Ternario si - ni- n

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70, 178-184 (1987)

Phase Diagrams

of the Ternary


Mn, Fe, Co, Ni-Si-N*

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 investigated and isothermalsections at 900°C (Fe-Si-N, Ni-Si-N), at 1000°C(Mn-Si-N, Co-Si-N) and at 1150°C(Fe-Si-N) are presented. In the system Mn-Si-N, S&N4 coexists with MnSiN2, Mn,Si, Mn& MnSi, and MnSizmX. In the systems Fe, Co, Ni-Si-N, S&N4 coexists with all binary silicides but reacts rapidly with iron above 1120 f lO”C, and cobalt and nickel above 1170 2 10°C to form binary silicides and nitrogen
gas. 0 1987 AcademicPress, Inc

rhombic, space group Pna2,, a = 0.5258 nm, b = 0.6511 nm, and c = 0.5070 nm (4). Silicon nitride is one of the most attrac- MnSiN2 was found to form as well by tive advanced ceramic materials of today. reaction of manganese with silicon under Although much is known regarding wetting, nitrogen (3). The decomposition of MnSiN2 metallizing, and joining S&N4 to base met- into MnSi and N2gas starts under nitrogen als no rationale of these data in the form of (IO’ Pa) above 1300°C and under argon phase diagrams is available. This prompted above 800°C (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- 700°C (5). Thisreaction is described to be fast and violent at higher temperatures, sented here. especially above the melting point of iron (1, 2, 6). At 12OO”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”) (I) and is reported to react violentlywith S&N4 at 1270°C under vacuum as well ture of 1300°C is reported to be necessary as in inert gas (2). The compounds iden- to decompose the silicon nitride completely tified as the reaction products are MnSiN2, in an alloy Fe + 6 wt% S&N4 in order to obtain an nitride-free alloy (8). The same Mn,Si, and S&N4 @OO”C, argon) and Mn& and S&N4 (12OO”C,argon), respectively (3). author observed that at1150°C 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
Copyright All rights Q 1987 by Academic Press, Inc. of reproduction in any form reserved.





of S&N4cutting tools with iron and ironbased alloys in air. They conclude that the low melting 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 (11, 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 15OO”C, vacuum,wetting angle 6 = 76”) and Fez& (at 145o”C, vacuum, wetting angle 29 = 66”) (14). On the other hand nitriding FeSiz leads to the formation of S&N4 + Fe at 1200°C 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 silitides CoSi and “Co,Si” were found to be compatible with S&N4 (14). No bonding to the...