CECÍLIO ALVARES DA CUNHA

CECÍLIO ALVARES DA CUNHA

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High temperature erosion-oxidation resistance of thermally sprayed nanostructured Cr3C2-25(Ni-20Cr) coatings
2017 - CUNHA, CECILIO A. da; CORREA, OLANDIR V.; SAYEG, ISAAC J.; RAMANATHAN, LALGUDI V.
This study reports the high temperature erosion-oxidation (E-O) behavior of conventional and nanostructured Cr3C2-25(Ni-20Cr) coatings prepared by high velocity oxygen fuel (HVOF) spraying. As-received and nanostructured Cr3C2-25(Ni-20Cr) powders with mean crystallite sizes of 145 nm and 50 nm respectively, were used to prepare 120 - 200 μm thick coatings on AISI 310 samples. The E-O behavior of the coatings prepared with the as-received (AR) and nanostructured (NS) powders was determined as weight change in a custom designed rig at room temperature, 450, 700 and 800 ºC. The Vickers microhardness, Young’s Modulus and fracture toughness of the AR and NS coatings were determined, and the NS coatings exhibited higher values compared with the AR coatings. The E-O resistance of the NS coating was higher than that of AR coating at all temperatures, and particularly at 800 ºC. The increase in E-O resistance of the NS coatings is due to its superior mechanical properties as well as to the presence of some heterogeneities in the AR coatings. The E-O mechanisms of both types of the coatings are discussed, with special attention to that at high temperatures. The results suggest that at 800 ºC the E-O process is controlled by erosion of the oxide.
Structural and thermodynamic properties of nanocrystalline Cr3C2-25(Ni20Cr) composite powders produced by high-energy ball milling
2016 - CUNHA, CECILIO A.; CORREA, OLANDIR V.; SAYEG, ISSAC J.; LIMA, NELSON B.; RAMANATHAN, LALGUDI V.
Nanostructured coatings have been used to protect components exposed to severe service conditions. High energy milling is widely used to produce nanocrystalline feedstock of coating materials such as chromium carbide and tungsten carbide. This paper presents the structural and thermodynamic properties of Cr3C2-25(Ni20Cr) powders that were high energy milled for different times. During the high energy milling of Cr3C2-25(Ni20Cr) powder, severe plastic deformation takes place. A small part of the energy spent in this process is stored in the crystal lattice as deformation energy. The crystallite size and microstrain in nanocrystalline Cr3C2-25(Ni20Cr) powders milled for different times were determined by X-ray diffraction measurements. Differential scanning calorimetric (DSC) studies of the milled powders revealed a broad transformation, characteristic of a large exothermic reaction in the nanostructured powder. The enthalpy variation measured by DSC permitted determination of the deformation energy stored in the Cr3C2-25(Ni20Cr) powders milled for different times. These measurements also enabled calculation of the specific heat variation of the milled powders.
Effect of high energy milling parameters on nanostructured Cr3C2-Ni20Cr powder characteristics
2008 - CUNHA, C.A.; PADIAL, A.G.F.; LIMA, N.B. de; MARTINELLI, J.R.; CORREA, O.V.; RAMANATHAN, L.V.
Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In the last decade, thermal sprayed coatings using nanostructured feed stock of other materials has exhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated that nanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore posses improved performance characteristics. Preparation of nanostructured feed stock powders is the first step in the synthesis of nanostructured coatings and mechanical milling is an effective process to obtain the powders. Preliminary studies in which commercial Cr 3C2-NiCr powders were milled in hexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller in powders milled in nitrogen. This paper presents the effect of hexane content and milling parameters on Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reduced significantly the particle and crystallite sizes.
Microstructure and mechanical properties of thermal sprayed nanostructured Cr3C2-Ni20Cr coatings
2008 - CUNHA, CECILIO A. da; LIMA, NELSON B. de; MARTINELLI, JOSE R.; BRESSIANI, ANA H.A.; PADIAL, ARMANDO G.F.; RAMANATHAN, LALGUDI V.
Cr3C2-Ni20Cr coatings have been used for corrosion and wear resistant applications. However, one of the shortcomings of these coatings is its low hardness, and consequent low wear resistance, for long term high temperature applications. Nanostructured coatings of many materials have exhibited higher hardness and strength compared with conventional coatings of the same material. Consequently, nanostructured coatings of other materials, including Cr3C2-Ni20Cr have been attempted to enhance overall performance. In this study the effects of high energy milling parameters on Cr3C2- 25(Ni20Cr) powder characteristics as well as the microstructure and mechanical properties of nanostructured Cr3C2-25 (Ni20Cr) coatings formed by high velocity oxygen fuel (HVOF) spraying have been evaluated. The average particle size and crystallite size of milled Cr3C2-25 (Ni20Cr) powders decreased with increase in milling time and this decrease was more pronounced in nitrogen compared to that in hexane. This difference has been attributed to a cushioning effect in the latter medium. The coatings prepared with milled Cr3C2-25 (Ni20Cr) powders had a more uniform microstructure, were harder and had higher relative fracture toughness compared with coatings prepared with as-received powders.
Effect of Crsub(3)Csub(2)-NiCr powder characteristics on structure and properties of thermal sprayed nanostructured coatings
2010 - PADIAL, A.; CUNHA, C.A.; CORREA, O.V.; LIMA, N.B. de; RAMANATHAN, L.V.