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JOURNAL OF SOLID STATE CHEMISTRY 70, 178-184 (1987) Phase Diagrams of the Ternary Systems Mn, Fe, co, Ni-Si-N* to view nut*ge F. WEITZER AND J. C. SCHUSTER Institut fiir Physikalische Chemie, Universitiit Wien, Wtihringerstrasse 42, A-1090 Vienna, Austria Received December 20, 1986 Phase equilibria in the ternary systems Mn, Fe, Co, and Ni-Si-N are investlgated and isothermal sectlons at 9000C (Fe-Si-N, Ni-Si-N), at 1 oooacwn-Si-N, CO-Si-N) and at 11500C(Fe-Si-N) are presented. In the system Mn-Si-N, S&N4 coexists with MnSiN2, Mn,Si, Mnsi, and Mnsizrnx. In the systems pe, co, Ni.

Si-N, S&N4 coexiSts ith all binary silicides but reacts rapidly with iron above 1120 f IO”C, and cobalt and nickel above 1170 2 IOCC to form binary silicides and nitrogen gas. 0 1987 Academic Press, Inc diagrams is available. This prompted above 8000C (3). Silicon nitride is reported to decompose a systematic investigation of such transition metal-silicon-nitrogen systems and the in contact WIth iron at temperatures above first set of ternary phase diagrams is pre- 7000C (5). This reaction is described to be fast and violent at higher temperatures, sented here. specially above the meiting point of iron (1, 2, 6). At 1200″C, S&N4 whiskers are Literature Review observed to be dissolved in an Fe matrix Liquid manganese wets silicon nitride (29 (7). The reaction products found are binary iron silicides and nitrogen gas. A tempera— 74″) (l) and is reported to react violently with S&N4 at 12700C under vacuum as well ture of 1 300’C is reported to be necessary as in inert gas (2). The compounds iden- to decompose the sllicon nitride completely tified as the reaction products are MnSiN2, in an alloy Fe + 6 S in arder to obtain an nitride-free alioy (8).

The same Mn,Si, and S argom and and S (1200″C,argon), respectively (3). author observed hat at 1 1 500C the nitrogen The ternary phase MnSiN2 is ortho- evolution is reduced under vacuum compared to a hydrogen atmosphere. Tennen* Dedicated to Dr. H. Nowotny. house et al. (9) investigated the interaction 0022-45%187$3. 00 Copyright All rights Q 1 987 by Academic Press, Inc. of reproduction in any form reserved. Introduction 15 1987 by Academic Press, Inca of reproduction in any form reserved. 178 PRASE DIAGRAMS OF TERNARY SYSTEMS 179 of S&N4 cutting tools with iron and ironbased alloys in air.

They conclude that the low meltlng phase formed during machining is an oxide phase and does not occur in the ternary Fe-Si-N. Joining S&N4 to steel by hot pressing resulted in excellent bonding due to the formation of Fe-silicides in the interlayer. However, due to thermal expansion mismatching, low tensile strength (failure in the S&NJ) resulted (10). Iron is often used as an addition in silicon to aid nitridation. The reaction products found are S&N4 and iron silicides (1 1, Z2), which, however, are recognized to be the primary course of strength degradation in hot pressed silicon nitride (13).

These results are in agreement with the observation that no bonding takes place and S&N4 is apparently compatible with FeSi (at 1 500″C, vacuum, wetting angle 6 = 76″) and Fez& (at 450″C, vacuum, wetting angle 29 = 66″) (14). On the other hand nitriding FeSiz leads to the formation of S&N4 + Fe at 12000C according to Matsumoto et al. (15). Liquid cobalt is reported to decompose S&N4 (Z, 6) by the formation of binary silicides and nitrogen gas. The binary silltides Cosi and “Co,Si” were found to be compatible with S&N4 (14). No bonding to the ceramic was observed.

The wetting angles are 29 = 52″ and 6 < 40", respe S&N4 (14). No bonding to the ceramic was observed. The wetting angles are 29 = 52" and 6 < 40', respectively. Silicon nitride acts as diffusion barrier between Co and Si in shallow-junction VLSI evices (Z6). Liquid nickel is also reported to decompose S&N4 (l, 2, 6) under the formation of binary silicides and nitrogen gas. This reaction was observed to already take place at temperatures above 1 000cc (17). These observations are in accord with reports on the degradation of Si3N4 whiskers in a nickel matrix in the temperature range between 1000 and (7, 18-20).

