ABSTRACT: Ceramic matrix composites have attracted the interest of turbine manufacturers for use in coating hot sections because of their higher capacity to withstand high temperatures and because they have a lower requirement for air cooling. One of the most commonly used ceramic coatings is zirconia-yttria. However, its main disadvantage is the inherent fragility of ceramics, which limits the use of these materials in mechanical structures and industrial applications. Ceramics are generally reinforced with the incorporation of additives to reduce their brittleness and increase their mechanical strength and toughness. It is known that La2O3 which are potential source for stabilization of zirconia composites. In this context, ZrO2-Al2O3-La2O3 based ceramic matrix composites were developed for deposition of a thermal barrier coating on the substrate of exhaust nozzles of aerospace turbines varying the content of La2O3 by 5, 7 and 10 wt%. The composites were produced by a thermomechanical process and sintered at 1385 °C. The properties of these composites were studied by X-ray diffraction, relative density, scanning electron microscopy, and Vickers microhardness tests. The results indicate that the composite with 10% La2O3 has great potential for use as ceramic coatings of turbine exhaust nozzles in the aerospace industry.

Gamma tomography was used in this work to evaluate the recurrent defects in welding processes in naval steel sheets. It was used a first-generation equipment consisting of a source of Cesium-137, with activity of the order of 200 mCi, coupled to a Thallium-doped Sodium Iodide detector, NaI (Tl). For the study, specimens were produced in ASTM A131-AH36 steel sheets with 13.7 mm thickness; all welded by Metal Active Gas process. One reference sample was fabricated, with no macroscopically measurable defects and another welded under wind conditions producing a weld bead with different types of discontinuities. The microstructural characterization of welded joints made possible a qualitative evaluation between defective joints, in relation to the joint without defects. With the data of the tomography, 3D graphics were drawn that enabled the statistical survey and analysis of clusters of the results that allowed the localization and the dimensioning of the discontinuities that appeared as counting peaks in these graphics. It was revealed that the defective welding showed porosity of up to 39.28% of its volume, and the acceptable size crack must be less than 1 mm based on ASME-B31.3, showing the viability of the tomography for this type of nondestructive analysis.

In the present work niobium based complex cubic perovskite oxide Ba2AlNbO6 ceramics were produced, characterized and their stability in crude petroleum environment was studied for inert ceramic embedding used in petroleum extraction. Ba2AlNbO6 ceramic powder was prepared by means of thermo-mechanical processing. Structural characteristics of calcined material were investigated by powder X - ray diffractometry, which presented a single phase complex cubic perovskite structure with lattice parameter a = 8.3418 Å. Compacted Ba2AlNbO6 ceramics were sintered at 1150ºC during 72 hours in ambient atmosphere. The microstructure of the sintered ceramics was studied by scanning electron microscopy and mechanical behavior was studied by Vicker's micro-hardness testing. The sintered ceramics were submerged in crude petroleum for 60 days. The ceramics were taken out from petroleum periodically and subjected to structural, microstructural and mechanical characterizations. The results showed that the ceramics submerged in crude petroleum did not suffer any change at any stage of submersion. These characteristics make this material suitable for inert ceramic embedding for sensors used in petroleum extraction.

Residual stresses on welded joints have been studied by several methods. In this present work, residual stresses was measured by a novel methodology under development named Displacement of Coordinated Points (DCP). To evaluate anisotropy effects in steel plates, two directions of the weld bead were considered: Welding was performed in both parallel and transversal direction of rolled steel plate ASTM A131 grade AH36.The experiments showed higher values of the residual stress in the transversal direction of the lamination when compared with the longitudinal direction, evidencing the anisotropy effect of the material. It was also observed that the increasing in heat input induces higher residual stress.

The lamination process adds the anisotropy characteristic in the final product. This anisotropy influences the yield strength according to the direction in question, the difference between the value of the yield tension in one direction and the value of the yield tension in another direction referred to as the back stress. Naval plates were welded by the GMAW process in the longitudinal direction to the lamination and in the transverse direction, and with different thermal loads. The residual stresses were calculated by displacement coordinate points method (DCP) and the back stress was found by tensile tests in specimen subjected made with either the longitudinal lamination direction and transverse lamination direction. The material used was ASTM A131 naval steel grade AH-36. The welded plates with greater thermal load in the longitudinal direction presented smaller residual stress in this direction, in relation to the transverse lamination direction. In the welded plates with greater thermal load, in the transverse lamination direction, the displacements in different directions were close, showing that the back stress does not act reversing the displacement (flow). Finally, for the welded plates with lower thermal load, both welded in the longitudinal and transverse direction, the displacements were small. In addition, the back stress did not act reversing such displacements.

