Patricia Zambrano Robledo

Microstructural Development in a TRIP-780 Steel Joined by Friction Stir Welding (FSW): Quantitative Evaluations and Comparisons with EBSD Predictions

The present work describes the effect of FSW on the result microstructure in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) of a TRIP-780 steel. X-ray diffraction (XRD), optical microscopy (OM) and EBSD were used for determinations retained austenite (RA) in the SZ, It was found that the amount of RA developed in SZ was relatively large, (approximately 11% to 15%). In addition, recrystallization and the formation of a grain texture were resolved using EBSD. During FSW, the SZ experienced severe plastic deformation which lead to an increase in the temperature and consequently grain recrystallization. Moreover, it was found that the recrystallized grain structure and relatively high martensite levels developed in the SZ lead to a significant drop in the mechanical properties of the steel. In addition, microhardness profiles of the welded regions indicated that the hardness in both the SZ and TMAZ were relatively elevated confirming the development of martensite in these regions. In particular, to evaluate the mechanical strength of the weld, lap shear tensile test was conducted; exhibited the fracture zone in the SZ with shear fracture with uniformly distributed elongation shear dimples.

Coatings characterization of Ni-based alloy applied by HVOF

Purpose The thermal spraying technique of High-Velocity Oxygen Fuel (HVOF) coating was used to deposit coatings of an alloy composed of Ni-based substrates on stainless steel AISI 304. The aim of this study was to determine the mechanical properties such as hardness and bond strength that these coatings have when the spray distance is varied, as well as the microstructure and phases formed during the thermal spray process. Design/methodology/approach The coatings were applied by HVOF and characterized by scanning electron microscopy, image analysis, X-ray diffraction, microhardness and bond strength to analyze the mechanical properties. Findings The microstructure of the coatings showed low porosity, oxide content and interface contamination in the substrate–coating interface, without the presence of unmolten particles. The microhardness values reached 600 HV for the three spray distances used and the bond strength values reached over 55 MPa. Practical implications The use of coatings on aircraft components is growing dramatically owing to the high costs of advanced materials and the growing lifecycle requirements for high-performance systems, which are taken into account because of the variety of coatings and complexity of environmental factors. Originality/value The originality of this study lies in the development of new coating materials for the manufacture and protection of various turbine components. The value is based on the development of materials and processes to be used to manufacture them.

Análisis del rendimiento del torneado utilizando coeficiente de vida útil en relación al volumen de metal cortado

espanolLos aceros inoxidables austeniticos son materiales dificiles de mecanizar, debido a su alta resistencia, alta ductilidad y baja conductividad termica. El objetivo de este trabajo es proponer un nuevo criterio para evaluar el rendimiento del torneado de alta velocidad mediante la relacion del desgaste del flanco con el volumen de metal cortado. La influencia de los parametros de corte sobre el coeficiente de vida util en relacion al volumen de metal cortado fue analizada utilizando un analisis de varianza y de regresion multiple. La investigacion mostro un mejor rendimiento del inserto GC2015 en ambas velocidades de corte. El analisis de varianza factorial demostro un efecto significativo del tiempo de mecanizado en el coeficiente de vida util en relacion al volumen de metal cortado. EnglishThe austenitic stainless steels are difficult material to machine due to their high strength, high ductility and low thermal conductivity. The aim of this paper is to propose a new criterion for assessing the performance of high speed turning by relating the flank wear with the volume of material removed. The influence of cutting parameters on the coefficient of life in relation to the volume of material removed was analyzed using analysis of variance and multiple regression. The investigation showed a better performance with the GC 2015 insert in both cutting speed. The analysis of factorial variance showed a significant effect of the machinization time in the coefficient of life in relation to the volume of material removed.

Comportamiento a la Corrosión del Acero API X70 Soldado por el Proceso de Doble Arco Sumergido Inmerso en Diferentes Medios Corrosivos

Abstract The steels API X70 are applied in construction and fabrication of pipeline for transport of hydrocarbons, however, to lapse time are degrade due to environment to which are exposed, influencing on mode and corrosion rate on surface base metal (BM), heat zone affected (HAZ) and fusion zone (FZ). In order to know and evaluate the corrosion susceptibility in joints of API X70 steel submitted to different corrosives environment, several tests were carried out by process of double submerged arc welding (DSAW), which were immersed in different electrolytes: Sodium Chloride (3.5% NaCl) and Water (H2O) at room temperature for know its behavior. Electrochemical techniques were used of electrochemical noise (EN) and cyclic polarization curves (CPC) to obtain mode and corrosion rate produced for each of the samples analyzed, included the three zones: BM, HAZ and FZ. Further, characterization techniques were used such as optical microscopy (OM) and scanning electron microscopy (SEM) for superficial analysis. The welds’ majoirity have a mixed corrosion, with higher corrosion rate in 3.5% NaCl.