The evolution of texture during annealing of electroless Ni-Co-P deposits

The electroless Ni-Co-P alloy films containing up to 13.4% Co and 7.6% P were deposited on a 5086 aluminum alloy sheet using baths consisting of NiSO₄, CoSO₄, (NH₄)₂SO₄, NaH₂PO₂, sodium citrate and thiourea. The deposits were solid solutions having a grain size of 6 to 7nm and strong <111> texture. When the deposits were annealed for 2h, Ni₅P₂ was precipitated at 325°C and transformed into the stable Ni₃P phase at higher temperatures. During annealing the texture of deposit changed from <111> to <100>. The texture change was attributed to preferential growth of <100> grains at the expense of <111> grains to decrease the thermal strain energy of the deposits.     

Preparation of nickel-coated tungsten carbide powders by room temperature ultrasonic-assisted electroless plating

In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.     

In situ composite coating of titania-hydroxyapatite on commercially pure titanium by microwave processing

Microwave (MW) processing has been studied as an alternative method of hydroxyapatite (HA) based composite coatings on commercially pure titanium (CPTi) to enhance the bioactivity for orthopaedic and dental implant applications. The coating was formed by processing CPTi metal packed in HA and at 800 W microwave power for 22 min. The composition of the coating was found to be TiO₂ (rutile) as major phase along with HA as minor phase. The MW absorption of non-stoichiometric TiO₂ layer, which was grown during the initial hybrid heating, resulted in sintering of apatite particles interfacing them. The non-stoichiometric nature of TiO₂ was evident from the observed mid-gap bands in ultraviolet-visible diffusive reflectance (UV-VIS-DR) spectrum. The lamellar α structure of the substrate suggests that the processing temperature was above β transus of CPTi (1155 K). The oxygen stabilized α phase whose thickness increased with microwave processing time, was likely to be the reason for the increase in Young's Modulus and hardness of the substrate. The coating induced apatite precipitation in bioactivity test. The osteoblast cell adhesion test demonstrated cell spreading which is considered favourable for cell proliferation and differentiation. Thus, in situ composite coating of titania and HA on CPTi was obtained by a simple one-step process.     

Mechanical properties of quasicrystalline Al-Cu-Fe coatings with submicron-sized grains

Quasicrystalline Al-Cu-Fe coatings with submicron-sized grains (∼ 400 nm) were produced by electron beam PVD. Mechanical properties of the Al-Cu-Fe quasicrystalline coating and a bulk Al-Cu-Fe quasicrystalline specimen with an average grain size of about 50 μm were examined using a set of micro- and nanoindentation techniques (with plotting stress-strain curves). It has been found that the length of the hardening stage in the stress-strain curve at room temperature for the coating is essentially greater, and the softening is weaker as compared with those for the bulk specimen. Possible reasons for such mechanical behavior of the coatings are discussed. Nanoindentation tests have shown that stepwise plastic flow is observed in both bulk sample and coating.     

Apatite coatings onto titanium surfaces submitted to laser ablation with different energy densities

Apatite coatings were deposited on titanium surfaces modified by Nd:YVO₄ laser at different energy densities in environment atmosphere. Apatite was synthesized by sol-gel method using calcium nitrate and phosphoric acid as precursors. The titanium modified surfaces were dip-coated into precursor solution and pre-fired at 700 °C in air for 3 h. Analyses by XRD, FTIR and SEM showed the formation of a mixture of phases: hydroxyapatite (HA) and tricalcium phosphate (β-TCP) onto the surfaces submitted to laser ablation. Surface Rietveld analysis showed that a larger amount of non-stoichiometric oxides produced by laser ablation resulted in greater formation of HA on the coating. However, more of the β-TCP phase than HA was observed on surfaces with low amounts of oxides.     

In-depth distribution of rusts on a plain carbon steel and weathering steels exposed to coastal-industrial atmosphere for 17 years

In-depth distribution of rusts on two weathering steels and a plain carbon steel exposed to atmosphere for 17 years under a bridge at a coastal + industrial region in Japan were studied. In the rust layer on all specimens, α-FeOOH, β-FeOOH, γ-FeOOH, Fe₃O₄ and so-called amorphous rust were found. Within rust layers, there were thick parts and thin parts, which were finely and complicatedly distributed on steels. Among these rust species, α-FeOOH was dominant on all specimens. α-FeOOH appeared almost homogeneously through the rust layer. Its concentration was higher on weathering steels than on plain carbon steel. β-FeOOH was found mainly at thick parts and was scarce at thin parts of rust layers. Concentration of α-FeOOH was higher and that of γ-FeOOH was lower on weathering steels than on plain carbon steel. Amorphous rust was located at the bottom of the rust layer irrespective of steel types. Concentration of magnetite was negatively correlated with concentration of β-FeOOH.     

Effect of N, C and B interstitial atoms on local bonding structure in mechanically activated TiH2/h-BN, TiH2/C, and TiH2/B mixtures

Mechanically activated TiH₂/h-BN, TiH₂/C and TiH₂/B mixtures was studied by temperature-programmed desorption, X-ray diffraction, transmission electron microscopy and X-ray emission spectroscopy. Ball milling in the presence of additives results in a modification of hydrogen occupation sites. Additional Ti-N, Ti-C or Ti-B bonds from chemical bonding of Ti with interstitial N, C and B atoms, are formed in TiH₂ due to contact of TiH₂ nanoparticles with the respective additive matrix materials. Mixed configurations around Ti atoms with proportional combination of local Ti-H and Ti-N, Ti-C or Ti-B bonds significantly decrease the thermal stability of TiH₂. The effect is most pronounced when boron is the additive.