Julius C. Schuster

Summary of constitutional data on the Aluminum-Carbon-Titanium system

The constitution of the titanium-aluminum-carbon ternary system has been investigated combining critical evaluation of literature data with new experimental results. Three ternary phases occur in this system: Ti3AlC, Ti2AlC, and newly discovered Ti3AlC2. As analyzed by wet chemistry methods, all three phases are carbon deficient with respect to their “ideal≓ stoichiometry, which is based on the crystal structure formula. Ti2AlC and Ti3AlC melt incongruently at 1625 ± 10 ‡ and 1580 ± 10 ‡, respectively. Ti3AlC2 decomposes in the solid state. The two isothermal sections at 1000 and 1300 ‡ investigated experimentally are corroborated by thermochemical calculations. A projection of the liquidus surface is given, and a reaction scheme linking this liquidus projection with the isothermal sections observed is proposed.

Reassessment of the binary Aluminum-Titanium phase diagram

All available literature on the constitution of Ti−Al is reviewed. Based on a critical evaluation of these data the phase diagram for this system is assessed.

The ternary system titanium-aluminum-nitrogen

The phase equilibria in the ternary system titanium-aluminum-nitrogen are investigated for two isothermal sections. At 1273 K one encounters the H-phase Ti2AlN (a = 0.29912 nm, c = 1.3621 nm) and the cubic perovskite-type phase Ti3AlN (a = 0.41120 nm). At 1573 K one encounters additionally Ti3Al2N2 (space group: P31c, hexagonal axes a = 0.29875 nm, c = 2.3350 nm). α-Titanium dissolves nitrogen and aluminum to a large extent, but no solubility of the third element was detected in any of the other binary phases.

Reassessment of the Al–Mn system and a thermodynamic description of the Al–Mg–Mn system

Abstract A thermodynamic optimization for the Al – Mn system is performed by considering reliable literature data and newly measured phase equilibria on the Al-rich side. Using X-ray diffraction, differential thermal analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy methods, the melting behavior of λ-Al4Mn was correctly elucidated, and two invariant reactions associated with λ-Al4Mn (L + μ-Al4Mn λ-Al4Mn at 721 ± 2 °C and L + λ-Al4Mn Al6Mn at 704 ± 2 °C) are observed. The model Al12Mn4(Al, Mn)10 previously used for Al8Mn5 was modified to be Al12Mn5(Al, Mn)9 based on crystal structure data. In addition, the high-temperature form of Al11Mn4 is included in the assessment. Employing fewer adjustable parameters than previous assessments, the present description of the Al – Mn system yields a better overall agreement with the experimental phase diagram and thermodynamic data. The obtained thermodynamic description for the Al – Mn system is then combined with those in the Al – Mg and Mg – Mn systems to form a basis for a ternary assessment. The thermodynamic parameters for ternary liquid and ternary compound Mn2Mg3Al18 (τ) are evaluated on the basis of critically assessed experimental data. The enthalpy of formation for τ resulting from CALPHAD (CALculation of PHAse Diagrams) approach agrees reasonably with that via first-principles methodology. Comparisons between the calculated and measured phase equilibria in the Al – Mg – Mn system show that the accurate experimental information is satisfactorily accounted for by the present description. A reaction scheme for the whole ternary system is presented for practical applications.

The AI-Ali8Mo3 section of the binary system aluminum-molybdenum

The constitution of the partial system Al-Al8Mo3 is investigated using differential thermal analysis (DTA) and X-ray diffraction data. Ten (10) intermetallic phases are observed, and their stability ranges with respect to composition as well as temperature are determined. The crystal structures of Al12Mo, Al5Mo(h), Al4Mo(h), and Al8Mo3 are corroborated, confirming literature data. The crystal structures of the phases Al5Mo(ht), Al5Mo(r), Al3+xMo1-x(h), and Al3Mo(h) are newly determined. For the phases “Al22Mo5” and “Al17Mo4,” powder diffraction patterns are obtained. The revised phase diagram Al-Mo (up to 28 at. pct Mo) is presented.

