Thermodynamic considerations for the stability of Ni and Cr compounds developed under PWR environments (PH2O and PH2) are experimentally tested. In particular, the experimental outcome indicates that Ni(OH)2 and CrOOH are thermodynamically stable products under actual PWR conditions (T < 360°C and Pressures of up to 20 MPa). Accordingly, a mechanism is proposed to explain crack initiation and growth in inconel alloy 600 along the gbs. The mechanism is based on the existing thermodynamic potential for the transformation of a protective NiO surface layer into an amorphous non-protective Ni(OH)2 gel. This gel is also expected to form along the gbs by exposing the gb Ni-rich regions to H2 supersaturated water steam. Crack initiation is then favored by tensile stressing of the gb regions which can easily rupture the brittle gel film. Repeating the sequence of reactions as fresh Ni is exposed to the environment is expected to also account for crack growth in Inconel alloy 600. The proposed crack initiation mechanism is not expected to occur in alloy 690 where a protective Cr2O3 film covers the metal surface. Yet, if a pre-existing crack is present in alloy 690, crack propagation would occur in the same manner as in alloy 600.

Physical and mathematical modeling of jet-bath interactions in electric arc furnaces represent valuable tools to obtain a better fundamental understanding of oxygen gas injection into the furnace. In this work, a 3D mathematical model is developed based on the two phase approach called Volume of Fluid (VOF), which is able to predict free surface deformations and it is coded in the commercial fluid dynamics software FLUENTTM. Validation of the mathematical model is achieved by measurements on a transparent water physical model. Measurements of free surface depressions through a high velocity camera and velocity patterns are recorded through a Particle Image Velocimetry (PIV) Technique. Flow patterns and depression geometry are identified and characterized as function of process parameters like distance from nozzle to bath, gas flow rate and impingement angle of the gas jet into the bath. A reasonable agreement is found between simulated and experimental results.

In following are presented the characterization results of nanostructured hybrid composites using alumina matrix reinforced with nanostructured particles of Ni, Ti and soot. The soot used in this work is the byproduct from the synthesis of Carbon Nanotubes (CNT) or fullerene and contains traces (>1wt%) of either CNT or fullerene. Ni and Ti are used in this work for their inherent catalytic ability for heterogeneous nucleation of carbon nanostructures (nanotubes, fullerenes). The hybrid composites are produced by a combination of methods including mechanical milling, sonication, and Spark Plasma Sintering (SPS). Mechanical milling is conducted in high energy mills, the milled and as manufactured powders are sonicated to assure their dispersion, homogeneity and promote percolation of the components during sintering. Mechanical milling and SPS have positive effects to promote the synthesis of different carbon nanoparticles. For instance, it is observed that mechanical milling of fullerene soot sponsors the synthesis of nanostructured diamond particles and using SPS can be synthesized diamond too and fullerene. Although, it is important to notice that SPS conditions are critical to the amount and type of synthesized particles. The use of CNT soot sponsors porosity, hence lower density resulting in an ideal material for membrane and porous media applications. The results of characterization (X-Ray diffraction, electron microscopy (scanning and transmission)) and the mechanical properties (Vickers microhardness) are discussed accordingly.

Thermal evaporation is used to deposit thin films of CuZnAl on silicon substrates. For this purpose, a CuZnAl shape memory alloy is used as evaporation source. The chemical composition and the phases present in the films are evaluated at two different deposition rates: 7 and 0.2 Å/s. The thin films are heat treated to promote the diffusion of the elements and characterized by X-ray Diffraction, Energy Dispersive X-ray Spectroscopy and Scanning Transmission Electron Microscopy (STEM). It is shown that the chemical composition of the thin films is significantly different to that of the CuZnAl alloy used as evaporation source. Moreover, the films produced at 7 Å/s show a significant loss of Zn, contrary to the results obtained using a deposition rate of 0.2 Å/s. It is also observed that the composition varies across the thickness of the film, suggesting that the various alloying elements are evaporated at different rates during the deposition process. Finally the predominant phases present in the films belong to the AlxCuy family.

A new computational algorithm is introduced for packing simulation of spherical elements/particles into an imaginary container with three main possible geometries, cubic, cylindrical and spherical. The performance of the algorithm depends directly on the strategy or logic considered to solve the problem and the quality of its computational implementation. The combination of these two factors let the packing algorithm here presented and named as Octant Packing Random Algorithm (OPRA) to reduce the computation time between 2 and 127 times, when compared with the simplest or classical Packing Algorithm. OPRA is designed to reduce the number of comparisons needed to accept or reject a new position for an element/particle to be allocated into the virtual container. OPRA considers the container as if it were divided into 8 equal cells or octants limiting the overlap detection for a new position.

