The Spencer Group SpMCBN Database

for

Refractory Alloy-Carbide, -Nitride, -Boride and -Silicide Systems

General

The Spencer Group Non-Oxide Refractories Database, SpMCBN, contains assessed thermodynamic parameters for binary and ternary alloys of high-temperature materials. These materials are frequently based on transition metal alloys and on their carbides, nitrides, borides, and silicides.

The alloys comprise Me1-Me2-C, Me1-Me2-N, Me1-Me2-B, Me1-Me2-Si, Me-C-N,

Me-C-B, Me-C-Si, Me-N-B, Me-N-Si, Me-B-Si and Me1-Me2-Me3 systems.

The elements included in the Database are:

B, C, N, Si with

Al, Ca, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, Re, Sc, Ta, Tc, Ti, V, W, Y, Zr

The SpMCBN Database version for FactSage 8.3 now includes 2 new binary and 24 new ternary systems. These relate in all but two cases to systems with boron, namely

C-N and C-Y

B-Al-Mn,, B-Al-Y, B-C-Ni, B-C-Y, B-Co-Fe, B-Co-Mn, B-Co-Ni, B-Co-Sc, B-Co-Ti, B-Cr-Mn, B-Cr-Re, B-Fe-Mn, B-Fe-Mo, B-Fe-Ni, B-Fe-Re, B-Fe-Y, B-Mo-Re,

B-Nb-Re, B-Ni-Y, B-Re-W, B-Sc-V, C-Co-Y, C-Fe-Y, C-Ni-Y

In its updated 2023 Version, calculations of thermodynamic properties and phase diagrams can be carried out for ca. 272 binary, and 585 ternary systems, for the individual temperatures or temperature ranges covered by the available experimental information.

In the Database version for FactSage 8.2, modelling of approximately 60 “end-members” associated with several different phases was completed to allow calculations for 4- or higher-component systems. This modelling has continued for boride phases in the present updated database, but such calculations should be viewed as interpolations of somewhat lower accuracy than that associated with the fully assessed lower-order systems. In addition, a small adjustment to the assessed data for the liquid phase of the Nb-C system now avoids calculation of an inverse miscibility gap at very high temperatures in the liquid phase.

The further growth in the number of assessed systems has necessitated the introduction of new elements into existing phases, as well as the self-compatible combination of phases occurring in different binary and ternary systems, but for which the thermodynamic modeling used by different authors is not compatible and often represents differing ranges of stoichiometry.

It is not a realistic proposition to carry out the massive and time-consuming amount of work required to produce self-compatible re-assessments of those systems for which there is incompatibility in the published modeling. For this reason, development of the present database has been achieved, in some cases, by simplification of certain phases, such as the MU and LAVES phases, which often display limited ranges of stoichiometry, to line compounds. This allows calculations for higher-order systems which are still of satisfactory reliability with respect both to thermodynamic properties and phase equilibria.

The simplified modeling used for certain frequently occurring phases observed in refractory alloy systems is exemplified here for the MU phase.

The MU-Phase description in the SpMCBN Database is based on a 3-sublattice model with site occupation 7:2:4. The element occupation of the lattices is

7: Co, Cr, Fe, Mn, Mo, Nb, Ni, Ta, V

2: Mn, Mo, Nb, Ta, Ti, V, W, Zr

4: Co, Cr, Fe, Mn, Mo, Nb, Ni, Ta, Ti, V, W, Zr

Because the MU-Phase has the general stoichiometry of M7X6 (where M and X are the two elements involved) the model does not allow representation of those systems in which Co, Fe, and Ni correspond to X6 in the formula (e.g. Ta7Ni6, Nb7Ni6, Nb7Co6, etc.), because Co, Fe and Ni are not present on the sublattice with occupation 2.

For this reason, the M7C6 phase has been created with stoichiometry M7X6 or X7M6, as a simplification allowing the MU-Phase to be treated as a line compound as and where necessary.

This simplified stoichiometric format, used for phases displaying small ranges of composition allows mixing descriptions in higher-order systems not only for the MU-Phase, but also for other non-stoichiometric phases which appear frequently in refractory metal alloys. Examples of the effect of some simplifications on calculated binary phase equilibria are illustrated in the following diagrams.

Because these simplifications have relevance for many ternary systems, it has been necessary to rename several phases. This has resulted in revised phase diagram figures in the FactSage Documentation.

