Materials Science Forum Vols. 539-543

Abstract: Advanced TiC/a-C:H nanocomposite coatings have been produced via reactive deposition in a closed-field unbalanced magnetron sputtering system. In this paper, we report on the tribological behavior of TiC/a-C:H nanocomposite coatings in which ultra-low friction is tailored with superior wear resistance, being two properties often difficult to achieve simultaneously. In-situ monitoring the wear depth at nanometer scale reveals that the self-lubricating effects are induced by the formation of transfer films on the surface of ball counterpart. In addition, the CoF of TiC/a-C:H nanocomposite coatings decreases with decreasing relative humidity. This phenomenon can be interpreted in terms of water molecule interactions with the wear track. The influence of the volume fraction and grain size of TiC nanocrystallites on the coating properties has been examined. A superior wear resistance at a level of 10-17 m³/(N m lap) has been achieved under the condition of super-low friction and high toughness, both of which require fine TiC nano-particles (e.g. 2 nm) and a wide matrix separation that must be comparable to the dimensions of the nano-particles.

Abstract: In this study, the grain refinement near the surface of metal workpiece using hot shot peening was investigated to improve the surface properties of the workpiece. In this process, the grains were refined due to plastic deformation generated by the collision of a lot of shots under hot working conditions. A model experiment using two shots was carried out to examine the effects of the amount of deformation, the processing temperature and the time interval of the collision on grain size. In the experiment, the workpieces were stainless steel SUS304 and commercially pure copper. It was found that the global surface layer successfully attained to the fine grains by means of hot shot peening.

Abstract: MCrAlY-typed coatings are conventional for applications to land-based turbines against hightemperature oxidation and corrosion. However, improvements are still currently expected from innovations in the coating process and/or in the selection of the starting materials. Both types of innovations were studied in the present work. The former consisted in cold spray as a substitute for plasma spray which is conventionally used as the coating process. The latter consisted in developing mechanically-alloyed powders to be suitable for the targeted application especially. In this study, coating-substrate adhesion was considered as the justice of the peace to assess improvements from these innovations. This was determined using the LAser Shock Adhesion Test, namely LASAT, which was recently developed as innovative adhesion testing of thermal spray coatings. Among the main results, mechanical alloying was shown to be satisfactory to result in an homogeneous powder from the mixing of CoNiCrAlY with Mo. This powder could be coldsprayed, all the more easily because of a fine grain size. Results were compared with those obtained from conventional commercial pre-alloyed powders. As a general result, it was shown that cold spray could lead to highly-dense and high-adhesion MCrAlY-typed coatings onto Inconel 625 even though the process is usually claimed to be convenient for high-ductility materials such as copper. Incidentally, LASAT was confirmed to be a flexible and powerful testing tool to study adhesion; which resulted in the ranking of the various types of coatings involved in the work. Results are discussed in the light of an experimental simulation of the impinging of cold-sprayed particles using so-called “laser flier impact experiments”. In this development of this simulation approach to cold spray, the flier was made of a 50μm-thick disc machined from HIP’ed CoNiCrAlY.

Abstract: In this work two different synthesis processes for Single-Wall Carbon Nanotubes deposition (such as the Hot Filament-Chemical Vapor Deposition, HF-CVD, and the electrophoretic deposition, EPD) on microwire surfaces, were described. Then, the morphological and structural characterization of SWNT-modified microwires were performed by Scanning Electron Microscopy (FE-SEM) and Raman Spectroscopy, respectively. Finally, the nanostrcutured microelectrodes were electrochemically characterized using NADH, NAD+, epinephrine, and ascorbic acid (AA), useful biological molecules to develop electrochemical sensors and biosensors.

