Carlos Mauricio Lepienski

Publications (137) View all

• Source

  Available from: Luiz Fernando Zagonel

  Article: Nanosized precipitates in H13 tool steel low temperature plasma nitriding

  L. F. Zagonel, J. Bettini, R. L. O. Basso, P. Paredez, H. Pinto, C. M. Lepienski, F. Alvarez
  [show abstract] [hide abstract]
  ABSTRACT: A comprehensive study of pulsed nitriding in AISI H13 tool steel at low temperature (400{\deg}C) is reported for several durations. X-ray diffraction results reveal that a nitrogen enriched compound (Epsilon-Fe2-3N, iron nitride) builds up on the surface within the first process hour despite the low process temperature. Beneath the surface, X-ray Wavelength Dispersive Spectroscopy (WDS) in a Scanning Electron Microscope (SEM) indicates relatively higher nitrogen concentrations (up to 12 at.%) within the diffusion layer while microscopic nitrides are not formed and existing carbides are not dissolved. Moreover, in the diffusion layer, nitrogen is found to be dispersed in the matrix and forming nanosized precipitates. The small coherent precipitates are observed by High-Resolution Transmission Electron Microscopy (HR-TEM) while the presence of nitrogen is confirmed by electron energy loss spectroscopy (EELS). Hardness tests show that the material hardness increases linearly with the nitrogen concentration, reaching up to 14.5 GPa in the surface while the Young Modulus remains essentially unaffected. Indeed, the original steel microstructure is well preserved even in the nitrogen diffusion layer. Nitrogen profiles show a case depth of about ~43 microns after nine hours of nitriding process. These results indicate that pulsed plasma nitriding is highly efficient even at such low temperatures and that at this process temperature it is possible to form thick and hard nitrided layers with satisfactory mechanical properties. This process can be particularly interesting to enhance the surface hardness of tool steels without exposing the workpiece to high temperatures and altering its bulk microstructure.
  08/2012;
• Article: Plasma immersion ion implantation with auxiliary heating: application to SS304 stainless steel

  M. Ueda, A. S. Geraldo, C. B. Mello, C. M. Lepienski
  [show abstract] [hide abstract]
  ABSTRACT: In the present experiment, we heated the sample holding fixture using a shielded resistive wire wound around it and the SS samples were subjected to nitrogen glow discharge plasma PIII with moderate voltages of 10 kV, in different temperatures (250 °C, 270 °C, 350 °C and 390 °C). Then, we compared them to the samples obtained by PIII in which the final temperature of 350 °C was reached, solely by the bombardment of accelerated ions. X-ray diffraction results indicated a much higher efficiency of auxiliary heated PIII mode com- pared to the ordinary PIII. Very prominent γN peaks were observed for the first mode, indicating large concentration of nitrogen in thick layers, confirmed by the nitrogen profiles measured by GDOS technique. Improved mechanical and tribological properties were obtained for SS304 samples treated by the PIII with auxiliary heating, more than for ordinary PIII. Corrosion resistance of treated samples was maintained or it was slightly lower compared to the reference sample. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
  physica status solidi (c) 03/2008; 5(4):977 - 980.
• Article: Hardness and elastic modulus of TiO2 anodic films measured by instrumented indentation.

  Paulo Soares, Alexandre Mikowski, Carlos M Lepienski, Emanuel Santos, Glória A Soares, Vitoldo Swinka Filho, Neide K Kuromoto
  [show abstract] [hide abstract]
  ABSTRACT: The aim of this work was to investigate the mechanical properties of the titanium anodic films (TiO2) produced by anodic oxidation under galvanostatic conditions, using a 1.4M phosphoric acid electrolyte, with different current densities (J) on commercially pure titanium (cp-Ti). The morphology of the oxide films were observed by scanning electron microscopy (SEM), whereas the composition of the film was determined by Raman spectroscopy. Porosity, average roughness (Ra) and thickness of the TiO2 films increased with the applied J. Hardness and elastic modulus were measured by instrumented indentation technique, and the influence of the substrate was corrected using analytical models. The anodic films presented higher hardness and lower elastic modulus values compared with the cp-Ti.
  Journal of Biomedical Materials Research Part B Applied Biomaterials 03/2008; 84(2):524-30. · 2.15 Impact Factor
• Article: Depth-Sensing Indentation on REBa2Cu3O(7-\delta) Single Crystals obtained from Xenotime Mineral

  Francisco Carlos Serbena, Carlos Eugênio Foerster, Alcione Roberto Jurelo, Alexandre Mikowski, Pedro Rodrigues Júnior, Célia Regina Carubelli, Carlos Maurício Lepienski
  [show abstract] [hide abstract]
  ABSTRACT: A natural mixture of heavy rare earths oxides extracted from xenotime mineral have been used to prepare large single crystals of high-temperature REBa2Cu3O(7-\delta) superconductor grown using the CuO-BaO self-flux method. Its mechanical properties along the ab-plane were characterized using instrumented indentation. Hardness and elastic modulus were obtained by the Oliver and Pharr method and corresponds to 7.4 \pm 0.2 GPa and in range 135-175 GPa at small depths, respectively. Increasing the load promotes the nucleation of lateral cracks that causes a decrease in hardness and the measured elastic modulus by instrumented indentation at higher loads. The indentation fracture toughness was estimated by measuring the radial crack length from cube-corner indentations at various loads and was 0.8 \pm 0.2 MPa.m1/2. The observed slip systems of REBa2Cu3O(7-\delta) single crystals were [100](001) and [010](001), the same as for YBa2Cu3O(7-\delta) single crystals. The initial stages of deformation and fracture in the indentation process were investigated. The hardness and elastic modulus were not strongly modified by the crystallographic orientation in the ab-plane. This was interpreted in terms of the resolved shear stresses in the active slip systems. Evidence of cracking along the {100} and {110} planes on the ab-plane was observed. As a conclusion, the mechanical properties of REBa2Cu3O(7-\delta) single crystals prepared from xenotime are equivalent to those of YBa2Cu3O(7-\delta) single crystals produced by conventional rare earths oxides.
  05/2012;
• Article: Gamma radiation effects on mechanical properties and morphology of a polyurethane derivate from castor oil

  Elaine Cristina Azevedo, Gilberto Orivaldo Chierice, Salvador Claro Neto, Daniel Scheidegger Soboll, Eduardo Mauro Nascimento, Carlos Mauricio Lepienski
  [show abstract] [hide abstract]
  ABSTRACT: In this study, an adhesive of a polyurethane derivate from castor oil was irradiated with gamma radiation from a 60Co source, at doses from 0.2 to 25 kGy. This adhesive polyurethane is considered for use in hospital furniture because it does not liberate dangerous solvents. Hardness and elastic modulus were measured by instrumented indentation with a pyramidal Berkovich indenter, using loads from 0.08–40 mN with a nanoindenter XP. The instrumented indentation hardness was 110 MPa for an untreated sample, increasing to 124 MPa after irradiation with 25 kGy, at penetration depths of about 5 μm. The increases in elastic modulus induced by radiation were less pronounced. This polyurethane is naturally cross-linked and the relative modifications in the hardness are attributed to an additional cross-linking process induced by radiation. X-ray diffraction indicates a slight increase in crystallinity. The roughness measured by atomic force microscopy increases after gamma irradiation.
  Radiation Effects and Defects in Solids 03/2011; 166(3):208-214. · 0.40 Impact Factor