Materials Science Forum Vols. 475-479

Abstract: Ternary chromium aluminium nitride (Cr,Al)N coatings were produced by reactive magnetron co-sputtering technique at different nitrogen deposition pressures. Densified nanostructured coatings with grain size below 100 nm were obtained under critically controlled deposition conditions at low nitrogen partial pressures. The nanostructured coatings were generally of improved surface roughness and properties. Microhardness measurements showed that the coatings had much higher hardness than those of coarser grain sizes. It is believed that the refinement of the coating structure at low nitrogen pressures is associated with a larger number of atoms/molecules depositing on the substrate with higher energies, thus enhancing the adatom mobility and nucleated cluster formation in the coatings. The relationship between the grain size reduction and the deposition rate of the coatings was analysed.

Abstract: Chromium chloride (CrCl3) or chromium sulfate(Cr2(SO4)3) content increased trivalent chrome deposition rate. The addition of formic acid and the relative content change of potassium hydroxide decreased the trivalent chrome deposition rate. Industrially applicable trivalent chromium layers with more than 200 µm thick were well prepared at the conditions of pH with the range of 1.3-1.8, electrical current density of 5.0-5.6 A/cm2 and applied voltage of 4.0-5.9V. Average microhardnesses of the chromium layers prepared in the chromium chloride and chromium sulfate solutions are about 803-820 and 700-712 Hv, respectivevly. The wear resistance of the trivalent chromium layers was improved by plating voltage which was related to residual compressive stress on the chomium layer.

Abstract: A series of [FePt(4min)/Fe(tFe)]10 multilayers were prepared by RF magnetron sputtering and post annealing. The structures, morphology, composition, and magnetic properties were measured by XRD, SEM, EDX and VSM. X-ray diffraction showed that lattice constants of FePt phase changed with Fe layer thickness and annealing temperature. Both a and c are smaller than the standard values and a decreases as the deposition time of Fe layer increases. The grain sizes of samples annealed at 500°C increase slightly, while those at 600°C increase sharply as Fe layer decreases. The coercivities decrease with the deposition time of Fe layer, and the energy product (BH)max reaches a maximum at Fe layer deposition time of 3 minutes.

Abstract: Magnetic ripple structure of Fe84Nb7B9 is studied by electron holography. The correlation exchange length, effective exchange and anisotropy constants are estimated from a field dependence of ripple wavelength. The function of ripple theory is adjusted with a decay constant, which reflects influence of stray field on the ripple structure. A magnetic hardness at elevated temperature is also observed and analyzed.

Abstract: A novel method to observe the electrostatic field distribution with a conventional transmission electron microscope has been developed. The method allows measurements of a potential difference less than 1V/µm. This method can be performed in any kind of conventional transmission electron microscope and applied to the observation of the electric/magnetic field at the level of a specimen.

Abstract: Nanometer-sized W-dendritic form structure was fabricated with electron-beam-induced deposition (EBID) in a 200 kV transmission electron microscope. The as-prepared nanodendrites are composed of W-nanocrystals and amorphous. The as-prepared nanodendrites were then irradiated with 1 MeV electron beam in a high voltage transmission electron microscope. The effect of the irradiation is investigated. The irradiation transformed effectively almost all the amorphous part to crystalline state. Morphology of the nanodendrite also changes. The irradiation induced crystallization and morphology change are discussed.

Abstract: The effects of hydrogen on dislocations in Ni-Cr alloys have been investigated by TEM observations using single crystals. The deformation mode of Ni-Cr alloys is characterized by planar dislocations in the absence of hydrogen. However, hydrogen charging changed the dislocation configurations to promote curved dislocations, where the Shockley partials frequently constrict to make nodes and cross-slip. The hydrogen-affected dislocations are enhanced with increasing Ni content. The effect of hydrogen on superdislocations of Ni2Cr superstructure has been also investigated using an aged alloy. While the deformation mode in Ni2Cr superlattice is classified as 5 variants of superdislocation triplets and one variant of ordinary dislocations, the hydrogen charging has preferred the ordinary dislocations. The results suggest that the charged hydrogen changes the local plasticity to affect the deformation dynamics in Ni-Cr alloys.

Abstract: The present paper describes the nature of crack tip plasticity in silicon crystals examined by high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Firstly, AFM images around a crack tip are presented, where the formation of fine slip bands with the step heights of one or two nanometers is demonstrated. Secondly, crack-tip dislocations observed by HVEM are exhibited, where it is emphasized that dislocation characterization is essential to consider the relief mechanism of crack-tip stress concentration.