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Polycrystalline Fe2AlB2 bulk including minor Al2O3 is synthesized by reactive hot pressing from Fe, Al, and B powders at 1200 °C and 30 MPa for 30 min, with a relative density of 96%. The present approach enables a markedly reduced holding time compared with previous studies. The derived Fe2AlB2 shows an electrical resistivity of 2.27±0.01 μΩ·m, Vickers hardness of 10.2±0.2 GPa, flexural strength of 232±25 MPa, compressive strength of 2101±202 MPa, fracture toughness of 5.4±0.2 MPa·m1/2 and work of fracture of 117±12 J/m2. No dominant indentation cracks are observed, indicating that Fe2AlB2 may be quite damage tolerant. Interestingly, a non-catastrophic failure is present in the SENB test, with a high work of fracture. The energy-absorbing mechanisms in inhibiting crack formation are delamination and pullout of Fe2AlB2 grains. This article is protected by copyright. All rights reserved.

The thermal shock behavior of Ti2AlC synthesized by means of self-propagating high temperature combustion synthesis with pseudo hot isostatic pressing is investigated, with a focus on the effect of the quenching temperature and quenching times. In general, Ti2AlC exhibits a better thermal shock resistance than typical brittle ceramics like Al2O3. Although the flexural strength decreases quickly in the temperature range of 300-500 °C, no discontinuous decrease in the retained strength is observed in Ti2AlC which, as with other MAX phases, differs from the behavior of typical brittle ceramics. Overall, the initial strength (grain size) plays a determining role in the thermal shock behavior of Ti2AlC and other MAX phases. On increasing quench times to 5 cycles, the retained flexural strength decreases further, however with a lower rate of decrease compared to the first quench. Quenching at 300 °C and above, voids after the pullout of grains and cracks are present, which however are absent in the un-quenched samples, indicating the weakening of bonding among grains and the induced damage around the grain boundary during the thermal shock. This article is protected by copyright. All rights reserved.

To understand the potential for use of the Hf–Al–C ternary compounds, (HfC)nAl3C2 (Hf2Al3C4 and Hf3Al3C5) and (HfC)nAl4C3 (Hf2Al4C5 and Hf3Al4C6) were investigated using density functional theory, including crystal structure, electronic structure, compressibility, and elastic properties. The theoretical density of (HfC)nAl3C2 (4.10–4.16 g/cm3) is higher than that of (HfC)nAl4C3 (3.92–3.98 g/cm3), due to the smaller number of lighter Al–C layers. With increasing numbers of Hf–C layers, the Hf–C and Al–C bond lengths remain almost unchanged. In none of the compounds is there a gap around the Fermi energy (Ef), which implies they are metal-like conductors. With increasing pressure, there is greater shrinkage along the c axis than the a axis. The bond stiffness increases with increasing pressure. In general, (HfC)nAl3C2 has higher elastic stiffness than (HfC)nAl4C3, with the moduli increasing with the number of Hf–C layers. The Hf–Al–C compounds as well as the brittle Zr–Al–C compounds all have low shear moduli/bulk moduli ratio (G/B) from 0.71 to 0.78, suggesting that the G/B ratio is not always a suitable measure of ductility.

The growth of high In content InGaN with sufficiently high crystal quality is challenging due to the differences in the GaN and InN thermodynamics. The surprisingly different thermodynamics is due to a complex competition between strain and chemistry and mediated by the different indium and gallium atomic radii as well as their different bonding enthalpies with nitrogen. In the present work, we investigate bulk and surface thermodynamics of molecular beam epitaxial (MBE) growth of InxGa1−xN for the technologically relevant (0001) and growth planes by means of density functional theory calculations. Our calculations confirm that coherent growth fully suppresses phase separation through spinodal decomposition. However, the biaxial strain is found to have a marginal effect on the critical temperatures for InxGa1−xN decomposition. Furthermore, the thermal stability of excess indium is found to be remarkably higher on N-polar surfaces than on the Ga-polar surfaces. Phase diagram of In covered (a) Ga-polar and (b) N-polar surfaces as function of In pressure.