The apparent compatibility of S&N4 with NizSi was concluded from the wetting angle of N&Si on S&N4 (8 = 108″, no wetting) (14). Nitriding silicon with the addition of Ni results in the formation of nickel silicides besides S&N4 (11). Phase diagram ata of the binar,’ siliconmetal and nitrogen-metal systems are taken from literature references: Mn-Si from Moffatt (22); Fe- Si from Schiirmann and Hensgen (22); Co-Si from Hansen (23) updated by the work of van den Boomgaard and Carpay (24) as well as Kiister et al. (25); Ni-Si from Osawa and Okamoto (26), Oya and Suzuki (27), and Ellner et al. 28); Mn-N from Zwicker (29), Lihl et al. (30), and Kudielka and Grabke (31); Fe-N from Kubaschewski von Goldbeck (32). No phase diagrams are reported for CO-N and Ni-N. Crystal structure data of the intermediate phases are compiled by Villars and Co-N and Ni-N. Crystal structure data ofthe intermediate phases are compiled by Villars and Calvert (33). Experimental Procedures In order to identify all binary silicide phases and to obtain master alloys for further preparation, binary metal- Silicon alloys were prepared by arc melting under argon (99. 99% pure) from powders or ingots of the constituting elements using the starting materials listed below. ‘ Ternary compositions were prepared by mixing powders of these master alloys and binary nitride powders. These ternary mixtures were cold pressed and sintered in evacuated quartz tubes lined with MO or Ta foila X-ray iffraction (CoKcr, radiation, CrKa radiation) was performed on all alloys using ‘ Sllicon powder, purity m9g. 9%, from Apha Div. , Ventron Corp. , USA; Silicon lump, purity m99. 9999%, from Alpha Div. Ventron Corp. , USA; iron powder, purity 99. 5%, impurities (in ppm): Ni 600, C < 600, O < 2000, frorn Fluka AG, switzerland; cobalt powcter, purity 99. 8%, impurities (in ppm): Cu < 50, Pb < 50, Fe < 500, Zn < 50, Ni 500, Mn 50; from Fluka AC, switzerland; nickel powder, purity mgg. 9%, from Alpha Div. , Ventron Corp. , USA; silicon nitride (mixture of a-S and P-Si3N4), powder 58% Si; from Alpha Div. , Ventron Corp. , USA; manganese nitride (Mn*N) powder, purity 99. 9%, from Apha DIV. , Ventron Corp. 80 WEITZER AND SCHUSTER was formed at 10000C upon reaction of S with mangane Ventron Corp. was formed at 10000C upon reaction of S with manganese. MnSiN2 coexists in the absence of external nitrogen pressure with Si3N4, Mn$i, p-Mn(s. s. ), and nitrogen gas (Fig. 1). The lattice parameters found are a 0. 52656 nm, b — 0. 65222 nm, c 0. 50737 nm (Si-nch) and a = 0. 52678 nm, b = 0. 65208 nm, c = 0. 50693 nm (Mn-rich). MnSiN2 may therefore be considered a line compound having only a very narrow homogeneity range.

A three-phase field (MnSiNz + Mn$Si + @Mn(s. s. )) was observed. Hence the stability of Mn$i2, which was found to exist in the binary Mn-Si system at this temperature, is conS + xMe – + + 2N2 t . fined to compositions close to the binary Furthermore the nitrogen gas acts as trans- Mn-Si by a tieline between Mn$i and porting agents for metallic vapors which are p-Mn(s. s. ). S coexists with MnSiz—, deposited on the quartz window, therefore MnSi, Mn&, and MnSi besides MnSiNz virtually bringing to an end the optical (Table l).

No solubility of nitrogen was temperature measurements at the onset of observed in any f the manganese silicides. If the external nitrogen pressure is not the reaction. negligible the formation of y-Mn(s. s. ) modifies the phase equilibria at the Mn-rich Results and Discussion corner of the ternary system (Fig. 2). With further increase of the external nitrogen The Ternary System Manganesepartial pre PAGF 15 With further increase of the external nitrogen The Ternary System Manganesepartlal pressure, manganese nitrides richer Silicon- Nitrogen in nitrogen coexist with MnSiNz.