The ternary systems ScAlN and YAlN

Abstract In the ternary ScAlN system a perovskite-type phase Sc3AlN1 − x (a = 0.4396–0.4435 nm) occurs at 1273 K. This phase is in equilibrium with ScN, Sc(solid solution), Sc2Al and ScAl. AlN does not coexist with scandium but does so with ScN, ScAl2 and ScAl3. The binary phase ScAl was found to be orthorhombic with a = 0.502 99 nm, b = 0.989 45 nm and c = 0.312 63 nm. In the Y-Al-N system no ternary phase was found. AlN reacts with up to 40 at.% Y to yield YN and YAl2. Isothermal sections at 1273 K are presented for both ternary systems.

Structural chemistry of complex carbides and related compounds

Abstract Complex carbides formed in ternary systems of a transition element (M), a B-group element (M′), and carbon and having a formula M2M′C (H-phase) or M3M′C (perovskite carbide) occur frequently. This reflects the simple geometry of the atomic arrangement of the metals and the filling mode by an interstitial stabilizer such as carbon or nitrogen. The phase relationship of the ternary combinations {Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, and Ni}-aluminum-carbon was investigated. New complex carbides were found with the corresponding zirconium, hafnium, and tantalum combinations. The crystal structures in the case of Zr- and Hf-containing complex carbides can be characterized by a twelve-metal-layer sequence and by a ten-metal-layer sequence with carbon atoms again filling octahedral voids. The transition of structure types from TiC, Ti2AlC, Ti3SiC2, ZrAlC2, Zr2Al3C5, to Al4C3 is also discussed.

Phase diagrams of the ternary systems Mn, Fe, Co, NiSiN

Abstract Phase equilibria in the ternary systems Mn, Fe, Co, and NiSiN are investigated and isothermal sections 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, Si3N4 coexists with MnSiN2, Mn3Si, Mn5Si3, MnSi, and MnSi2−x. In the systems Fe, Co, NiSiN, Si3N4 coexists with all binary silicides but reacts rapidly with iron above 1120 ± 10°C, and cobalt and nickel above 1170 ± 10°C to form binary silicides and nitrogen gas.

Interfacial structure and reaction mechanism of AlN/Ti joints

Bonding of AlN to Ti was performed at high temperatures in vacuum. The bonding temperature ranged from 1323 to 1473 K, while the bonding time varied from 7.2 up to 72 ks. The reaction products were examined using elemental analysis and X-ray diffraction. TiN, Ti3AlN (τ1), and Ti3Al were observed at the AlN/Ti interface, having various thickness at different bonding conditions. The thickness of TiN and Ti3AlN layers grew slowly with bonding time. On the other hand, growth of the Ti3Al layer followed Fick’s law. The activation energy of its growth was found to be 146 kJ mol-1. When thinner Ti foil (20 μm) was joined to AlN at 1473 K for a long time (39.6 ks), the Ti central layer has completely consumed and another ternary compound Ti2AlN(τ2) started to form. A maximum bond strength was achieved for an AlN/Ti (20 μm) joint made at 1473 K for 28.8 ks, after which the bond strength of the joint deteriorated severely.

Silicon nitride-metal joints: phase equilibria in the systems Si3Ni4―Cr, Mo, W and Re

Phase diagrams in the ternaries Cr-Si-N, Mo-Si-N, W-Si-N and Re-Si-N are established. No ternary phase is found. Si3N4 coexist under argon at 1273 K with all binary Cr-silicides but not with chromium, with MoSi2 and Mo5Si3 but not with Mo3Si or molybdenum, with WSi2, W5Si3 and tungsten, and with ReSi2, Re17Si9 and rhenium. At 1673 K, Si3N4 is found in coexistence with Cr5Si3, MoSi2, Mo5Si3, WSi2, W5Si3, ReSi2 and Re17Si9. The implications of these phase equilibria for joining silicon nitride with low thermal expansion metals are discussed.