Abstract: Hot-dip galvanized transformation induced plasticity (TRIP) steel sheets were recently developed for automotive applications. The microstructure and the adhesion of zinc coated CMnSi TRIP steel alloyed with P were studied. The α-Zn coating adjacent to the steel substrate consists of a continuous η-Fe2Al5-xZnx inhibition layer with columnar ζ-FeZn13 intermetallic particles on top. Along the interface between the inhibition layer and the steel substrate Mn/Mn-P oxides were frequently observed. Although these oxides at the steel surface reduce the adhesion between the zinc coating and the TRIP steel, they do not cause any bare spots during galvanizing. Upon tensile deformation of the galvanized steel sheet, cracking along the α-zinc grain boundaries preceded fracture of the interface between the α-Zn layer and the inhibition layer. After 4 % deformation the average interface crack length increased linearly with the applied strain. This interface fracture was strongly influenced by the crystalline orientation of the α-Zn grains.

Abstract: Authors have reported theses concerning the cast defect for publication in journal of Japanese Foundry Engineering Society and AFS Transactions. This is a review of these reports. There are various factors in the casting defect that occurs in the article of casting metal, and specific of the generation factor is difficult. Moreover, it is necessary to decrease the casting defect to reduce the cost of goods manufactured and energy of production. It is effective to the evaluation and the classification method of the casting defect to employ Scanning Electron Microscopy with Energy Dispersion Spectrometer (SEM-EDS) and Electron Probe Micro-Analysis (EPMA). Casting defects chose the one that the incidence was high and specific of the generation factor is difficult, and the pinhole defect and inclusion defects were classified according to the generation factor, and penetration defect showed the relation of physical factor, chemical factor, and those interactions, and examined whether specific of the factor was possible by the surface analysis equipment about other defects (Blow hole, Shrinkage, Orange peel, Cold shut, Cracks and Veining).

Abstract: Laser shock processing (LSP) has been presented as an effective technology for improving surface mechanical and corrosion properties of metals, and is being developed as a practical process amenable to production engineering. The main acknowledged advantages of the laser shock processing technique consist on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly, the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. In the present paper, practical results at laboratory scale on the application of Laser Shock Processing are presented showing the obtained tensile residual stresses relaxation along with corresponding preliminary results about the resulting mechanical properties improvement induced by the treatment. Additionally, the influence of different irradiation parameters will be presented along with a physical interpretation of the mechanical effects induced in the materials by the characteristic fast laser-plasma interaction regime occurring in the process and model based assessments on the real possibilities of the technique as a substitutive of traditional techniques as, for example, shot peening. From a specific point of view, a critical analysis of the relative influences of coupled thermal and mechanical stress and deformation effects during LSP is presented.

Abstract: Al2O3 nano-particles were coated on the surface of LiNi1/3Co1/3Mn1/3O2 powder using a sol-gel method. The as-prepared Al2O3 nano-particle was identified to the cubic structure of Al2O3. The average size of the isolated Al2O3 nano-particles after heat treatments was calculated to be ~ 4 nm. The XRD showed that the structure of LiNi1/3Co1/3Mn1/3O2 was not affected by the Al2O3 coating. At 3 wt.% Al2O3 coatings on LiNi1/3Co1/3Mn1/3O2, the cyclic-life performance and rate capability were improved. However, heavier coatings (5 wt.%) on LiNi1/3Co1/3Mn1/3O2 dramatically decreased the discharge capacity and rate capability.

Abstract: Plasma spray deposition of hydroxyapatite (HA) coatings is a well established commercial process. When deposited on metallic substrates, these coatings have been shown to promote bone fixation and osteconductivity. A concern with current coatings is the formation of relatively large debris particles during resorption. The size of the debris is related to the particle size of the powder injected into the plasma during the deposition process. The use of solution precursors or dispersions of fine particle size powders as the feedstock for plasma spraying has been shown to produce submicron/nanocrystalline structured coatings from relatively inexpensive precursors. Nanocrystalline HA coatings may improve the resorption of the coating in the body, avoiding the irritant effect of large particles which may be seen in current thermal sprayed HA coatings. We have explored the use of sols prepared from several different precursors as the feedstock for the plasma spray deposition of HA coatings on Ti6Al4V substrates, employing statistical design of experiments to establish optimal deposition conditions. We report on the formation and the characteristics of the coatings as a function of the deposition parameters. The presence of different Ca-P crystalline and amorphous phases was assessed by X-ray diffraction analysis. The coating microstructure was characterized by scanning/transmission electron microscopy. The suitability of the technique to coat biomedical implants is discussed.