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Hernandez-Sanchez E.,National Polytechnic Institute of Mexico | Chino-Ulloa A.,National Polytechnic Institute of Mexico | Velazquez J.C.,PEMEX | Herrera-Hernandez H.,National Autonomous University of Mexico | And 2 more authors.
Advances in Materials Science and Engineering

The effect of environmental humidity on the self-lubricating properties of a thin film of boric acid (H3BO3) was evaluated. H3BO4 films were successfully formed on the surface of AISI 316L steel. The study was conducted on AISI 316L steel because of its use in biomedical applications. First, the samples were exposed to boriding to generate a continuous surface layer of iron borides. The samples were then exposed to a short annealing process (SAP) at 1023 K for 5 min and cooled to room temperature while controlling the relative humidity (RH). Five different RH conditions were tested. The purpose of SAP was to promote the formation of a surface film of boric acid from the boron atoms present in the iron boride layers. The presence of the boric acid at the surface of the borided layer was confirmed by Raman spectroscopy and X-ray diffraction (XRD). The self-lubricating capability of the films was demonstrated using the pin-on-disk technique. The influence of RH was reflected by the friction coefficient (FC), as the samples cooled with 20% of RH exhibited FC values of 0.16, whereas the samples cooled at 60% RH showed FC values of 0.02. © 2015 E. Hernández-Sanchez et al. Source

Garcia-Vazquez F.,Corporacion Mexicana de Investigacion en Materiales | Aguirre A.,Corporacion Mexicana de Investigacion en Materiales | Hernandez-Garcia H.M.,Corporacion Mexicana de Investigacion en Materiales | Santiago-Bautista L.,Corporacion Mexicana de Investigacion en Materiales | And 2 more authors.
Materials Science Forum

Plasma Transferred Arc (PTA) process is increasingly used in applications where enhancement of wear, corrosion and heat resistance of metals surface is required. The shape of weld bead geometry affected by the PTA welding process parameters is an indication of the quality of the weld. PTA is a versatile method of depositing high-quality metallurgically fused deposits on relatively low cost surfaces. The overlay deposited is an alloy that is hard and more corrosion resistant than counterparts laid down by Gas Tungsten Arc Welding (GTAW) or Oxy Fuel Welding (OFW) processes. Weld deposits are characterized by very low levels of inclusions, oxides, and discontinuities. This process produces smooth deposits that significantly reduce the amount of post weld machining required. Metal-Mechanic industry continuously requires recovering tool steel components subjected to severe wear. The steel known as D2 is considered to be a high carbon, high chromium cold work tool steel. In this research, weld beads were deposited on D2 steel by using PTA process with different parameters as welding current and travel speed using base nickel filler metal. In order to evaluate the metallurgical features on the weld beads/substrate interface a microstructural characterization was performed by using Scanning Electron Microscopy (SEM) and to evaluate the mechanical properties was conducted the wear test. © (2013) Trans Tech Publications, Switzerland. Source

Gomez-Vargas O.A.,Monterrey Institute of Technology | Solis-Romero J.,Tlalnepantla Institute of Technology | Figueroa-Lopez U.,Monterrey Institute of Technology | Ortiz-Dominguez M.,Autonomous University of the State of Hidalgo | And 2 more authors.
Materials Letters

To alleviate spallation and crack difficulties exhibited by a borided metallic surface when it is subjected to a normal, heavy and sliding load under dry conditions, a boron nitride coating was produced on pure iron in two stages: boriding the iron surface at 950°C for 6 h and then nitriding the pre-borided iron at 550°C for 6 h. The powder-pack technique was used in both stages. XRD measurements confirmed that the grown layers were nitrides and duplex borides. The produced diffusion of the layers reached 240 μm in depth as measured by SEM images. The measured microhardness across the case favoured the interphase cohesion between the iron nitrides and iron borides layers. Consequently, the multicomponent coating exhibited superior wear resistance to an applied normal load under dry sliding contact conditions in comparison to borided iron. © 2016 Elsevier B.V. All rights reserved. Source

Mendoza O.,Justo Sierra University | Vargas B.,Tlalnepantla Institute of Technology | Mendoza J.,CINVESTAV
IEEE Latin America Transactions

Digital processing on fractographic images of fracture surfaces was performed, for the weld metal aged at 250 ; C for 500 and 900 hours. The digital analysis on fractographs was carried out using mathematical morphology and morphological transformation in order to gain specific structures of the images. The results showed that the mechanism of growth and coalescence of microcavities can be observed during the fractographic image segmentation. © 2003-2012 IEEE. Source

Vargas-Arista B.,Tlalnepantla Institute of Technology | Balvantin A.,CINVESTAV | Baltazar A.,CINVESTAV | Garcia-Vazquez F.,Corporacion Mexicana de Investigacion en Materiales
Materials Science and Engineering A

In this paper, artificial aging of welded joints of an API 5L X52 steel pipeline was studied using ultrasonic spectral analysis. The joints were welded using submerged arc welding process and isothermally aged at 250 °C for different time intervals. Ultrasonic measurements were carried out using a high precision water immersion ultrasonic scanner which produces C-scan maps of the tested weld samples. The results of these measurements show that ultrasonic velocity was not significantly affected by aging time; only small variations were detected associated with the degradation of strength and hardness properties. On the other hand, ultrasonic attenuation measurements were more sensitive to aging in both the weld pool and base metal. An increase in the attenuation coefficient during early aging time was linked to the precipitation of fine nanocarbides and an increase in ferrite grain size. After 200. h of aging time, the attenuation coefficient decreased monotonically, this was found to be related to the nanoparticle coarsening and ferrite grain growth after long periods of over-aging time. This phenomenon was larger in the weld pool than in the base metal due to a higher increase in carbide precipitations and their lower coarsening. These results could lead to the development of a non-destructive testing method for monitoring degradation of welded pipelines having extensive years of service under over-aging conditions. © 2012 Elsevier B.V. Source

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