Maria do Carmo de Andrade Nono

Compaction Behavior Study of Powder Composed by Nanoparticle Agglomerates and Aggregates

Ceramic powder compaction by pressing requires weak-agglomerated powders to obtain high dense compacts and consequently dense sintered ceramic body. In this work powders with different agglomerated and/or aggregated size distributions was compacted by uniaxial and isostatic pressing. The powder and compacts were characterized by mercury and nitrogen porosimetry, BET and SEM. Analysis of X-rays diffraction peaks was used to determine the particle size (diameter). The Scherrer method was used to obtain the estimated average nanoparticle size. The results showed that all aggregated and weak agglomerated powders were composed by nanoparticles. This study indicated that the nanoparticle aggregates and weak agglomerates were destroyed during the pressing stage conducting to a increase of the packing degree of the powder particles.

Tetragonal-to-Monoclinic Transformation Influence on the Mechanical Properties of CeO2- ZrO2 Ceramics

CeO2- ZrO2 ceramics are considered a candidate material for applications as structural high performance ceramics. In this work are presented and discussed the tetragonal-to-monoclinic stress-induced transformation influence on the mechanical properties in these ceramics. Sintered ceramics were fabricated from powders mixtures containing ZrO2 and 8 to 14 CeO2 % mol. SEM observations were used to study de ceramic microstructures and X-rays diffraction to identification and determination of tetragonal and monoclinic phases. It was adopted the 4-point bending tests, Vickers surface hardness and fracture toughness technique to the determination of the mechanical parameters. The results showed that the mechanical properties were strongly dependent of the CeO2 content, the microstructure and the fraction of tetragonal-to-monoclinic stress-induced transformation.

Electron Beam-Physical Vapour Deposition of Zirconia Co-Doped with Yttria and Niobia

Turbine blades of airplanes and thermoelectric plants work in adverse conditions, with corrosive environment and high temperature and pressure. One way to improve the life or the working temperature of the blades is by the use of special coatings over metallic material applied by Electron Beam – Physical Vapour Deposition (EB-PVD). The most usual material for this application is zirconia doped with yttria. Addition of niobia, as a co-dopant in the Y2O3-ZrO2 system, can reduce the thermal conductivity and improve mechanical properties of the coating. The purpose of this work is to show the influence of the addition of niobia on microstructure of ceramic coating taking in to consideration X-ray diffraction and scanning electron microscopy observations. First result shows a columnar structure with only tetragonal phase in the ceramic coating in the chemical composition range studied.

Comparative Study on Turning CI and CGI Using Silicon Nitride Cutting Tools

There has been a great interest for improving the machining of cast iron materials in the automotive and other industries. Comparative studies for tool used to machine grey cast iron (CI) and compacted graphite iron (CGI) on dry machining were also performed in order to find out why in this case the tool lifetime is not significantly higher. However the machining these materials while considering turning with the traditional high-speed steel and carbide cutting tools present any disadvantages. One of these disadvantages is that all the traditional machining processes involve the cooling fluid to remove the heat generated on workpiece due to friction during cutting. This paper present a new generation of ceramic cutting tool exhibiting improved properties and important advances in machining CI and CGI. The tool performance was analyzed in function of flank wear, temperature and roughness, while can be observed that main effects were found for tool wear, were abrasion to CI and inter-diffusion of constituting elements between tool and CGI, causing crater. However the difference in tool lifetime can be explained by the formation of a MnS layer on the tool surface in the case of grey CI. This layer is missing in the case of CGI.

Turning of Compacted Graphite Iron Using Commercial TiN Coated Si3N4 under Dry Machining Conditions

Due to their high hardness and wear resistance Si3N4 based ceramics are one of the most suitable cutting tool materials for machining hardened materials. Therefore, their high degree of brittleness usually leads to inconsistent results and sudden catastrophic failures. Improvement of the functional properties these tools and reduction of the ecological threats may be accomplished by employing the technology of putting down hard coatings on tools in the state-of-the-art PVD processes, mostly by improvement of the tribological contact conditions in the cutting zone and by eliminating the cutting fluids. However in this paper was used a Si3N4 based cutting tool commercial with a layer TiN coating. In this investigation, the performance of TiN coating was assessed on turning used to machine an automotive grade compacted graphite iron. As part of the study were used to characterise the performance of cutting tool, flank wear, temperature and roughness. The results showed that the layer TiN coating failed to dry compacted graphite iron under aggressive machining conditions. However, using the measurement of flank wear technique, the average tool life of was increased by Vc=160 m/min.The latter was also observed using a toolmakers microscope and scanning electron microscopy (SEM).

Influence of Zirconia Plasma-Sprayed Coating on Creep of the Ti-6Al-4V Alloy

The titanium affinity by oxygen is one of main factors that limit the application of their alloys as structural materials at high temperatures. Notables advances have been obeserved in the development of titanium alloys with the objective of improving the specific high temperature strength and creep-resistance properties. However, the surface oxidation limits the use of these alloys in temperatures up to 600°C. The objective of this work was estimate the influence of the plasma-sprayed coatings for oxidation protection on creep of the Ti-6Al-4V alloy, focusing on the determination of the experimental parameters related to the primary and secondary creep states. Constant load creep tests were conducted with Ti-6Al-4V alloy in air for coated and uncoated samples and in nitrogen atmosphere for uncoated samples at 500°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V specimens. Results indicated the creep resistance of the coated alloy was greater than uncoated in air, but nitrogen atmosphere was more efficient in oxidation protection. Previously reported results about the activation energies and the stress exponents values indicate that the primary and stationary creep, for both test conditions, was probably controlled by dislocation climb. Occurred a decreasing of steady state creep in function of the reduction of oxidation process, showing that Ti-6Al-4V alloy lifetime was strongly affected by the atmosphere due the oxidation suffered by the material.

