X.K. Meng

Indentation size dependent plastic deformation of nanocrystalline and ultrafine grain Cu films at nanoscale

Nanoindentation creep tests were performed in the depth range from about 28 to 190 nm on nanocrystalline (NC) and ultrafine grain (UFG) Cu films. Pronounced indentation size effects on hardness, creep strain rate (e), and strain rate sensitivity (mc) are observed. Both e and mc are dependent not only on contact depth (hc) but also on grain size. The experiment results and analysis support that the creep deformation of NC and UFG Cu is dominated by grain-boundary-mediated process and diffusion along the interface of tip sample, respectively, under a critical hc and dislocation-mediated process begin to work as hc increases further.

The synthesis and mechanical property evaluation of Ni/Ni3Al microlaminates

Abstract Alternating layers of Ni and Ni–Al were magnetron sputter deposited at room temperature, and then annealed at 1073 K in a high vacuum furnace for an hour to produce Ni/Ni 3 Al microlaminates with controlled composition, spacing, and volume fraction of the layer. The annealed composite was confirmed to be Ni and Ni 3 Al by transmission electron microscope (TEM). The film parameters were evaluated by fitting the measured dispersion curve to a theoretical model. For Ni/Ni 3 Al laminated composites, a density of 7500±100 kg/m 3 , Youngs modulus of 280±10 GPa, and a thickness of 140±5 μm, were found.

Size-dependent Curie transition of Ni nanocrystals

The mechanical spectroscopy and magnetization measurements are performed on Ni nanocrystals from room temperature to 650 K. It is found that the peak temperatures of internal friction are in agreement with the corresponding Curie temperatures of Ni nanocrystals obtained from the magnetization-temperature curves, showing that the traditional mechanical spectroscopy can also be employed to investigate the Curie transition of ferromagnetic nanocrystals. Moreover, the analytical model for size-dependent Curie temperature is proposed in terms of a size-dependent melting temperature model. The Curie temperature drops with decreasing grain size in Ni nanocrystals, which agrees with the corresponding experimental results.

Facile synthesis of superparamagnetic Ni–Fe ultrafine nanoalloy nanoparticles with equilibrium ordered phase structure via a sol–gel process

Ni-Fe nanoalloy nanoparticles with an average grain size of 4 nm in diameter have been prepared by a sol-gel method under a hydrogen atmosphere where ethanol and oleic acid have been used as solvent and surfactant, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) examinations of the nanoparticles show the occurrence of (111), (200), (220) and (311) diffraction peaks and rings, meaning that the nanoparticles have a face-centered-cubic phase structure. Moreover, a superlattice diffraction peak and a diffraction ring/spot can also be observed in XRD and SAED results, indicating the formation of an equilibrium ordered L1(2) phase structure. The as-prepared Ni-Fe nanoalloy particles show typical superparamagnetic behavior at room temperature and the blocking temperature of the nanoparticles is determined to be about 50 K.

Temperature-coefficient-of-resistance characteristics of sputter-deposited NixAl1−x thin films for 0.5<x<1

Abstract By investigating the thermal variations of electrical resistance of a range of NixAl1−x sputter-deposited films, where x=0.5–1, it was found that a thermally-activated transition from the insulator to metal state on increasing temperature occurred only within a narrow range of x from 0.75 to 0.8. At all other values of x investigated, the conduction behavior of the films appeared to be metallic as expected. The same observations were made on two different sputtering systems with different deposition conditions, indicating that the electrical transition from x=0.75 to 0.8 is a highly reproducible phenomenon.

Optical waveguiding properties of highly 〈100〉 textured PLT thin films prepared by pulsed laser deposition

Abstract The optical waveguiding properties of Pb 0.72 La 0.28 TiO 3 (abbreviated as PLT) films prepared on MgO coated (100) LiF substrates by pulsed laser deposition were studied. The films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which revealed that highly 〈100〉 textured PLT thin films with small surface roughness were achieved. The transmittance spectra of the films, measured using a double beam photo-electrometer, showed that the as grown films exhibited the average transmittance of 75% in the wavelength range of 400–2000 nm. The optical waveguiding properties were evaluated by the optical prism-film coupling method, which indicated that the m-lines of transverse-electric (TE) and transverse-magnetic (TM) multimodes were distinct.

Rolling deformation induced reduction of rate sensitivity and enhancement of hardness in nanocrystalline NiFe alloys

Both hardness (H) and rate sensitivity (m) of nanocrystalline NiFe alloys were studied by nanoindentation testing. It was found that H increases, and m decreases after rolling in the alloys. It is interesting that the decrease in m by rolling is totally contrary to the conventional coarse grain alloys. The dislocation density is remarkably enhanced by rolling deformation, which leads to the hardening behaviour of the samples. The dislocation absorbed at the grain boundary (GB) and/or sub-GB and grain growth by rolling are responsible for the reduced m of the rolled alloys.

Fabrication of NiAl thin film by PLD and properties of Ni3Al thin coatings

Abstract The as-deposited NiAl films, fabricated at 673 K by pulsed laser deposition (PLD), were annealed at 1073 K for 1 h to produce a new type of intermetallic coating with a two-phase Ni 3 Al+Ni equiaxed grain structure. Due to the similarities between Ni 3 Al and Ni in lattice parameters and crystallography, the coatings exhibit good adhesion to the substrates, and at the same time, provide the latter with significantly improved surface strength (hardness) and corrosion resistance.

Annealing improved ductility and fracture toughness of nanocrystalline Cu films on flexible substrates

In this paper, the effect of annealing temperature (T) on the ductility of 50 nm thick nanocrystalline (NC) Cu films adhered to flexible substrates was investigated by a uniaxial tension test. It was found that the ductility and the fracture toughness (Gc) can be significantly improved through an annealing treatment. The crack onset strain of the 300 °C annealed Cu film is 18.1%, which is about twice that of the as-deposited NC Cu film. In addition, Gc of the 300 °C annealed Cu film is 1833 J m−2, which is nearly three times that of the as-deposited NC Cu film. Focused ion beam results indicate that the as-deposited film fractures with delamination and strain localization coevolving, while the as-annealed film fractures by adhering well to the substrate. At a higher T, the tensile residual stress is lower, the microstructure is more stable, and a diffusion or compound interface is generated, resulting in a better bonding between the film and the substrate. In this case, the strain localization is suppressed more effectively, causing improved ductility and Gc. Whether the film is as-deposited or as-annealed, the saturated crack spacing is about 1.41 µm, which accords well with the theoretical analysis. Intergranular fracture is suggested to be the main fracture mechanism.

A Monte Carlo approach of phase separation in binary alloys with mobile vacancies

Abstract A two-dimensional Monte Carlo approach of phase separation in binary (A + B) alloys containing vacancies has been developed. This approach involves both swamp of atom-atom pairs and atom-vacancy (V) pairs in lattices. The thermodynamics of atom jumping, atom-atom and atom-vacancy exchange have been derived. The phase separation in both symmetric and asymmetric alloys has been simulated. Based on the present approach a normal dynamics of phase separation has been revealed. It has been found that the concentration of vacancies in the lattice has a marked influence on kinetics of phase separation.