Thus All phases and crystal structures reported for the binary system Mn-Si (21, 33) could be corroborated and are confirmed. Mn&, found at 700″C, could not be obisothermal section 1273 K served at temperatures of 8000C and above. No other discrepancies with the established phase diagram are observed. The lattice parameters found are MnbSi (Mno. S&Si0. t-s, 1. 08916 nm, c = 1. 92056 nm; Mn& (Mno. slsSio. lss,t-phase), u — 1 . 70195 nm, b – 2. 86750 nm, c = 0. 46675 nm; Mn$i a = 0. 57242 nm; MnSSi2 a = 0. 89001 nm, c 0. 87084 nm, Mn&a = 0. 68988 nm, c 0. 8096 nm; MnSl a = 0,45593 nm; and a = 0,55309 r,m, c = 6,54763 nm. The lattice parameter of p-Mn(s. s) in an alloy Mno. sOSio. annealed at 8000C was a iO FIG. . Isothermal section of the ternary system = 0. 62869 nm. Mn-Si-N at 10000C (in the absence of external nitroln the ternary system the phase MnSiNz gen pressure). Guinier or Debye-Scherrer cameras. In several ternary systems silicon nitride coexists with the transition metal at 10000C. In order to determine the temperature at which reaction takes place, a large pellet (5-10 g) of the cold compacted powder mixture (S&N4 30 at. Me) was placed in an RF furnace under vacuum and heated slowly. Monitoring with an optical 30 at. % Me) was placed in an RF furnace under vacuum and heated slowly. Monitonng With an optical pyrometer the increase in temperature versus the gas pressure (on a logarithmic scale WIth arbitrary units) permits direct observatlon of the onset of gas evolution resulting from the reaction PHASE DIAGRAMS OF TERNARY TABLE I SYSTEMS 181 SOLID-STATE REACTION PRODUCTS OBSERVED THE SYSTEMMn- Si-N IN UPONANNEALING AT -(EVACUATED QUARTZTUBES) MnO_366SiO. 34 (am) Mno. soSio. so(am) 375 carro carro Mno -issi0. –(arro 25 (arn) MnO,818 (am) Mn 0. 85 (am) s”i’ (am) Mno d&o + + + + + + * + S&N4 (15 at. % S&N4 (15 at. % S&N4 (15 at. % S&N4 (15 at. % S&N4 (15 at. % “N, (20 at. % Si3N4 (20 at. Si3N4 (15 at. % Si3N4 (15 at. % N) N) N) N) N) N) N) N) N) + + –3 –3 + + + + + S&N, + MnSi,-, S&N. , + MnSi + S&N4 + MnSSiz S&N4 + MnSSi3 + Mn3Si Si3N4 + Mn,Si + MIISINZ S&N4 + Mn,Si + VIIISINZ Vln$i + MnSiNZ + Mr1SiNZ 4 p-Mn(s. s. ) Mn,Si 4 MnsiNz + p-Mn(s. s. ) Nore. am stands for arc-melted. nd cr-Fe (Table II). At 1 1 50ac (Fig. 4) S&N4 is decomposed by pure iron, forming a-pe containing 6-8 at. % Si in solid solution. The onset of this decomposition reaction was observed at 1120 ? IODC. All other binary phases stable 1 1 SOCC were found to coexist WIth S&N4 (Table II). However, as mentioned in the previous ection, the phase Fe2Si could not be observed, probably II). However, as mentioned in the previous section, the phase Fe2Si could not be observed, probably due to insuficient quenching.

SpeciThe Ternary System Iron-Siliconmens along the tieline S&N4 + FezSi Nitrogen showed the X-ray diffraction patterns of All phases and crystal structures re- Si3N4, Fe& and Fe$i. It was not possible ported for the binary Fe-Si system (22, 23) are corroborated and confirmed. According to Kudielka (34) the high-temperature phase FeSi is hexagonal; however, quenching in water was claimed to be insuficient to retain the exagonal symmetry and a primitive cubic pattern is obtained instead (35). The lattice parameters found are for Fe2Sis: a = 0. 6879 nm, c 0. 51281 nm; Fe&: a 0. 98789 nm, b 0. 78038 nm, c = O. 78408 nm; FeSi: a = 0. 44844 r,m; FeSi3: a = 0,67426 nm, c = 0. 47146 nm; a2-Fe$i: a = 0. 281 00 nm at the Si-rich phase boundary; a,-Fe$i: a = 05650 nm (at 75 at. % Fe). Two isothermal sections have been established in the ternary Fe-Si-N. At 9000C FIG. 2. Isothermal section of the ternary system (Fig. 3) S&N4 was found to coexist with all Mn-Si-N at 10000C (external nitrogen pressure not binary silicides stable at this temperature negligible). om temperature X-ray diffraction of alloys annealed at 1273 K under 5 X 104 Pa nitrogen and quenched to liquid nitrogen temperature shows the formation of cubic &-Mn4N. However, in situ high-temperature X-ray diffraction o shows the formation of cubic &-Mn4N. However, in situ high- temperature X-ray diffraction of a specimen having the same nominal composition indicates the existence of a hexagonal phase at 1273 K, confirming Kudielka and co-workers (31 182 isothermal section 1173 1423 Si FIG. 3. Isothermal section of the ternary system Fe-Si-N at 9000C (in the absence of external nitrogen pressure). 20 FepSiS 40 Fasi