Quasi-continuous Network Research Articles

Fabrication of aluminum matrix composites by quick spontaneous infiltration process through combustion reaction of Al–Ti–B4C–CuO powder mixtures in molten aluminum

A novel, quick, spontaneous infiltration process that combines with a combustion reaction from a powder mixture of Al–Ti–B4C–CuO is presented. The process is realized in a simple and economical way, with the whole process being performed in air in a few minutes. The microstructures of the composites exhibit quasi-continuous three-dimensional network structures composed of infiltrated aluminum and B4C particles surrounded by the aggregates of the reaction products. The composites exhibit a high elastic modulus with a low coefficient of thermal expansion.

Effects of sintering parameters on the microstructure and tensile properties of in situ TiBw/Ti6Al4V composites with a novel network architecture

In order to better understand the relationship of processing–structure–mechanical properties of in situ TiB whisker reinforced Ti6Al4V (TiBw/Ti64) composites with a novel network architecture, the effects of sintering parameters on the microstructure and tensile properties of the composites were investigated. TiB whiskers with the highest aspect ratio and the coarsest whiskers were obtained at 1100 °C and 1200 °C due to the skips of whisker growth speeds along the [0 1 0] direction and the [0 0 1] and [1 0 0] directions, respectively. Additionally, TiB whisker with a claw-like structure can be synthesized from one TiB 2 polycrystal parent. The quasi-continuous network architecture of TiBw/Ti64 composites can be achieved at higher sintering temperatures more than 1200 °C. The prepared composites with the quasi-continuous network architecture exhibit a superior combination of tensile properties.

Room temperature tensile fracture characteristics of in situ TiBw/Ti6Al4V composites with a quasi-continuous network architecture

In situ TiB-whisker-reinforced Ti6Al4V matrix composites with a quasi-continuous network reinforcement distribution exhibited an improved combination of room temperature tensile properties compared to the composites with a uniform reinforcement distribution. The unique microstructure consisting of a whisker-rich boundary region and a whisker-lean matrix region leads to unique fracture characteristics . Under tensile stress, the main crack follows the TiBw-rich region, which imparts the superior strengthening effect of TiBw. The relatively large TiBw-lean region contributes positively to the elongation to failure of the composites.

Structural and magnetic properties of NiMnSb/InGaAs/InP(001)

The structural and magnetic properties of NiMnSb films, 5–120 nm thick, grown on InGaAs/InP(001) substrates by molecular-beam epitaxy, were studied by x-ray diffraction, transmission electron microscopy (TEM), and ferromagnetic resonance (FMR) techniques. X-ray diffraction and TEM studies show that the NiMnSb films had the expected half-Heusler structure, and films up to 120 nm were pseudomorphically strained at the interface, greater than the critical thickness for this system, about 70 nm (0.6% mismatch to InP). No interfacial misfit dislocations were detected up to 85 nm, however, relaxation in the surface regions of films thicker than 40 nm was evident in x-ray reciprocal space maps. TEM investigations show that bulk, planar defects are present beginning in the thinnest film (10 nm). Their density remains constant but they gradually increase in size with increasing film thickness. By 40 nm these defects have overlapped to form a quasicontinuous network aligned closely with ⟨100⟩ in-plane directions. The associated strain fields and or compositional ordering from these defects introduced a reduction in crystal symmetry that influenced the magnetic properties. The in-plane and perpendicular FMR anisotropies are not well described by bulk and interface contributions. In thick films, the in-plane uniaxial and fourfold anisotropies increased with increasing film thickness. The lattice defects resulted in a large extrinsic magnetic damping caused by two-magnon scattering, an increase in the coersive field with increasing film thickness, and a lower magnetic moment (3.6 Bohr magnetons) compared to the expected value for the bulk crystals (4 Bohr magnetons).