CECÍLIO ALVARES DA CUNHA

CECÍLIO ALVARES DA CUNHA

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Mechanical, structural and thermodynamic features of high energy milled Cr3C2-25(Ni20Cr) composite powders
2018 - RAMANATHAN, L.V.; CORREA, O.V.; LIMA, N.B.; CUNHA, C.A. da; SAYEG, I.J.
This paper presents mechanical, microstructural and thermodynamic features of Cr3C2-25(Ni20Cr) powders that were high energy milled for different times. Severe plastic deformation is introduced in the powders and a small part of the energy spent in the process is stored in the crystal lattice. Crystallite size, microstrain and lattice parameter of the powders were determined using x-ray diffraction measurements (Rietveld method). The evolution of microstrain with crystallite size revealed a critical crystallite size (DCRIT = 28 nm; tMill = 16 h), where the microstrain reached a maximum [?MAX (%) = 1.17], and then decreased. The lattice parameter showed an opposite behavior (aMIN = 3.5417A). This suggested occurrence of “size effects” and aspects related to strain gradient plasticity are discussed. Stored energy in the crystal lattice was determined from enthalpy variation of the powders, and the graph of ?H vs 1/D also showed a maximum (?HMAX = 722 mcal) for powders milled for 16 h. Microstructural features like small angle grain boundaries and microtwins where studied by TEM. The influence of grain boundaries on microstrain was studied. Modifications in microstructure are discussed based on dislocation density, which is related to crystallite size and microstrain in the crystal lattice. A model for dislocation density evolution has been suggested. The dislocation density at the critical crystallite size was around 1.7 x 1011 cm-2. The dimensions of the slip bands in the material were estimated (xMAX = 3.1 ?m).
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 WC-Co powder features, composition and thermal stability
2011 - PADIAL, A.G.; CUNHA, C.A.; CORREA, O.V.; LIMA, N.B.; RAMANATHAN, L.V.
Nanostructured coatings to protect metallic materials at high temperatures
2013 - FERNANDES, S.M.C.; PILLIS, M.F.; CUNHA, C.A.; CORREA, O.V.; RAMANATHAN, L.V.
Thermal stability and erosin-oxidation behaviour of nanostructured Crsub(3)Csub(2)-Ni20Cr coatings
2010 - PADIAL, A.; CUNHA, C.A.; CORREA, O.V.; RAMANATHAN, L.V.
Mechanical properties and erosion-oxidation resistance of thermally sprayed nanostructured Crsub(3)Csub(2)-25(Ni-20Cr) coatings
2012 - CUNHA, C.A.; CORREA, O.V.; SAYEG, I.J.; LIMA, N.B. de; RAMANATHAN, L.V.
Structural and thermodynamic properties of Crsub(3)Csub(2)-25(Ni20Cr) powders produced by high energy milling
2012 - CUNHA, C.A.; CORREA, O.V.; SAYEG, I.J.; LIMA, N.B. de; RAMANATHAN, L.V.
Preparation and properties of nanostructured WC-Co composite powders and coatings
2012 - PADIAL, A.G.; CUNHA, C.A. da; CORREA, O.V.; LIMA, N.B.; RAMANATHAN, L.V.
Mechanical and structural properties of thermal sprayed Crsub(3)Crsub(2)-25(Ni20Cr) nanocomposite coatings
2012 - CUNHA, CECILIO A. da; CORREA, OLANDIR V.; SAYEG, ISSAC J.; LIMA, NELSON B. de; RAMANATHAN, LALGUDI V.