 362025 Vladikavkaz, Russia M.V. Lomonosov Moscow State University, Leninskie Gory, 119899 GSP, Moscow, Russia c All-Russia Research Institute of Automatics, Moscow, Russia b
a r t i c l e
i n f o
Article history: Received 30 August 2007 Received in revised form 18 July 2008 Accepted 29 July 2008 Available online 12 December 2008 Keywords: Nanostructured materials Mechanical alloying Phase transitions X-ray diffraction
a b s t r a c t Ni75 Nb12 B13 alloys were synthesized by mechanical alloying (MA) of individual Ni, Nb and B components. X-ray investigation showed the formation of Ni (Nb, B) solid solution and amorphous phase at the intermediate stage of milling. Metastable phases formed by MA turned into Ni (Nb), Ni21 Nb2 B6 and Ni3 Nb stable phases during heating up to 720 ◦ C. The exothermal effects on DSC curves were caused with these processes. The disintegration of Ni (Nb, B) solid solution and crystallization of an amorphous phase resulted in the stable phases formation during the milling prolongation as well as after thermal treatment. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Ni-based nanocrystalline alloys with the additives of Nb and B could have potential technological use as nanocomposits strengthened by boride phases. The ternary Ni–Nb–B alloys obtained by means of rapidly quenching (RQ) from the liquid state were studied in the papers [1,2]. It was noted that RQ-alloys containing 75–80 at.% of Ni with different correlation of Nb and B are lightly amorphized. The Ni75 Nb12 B13 alloy was obtained as an amorphous one at RQ of 106 К/s [3]. Researches connected with the mechanochemical synthesis and description of the structure of the Ni–Nb–B alloys is not found in literature. In the present paper we undertake the analysis of the structure of the Ni75 Nb12 B13 alloy obtained by mechanical alloying. Thermal stability of the phases formed by MA was also determined, as well as the final structure of the alloy after the thermal treatment. 2. Experimental procedures The mechanochemical synthesis was conducted by means of milling the mixtures powders of nickel (99.99%) with the size of the particles 70–100 mkm, of niobium (99.96%) with the size of the particles ∼100 mkm and amorphous boron (99.88%). Water-cooled planetary ball mill of the type MAPF-2M with the container and balls from hardened steel was used. Milling was conducted under the protection
∗ Corresponding author. Tel.: +7 867 2 53 10 93; fax: +7 867 2 53 10 93. E-mail address: [email protected] (L.M. Kubalova). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.07.167
atmosphere of argon. The mass of the mixture loaded was 9 g, the ratio of the mass of the balls to the mass of the powder was 6:1. The energy capacity of milling was 10 W/g that characterizes the mill as a high power one. Under such milling conditions the temperature fluctuation in the drum can be from 80 to 230 ◦ C [4], but at using the 3-min cycling time of this operation the temperature in the container does not exceed 80–100 ◦ C. The chemical analysis of the obtained powders was performed by means of an X-ray micro analyzer Camebax–Microbeam according to the characteristics spectra of К-series (˛ and ˇ) of Ni and Nb. The content of Ni and Nb in the mechanically synthesized alloys differed from the nominal one by ±1.1 mass.% Ni and 0.4–1.0 mass.% Nb according to the results of 7–10 measurements. After 3 h of milling presence of Fe about 1.8–2 mass.% was observed that caused by the abrasive friction of the drum and the balls. The alloys were investigated by the methods of X-ray diffraction analysis (DRON-4-07) with using Cu K␣-radiation and the differential scanning calorimetry (PerkinElmer DSC-7) with 40 K/min heating in the temperature region of 50–720 ◦ C. Processing of the diffractograms was made by means of X-rays program complex.