Development of ZrO2-TiO2 Porous Ceramic as Soil Humidity Sensor for Application in Environmental Monitoring

Due to the necessity of the automation and control of processes in agriculture, as well as to the crescent interest for the environmental monitoring, efforts have been demanded in the development of more versatile, reliable sensors and sensor systems with smaller cost [1-2]. In this sense, the search of new materials, the modeling study of sensor and the development of new measurement techniques and processing of signs have been orientating the progress in this area [3-4]. In this work, the results of the characterization analyses of sensor elements of ZrO2-TiO2 porous ceramic for application as soil humidity sensor, are shown and discussed. These ceramics were obtained from the mechanical mixture of ZrO2- TiO2 powders and sintered at 1000, 1100 and 1200 oC, for obtaining different porosities. The characterization of the ceramic was carried out using measurements of B.E.T.; nitrogen and mercury porosimetry; scanning electronic microscopy and X-ray diffraction. The porous ceramic characterization as soil humidity sensor element was accomplished through capacitance and impedance measurements using a RLC bridge. The ceramic sensor elements were immersed in the selected and previously characterized soils, the humidities of which were defined in accordance with Atterberg limits, more exactly liquid limit. The results obtained for specific surface area, distribution curves of pore size, microstructure, crystalline phases and sensibility to the soil humidity showed that the ZrO2-TiO2 porous ceramic sintered at 1100 oC presents a great potential to be applied as sensor element for soil humidity monitoring.

Characterisation of Titanium Nitride Thin Films Deposited by Cathodic Arc Plasma Technique on AISI D6 Tool Steel

TiN thin film has been produced on the surface of AISI D6 tool steel by using a titanium interlayer. In this work, the morphology, the microstructure and interface depth profile of TiN films deposited at two substrate temperatures (220 oC and 450 oC) in the coating process are presented and discussed. The AISI D6 tool steel substrates were coated with titanium thin film as the underlayer and with TiN thin film as the top layer. They were deposited by conventional cathodic arc process. The surfaces of TiN films were observed by scanning electron microscopy (SEM). The microstructure of these samples was analysed by X-ray diffractometry (XRD). The influence of the substrate temperature on the TiN film-Ti film-AISI D6 interface region were investigated by energy dispersive spectrometry (EDS) and its cross section were observed using backscattered electron image (BEI). The results showed that TiN films deposited at 220 oC formed a film of strongly (111) preferred orientation, while in 450 oC formed a film of (111) and (220) preferred orientation. The thickness of the TiN films increased with increasing substrate temperature. The results show that the interface region of the TiN film-Ti film-AISI D6 substrate system was significantly improved when higher substrate temperature during deposition is used.

Nucleation and growth microstructural study of ti films on 304 SS substrates

Coating of steel surfaces with titanium films has been studied with the objective to protect them against corrosion, and to create an intermediate film for CVD diamond and TiN film deposition. In this work, the nucleation, growth mechanisms and microstructural formation of the titanium films deposited on 304 stainless steel (304 SS) substrate are presented and discussed. The titanium films of variable thickness were obtained by vapour phase deposition produced by electron beam. The surfaces of these samples were observed by scanning electron microscopy. The cross sections of these samples were observed by using an atomic force microscope. The Ti film-304 SS interfaces were analyzed by X-ray diffraction. The results showed that titanium films have a columnar growth. The Ti film-304 SS interface had a residual compression stress at room temperature due to the interdiffusion process.

Microstructure Study and Crystalline Phase Formation on Nb2O5-Ba9Ti2O20 Microwave Resonators

We report on the development of barium nanotitanate (Ba 2 Ti 9 O 20 ) dielectric resonators (DRs) for microwave applications and their characterization regarding ceramic and high-frequency dielectric properties. Those DRs should meet the requirements of the dielectric constant as well as the quality factor high values and frequency high stability, for application as local oscillator of an INPE Communication Satellite. The ceramic were prepared using suitable powder mixtures composed of 0.818 BaCO 3 -0.182 TiO 2 without and with addition of some contents of Nb 2 O 5 (0.1, 0.2 and 0.4 % mol), compacted by isostatic pressing with 300 MPa and sintering at 1360°C in appropriate atmosphere. The initial powders and the sintered ceramics were characterized by X-rays diffraction and scanning electronic microscopy. The values of dielectric constant, resonance frequency, loaded quality factor due to the dielectric losses, and coefficient of frequency variation with the temperature was obtained using a special metallic box for these measurements. The comparative analyses of these results showed that the Nb 2 O 5 content increases the amount of the formed phase Ba 2 Ti 9 O 20 and the ceramic densification degree.