Papers by Author: Clarice Terui Kunioshi

Abstract: Particle reinforced metal matrix composite (MMC) coatings have been developed due to property combinations such as increased hardness, high creep/fatigue resistance as well as superior wear and oxidation resistance. MMC coatings can be produced by various techniques, which include powder metallurgy (plasma spray and HVOF processes), liquid metal processes and electrodeposition. This paper presents the development of the electrodeposition process to obtain nickel-alumina composites. The process conditions were optimized and based on these gradient nickel-alumina composites were prepared. Microstructural characterization and hardness determinations were carried out. The effect of process parameters on the amount and distribution of alumina particles as well as morphology of the deposits with and without alumina gradients are presented and discussed.

Abstract: Al-Si hypereutectic alloys produced by spray forming represent an important technological development for application in the aeronautical and automotive industries. Due to some special properties these alloys find application as cylinder liners, mainly due to their high strength and wear resistance. Much research has been carried out to evaluate the mechanical properties of these alloys but the literature on their corrosion performance is still very scarce. In this study, the corrosion behaviour of a spray formed Al-Si-Cu hypereutectic alloy was investigated by electrochemical impedance spectroscopy (EIS) in acid (pH 3.3), neutral (pH 7) and alkaline (pH 11) solutions. Intense localized attack occurred in the acid electrolyte and the impedance decreased with time of immersion. In the neutral medium, the alloy was passivated but localized attack also occurred on weak areas of the passive film. In the alkaline medium, precipitation of corrosion products occurred during the first hours of immersion causing the increase of impedance but thickening of this layer led to cracks growth with time and, consequently, to the exposure of metallic substrate, resulting in the decrease in impedance for longer periods.

Abstract: The erosion-oxidation (E-O) behavior of high velocity oxy fuel (HVOF) sprayed Ni20Cr alloy as well as WC and Cr3C2 cermet coatings on a steel substrate were studied. The E-O tests were carried out in a rig with specimen assemblies that were rotated through a fluidized bed of erodent particles in the temperature range 500-850°C and with erodent impact velocities of 2.5-19.5 ms-1. Alumina powder (~200Am) was used as the erodent. The E-O resistance of the coatings was determined as wastage, as a function of temperature. The three coatings did not exhibit any significant change in E-O at temperatures up to 500-600°C. At higher temperatures, wastage increased with temperature, reached a maximum at 700°C and then decreased with further increase in temperature. Different E-O regimes were identified. The specimen surfaces were examined in a scanning electron microscope and their roughness determined. E-O maps have been drawn that define conditions under which the coatings undergo low, moderate and severe wastage.

Abstract: This study investigates the in vitro corrosion and cytotoxicity response of AISI 316L stainless steel produced by powder injection molding (PIM) technology in a solution that simulates physiological fluids (MEM) by electrochemical techniques and neutral red uptake cytotoxicity assay. The results were compared with those of AISI 316L produced by conventional metallurgy. Both steels showed high corrosion resistance and no toxic effect in the cytotoxicity test. The corrosion products were analyzed by instrumental neutron activation analysis (INAA). The surfaces of the alloys were evaluated before and after corrosion test by scanning electron microscopy and a passive behaviour was indicated supporting the results from other techniques.