Synthesis, properties and thermal decomposition of the Ta4AlC3 MAX phase

Abstract

The present work describes a synthesis route for bulk Ta4AlC3 MAX phase ceramics with high phase purity. Pressure-assisted densification was achieved by both hot pressing and spark plasma sintering of Ta2H, Al and C powder mixtures in the 1200-1650°C range. The phases present and microstructures were characterized as a function of the sintering temperature by X-ray diffraction and scanning electron microscopy. High-purity -Ta4AlC3 was obtained by hot pressing at 1500°C for 30 min at 30 MPa. The β-Ta4AlC3 allotrope was observed in the samples produced by SPS. The Young's modulus, Vickers hardness, flexural strength and single-edge V-notch beam fracture toughness of the high-purity bulk sample were determined. The thermal decomposition of Ta4AlC3 into TaCx and Al vapour in high (10 -5 mbar) vacuum at 1200°C and 1250°C was also investigated, as a possible processing route to produce porous TaCx components.

Ta-based 413 and 211 MAX phase solid solutions with Hf and Nb

“…The first aim of this study is to explore whether it would be possible to produce bulk MAX phase-based ceramics with the (Ta1-x,Hfx)4AlC3 overall stoichiometry. These ceramics would then serve as precursors for the synthesis of pseudo-binary (Ta1-x,Hfx)4C3 solid solutions, based on the known tendency of Ta-based MAX phase compounds to decompose at high temperatures in vacuum due to the evaporation of Al, as reported in recent work [10]. This study was also motivated by the fact that ternary Ta-and Hf-based MAX phase compounds (i.e., Ta2AlC, Hf2AlC, Hf3AlC2, and Ta4AlC3) have been produced as highly pure bulk ceramics by reactive uniaxial hot pressing (HP) of Ta2H-Al-C and HfH2-Al-C powder mixtures [10][11][12][13].…”

“…The refined Ta2H powder was mixed with HfH2 (particle size <10 μm, purity >98%, Rockwood Lithium, grade PS, Germany), NbH0.89 (particle size <40 μm, CBMM, Brazil), Al (particle size <5 μm, purity >99%, Atlantic Equipment Engineers, USA), and graphite (particle size <5 μm, purity >99%, Asbury Graphite Mills, USA) to obtain the various (Tax,Hf1-x)4AlC3 and (Tax,Nb1-x)4AlC3 starting powder compositions. A 25% molar excess of Al and a 13% substoichiometric C content were chosen to inhibit the formation of TaCy, HfCy and (Tax,Hf1-x)Cy carbides, as suggested previously [10,15]. For the synthesis of Sn-containing double solid solutions, metallic Sn powder (particle size <5 μm, purity >99%, Atlantic Equipment Engineers, USA) was used.…”

Compatibility of Zr2AlC MAX phase-based ceramics with oxygen-poor, static liquid lead–bismuth eutectic

“…The basal plane delaminations reflect the loss of Al due to the vacuum environment, while the formation of Al2O3 indicates that the Zr2AlC ceramic acted as a getter for the oxygen impurities in the quartz tube used for sample encapsulation. MAX phase decomposition according to the general reaction [Mn+1AXn  Mn+1Xn + A] has been reported for Ti2AlC, Ti3AlC2, Ti3SiC2, Ti2AlN, Ti4AlN3 [37], Ta4AlC3 [38] (via Al sublimation), Zr2(Al0.42,Bi0.58)C (upon pressure application, [39]), and Cr2AlC (in low-oxygen content Ar, [40]). In all cases, however, the reported decomposition temperatures were above 1200°C [37][38][39][40], while, in this work, the Zr2AlC ceramic was vacuum-annealed at 500C, which is too low to trigger a conventional MAX phase decomposition.…”

“…MAX phase decomposition according to the general reaction [Mn+1AXn  Mn+1Xn + A] has been reported for Ti2AlC, Ti3AlC2, Ti3SiC2, Ti2AlN, Ti4AlN3 [37], Ta4AlC3 [38] (via Al sublimation), Zr2(Al0.42,Bi0.58)C (upon pressure application, [39]), and Cr2AlC (in low-oxygen content Ar, [40]). In all cases, however, the reported decomposition temperatures were above 1200°C [37][38][39][40], while, in this work, the Zr2AlC ceramic was vacuum-annealed at 500C, which is too low to trigger a conventional MAX phase decomposition. The observed (limited) transformation of Zr2AlC to ZrC and Al3Zr2 could only be attributed to elemental redistribution occurring during vacuum annealing, which presumably destabilised the MAX phase crystal structure, favoring the formation of the competing phases ZrC and Al3Zr2.…”

First Principles Investigations of Ta4AlX3 (X= B, C, N) MAX Phase Ceramics

“…With the motivation of these studies, Ta 4 AlB 3 MAX phase boride with Ta 4 AlC 3 MAX phase carbide and Ta 4 AlN 3 MAX phase nitride have been studied using density functional theory and the effect of the B substitution for the X atom in Ta 4 AlX 3 MAX phase ceramics have been investigated in this study. Recently, Ta 4 AlC 3 have been synthesized using hot pressing and spark plasma sintering methods [27] and there are several studies both experimentally and theoretically for Ta 4 AlC 3 ceramic [28][29][30][31][32][33][34][35][36][37] and only one theoretical study for Ta 4 AlN 3 ceramic [38] in the literature. The electronic and mechanical properties of Ta 4 AlC 3 ceramic were investigated while the mechanical properties of Ta 4 AlN 3 ceramic was investigated before this study.…”