Calculations for binary systems are generally not affected by this issue, but when calculating ternary (and higher-order) phase equilibria, it is recommended that the user retain the pre-selected phases used in producing the calculated phase diagrams for the SpMCBN Database shown in the Documentation. All phases relevant for a system of interest can be viewed by selecting ‘File’ in the top left-hand corner of the components page of the Phase Diagram module, then ‘Directories’ and then ‘SpMCBN phase diagrams.’ This will generate a list of all phase diagrams in the SpMCBN Database and choice of a particular system(s) from the list will reveal which compound and solution phase selections were made from the available choices to produce the illustrated phase diagram(s).

The following stoichiometries and the corresponding phase names represent simplifications used frequently in ternary phase diagram calculations.

Phase Stoichiometry Phase Name(s)

A7B2 C7NT

A3B CFN3

A2B CFN2

A7B6 M7C6

AB CFNT

AB2 CNT2

A further development of the SpMCBN Database in FactSage 8.1 was represented by the introduction of volumetric and thermal conductivity parameters for 184 pure solid phases. Volumetric properties (density at 298.15K, volumetric thermal expansivity, compressibility and derivative of the Bulk Modulus) and thermal conductivity parameters (based on the Debye Temperature, Gruneisen Parameter, and atoms per crystallographic cell) are now available for the following carbides, nitrides and borides:

Carbides

AlTi2C	AlTi3C	Co₃AlC	Cr₂AlC	Cr₂₃C₆	Cr₇C₃	Cr₃C₂	Fe₃AlC	Hf₃Al₃C₅	Hf₅Al₃C
Hf₂Al₃C₄	Mn₅C₂	Mn₇C₃	Mn₂₃C₆	MoC	Mo₃Al₂C	Mo₃Ni₃C	Mo₆Ni₆C	Nb₂AlC	Nb₄Co₂C
Nb₄Ni₂C	Sc₃C₄	Sc₄C₃	Ta₂AlC	Ta₅Al₃C	Ta₄Co₂C	V₂AlC	WC	Zr₃Al₃C₅	Zr₅Al₃C

Nitrides

h-AlN	h-BN	Co₄N	Co₂V₄N	Hf₃AlN	Hf₅Al₃N	Hf₂N	Hf₃N₂	Hf₄N₃	Mn₄N
Mn₆N₄	MnSiN₂	Nb₃Al₂N	Nb₄Co₂N	Nb₃Fe₃N	Nb₄Ni₂N	Ni₂V₄N	ScN	Si3N4	TaMoN
TaN_S1	Ta₄Ni₂N	Ti₂AlN	Ti₃AlN	Ti2N	WN_S1	YN	Zr₃AlN	Zr₅Al₃N

Borides

AlB₂	CaB₆	CoB	Co₂B	Co₃B	CrB	CrB₂	Cr₃B₄	Cr₂B	CrB₄
FeB	Fe₂B	FeB₂	HfB₂	MgB₂	MgB₄	MgB₇	MnB	MnB₂	MnB₄
Mn₂B	Mn₃B₄	MoB	MoB₂	MoB₄	Mo₂B	Mo₃B₂	NbB	NbB₂	Nb₃B₂
Nb₃B₄	NiB	Ni₂B	Ni₃B	Ni₄B₃	ReB₂	Re₃B	Re₇B₃	ScB₂	ScB₁₂
TaB	TaB₂	Ta₂B	Ta₃B₂	Ta₃B₄	TcB₂	Tc₃B	Tc₇B₃	TiB	TiB₂
Ti₂B	Ti₃B₄	VB	VB₂	V₂B₃	V₃B₂	V₃B₄	W₂B	WB₄	YB₂
YB₄	YB₆	YB₁₂	ZrB	ZrB₂	ZrB₁₂
AlCr₂B₂	AlCr₃B₄	AlFe₂B₂	Co₂₁Cr₂B₆	Co₂₁Hf₂B₆	Co₂₀V₃B₆	CoVB₃	Cr₅B₃	CrSc₂B₆	HfCo₃B₂
Hf₉Mo₄B	Hf₂Ni₂₁B₆	MoAlB	MoCoB	Mo₂CoB₂	Mo₂Co₂₁B₆	Mo₂NiB₂	Mo₅SiB₂	MoTiB₂	MoYB₄
Nb₂Co₂₁B₆	Nb₃Co₄B₇	Nb₃Co₅B₂	NbFeB	Ni₂₀Al_l3B₆	NiCr₃B₆	Ni₃Cr₂B₆	NiScB4	Ni₂₁Sc₂B₆	Ni₆Si₂B
Re₃Al₂B	ReCoB	Re₅Co₂B₄	ReTi₂B₂	ReYB₄	ReY₂B₆	ReY₃B₇	Re₄YB₄	Ta₂Co₂₁B₆	Ta₃Co₅B₂
Ta₂Ni₂₁B₆	WCoB	W₂CoB₂	W₂Co₂₁B₆	W₂FeB₂	W₃Hf₉B₂	W₂NiB₂	WY₃B₇	YCoB₄	YCo₂B₂
YCo₃B₂	YCo₄B	YCo₁₂B₆	YCrB₄	Y₅Si₂B₈	Zr₂Co₂₁B₆	Zr₂Ni₂₁B₆

