This study reports on the first experimental evidence of the existence of the Zr 2 AlC MAX phase, synthesised by means of reactive hot pressing of a ZrH 2 , Al and C powder mixture. The crystal structure of this compound was investigated by X-ray and neutron diffraction. The lattice parameters were determined and confirmed by high-resolution transmission electron microscopy. The effect of varying the synthesis temperature was investigated, indicating a relatively narrow temperature window

The addition of Nb and Sn to Zr2AlC is investigated, targeting the synthesis of a Zr-rich bulk MAX phase free of ZrC. The 211 phase formation in the two quaternary Zr-Nb-Al-C and Zr-Al-Sn-C systems is evaluated. Solubility over the entire compositional range in (Zr, Nb)2AlC and Zr2(Al, Sn)C is observed. In terms of effectiveness, the addition of Sn is preferred over the addition of Nb, as the former is selectively incorporated into the 211 structure. A combinatorial approach results in the formation of phase-pure (Zr0.8, Nb0.2)2(Al0.5, Sn0.5)C. The effect of the added solutes on the microstructure and crystallographic parameters is investigated. The addition of Nb and Sn reduces the distortion parameter of the trigonal prism compared to pure Zr2AlC. Therefore, an attempt is made to establish a more general stability criterion for the M2AC structure based on the steric relationship between the atoms in the M6A trigonal prism. Inspired by the Hume-Rothery rules, it is suggested that comparable atomic radii of the M- and A-atoms provide a good starting point to obtain a stable 211 MAX phase.

We demonstrate intersuband InGaN/(Al)GaN quantum well infrared photodetectors grown on a free standing non-polar m-plane GaN substrate. The devices are grown by metal organic chemical vapor deposition and exhibit TM-polarized photocurrent at peak wavelengths of 7.5 and 9.3 μm at temperature of 14 K. Based on the experimental data of intersubband and interband transition energies and 8-band k · p Schrödinger-Poisson solver calculations, we were able to estimate the conduction band offset to valence band offset discontinuity ratio (ΔEc:ΔEv) of 57:43 for In0.1Ga0.9N/GaN and 55:45, for In0.095GA0.905N/Al0.07Ga0.93N non-polar m-plane multi-quantum well structures.

Additively-manufactured Ti-6Al-4V (Ti64) exhibits high strength but in some cases inferior elongation to those of conventionally manufactured materials. Post-processing of additively manufactured Ti64 components is investigated to modify the mechanical properties for specific applications while still utilizing the benefits of the additive manufacturing process. The mechanical properties and fatigue resistance of Ti64 samples made by electron beam melting were tested in the as-built state. Several heat treatments (up to 1000 °C) were performed to study their effect on the microstructure and mechanical properties. Phase content during heating was tested with high reliability by neutron diffraction at Los Alamos National Laboratory. Two different hot isostatic pressings (HIP) cycles were tested, one at low temperature (780 °C), the other is at the standard temperature (920 °C). The results show that lowering the HIP holding temperature retains the fine microstructure (~1% β phase) and the 0.2% proof stress of the as-built samples (1038 MPa), but gives rise to higher elongation (~14%) and better fatigue life. The material subjected to a higher HIP temperature had a coarser microstructure, more residual β phase (~2% difference), displayed slightly lower Vickers hardness (~15 HV10N), 0.2% proof stress (~60 MPa) and ultimate stresses (~40 MPa) than the material HIP’ed at 780 °C, but had superior elongation (~6%) and fatigue resistance. Heat treatment at 1000 °C entirely altered the microstructure (~7% β phase), yield elongation of 13.7% but decrease the 0.2% proof-stress to 927 MPa. The results of the HIP at 780 °C imply it would be beneficial to lower the standard ASTM HIP temperature for Ti6Al4V additively manufactured by electron beam melting.

We report on ultrafast GaN/AlGaN waveguide quantum cascade detectors with a peak detection wavelength of 1.5 μm. Mesa devices with a size of 7 × 7 and 10 × 10 μm2 have been fabricated with radio-frequency impedance-matched access lines. A strong enhancement of the responsivity is reported by illuminating the waveguide facet, with respect to illumination of the top surface. The room temperature responsivity is estimated to be higher than 9.5 ± 2 and 7.8 ± 2 mA/W, while the −3dB frequency response is extracted to be 42 and 37.4 GHz for 7 × 7 and 10 × 10 μm2 devices, respectively.