Hector Reynaldo Meneses Costa

Characterization of FeCr and FeCoCr alloy coatings of carbon steels for marine environment applications

This paper presents the adhesive strength results of FeCr and FeCoCr deposits produced by electric arc thermal spray process on carbon steel plates. Five chemical compositions were tested to give a large panel of possibility. Coatings were characterized by several methods to result in a performance screening. The main assessment of microstructural morphology was made by scanning electron microscopy (SEM). The mechanical strength of coatings was evaluated by standard pull-off test. The corrosion resistance was analyzed in salt-spray test. The morphology of coatings exhibits characteristics of lamellar microstructures with incompletely melted particles together with a distribution of similarly oriented oxides. The adhesive strength of FeCoCr alloy coatings was higher amongst all studied conditions. All sealed conditions presented low corrosion in salt-spray exposure. Additionally, a new FeCoCr alloy was studied to reduce pores and microcracks that are frequently found in traditional FeCr and FeCrNi alloys. Based on the performed characterizations, the findings suggested that the FeCoCr deposition, with an epoxy sealing, is suitable to be used as an efficient coating of carbon steel in aggressive marine environments.

Influence of Welding Parameters in Substrate/Coating of Galvanized Sheets Using Resistance Spot Welding

The main objective of this work is to propose an optimization of welding parameters through the process of resistance spot welding, applied to Interstitial Free (IF) steel sheets in order to increase the life of conventional copper electrodes. The methodology consisted of using a weld tester in order to ensure the accuracy of values. The main parameters selected through a survey of the weldability were: force, time and welding current. To evaluate the resistance of the weld and the electrode wear, mechanical tests were performed like tensile-shear, cross-tension, peel test and microhardness. A microstructural evaluation by optical microscopy (OM) and scanning electron microscopy (SEM) was made. The results show reducing the thickness of the coating in the weld region and macro and microstructures were observed. Through the tensile-shear and cross-tension tests were verified using electrodes caps up to 1250 points with acceptable welds. The microhardness test results indicated significant hardness increase in weld nugget elucidated by differences in microconstituents evaluated by OM and SEM. The methodology used for parameter selection has highlighted an optimal combination with 200kgf electrodes force, 9cy welding time and 7.8 kA welding current, in overlap IF steel sheets with 0.75mm of thickness, thereby increasing the lifetime of the electrode and ensures a better quality of welds and the consequent reduction of energy applied to the weld process.

Correlation Between Chemical Composition and Adherence of Cr and Co Coatings Deposited by Electric Arc

This paper presents the adhesive strength of FeCr and FeCoCr coatings produced by electric arc thermal spray process on carbon steel plates. Carbon steels are not resistant to corrosion and several methods are used in surface engineering to protect them from aggressive environments such as the marine one. The main objective of this work is the evaluation of the mechanical and metallurgical properties of coatings produced by thermal spray on carbon steel. Five chemical compositions were tested in order to give a large panel of possibility. Coatings were characterized by several methods to result in a screening of performance. The physical properties of coatings were also evaluated by adhesion quantification, using pull-off test, and microhardness measurement. The assessment of microstructural morphology by X-ray diffraction (XRD) and scanning electron microscopy (SEM) was made. The open circuit potential was monitored to evaluate the corrosion tendency. SEM results showed uniformity in the deposited layer and low amount of oxide and porosity. The adhesive strength of FeCoCr alloy coatings was higher than other coating conditions. In the immersion test, all sealed conditions presented high corrosion potential. Semi-quantitative phase calculation was performed by the Rietveld method using XRD. The presence of FeCr, FeCo, and austenite phases was determined. Based on the performed characterizations, the findings suggested that the FeCrCo deposition, with an epoxy sealing, is suitable to be used as an efficient coating of carbon steel in aggressive corrosive environments.

A Methodology for Evaluation of Life Fraction Using Cr-Mo Steel under Creep Conditions

The quantification methodology used to predict the residual life of Cr-Mo steel was microstructure/life fraction correlation under creep conditions. Microstructural evolution has been correlated with accelerated creep testing progress during testing at constant load and a temperature of 600°C, as well as with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Experimental results from TEM revealed six distinct stages, which were directly related to the life fraction values obtained. However, in the case of MEV, five stages were found. This difference is likely due to the better analysis possible via TEM of both microstructural evolution and types of carbides formed during the creep process. In addition, an evolution map is proposed to allow for easy interpretation of the relationship between microstructural characteristics and life fraction.

Cobalt-Base Superalloy Coating Using GTAW Process

In harsh operational conditions, the low-alloy steels need to be protected from the environment. Thus, against corrosion and wear, an ordinary choice is metallic cladding. In this sense, the present study aimed to evaluate the properties of cobalt base superalloy coating deposited by gas tungsten welding process (GTAW) on steel SAE 4140. A circumferential weld was chosen due to its critical restraint. Four coating conditions were studied varying the welding currents. A microstructural evaluation was done using optical and scanning electron microscopy. The physical properties of coatings were additionally evaluated by microhardness measurement and dilution quantification. The results obtained indicated, for all conditions, a uniformity of layers. However, the deposited weld characteristics are strongly dependent on welding parameters. For the welding parameters studied, the maximum dilution of 60.8% was observed in coatings with austenitic and dendrite microstructures welded with 110 A current. Moreover, the metallographic analysis and microhardness tests showed, for some cases, the presence of partially diluted zone, a microstructural layer in the transition region of base metal and coating. The welding performed with current of 90 A showed the best combination of microhardness and dilution aspects, without defects in coating.