Since their appearance during in the 1940 decade, nickel-base alloys are appreciated for their superior mechanical properties and microstructural stability at elevated temperatures and high stresses. They are typically used in jet-engines and land-based turbines for energy generation. Such materials, known as superalloys are in constant evolution as designers are encouraged to propose more efficient and powerful systems of propulsion and energy generation. This evolution leads to conceive and manufacture new superalloys capable to fulfill higher requirements. Alloy 718Plus® is emerging as an alternative material for the design and construction of components to be used in jet-engines and land-based turbines for energy generation. 718Plus® is a precipitation hardened nickel-base alloy designed to have the stability of superalloys similar to Waspaloy and the good processing characteristics of other materials as the 718 alloy. Since the early 2000 decade, ATI Allvac has lead a complete program in order to validate capabilities and properties of the 718Plus® alloy. Objectives for this effort include a characterization and its introduction as a viable material for the design and manufacture of components to be installed technologically. As part of this project, contoured rings made of 718Plus® are rolled considering industrial conditions. Several heat treatments, involving solution and precipitation processes are performed on segments extracted from involved contoured rings. Effects of such hot-working conditions and heat treatment procedures on properties as forgeability, tensile, hardness and stress-rupture characteristics are evaluated. Optical and electron microscopy are performed to evaluate microstructural properties as grain size and promotion of precipitates, in order to complement reported results.

Aluminum alloy series 2xxx, 6xxx, 7xxxx and 8xxx enjoy the widest use in aircraft structural applications. Among these materials, aluminum alloy 2024 remains the most commonly used and especially in T351 temper situation. The fatigue crack propagation behaviour of aluminum alloy 2024 T351 has been investigated using V-notch specimen in four bending test. A series of stress ratios from 0.10 to 0.50 was investigated in order to observe the influence of stress ratio on the fatigue life and fatigue crack growth rate (FCGR). The increase in FCGR, which occurs as the stress ratio is increased from 0.10 to 0.50, is generally attributed to an extrinsic crack opening effect. In T-S orientation and at low stress intensity factor, the increasing of stress ratio increase the FCG. Experimental results are presented by Paris law when coefficients C and m are affected by stress ratio. Contrary, at high stress intensity factor, the effect of stress ratio is reversed. We notice a decreasing of fatigue crack growth rate with an increasing of stress ratio. This effect may be explained by microstructure effect in (T-S) crack growth. The analysis of stress ratio effect by Elber model, shown that this model gives bad interpolation in this situation and the parameter characterized the crack closure factor will be adjusted.

This work aims to investigate the influence of tempering temperature in the wear resistance of AISI T15 HSS tools produced by two different sintering processes – hot isostatic pressing (HIP) and liquid phase vacuum sintering. All materials are submitted to annealing at 870°C, quenching at 1210°C and triple tempering at 540, 550 and 560 °C. Density measurements, hardness and bend strength (transversal rupture strength – TRS) tests are accomplished. To identify the present phases and to evaluate the obtained microstructures, analysis in optical microscopy, SEM and EDX are done. Interchangeable inserts are manufactured by electrical discharge machining process. Frontal machining without coolant of normalized AISI 1045 steel plates is employed. The cutting forces are monitored via a transducer basically constituted of an instrumented table with four load cells mounted with “Strain Gages” sensors capable to measure the cutting efforts. The tools wear is analyzed and used to estimate the performance of two different HSS tools. For both investigated materials, the tools tempered at 540 °C show the lowest wearing.

Magnetic properties of grain non-oriented low-C electrical steels are improved when the hot rolled strip is annealed (HBA) prior to cold rolling and final annealing treatments. This improvement results from development of a {100}<uvw> texture in the large grained ferrite microstructure produced during final annealing. HBA at 800–850 °C results in rapid decarburization and elimination of carbide particles which have caused concerns about the suitability of the mechanical properties in the final product. In this work, samples taken from a hot rolled electrical steel coil are subjected to HBA during 150 minutes at 850 °C, cold rolled and finally annealed three minutes at temperatures between 700 and 1000 °C. The resulting tensile properties are compared with those of samples subjected to a similar processing route but without the HBA treatment and samples of industrially semi-processed grain non-oriented electrical steel decarburized 16 hours at 750 °C. It is shown that the yield strength of samples with and without HBA depends on the final grain size according to the Hall-Petch relationship; the final grain size depends strongly on annealing temperature. However, the HBA treatment causes the strength to decrease by a factor of about 2.5 and the ductility to increase by a factor of about 1.5. It is observed that the microstructure and tensile properties of the semi-processed electrical steel subjected to a final decarburization annealing are identical to those observed in material subjected to HBA in the present work. These results indicate that the HBA treatment not only improves the magnetic properties but also leads to a significant reduction of production time for grain non-oriented electrical steels.

