Precipitate strengthening in nanostructured metallic material composites

Nanostructured metallic material (NMM) composites are a new class of materials that exhibit high structural stability, mechanical strength, high ductility, toughness and resistance to fracture and fatigue; these properties suggest that these materials can play a leading role in the future micromechanical devices. However, before those materials are put into service in any significant applications, many important fundamental issues remain to be understood. Among them, is the question of the strengthening of NMM using second phase particles and if the addition of precipitates will strengthen the structures in the same manner as in bulk crystalline solids. This issue is addressed in this work by performing molecular dynamics simulations on NMM with precipitates of various sizes and comparing the results with the same structure without precipitates. In this view, Cu/Nb bilayer thin films with spherical Nb particles inside the Cu layer were examined using molecular dynamics simulations and show a significant improvement on their mechanical behavior, compared to similar structures without particles. Furthermore, an analytical model is developed that explains the strengthening behavior of an NMM that has precipitates inside one layer. The theoretical results show a qualitative agreement with the finding of the atomistic simulations.     

Structural investigations on Nd-doped silica nanocomposites: effect of sintering temperature and dopant concentration

Neodymium-doped silica nanocomposites were prepared from an acid-catalysed sol–gel solution followed by heat treatment. The structural and microstructural properties of the prepared samples as a function of sintering temperature and Nd concentration are reported. Fourier transform infrared spectra show that phase separation occurs during heat treatment. The presence of Nd₂O₃ and α-Nd₂Si₂O₇ phases in the samples was established by X-ray diffraction (XRD), and transmission electron microscopy (TEM) micrographs revealed the microstructure of the nanocomposites. From XRD patterns, the crystallite size was determined using the Debye–Scherrer formula, while the particle size was estimated from TEM micrographs. The results suggest that sintering at high temperature enhances the crystallinity and density of Nd₂O₃–SiO₂ nanocomposites, while the high concentration of neodymium prevents the crystallization of SiO₂.     

Crystallization and thermal stability of polypropylene/multi-wall carbon nanotube nanocomposites

Polypropylene (PP)/multi-wall carbon nanotube (MWCNT) nanocomposites were prepared via a melt compounding method using a twin-screw extruder. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the crystallization and thermal stability of the nanocomposites. The DSC analysis results revealed that the existence of MWCNTs in a PP matrix, which acted as a nucleating agent enhancing the crystallization process of PP matrix. This behaviour was manifested by an increase in the crystallization temperature and crystallinity index of the nanocomposites. Additionally, the TGA results showed that the addition of MWCNTs dramatically increased the thermal stability of the PP/MWCNT nanocomposites. Generally, MWCNT type C-70P showed improved crystallization and better thermal stability of the nanocomposites compared to type C-150P.     

Precipitation of an icosahedral quasicrystalline phase in Hf59Ni8Cu20Al10Ti3 metallic glass

The crystallization process of a Hf₅₉Ni₈Cu₂₀Al₁₀Ti₃     

Nanoindentation study of size effects in nickel–graphene nanocomposites

Metal–graphene nanocomposites find applications in nanoscale devices, as functional materials and can serve as a test bed to gain insight into fundamental deformation mechanisms of metals under geometric confinement. Here, we report full atomistic nanoindentation simulations for nickel–graphene nanocomposites with varied numbers of layers of graphene sheets to investigate the size effects on the hardness, and to understand how emerging dislocation loops interact with the nickel–graphene interface under varied geometric confinements. A detailed analysis of the plastic deformation mechanism shows that as dislocation loops reach the nickel–graphene interface, the local bending of the graphene sheet is altered and further dislocation propagation is blocked. An increase in the number of graphene layers decreases the hardness, but increases the maximum elastic deformation of the nickel–graphene nanocomposites. These findings indicate that the mechanical properties of nickel–graphene nanocomposites can be engineered by controlling the thickness of nickel and graphene layers, respectively.     

Synthesis of nanostructured vanadium powder by high-energy ball milling: X-ray diffraction and high-resolution electron microscopy characterization

Vanadium metal powders, ball milled with different surfactants viz., stearic acid, KCl and NaCl, have been studied by X-ray diffraction and transmission electron microscopy. The surfactants alter the microstructural and morphological characteristics of the powders. Ball milling with stearic acid results in solid-state amorphization, while powders milled with KCl yield vanadium–tungsten carbide nanocomposite mixtures. NaCl proved to be an excellent surfactant for obtaining nanostructured fusion-grade vanadium powders. In order to understand the reaction mechanism behind any interstitial addition in the ball-milled powders, CHNOS analysis was performed.     

Assessment of tensile interphase profile of PVC/TiO2 polymer nanocomposites

The tensile properties of polymer nanocomposites depend dominantly on their interphase profile. The interfacial layer adhesion B-parameter, the relative interphase tensile strength (σ_IR) and the Z-interphase parameter for the central layer are quantified for assessment of tensile interphase properties of PVC/TiO₂ polymer nanocomposites. The redeveloped Pukanszky model is employed to determine the layer adhesion B-parameter of interphases. The study shows that the tensile strength of the interphase σ_I, as well as σ_IR and the B- and Z-parameters of the central layer of the interphase, are significantly correlated with the tensile strength of the nanocomposites.