The evenmatched welding conditions in FCAW-G process were used in API 5L X80 steel. In this study, two joint geometries (bevel 25° and 35°) with different process parameters were used. Each type of joint was welded with one type of consumable: AWS E81T1-Ni1C (evenmatched), with variation of heat input. During welding the voltage and current varied in a range, in order to preserve the transfer mode by short circuit. For each welded joint, it was studied the influence of these welding parameters in the weld metal's quality and, the influence of the bevel angle in the extent of heat affected zones and their correlated mechanical properties. The microstructures were characterized by optical and scanning microscopy, in which the qualitative analyses of microconstituents were performed in transverse sections of weld bead. The mechanical properties for each condition were obtained by uniaxial tensile, hardness, impact and bending tests, allowing the comparison between the different parameters. The tensile test results obtained with a smaller bezel angle had mechanical resistance slightly higher than those of bigger angle joint. Consumables with the same mechanical strength of the base metal (evenmatched) presented performances consistent with their levels of resistance and proved to be viable, depending on the application.

Many studies propose thermomechanical routes to improve HSLA (high strength low alloy) steels by microstructural modification but ignore the study of occurrence of CSL boundaries. The occurrence of these special boundaries is influenced by thermomechanical treatment in which the modification of misorientation profile is related with the increase of Σ3 and Σ11 boundaries and inhibition of Σ5 Σ7 and Σ9 ones. The formation of Σ3 boundaries, beneficial to improve strength, is highly stimulated by this treatment in which deformation plays an important role in the development of CSL boundaries.

Phase transformations in API 5L X80 steel were studied in different thermomechanical sequences with a view to increasing the fracture toughness of this steel. Dilatometry tests performed on the quenched steel detected a phase transformation occurred, during heating, in the temperature range 593-618 K. This phase transformation was identified as the dissolution of M-A islands. Based on preliminary dilatometric tests, ten thermal and thermomechanical treatments were performed on X80 steel samples. Initially, the material was hot rolled and quenched and only quenched. On the material without deformation, aging was also performed at temperatures of 603, 673, 723, 773, 823 and 873 K. These treatments resulted in the formation of the acicular ferrite constituent, among others. Tensile tests showed that the aging treatments produced reductions in yield strength and increases in the elongation and toughness of X80 steel. All the treatments resulted in an increase in the tensile strength of steel.

Residual stresses in a welded joint of ASTM A131 grade AH32 steel was measured either by the X-ray diffraction or by displacements of referenced points measured on a coordinate measuring machine before and after heat treatment. For all tests, the welding was performed with Shielded Metal Arc Welding, vertical-up position, by a certified welder. After welding, some specimens were subjected to marking, made through small holes evenly spaced and mapped on a coordinate measuring machine. After labeling, the samples were subjected to heat treatment at temperatures nearby recrystallization. After heat treatment, the samples were subjected to new measurements by coordinate measuring machine to evaluate the displacements of the points produced by the recrystallization. In parallel, residual stress measurements were made by XRD for validation of this new methodology. The results obtained either by X-ray or by coordinate measuring machine showed a good correlation between the two measurement methodologies employed.

In this workmatrix consolidation mechanism has been investigated in 1D-Ti/SiC/C composites produced by Continuous Binder-Powder Coating - CBPC. Titanium metal matrix composites reinforced with continuous SiC/C filaments were analysed in different densification conditions. The results show that during processing, densification occurs by several mechanisms including a complex elasto-viscoplastic flow and diffusion bonding. The matrix consolidation depends on many processing conditions such as pressure and temperature, mainly. Using correct conditions of pressure and temperature, the titanium matrix composites produced by this process present a good matrix consolidation without porosity and a weak interaction between matrix and fiber. These good agreements between matrix consolidation and weak chemical interaction between matrix and fibre are obtained when pressures up to 150 MPa and temperatures below β-transus are applied. In these conditions, supplementary heat treatments can be performed either in alpha or beta domains.