This paper presents results on the impact of Laser CO2 process variables on the weldability, phase transformations and tensile properties of a TRIP800 Steel. The microstructure of this steel is comprised of ferrite, bainite and retained austenite phases. This is obtained by controlled cooling from the intercritical annealing temperature to the isothermal bainitic holding temperature. These steels have been increasingly used in the last 10 years in the automotive industry and for these materials to be used effectively; the influence of material and the CO2 laser welding process condition must be clearly understood. Hence, in this work the effect of the welding process on the resultant microstructures and on the exhibited mechanical properties is investigated. It is found that the tensile strength of welded specimens falls below 800 MPa and that the elongation becomes 15 % or lower. In turn, this clearly indicates that the implemented laser welding process leads to a reduction in the TRIP800 steel toughness.

The mechanism of recrystallization as a result of annealing during 600–7200 seconds at 700 °C of a Si-Al, low C electrical steel strip is investigated in samples deformed in tension. The evolution of grain size during annealing is evaluated by optical microscopy and electron backscatter diffraction in the scanning electron microscope. It is found that grain growth starts after an incubation time of 600 s with no apparent evidence of primary recrystallization. After that, the grain size-time relationship exhibits two different stages. Initially, the grain size increases linearly with time up to about 3600 s. During this time, some selected grains grow until they consume the deformed microstructure. In the second stage, the rate of growth decreases significantly and a final grain size of about 150 m is reached after 7200 seconds of annealing. Grain orientation spread maps obtained from EBSD data of deformed and partially recrystallized samples during the stage of linear growth reveals that the growing grains exhibit lower misorientation and therefore smaller stored energy than the non-recrystallized matrix grains. Analysis of image quality maps reveal that the IQ values for {100}<uvw>orientations are higher than those observed for {111}<uvw>orientations thus suggesting that the {100}<uvw>orientations grow at the expense of {111}<uvw>orientations by a mechanism of strain-induced boundary migration.

Brazing is a unique method to permanently join a wide range of materials without oxidation. It has wide commercial application in fabricating components. This paper discusses results regarding the brazing process of 304 stainless steel. The experimental brazing is carried out using a nickel-based (Ni-11Cr-3.5Si-2.25B-3.5Fe) filler alloy. In this process, boron and silicon are incorporated to reduce the melting point, however they form hard and brittle intermetallic compounds with nickel (eutectic phases) which are detrimental to the mechanical properties of brazed joints. This investigation deals with the effects of holding time and brazing temperature on the microstructure of joint and base metal, intermetallic phases formation within the brazed joint as well as measurement of the tensile strength. The results show that a maximum tensile strength of 464 MPa is obtained at 1120°C and 4 h holding time. The shortest holding times will make boron diffuse insufficiently and generate a great deal of brittle boride components.

The purpose of this work is to explore the capability of Fourier Thermal Analysis (FTA) to detect differences in solidification kinetics between unmodified and Sr modified eutectic Al-Si alloy obtained from the same base alloy. Experimental melts are produced in silicon carbide crucibles using an electrical resistance furnace and burdens of A356 alloy and commercial purity Si. The addition of strontium to the melts is accomplished using Al-10 pct Sr master alloy rod. Chemical composition is controlled using spark emission spectrometry. The changes in microstructure are characterized using optical microscopy. Thermal analysis are performed in cylindrical stainless steel cups coated with a thin layer of boron nitride, using two type-K thermocouples connected to a data acquisition system. Experimental cooling curves are numerically processed using FTA. Results show changes in solidification kinetics of eutectic Al-Si alloy with different Sr content. These changes, measured at the beginning and during solidification of the probes, can be related to the changes in nucleation and growth causing the differences detected during microstructural characterization of the probes.

Composites of M-2.5 mol. % Fullerene C60 composites (where M= Fe or Al) are prepared by mechanical milling and Spark Plasma Sintering (SPS). The SPS technique has been used to consolidate the resulting powders and preserve the massive nanostructure. Results of X-Ray Diffraction and Raman Spectroscopy show that larger milling balls (9.6 mm in diameter) produce transformation of the fullerene phase during mechanical milling. Alternatively smaller milling balls (4.9 mm in diameter) allow retention of the fullerene phase. SEM shows homogeneous powders with different particle sizes depending on milling times. Sintering produces nanostructured composite materials with different reinforcing phases including C60 fullerenes, diamonds and metal carbides. The presence of each phase depends characteristically on the energy input during milling. Transmission Electron Microscopy (TEM) and Raman Spectroscopy show evidence of the spatial distribution and nature of phases. Diamonds and carbides can be identified for the sintered Fe containing composites with a relatively high volume fraction.

