Materials Science Forum Vol. 805

Abstract: Schiff bases m-toluene N-Salicylideneaniline (m-TOL), (B) m-nitro-N- Salicylideneaniline (m-NTR) and (C) m-methoxy-N-salicylideneaniline (m-MTX) and cerium ions were studied added to 3.5 wt.% NaCl solution and added to the hybrid film based tetraethoxysilane (TEOS) e 3-methacryloxypropyltrimethoxysilane (MPTS). The polarization measurements showed lower current densities for the steel in NaCl with m-MTX, indicating that the m-MTX may be acting as an inhibitor. The hybrid films were doped with the m-MTX, Ce (III) or Ce (IV). Electrochemical measurements of open circuit potential (E_OC), polarization curves and electrochemical impedance spectroscopy (EIS), were used to evaluate the corrosion behavior of the hybrid films. According Electrochemical Impedance measurements, all hybrid films, provided protection to the carbon steel. The films doped with Ce (IV), provided greater protection than the other, which indicates that this is the most suitable dopant for use in films.

Abstract: The main aim of this paper is to study copper ions electroplating, evaluating the cathodic current efficacy, from cyanide ion free alkaline baths, stabilized by different complexant agents for the Cu²⁺ ions. The cathodic current efficacy was assessed through quartz microbalance measurements, employing different current modulations. Results revealed that the pulsed current application has great influence on the cathodic current efficacy during electroplating in the baths under study.

Abstract: The metallographic technical preparation influence on hot dip deposited zinc layer intermetallic phases investigation and distribution was the aim objective in this work. The base material was SAE 1020 carbon steel and specimens with and without zinc layer detachment was selected after the submission to adherence test base on hammer impact. Three different grinding and polishing technique were employed and the phases were investigated by optical metallographic technical as well as through a scanning electron microscope with an EDS system. The different metallographic techniques have no effect on the phase determination and distribution.

Abstract: Copper-niobium composite electrocoatings were obtained by co-electrodeposition in acidic copper sulfate bath containing suspended niobium particles. The amount of incorporated particles was evaluated using a Central Composite Design (CCD) with three factors of control (cathodic current density, stirring rate and particle concentration in the bath) at three levels each. A great influence of particle concentration was observed. The stirring rate also had influence but to a lower extent and the cathodic current density was the least significant factor. The combination, both cathodic current density and particle concentration at the highest levels and stirring rate at the lowest level, led to the highest amount of incorporated particles. The behavior was not linear between the high and low levels for all factors. The roughness of the composites was higher than the pure copper coatings and increased with increasing current density. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to copper matrix grain refinement and increased with the increase of both current density and incorporated particle volume fraction.

Abstract: Before metallic materials are painted, surface pre-treatments are usually applied, these are known as conversion treatments. Such treatments aim to slow the degradation of the organic coating/metallic substrate system in aggressive environments. Amongst the most effective conversion coatings for aluminum and its alloys, is the chromatization. However, the high toxicity of this process waste has led industry to ban the chromatization process from the market and seek new procedures to protect metallic surfaces which, at the same time, present lower toxicity and are efficient to protect against corrosion. This study aims to obtain a coating composed of aluminum oxide on the Al AA 3003 alloy, as a potential method to substitute the chromatization process. A study on the protection properties against corrosion of the base metal, coated with oxide, was developed. Open circuit potential tests, electrochemical impedance spectroscopy, and anodic potentiodynamic polarization curves were carried out in a Na₂SO₄ 0,5 molL^-1 solution and pH 4,0. The morphology characterization was performed employing the scanning electronic microscopy (SEM). Results indicated that the new coating presented better behavior than the chromatized samples, suggesting that the former can substitute the chrome coating.

Abstract: This work studies the effect of double aging heat treatment on superalloy Inconel 718. The heat treatment followed two steps: Solid solution at 1095oC for 1h, and two steps of aging 955oC/1h - 720oC/6,5h - 720oC/1,5h + 620oC/8h. Parameters such as grain size, secondary phases distribution and qualitative analysis via SEM/EDS and Vickers hardness are used in order to evaluate the microstructural evolution. The results show increase of grain size and Vickers hardness, as well as a better distribution of secondary phases along the matrix.

Abstract: The 300M steel has emerged from the high strength SAE 4340 steel, which had been developed in order to obtain increased toughness and weldability in applications requiring better mechanical properties; some minor changes in the alloy elements were introduced: addition of vanadium, and raise in the silicon content. The laser surface hardening is a process in which the steel surface is heated below the melting point, in order to produce solid state phase transformations whithout changing the bulk. This work has evaluated which would be the best parameters for the laser carburizing heat treatment using a low power (50W) CO₂ laser, comparing and contrasting the resulting microstructure and hardness of both steels. The following CO₂ laser parameters were varied: speed, resolution and number of passes; power was kept constant. Carbon black was used as coating. After the surface laser treatment, the samples were cooled in air and the formation of a hardened layer and heat affected zone in both materials was observed. Samples were prepared for metallographic analysis, followed by optical and scanning electron microscopy observation. Layers presented a Vickers hardness value higher than the base metal and the hardened layer had a higher hardness value compared to the heat affect zone. The formation of martensite in the heat affected zone in both steels was observed, although not to the full extension, making this a multiphasic zone.

Abstract: This article was aimed at studying the influence of different aging times during the precipitation phase of the UNS S31803 (SAF 2205) duplex steel. To do so, all the test specimens were solution heat treated at 1050oC for 1 hour and quenched in water. After this step, the samples were aged at 850°C for periods of 10, 60 and 600 minutes and cooled in water. The aging heat treatments (TT) were performed in order to precipitate the sigma phase. Samples were subjected to microhardness and tensile tests so that the influence of the microstructural changes over the mechanical properties of the steel was assessed. Based on the microhardness and tensile test data, it was possible to verify a significant change over the mechanical properties of the UNS S31803 steel.

Abstract: This work aimed to obtain microstructural changes due to the springback effect in order to compare two conventional high strength steels: the interstitial free steel (IF) and the bake hardening steel (BH). The mechanical characterization of the springback effect was performed by a mechanical forming testing called as the three-point air bending. The geometric changes resulting from the forming process were measured by calculating the aspect ratio. The results show that the BH steel suffers a greater springback effect rate than the IF steel due to the greater mechanical strength of the BH steel, and to the variation of this steel’s aspect ratio, depending on the combination of elongation and mechanical strength. It was concluded that the heat treatment performed on the BH steel increased the mechanical strength of the material without losing its formability.

Abstract: NiCrAlC alloys are economical alternatives nickel superalloys to Co family Stellites^TM alloys, they are constituted by a dispersion of chromium carbides in a Ni3Al (γ’) intermetallic matrix. Mechanical Alloying (MA) allows better control of the carbides size and distribution in NiCrAlC matrix after sintering, although high porosity has been observed after uniaxial compaction and sintering of NiCrAlC alloys processed by MA. This research investigated the employment viability of pre-sintering heat-treatments followed by a new uniaxial compression in order to reduce porosity after final sintering. The characterization of the processed material by optical metallography and quantitative stereography appoints to the viability of this conception to reduce the porosity of NiCrAlC alloys processed by Mechanical Alloying.