3. Results and discussion The changes of X-ray spectra, shown in Fig. 1, indicate the sequence of structural transformations during milling of the Ni, Nb and B powder mixture. Thus, after 2 h of MA there is already no line of Nb in the diffractogram. The presence of boron in the MA alloy as an individual phase is impossible to detect because of amorphous boron was deliberately used in the powder mixtures. The diffractogram shown in Fig. 1b contains only the strongly widened reflections of fcc phase that are shifted to the minor angles as compared to the position of the Ni lines. This fact indicates that the mechanochemical reaction between components of the mixture
L.M. Kubalova et al. / Journal of Alloys and Compounds 483 (2009) 86–88
87
Fig. 2. The isolation the scattering component of an amorphous phase from experimental diffractogram: (1) XRD of the alloy after 2 h of milling; (2) calculated diffractogram of nanocrystalline fcc phase; (3) a scattering of an amorphous phase.
Fig. 1. Diffractograms of Ni75 Nb12 B13 alloys obtained after different milling time: initial mixture of the components (a); 2 h of MA (b); 4 h of MA (c); 8 h of MA (d).
resulted in the formation of the solid solution of Nb and partially of B in fcc lattice of Ni. The substructure of fcc phase is characterized by the domain size of about 7 nm and the medium lattice microdeformation ε2 1/2 ≈ 1.3%. The lattice parameter of Ni (Nb, B) solid solution is equal to 0.3568 nm (аNi = 0.3524 nm). If we assume that only Nb dissolves into the Ni lattice during the chemical interaction of the components and B remains as the second amorphous phase, then according to [5] the lattice parameter of Ni (Nb) should be equal to 0.3575 nm. The lesser value of the lattice parameter of fcc phase may be explained by the supplementary dissolution of B in Ni. The formation of Ni (Nb, B) solid solution occurs by means of the substitution of Ni positions by Nb and B (rNb = 0.146 nm [6], rB = 0.086 nm [7]). In Fig. 2 one can see the higher background of X-ray noncoherent scattering in the region of (1 1 1) and (2 0 0) lines. Using the Lorenz function, we modeled the diffraction spectrum of the nanocrystalline fcc phase with the lattice parameter of a = 0.3568 nm. This calculated spectrum was subtracted from the experimental one. Residual part of the spectrum contains the “amorphous halo” in the region 2 = 35–50◦ (Cu K␣-radiation). Similar halo was observed in the diffractogram of the fully amorphous RQ-alloy of the same composition [3]. Therefore one can conclude that the amorphous phase is presented in the mechanically synthesized alloy. The further milling of Ni (Nb, B) solid solutions resulted in their partial dissociation. Thus, in the diffractogram of the Ni75 Nb12 B13 alloy after 4 h of MA (Fig. 1c and d) one can see Ni (Nb, B) lines and the weak reflections of the cubic phase (Ni21 Nb2 B6 ). Prolongation of milling up to 8 h leaded to the increasing of the line intensity of phase and the appearance of Ni3 B lines. Both formed phases are stable. These phases are characteristic for the equilibrium alloy of this composition according to the data of the Ni–Nb–B diagram [8,9].
Calorimetric measurements of MA alloys during the continuous heating in 80–720 ◦ C temperature range revealed the presence of exothermal effects on DSC curves (Fig. 3). One can see two exothermal peaks with Tmax (1) = 483 ◦ C and Tmax (2) = 630 ◦ C on DSC curve of the alloy obtained after 2 h of MA. The temperature region of the first exothermal peak corresponds to 450–518 ◦ C (H = −2.3 J/g). The second more expressed exothermal effect starts from 530 ◦ C and extends up to the final heating point in the calorimeter. The first exothermal effect is caused by the process of an amorphous phase crystallization that was formed during MA. The same temperature range and Tmax were observed in DSC experiment [3] for an amorphous RQ-alloy of the Ni75 Nb12 B13 composition. Two exothermal effects on DSC curve of the alloy obtained after 4 h of MA there are also present, however the value of the first peak has become
Fig. 3. DSC curves of Ni75 Nb12 B13 alloys synthesized at different time of milling: 2 h of MA (a); 4 h of MA (b); 8 h of MA (c).
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Fig. 5. Fragment of the phase fields of Ni–Nb–B equilibrium diagram [9] and the position of stable (1) and metastable (2) Ni75 Nb12 B13 alloy.