The aim of this work is the characterization of some graphite-metal couples prepared by mechanical milling (MM). The morphological and microstructural changes during MM of graphite processed with metallic powders of Cu, Ni and Ag (10 and 15 at. %) are studied. Milling is performed in a high-energy ball mill under an inert atmosphere during 1, 4 and 8 hours. The process is also repeated with a pure graphite sample in order to compare the role of metal type and concentration on the morphological characteristics of milled samples. The results show that increasing the concentration of metal particles accelerates the milling process as a result of faster work hardening and particle fracture. The results of X-ray diffraction analysis show that some crystallographic characteristics of the milled couples change as a function of milling time and metal addition. Also, SEM-EDS studies show an important effect of milling time on metal particle distribution in the prepared graphite couples.

Carbon nanotubes (CNTs) synthesized by a chemical vapor deposition (CVD) method and the 2024 aluminum alloy (Al2024) are used in the production of Al2024-CNTs composites. An homogeneous dispersion of the CNTs into the aluminum matrix is achieved by a mechanical milling processing. CNTs keet their morphology after milling and sintering processes. Formation of aluminum carbide as a function of CNTs contents is observed. Formation of equilibrium phases during sintering is observed by electron microscopy. CNTs and aluminum carbide in the composites are characterized by transmission electron microscopy. Hardness results of sintered products show an increment of up to 285% over the unreinforced alloy prepared by the same route.

In this work, an Al-bronze alloy is reinforced with TiC through reaction of the alloy melt with methane gas. The resultant alloy is then centrifugally cast in cylindrical molds. It is found that the surface at the inner diameter of the cast contained in-situ produced TiC as well as Fe-rich inclusions. Metallographic observations using optical and scanning electron microscopy confirmed the presence of TiC particles (30 % volume), alpha and beta grains including iron precipitates. Cylindrical pins are machined from the inner surface and tested under various conditions in a three pin on disk Falex machine. Pins are tested under a constant load of 2.86 MPa and friction and wear rates are determined from measurements of weight losses versus wear lengths. It is found that under the applied load the reinforced material exhibits high friction and relatively low wear when compared with the unreinforced material. Apparently, under these conditions the TiC particles become abrasive particles thus contributing to wear of the steel counter-face through three body abrasive wear.

In this work, a method is considered to produce uniform nanoceria surface coatings on 316L stainless steel such as dipping. Coated steels using the aforementioned method are exposed to high temperature 800–1000°C and their oxidation behavior is investigated. It is found that the nanoceria particles in the implemented coatings exhibit some growth during high temperature exposure. In addition, thermogravimetric determinations of oxidation resistance in coated and bare samples at 900°C clearly indicates that the nanoceria coated stainless steels exhibits a two fold reduction in mass gain when compared with bare ones. Optical and scanning electron microscopy are employed to characterize the developed oxide scale morphologies. It is found that in areas are nanoceria is not uniformly coated, Fe-rich oxide islands develop, whereas in coated regions the scale is Cr and Ce rich indicating that the scale is probably a Ce doped Cr oxide.

In this study, polymer-matrix composites are fabricated by mixing liquid epoxy resin with 0, 15, 20 and 25 wt % of PET. PET is used as a reinforcement material since it can be recycled and this implies a beneficial environmental impact. After mixing, specimens are dried at room temperature during 24 h and then cured at 150°C during 0.5, 0.75 and 1 h. Then mechanical tests are performed. Experimental results obtained from the flexion test for 100 % epoxy resin and 15 % PET samples, without curing treatment show values of 30 and 21 MPa, respectively. Flexure strength values for the same samples but after curing treatment are: 56, 90, 32 MPa and 69, 64, 70 MPa, for 0.5, 0.75 and 1 h of treatment, respectively. These data show an important increase in the flexure strength for the sample reinforced with 15 % PET and curing time of 1h. This is most likely due to the behavior of PET's powders at this temperature and time. They can partially melt improving the adhesion to the polymeric matrix. For a curing time of 0.75h, this property decreases, due to the high porosity developed in the composite and the poor adhesion between polymeric matrix and reinforced material.

A three-dimensional numerical model capable of predicting structural behavior of concrete under various loading conditions is developed. Concrete, as a composite material, is represented by the mechanically strong aggregates of various shapes and sizes incorporated into a cement matrix. The most important aspect of concrete modeling involves an accurate representation of the spatial distribution of the aggregate particles.

A micromechanical heterogeneous model based on prescribed spatial distribution of aggregates is developed. This model allows to compute the effective material properties of concrete using a representative cell homogenization approach. The results of numerical analysis of this model are compared to the models of particulate composite material.