The database is based on, and is compatible with, assessed data for relevant binary, and some ternary systems from the SGTE2014 Solution Database, but the SpMCBN Database incorporates thermodynamic parameters for very many previously un-assessed systems.

The general procedure used in obtaining assessed parameters for the solution and compound phases of the large number of previously un-assessed ternary systems in the SpMCBN Database has been to combine the phase boundary information contained in the ASM Handbook of Ternary Alloy Phase Diagrams, 1995, and in the more recent ASM Alloy Phase Diagram Database, 2016, with available assessed thermodynamic data for the appropriate binary sub-systems. This has allowed a completely compatible set of values to be derived to describe binary and ternary thermodynamic properties and phase equilibria for a particular system. Because the ASM compilations often present, for a given binary or ternary system, several published phase diagrams which differ from each other, those authors of the diagram to which greatest weight has been given in the present assessment work, are listed in the references accompanying the database.

There is a great scarcity of published experimental thermodynamic values for the phases of ternary systems, especially for refractory alloys. For this reason, the simplification of additivity of element entropy and heat capacity data has been used frequently as the basis for obtaining a complete set of thermodynamic values for ternary compounds. Enthalpies of formation and standard entropies of the compounds have then been derived to give consistency with the published phase equilibria.

While no data for oxide systems have been included in the database, several of the elements

listed above are important in refractory oxide materials. Reactions of the alloy, carbide, nitride, boride and silicide systems with such refractory oxides and with oxygen-containing gas atmospheres can be calculated using FactSage by selecting the SpMCBN database together with appropriate combinations of the FToxid, FACTPS and SGPS databases for the materials in question.

The significant experimental difficulties associated with the determination of phase equilibria and thermodynamic properties of materials at high temperatures result in a generally lower accuracy of the assessed thermodynamic parameters for refractory systems. Many of the published experimental ternary phase diagrams originate from work carried out some 30 or more years ago, and in some cases now show incompatibility with accepted binary phase equilibria. However, the data in the SpMCBN database are believed to allow generally reliable calculation of thermodynamic properties and phase equilibria for the temperatures and temperature ranges covered by the phase diagrams accompanying the documentation of this database.

The reliability of the assessment for an individual binary or ternary system is summarized under “assessments” in the documentation for the SpMCBN Database. All the assessed systems are presented with colour-coding for the quality of the assessment, in tables headed

SpMCBN Binary Assessments

Ternary Systems with Boron

Ternary Systems with Carbon

Ternary Systems with Nitrogen

Ternary Systems with Silicon

Ternary Alloy Systems without B, C, N or Si.

The term “refractory” applied to materials with applications in high-temperature structures or equipment is somewhat indefinite, but generally implies a use above about 1000°C (1273K).

The major applications of the SpMCBN Database relate to the ever-expanding field of non-oxide refractories based on carbides, nitrides, borides and silicides. These are finding wide use, in combination with appropriate elements, to produce hard, high melting temperature materials. Some examples of use are in furnace construction, high-temperature coatings, cutting tools, abrasives, aircraft brake linings, rockets, jets, turbines, and nuclear power plants.

Specific information on the phases present in each alloy system and references to the individual unary, binary and ternary systems in the database can be obtained by consulting the documentation for the SpMCBN Database.

N.B. The SpMCBN Database includes many of the elements which are important in steels. It is emphasized, however, that for calculations related to the production and heat-treatment of steels, the FSstel Database should be selected. The assessed data contained in FSstel are based on the much greater amount of accurate experimental data available specifically for steel compositions, than are available for refractory Fe-containing alloys.

Further information on the development and application of the SpMCBN Database can be found in the following two references:

P.J. Spencer, Development of a thermodynamic database for refractory boride, carbide, nitride and silicide systems, Proceedings Materials Science and Technology 2017 (MS&T17), 1230-1238.

S. Saxena, P. Spencer, V. Drozd, An alternative, environmentally-friendly production process for refractory metal carbides and syngas using methane reduction of the oxide ores, Monatshefte für Chemie in memoriam Heinz Gamsjäger, 149 (2018) 411-422.