4. Conclusions
Fig. 4. Diffractograms of Ni75 Nb12 B13 alloys obtained at different milling time and annealed at 720 ◦ C: 2 h of MA (a); 4 h of MA (b); 8 h of MA (c).
much more (H = −36 J/g) and the second one is shifted to lower temperature values. The second exothermal effect is caused, in both cases, by the partial disintegration of Ni (Nb, B) solid solution and the phase formation. Noticeable exothermal effects are not observed on the curve (Fig. 3c) for the Ni75 Nb12 B13 alloy obtained after 8 h of MA since the stable and Ni3 B phases were already formed under the deformation action. Total thermal effect during heating of this sample caused evidently by the relaxation processes that take place during the transition from the non-equilibrium alloy to the equilibrium one. Diffractograms in Fig. 4 are shown the phase composition of the alloys after 2 and 8 h of MA and annealing in the calorimeter up to 720 ◦ C. A partial disintegration of the solid solution and formation of only phase one can see from the diffractogram of the alloy after 2 h of MA and following heating up to 720 ◦ C (Fig. 4a). The lattice parameter of fcc phase increased up to 0.3585 nm since boron contained in the solid solution was spent on the phase formation and the solid solution was enriched by niobium. Such value of the lattice parameter corresponds the solid solution containing up to 11–12 at.% Nb and it is supersaturated and metastable. The diffractogram in Fig. 4b for the annealed alloy obtained after 8 h of MA shows the presence of three phases – Ni (Nb), Ni21 Nb2 B6 and Ni3 Nb. According to the equilibrium phase diagram [9] (see Fig. 5) just these phases have to contain in the alloy of Ni75 Nb12 B13 composition. Therefore the alloy becomes equilibrium already at 720 ◦ C.
The mechanochemical synthesis of the Ni75 Nb12 B13 alloy by high energy milling of individual components at the intermediate stage resulted in the formation of the Ni (Nb, B) solid solution and an amorphous phase. But completely amorphous alloy is not formed because of the prolonged deformation action resulted in the disintegration of the supersaturated solid solution and crystallization of an amorphous phase. The formation of Ni21 Nb2 B6 () and Ni3 Nb phases with the stable chemical bond of the metals with boron interrupts the amorphization process. In this case the influence of deformation promotes the transition of the metastable phases in the MA alloy to the stable phases that is analogous to the thermal treatment. Acknowledgments This research was supported by Russian Foundation for Basic Research (Projects no. 06-03-96651 and 08-02-00392) and by the Federal Agency of Science and Innovations (FASI) of Russian Federation under contract #02.552.11.7035 using equipment of joint research center of North-Ossetian State University. References [1] I.W. Donald, K.D. Ward, H.A. Davies, Proceedings of the 4th International Conference on Rapidly Quenched Metals, Sendai, 1981, pp. 597–600. [2] J. Reeve, H.A. Davies, I.W. Donald, Proceedings of the 4th International Conference on Rapidly Quenched Metals, Sendai, 1981, pp. 815–818. [3] V.I. Fadeeva, L.M. Kubalova, D.V. Varganov, I.N. Shabanova, in: P. Duhaj, P. Mrafko, P. Svec (Eds.), Proceedings of the Second International Conference on Amorphous Metallic Materials, Smolenice, CSSR, May 22–26, Trans Tech Publications, Switzerland/Germany/UK/USA, 1989, pp. 113–118. [4] L.Yu. Pustov, S.D. Kaloshkin, V.V. Tcherdyntsev, I.A. Tomilin, J. Metastable Nanocryst. Mater. 360–362 (2001) 373–378. [5] S. Arajs, H. Chessin, R.V. Colvin, Phys. Status Solidi 3 (1963) 2337–2346. [6] H.J. Goldschmidt, Interstitial Alloys, Butterworth’s, London, 1967. [7] W.B. Pearson, The Crystal Chemistry and Physics of Metals and Alloys, WileyInterscience, New York, 1972. [8] J.D. Schöbel, H.H. Stadelmaich, Metallkunde 18 (1964) 1285–1287. [9] A.S. Sobolev, Y.B. Kuzma, T.F. Fedorov, Izv. AN USSR Neorg. Mater. 3 (1967) 638–643 (in Russian).